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Ultimate High Conductivity of Multilayer Graphene Examined by Multiprobe Scanning Tunneling Potentiometry on Artificially Grown High-Quality Graphite Thin Film
- Hiroyuki MogiHiroyuki MogiFaculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, JapanMore by Hiroyuki Mogi,
- Takafumi BambaTakafumi BambaFaculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, JapanMore by Takafumi Bamba,
- Mutsuaki MurakamiMutsuaki MurakamiMaterials Solutions New Research Engine, KANEKA Corporation, Osaka 566-0072, JapanMore by Mutsuaki Murakami,
- Yuki KawashimaYuki KawashimaMaterials Solutions New Research Engine, KANEKA Corporation, Osaka 566-0072, JapanMore by Yuki Kawashima,
- Masamichi YoshimuraMasamichi YoshimuraGraduate School of Engineering, Toyota Technological Institute, Nagoya 466-8511, JapanMore by Masamichi Yoshimura,
- Atsushi TaninakaAtsushi TaninakaFaculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, JapanMore by Atsushi Taninaka,
- Shoji YoshidaShoji YoshidaFaculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, JapanMore by Shoji Yoshida,
- Osamu TakeuchiOsamu TakeuchiFaculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, JapanMore by Osamu Takeuchi,
- Haruhiro OigawaHaruhiro OigawaFaculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, JapanMore by Haruhiro Oigawa, and
- Hidemi Shigekawa*Hidemi Shigekawa*E-mail: [email protected]Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, JapanMore by Hidemi Shigekawa
Copyright © 2019 American Chemical Society
Abstract
With the discovery of graphene, the excellent characteristics of graphite (multilayer graphene), such as high thermal and electric conductivities, heat resistance, and chemical stability, have also been attracting considerable attention again. However, the production of a large-area (>0.1 × 0.1 m2) graphite thin film with uniformly high electric conductivity, which will be indispensable in industrial applications, has been difficult because of its breakage occurring during the growth process. Recently, we have succeeded, for the first time, in growing large-area high-quality graphite films with thicknesses from ∼0.5 to ∼3 μm by an industrial method, providing a fundamental platform for examining and utilizing the intrinsic and ultimate characteristics of such a material. Here, as a step toward realizing such efforts, we performed microscopic measurements of electric conductivity by the method of multiprobe scanning tunneling potentiometry we have developed. Using the resistivity along the c-axis, ρc = 1.72 ± 0.04 mΩ·m, which was directly measured for the first time, we determined the resistivity in the ab-plane, ρab, to be 0.30 ± 0.01 μΩ·m, indicating that the conductance of the graphite thin film we grew is about 1.3 times the previous highest reported value for the highest grade single-crystal natural graphite with an ideal structure without grain boundaries or wrinkles (0.38 μΩ·m). Both the advantage of multilayer graphene, which is considered to reduce the effect of grain boundaries on conductance, and the decrease in conductance as an effect of wrinkles were directly evaluated.
Introduction
ARTICLE SECTIONS
Graphite is a material that has been used for a long time because of its excellent properties such as high electric and thermal conductivities, chemical stability, heat resistance, and low specific gravity. For example, the carrier mobility in the ab-plane of graphite is much larger than that of metals (for example: Cu, 16 cm2/(V·s); graphite basal plane, ∼10000 cm2/(V·s)). Thereby, the electric conductivity of graphite in the ab-plane, ∼25000 S/cm, is extremely high for a nonmetallic material. With the discovery of graphene,(1) further applications of graphite that utilize its outstanding properties as multilayer graphene, for example, as fabricable electrode materials for solar cells,(2) light-emitting diodes,(3) flat panel displays,(4) smart windows,(5) touch panels,(6) and Li-ion batteries,(7) in supercapacitors,(8,9) and as a superconductor,(10−12) have been actively studied. For a field-effect transistor (FET) channel formed by several layers of MoS2 with a multilayer graphene electrode prepared by peeling layers from a bulk graphite, a high mobility exceeding 104 cm2/(V·s) was achieved.(13) To advance these applications, it is highly desirable to develop a method of industrially obtaining high-quality thin-film graphite with a large area.
Kish graphite and highly oriented pyrolytic graphite (HOPG) are well-known artificial graphite materials, which are produced from the liquid phase (molten metal) and the gas phase, respectively.(14−16) Although the obtained materials are of good quality, it is difficult to produce large-area (on the order of 0.1 × 0.1 m2) thin films. As a possible means of overcoming this limitation, a polymer pyrolysis (PP) method for producing a graphite film from the solid phase by heating a polymer film at a high temperature has been extensively studied.(17−19) The PP method was developed in 1986, and many studies have since been reported on the production of large-area graphite films and large graphite blocks.(17,19) However, the thickness of the graphite thin films produced by the PP method has been limited to the range of 10–50 μm, and their electric and thermal conductivities were lower than those of Kish graphite and HOPG.(20) With decreasing film thickness, the shrinkage and expansion of the graphite thin films during the growth process caused their breakage during the heating process.(21) Therefore, the development of new techniques is highly desirable to produce thinner films.
Recently, the industrial growth of large-area high-quality graphite films with thicknesses from ∼0.5 to ∼3 μm has been successfully realized by devising a handling technique for materials during the growth process,(22) which provides a fundamental platform for examining and utilizing the intrinsic and ultimate characteristics of such materials. However, since the grain size of high-quality graphite films prepared by the PP method is on the order of micrometers, it is necessary to perform resistivity measurement on a similar scale, which has not yet been achieved. In general, the resistivity of graphite in the ab-plane has been measured using the conventional four-terminal method.(14,23) When measurement is performed by reducing the distance of electrodes, methods such as ion beam etching and lithography are used to form a one-dimensional (1D) device structure.(24,25) Therefore, it is difficult to clarify the effects of such physical and chemical processes on the characteristics of graphite. In addition, since graphite has large anisotropy between the resistivities in the ab-plane, ρab, and along the c-axis, ρc (ρc/ρab = 2500–5500(26) for pyrolytic graphite), the resistivity along the c-axis is an important factor. However, the resistivity in the c-axis direction has been measured by forming wiring on the surface of the graphite ab-plane,(26,27) and its direct measurement has not yet been realized because it is very difficult to prepare electrodes on the cross section of thin-film graphite by conventional methods such as lithography.
The four-probe method scanning tunneling microscopy (STM) was developed to measure the local electric conductivity of a sample.(28) In this method, four probes are brought into contact with the sample. Current is allowed to flow between the two outer probes, and the voltage is measured by the two inner probes, similarly to the conventional four-terminal method. It is possible to perform local measurements without the complicated pretreatment of the sample. However, in general, the four probes come in contact with the sample.
On the other hand, scanning tunneling potentiometry (STP) is a method of measuring the local potential below a probe tip that does not come in contact with the sample.(29,30) Current is allowed to flow between the two outer probes, and potentiometry is performed by using the inner STM probe. More accurate measurement becomes possible by adding a probe as a reference electrode (multiprobe STP: MP-STP). STM observation may also be performed simultaneously with the potentiometry measurement. However, when MP-STP is performed on a thin film such as graphite, the tip coming in contact with the film causes damage. In addition, the current path becomes three-dimensional (3D), and the direct measurement of the conductivity in the c-axis direction is required, which has not yet been achieved.
Here, we present the results obtained by MP-STP measurement in combination with the technique of atomic force microscopy (AFM). Local conductivity measurement was successfully performed on a 2.7 μm thick graphite film grown by the PP method. The resistivity along the c-axis was directly obtained for the first time by MP-STP measurement over a cross section. The highest conductivity in the ab-plane, which is ∼1.3 times that of single-crystal natural graphite (SCNG) and is considered to be an intrinsic and ultimate characteristics of multilayer graphite, was confirmed for the first time.
Results and Discussion
ARTICLE SECTIONS
Sample Preparation
Cracks and wrinkles forming in graphite films because of their shrinkage and expansion during the heating process have long been a technical problem. Generally, when the conventional industrial production method used for films thicker than 10 μm is applied to the fabrication of films with thicknesses of <3 μm, the films break and large-area films cannot be produced. Recently, we have improved the method of handling the polyimide (PI) membrane during the heating process, which is called the multipoint-support method and has enabled fabrication of high-quality large-area graphite thin films. Square graphite films with one side being 0.1 m and thicknesses from ∼0.5 to ∼3 μm were successfully grown (see the Methods section and ref (22) for details). As described in refs (17) and (22), although the quality of the sample deteriorates for a film with a thickness of about 10 μm because of the insufficient graphitization inside the film, graphitization occurs throughout the entire film with a thickness of about 3 μm or less. Therefore, in this experiment, measurement was performed by cleaving a sample of ∼2.7 μm thickness (reduced to ∼2.1 μm by cleaving) whose conductivity was highest in the ab-plane direction as confirmed by the macroscopic van der Pauw (VDP)(31) method.
Figure 1a shows a transmission electron microscopy (TEM) image of the sample. It can be seen that the layered structure of graphite is well formed. Figure 1b shows a scanning electron microscopy (SEM) image of the sample. The average grain size estimated by the channeling contrast method(32,33) was 7.48 μm. Figure 1c shows Raman spectra obtained before and after exfoliation. The D peak, which corresponds to defects, disappeared after exfoliation, indicating the high quality of the sample at the level of Raman evaluation. No millimeter-order wrinkles, which are formed during the growth by the PP method,(22) were detected as D signals in the Raman spectra.
Figure 1
Figure 1. Sample conditions and schematic illustrations of measurements. (a) Cross-sectional TEM image of a graphite sample. (b) Secondary electron microscopy (SEM) image. (c) Raman spectra obtained before and after exfoliation. The D peak corresponds to defects. The G peak, which corresponds to other factors such as strain and the dopant used, is shown for comparison with the D peak in intensity. (d) FIB–SEM system used to produce a cross section of graphite film and a SEM image of the obtained sample. (e) Setup of the MP-STP measurement. (f) Measurement sequence.
In MP-STP measurements, unlike macroscale sheet resistance measurements, current is applied from the upper surface of the sample via an almost ideal point contact. Therefore, since the current path is an essential factor in the analysis, it is important to accurately measure the thickness of the sample. The graphite film was fixed onto a mica substrate by using an epoxy insulating adhesive. After the resistivity of the sample in the ab-plane was measured by MP-STP, which will be explained later, the sample was transferred to the chamber of a focused-ion-beam (FIB) SEM system (Helios NanoLab 600i, FEI Inc.) schematically shown in Figure 1d. Then, to expose a clean cross section, the part of the sample used for the ab-plane measurement was sputtered to a depth of ∼3 μm perpendicular to the ab-plane by irradiating the surface with a focused 30 kV Ga+ ion beam in a vacuum chamber of ∼10–5 Pa. A SEM image of the obtained cross section is shown in Figure 1d. Because the contrast in the graphite cross section and the epoxy part in the secondary electron image was clearly different, as shown in the SEM image in Figure 1d, the thickness of the graphite film was successfully determined to be ∼2.1 μm. The ρab of this sample which is cut to a 0.01 × 0.01 m2 square measured by the VDP method was 0.427 μΩ·m, the lowest resistivity within the 0.5–3 μm thick films fabricated by the PP method.(22)
MP-STP Measurement over the ab-Plane
Figure 1e shows the experimental setup of MP-STP. Because layered materials such as graphite are very fragile, it is necessary for the probe to come in contact with the sample without damaging its surface when measuring the intrinsic electric conductivity. Therefore, three conductive AFM (c-AFM) cantilevers (PtIr5-coated, spring constant of 0.2 N/m, NANOSENSORS) were used as the contact probes. The contact between the cantilevers and the sample was confirmed by measuring the rapid increase in current. A constant current (Isample) was applied from probe 1 to probe 4, and the reference potential was measured by using probe 3. Because a soft contact by a cantilever tends to cause contact resistance fluctuations, a constant-current source was used instead of a constant-voltage source when applying a current to the sample. For STM and STP measurements, a probe made of electropolished tungsten (W) was used (probe 2). All the electric conduction measurements were performed in a UHV chamber (∼10–7 Pa) at room temperature, and the location of the tip apex on the surface was determined by optical microscopy (working distance, 25 mm; spatial resolution, ∼1 μm; Keyence Co., Ltd.) through the upper-side view port.
For the STM and STP measurements, a laboratory-built preamplifier was used to switch the circuit between the transimpedance amplifier mode (current measurement mode) and the potentiometer circuit mode (potentiometry mode) through a mechanical relay. Figure 1f shows a schematic of the STP measurement sequence. First, the preamplifier was set to the current measurement mode for STM imaging. Then, the scan was stopped at the measurement point in the image, and the tunnel resistance was decreased to about 10 MΩ orders by increasing the set-point current. Thereafter, the preamplifier was switched to the potentiometry mode, and the potential difference ΔΦ between the area immediately below the STM tip and probe 3 was measured.
When the applied current Isample is swept linearly, ΔΦ also changes linearly when the sample is metallic. Measurement errors, the fluctuation of the offset voltage due to such as the thermal electromotive force, can be eliminated by extracting the slope of ΔΦ/Isample. In addition, nonlinearity was sometimes observed in the current–voltage characteristics between probe 1 and probe 4 because of the effect of adhered materials at the AFM cantilever–sample contact point. This is considered to have caused the resistance at the contact point to change at certain applied voltages. However, the nonlinear change in resistance at the contact points of probes 1 and 4 can be eliminated by carrying out potentiometry to measure the potential difference ΔΦ between probes 2 and 3 with the four-tip probe method, while the position of probe 2 is changed. Namely, we can obtain the intrinsic resistivity of the sample by measuring ΔΦ generated by the applied constant current Isample, which is not affected by the nonlinear characteristics of the contact points. In fact, a linear ΔΦ–Isample curve, which reflects the metallic characteristics of the sample, was obtained.(34) By performing this process at each lattice point in the image during the STM scan, we obtained a 2D image of ΔΦ/Isample. Hereinafter, this measurement is called grid measurement.
The four-point probe method has been used for conductivity measurement in the past, and the validity of the analysis model has been confirmed by many measurements.(35) In this experiment, the AFM technique was used to minimize the contact force between the tip and the sample to suppress the damage to the sample, but the mechanism is the same as that of the previous method. Therefore, analysis can be performed using the same model.
For a sample with isotropic conductivity, the resistivity ρ can be represented as
(1)where siso,n–m is the distance between probe n and probe m (n, m: 1, 2, 3, 4) in the isotropic conduction model. To estimate the resistivity in the ab-plane, it is necessary to obtain an analytical formula by considering the conduction model (2D or 3D). The large anisotropy between the resistivity in the ab-plane and that along the c-axis was converted into the model with an isotropic resistivity using the scaling law(36,37) in
(2)where (x, y, z) and (xiso, yiso, ziso) represent the axes in the material with an anisotropic resistance and those in the converted space with an isotropic resistance, respectively. The x- and y-axes are in the ab-plane, and the z-axis corresponds to the c-axis direction. For a typical ratio of the electric conductivity of graphite (ρc/ρab = ∼5000(26)), when the length in the ab-plane and that along the c-axis are multiplied by 0.24 and 17, respectively, the model can be transformed into a rectangular model with an isotropic conductivity. Whether the conduction model is 2D or 3D is determined by the ratio of L′1–4 (distance between probe 1 and probe 4 after scaling) to t′ (the thickness of graphite after scaling); the model becomes 3D when t′/L′1–4 > 0.75.(38,39) In this experiment, by use of L1–4 = 23 μm and t = 2.1 μm, the ratio is t′/L′1–4 = 8.82 (L′1–4 = 5 μm, t′ = 44.1 μm), and a 3D model was employed. Finally, the analytic equation of the 3D conduction model considering the electric conductivity anisotropy between ρab and ρc is expressed as
(3)where sn–m is the actual distance between probe n and probe m (n, m: 1, 2, 3, 4). By applying the coordinate transformation of eq 2 to the interprobe distance siso,n–m in eq 1, and substituting ρ of eq 2 into eq 1, we obtain eq 3, which represents a model of the sample with anisotropic conductivity. Experiments were performed to obtain ρab by measuring ρc and the other parameters.
(1)where siso,n–m is the distance between probe n and probe m (n, m: 1, 2, 3, 4) in the isotropic conduction model. To estimate the resistivity in the ab-plane, it is necessary to obtain an analytical formula by considering the conduction model (2D or 3D). The large anisotropy between the resistivity in the ab-plane and that along the c-axis was converted into the model with an isotropic resistivity using the scaling law(36,37) in(2)where (x, y, z) and (xiso, yiso, ziso) represent the axes in the material with an anisotropic resistance and those in the converted space with an isotropic resistance, respectively. The x- and y-axes are in the ab-plane, and the z-axis corresponds to the c-axis direction. For a typical ratio of the electric conductivity of graphite (ρc/ρab = ∼5000(26)), when the length in the ab-plane and that along the c-axis are multiplied by 0.24 and 17, respectively, the model can be transformed into a rectangular model with an isotropic conductivity. Whether the conduction model is 2D or 3D is determined by the ratio of L′1–4 (distance between probe 1 and probe 4 after scaling) to t′ (the thickness of graphite after scaling); the model becomes 3D when t′/L′1–4 > 0.75.(38,39) In this experiment, by use of L1–4 = 23 μm and t = 2.1 μm, the ratio is t′/L′1–4 = 8.82 (L′1–4 = 5 μm, t′ = 44.1 μm), and a 3D model was employed. Finally, the analytic equation of the 3D conduction model considering the electric conductivity anisotropy between ρab and ρc is expressed as(3)where sn–m is the actual distance between probe n and probe m (n, m: 1, 2, 3, 4). By applying the coordinate transformation of eq 2 to the interprobe distance siso,n–m in eq 1, and substituting ρ of eq 2 into eq 1, we obtain eq 3, which represents a model of the sample with anisotropic conductivity. Experiments were performed to obtain ρab by measuring ρc and the other parameters.Figure 2a shows an optical microscopy image of the four probes during the measurement. As the current Isample flows from probe 1 to probe 4, ΔΦ between probe 2 and probe 3 was determined by a grid measurement. The scanning direction x of probe 1 was adjusted to be along the direction of Isample. The position of each probe was determined from the optical microscopy image considering the configuration of the cantilever, and the distances between the probes were estimated to be s1–2 = ∼9 μm, s2–4 = ∼27 μm, s1–3 = ∼16 μm, and s2–4 = ∼9 μm.
Figure 2
Figure 2. Results of MP-STM measurement in the ab-plane. (a) Optical microscopy image of the four probes during the measurement. (b) Topography image on which the grid measurement method was performed (1.5 × 1.5 μm2, tip bias Vt = 20 mV, and set-point current It = 30 pA). (c) 2D map of ΔΦ/Isample obtained over the surface in (b). The black arrow indicates the line corresponding to the green line in (b). (d) ΔΦ–Isample plot acquired in the black rectangles in (c). (e) Line profile of ΔΦ/Isample along the green line in (b). (f) Line profile of the topographic image along the green line in (b).
Figure 2b shows a topography image obtained over the area where the grid measurement was performed (1.5 × 1.5 μm2, tip bias Vt = 20 mV, and set-point current It = 30 pA), and the values of ΔΦ/Isample are shown in Figure 2c in a color scale. Although measurements at some points are missing in Figure 2c because we could not obtain the linear I–V curves at those points probably because of the fluctuations in the tunnel junction, atomic layer steps and grain boundaries were observed as indicated by the blue and black arrows, respectively.(40) As shown in Figure 2c, ΔΦ/Isample increased from left to right. The line indicated by the black arrow in Figure 2c shows the results obtained along the green line in Figure 2b, and the ΔΦ–Isample plot acquired in the black rectangles (1 to 3) is shown in Figure 2d. Each curve shows a linear characteristic, indicating that the sample is metallic, and the slopes of the curves are clearly different. The distribution of ΔΦ/Isample will later be discussed in comparison with the calculated results.
The line profiles of ΔΦ/Isample and the topographic image along the green line in Figure 2b are shown in Figures 2e and 2f, respectively. The ΔΦ/Isample plot is not sensitive to the surface structures; namely, there is no correspondence between the ΔΦ/Isample plot shown in Figure 2e and the structures of the atomic layer step and the grain boundary indicated by the blue and black triangles in Figures 2b and 2f. Namely, no voltage drop was observed at the grain boundaries.
Cross-Sectional STP Experiment and Analysis
To experimentally obtain ρc, we performed MP-STP measurement over a cross section, as schematically shown in Figure 3a (see the Methods section for details). Figure 3b shows an optical microscopy image of the upper side of the structure shown in Figure 3a. While applying a constant current through the Cu plates, the STM probe was made to approach the graphite cross section under observation with an optical microscope, and ΔΦ between the STM probe and the cantilever located in the Ag epoxy part was measured by STP.
Figure 3
Figure 3. Results of cross-sectional MP-STM measurement. (a) Setup of the MP-STP measurement over the cross section. (b) Optical microscopy image of the upper side of the structure shown in (a). (c) Tapping AFM topographic image of the surface shown in (b). (d) Amplitude image (differential image) of the topographic image shown in (c). (e) Line profile along the blue line shown in the topography image in (c). (f) 2D distribution of ΔΦ/Isample obtained by the grid measurement over a scanning range of 800 × 800 nm2. (g) Line profile of ΔΦ/Isample along the x-direction, in which ΔΦ/Isample was averaged in the y-direction.
Figure 3c shows a topographic image of the surface shown in Figure 3b obtained before the STP measurement by tapping AFM in the constant-amplitude mode. Figure 3d shows the amplitude image (differential image) of the topographic image, in which each edge region is clearly determined. The deep groove between the graphite and the silver epoxy on the left side is clearly observed. Figure 3e shows the line profile along the blue line shown in the topography image in Figure 3c. It was confirmed that the graphite part had a very flat cross section with a roughness of <3 nm. The slope observed on both sides is considered to have been formed during the cutting process.
Figure 3f shows the 2D distribution of ΔΦ/Isample obtained by grid measurement over a scanning range of 800 × 800 nm2. The scan direction x was parallel to the current direction. The feedback conditions were Vt = −3 mV and It = 10 pA. The topography image was acquired simultaneously with the STP measurement, and the cross-sectional surface was confirmed to be very flat (roughness p–p < 3 nm). ΔΦ/Isample was measured on each grid point by measuring ΔΦ while changing Isample stepwise between −9 and +9 mA. In this experiment, no nonlinearity was observed in the current–voltage characteristics at the contact point because of the formation of a wide contact area; therefore, ΔΦ was obtained from the difference between the two points (−9 and +9 mA). ΔΦ/Isample increases from left to right. The values averaged in the y-direction are shown in Figure 3g. The linearity was confirmed, from which the slope of ΔΦ/(Isampled) was obtained to be 2.45 ± 0.05 V A–1 m–1, where d is the length of the measured area along the x-direction. Therefore, ρc can be obtained from the simple 1D conduction model as
(4)where S, the area over which the graphite sample was measured by optical microscopy, was estimated to be 0.703 mm2. As shown in Figure 3a, a constant current was applied between the electrodes attached to both sides of the sample, and the voltage drop between them was measured by the four-probe method. Because the size of the ab-plane of the sample used is 1 mm × 0.7 mm, and the bulk part is very large compared with the edge area, the current that flowed on the bulk side is considered to be approximately equal to the applied constant current Isample. As a result, ρc was determined to be 1.72 ± 0.04 mΩ·m.
(4)where S, the area over which the graphite sample was measured by optical microscopy, was estimated to be 0.703 mm2. As shown in Figure 3a, a constant current was applied between the electrodes attached to both sides of the sample, and the voltage drop between them was measured by the four-probe method. Because the size of the ab-plane of the sample used is 1 mm × 0.7 mm, and the bulk part is very large compared with the edge area, the current that flowed on the bulk side is considered to be approximately equal to the applied constant current Isample. As a result, ρc was determined to be 1.72 ± 0.04 mΩ·m.Next, ρab was estimated from the data obtained from eq 3 and the value of ρc. Figure 4a shows a histogram of ρab calculated using the value of ΔΦ/Isample obtained at each grid point in Figure 2c by measuring the relationship shown in Figure 2d. From the peak value of the Gaussian fitting and its half-width at half-maximum, ρab was estimated to be 0.30 ± 0.01 μΩ·m. From these results, ρc/ρab was found to be ∼5.7 × 103. With this value, as shown in Figure 4b, if the length in the x- and y-directions is compressed 0.23 times and the length along the z-axis is stretched 18 times, transformation into an isotropic resistivity structure is realized. The scaling law applied to the isotropic conduction model was found to be t′/L′1–4 = 7.09 (t′ = 37.5 μm, L′1–4 = ∼ 5.3 μm). Because t′/L′1–4 > 0.75, it was confirmed that the application of the 3D model was reasonable.
Figure 4
Figure 4. Experimental and calculated results ρab. (a) Histogram of ρab calculated using ΔΦ/Isample obtained at each grid point in Figure 2c. (b) Scaling model from the original structure with high anisotropic resistivity (left) to the structure with isotropic resistivity. (c) 2D distribution of ΔΦ/Isample shown in Figure 2c. (d) ΔΦ/Isample obtained by calculation.
Finally, the 2D distribution of ΔΦ/Isample was calculated from the values of ρab and ρc. For comparison, the ΔΦ/Isample map in Figure 2c is shown in Figure 4c. Figure 4d shows the map of ΔΦ/Isample obtained by calculation using eq 3. Although the experimental values fluctuate because of the noise and the instability of the probe state, as shown in the histogram in Figure 4a, it was confirmed that the observed characteristics are consistent with the calculated values.
The ρab measured by the MP-STM method was estimated to be 0.30 ± 0.01 μΩ·m, which was about 30% lower than that (0.427 μΩ·m) obtained by the macroscale VDP method. This difference may be due to the fact that the measurement by the VDP method being performed in a region including grain boundaries. We made a simple estimation of their effects on the conductance.
In the case of a metallic material, the resistivity is expressed by Matthiesen’s rule as
(5)where ρT is the temperature-dependent term and the main factor, which originates from the scattering by phonons. ρimp is the term representing scattering due to impurities, which is considered to be independent of temperature. ρdef is the term related to defects. At room temperature, ρT is expected to be the dominant term, which is included in both MP-STP and VDP measurements. Therefore, assuming that the impurity level is low because of the controlled sample preparation environment, and thus the term ρimp is negligible, the difference between the results of MP-STP and VDP measurements is considered to be due to ρdef.
(5)where ρT is the temperature-dependent term and the main factor, which originates from the scattering by phonons. ρimp is the term representing scattering due to impurities, which is considered to be independent of temperature. ρdef is the term related to defects. At room temperature, ρT is expected to be the dominant term, which is included in both MP-STP and VDP measurements. Therefore, assuming that the impurity level is low because of the controlled sample preparation environment, and thus the term ρimp is negligible, the difference between the results of MP-STP and VDP measurements is considered to be due to ρdef.We discuss this result by converting the measurement conditions of a 0.01 × 0.01 m2 sheet of 2 μm thickness to a simple 1D resistance model. By use of an average grain size of 7.48 μm, the number of grain boundaries contained in each measurement area is roughly estimated to be ∼2 by MP-STP and ∼1337 by VDP. From these results and the resistivity ρab, the 1D resistance of the entire sheet is estimated to be ∼0.15 Ω by MP-STP (= R1D,MPSTP) and ∼0.21 Ω by VDP (= R1D,VDP). Assuming that the difference of ∼0.06 Ω (0.21–0.15 Ω) was only due to the difference in the number of grain boundaries contained in the measurement area, the resistance is ∼4.5 × 10–5 Ω (0.06/1335 Ω) per grain boundary. Using the grain boundary width of 10 nm(41) and the sample cross-sectional size (0.01 m × 2 μm), we estimated the resistivity of a grain boundary to be 9.0 × 10–5 Ω·m, which is lower than that in graphene reported previously (10–3–10–1 Ω·m).(41,42) The voltage drop at the grain boundaries is calculated to be ∼675 μV using the current density of ∼7.5 × 10–4 A/μm2 in the MP-STP measurement and the resistance of ∼4.5 × 10–5 Ω [7.5 × 10–4 A/μm2 × (0.01 m × 2 μm) × (4.5 × 10–5 Ω)] per a grain boundary. However, as shown in Figure 2e, the cross section microscopically obtained is almost linear, and the voltage drop observed in this experiment is less than the resolution of the system (∼10 μV).
The observed reduction in resistivity may be attributed to the effects originated from multilayer graphene. The effect of, for example, grain boundaries on the conductivity, which is very high in graphene,(41−44) is expected to be reduced in multilayer graphene because more conductive paths are formed in a multilayer structure because of the different locations of domains in the layers along the c-axis direction, parallel to the 2D sheet. In such a case, the effect of grain boundaries is reduced because current flows avoid the boundaries.
Therefore, what causes the difference between the values obtained by VDP and MP-STP methods? One possibility is the effect of the wrinkles shown in Figure 5a, which formed on the sample during heat treatment. Here, the sample was illuminated from right above, and the wrinkles in the direction of the shadow appeared widespread and black. Although it has been considered that the wrinkles formed are smooth, as observed in Figure 5b, and do not affect the resistance, to clarify its effect in more detail, the area including a wrinkle was measured by the four-point probe method.
Figure 5
Figure 5. Effect of wrinkles on the resistance of ρab. (a) Optical image of the wrinkles of the sample. (b) Optical image of the measured area with a wrinkle. (c) Optical image of the same area in (b) with a different light angle to make the wrinkle more visible. (d) Measurement area including a wrinkle. (e) Measurement area without wrinkle. (f) ΔΦ/Isample as a function of the position of tip 2. A and B correspond to those in (d). (g) ΔΦ/Isample as a function of the position of tip 2. C and D correspond to those in (e). Blue solid lines in (f) and (g) show the fitting curves obtained by using ρab as a parameter while retaining ρc constant.
Figure 5c shows an image of the same area shown in Figure 5b, in which the irradiation angle of light was changed to make the wrinkle appear. Figures 5f and 5g show the results of measurement across a wrinkle as shown in Figure 5d and in the area without wrinkles shown in Figure 5e, respectively. Fitting was performed using eq 3, where ρc was assumed to be constant and ρab was used as a fitting parameter. In Figure 5f, the obtained ρab (= 0.428 ± 0.01 μΩ·m) was almost the same as that (0.427 μΩ·m) obtained by the VDP method,(22) whereas the ρab (= 0.31 ± 0.01 μΩ·m) obtained for the area shown in Figure 5g was in good agreement with that obtained for the area shown in Figure 2 (0.30 ± 0.01 μΩ·m). That is the value obtained by VDP is affected by the smooth wrinkles. The slight deviation difference of the fitting curve from the experimental values between the left and right of the dotted line in Figure 5f may be due to the fact that the change in resistance is localized near the area surrounding the wrinkle.
SCNG is the graphite with the highest known conductivity, and although it is the result of measurement at the conventional macroscopic (millimeters) scale, we have used it because of its ideal structure without grain boundaries or wrinkles for comparison. However, the conductivity of SCNG is considered to be determined by the impurities contained during the crystal growth in addition to the effect of phonon vibration. In ref (47), the residual resistance (resistance components other than thermal phonons) of SCNG is shown to be 0.1 μΩ·m or less. This value is in good agreement with 0.08 μΩ·m, which is the difference between the current measurement result (0.30 μΩ·m) and that of SCNG (0.38 μΩ·m).
A more detailed examination of the area with wrinkles should be further studied, but the elimination of wrinkles is expected to provide high conductivity comparable to that in the ideal area. A method of eliminating wrinkles is currently underway. In addition, when forming thinner films by, for example, the chemical etching of multilayer graphite, it becomes increasingly difficult to evaluate the characteristics in the c-axis direction, and the method developed in this study is expected to play a key role. Analysis of dynamics by time-resolved measurement may give important information.(45,46)
Conclusion
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We performed measurements by MP-STP on a high-quality 2.7 μm thick graphite film with a large area fabricated by the PP method. In addition to the measurement of ρab over an ab-plane without wrinkles, MP-STP measurement over a cross section perpendicular to the ab-plane to acquire ρc along the c-axis was successfully achieved for the first time. The ρab, which was measured to be 0.427 μΩ·m by the VDP method, was found to be 0.30 ± 0.01 μΩ·m by MP-STP; that is, it was extremely lower than the previously reported lowest value of 0.38 μΩ·m for SCNG.(47) Although it is the result of four-terminal measurement at the conventional macroscopic (millimeters) scale, SCNG is the graphite with the highest known conductivity because of its ideal structure without grain boundaries or wrinkles. In fact, the residual resistance of SCNG, 0.1 μΩ·m or less, is in good agreement with 0.08 μΩ·m, which is the difference between the current measurement result (0.30 μΩ·m) and that of SCNG (0.38 μΩ·m). Therefore, the highest conductivity in the ab-plane, ∼1.3 times that of SCNG, may be the intrinsic and ultimate characteristic of multilayer graphite. The advantage of multilayer graphene, which reduces the effect of grain boundaries on conductance, was successfully confirmed. Therefore, when the density of wrinkles is decreased by improving the manufacturing conditions, it becomes possible to industrially produce large-area highest-quality graphite, which has never been produced. This is a major progress toward the realization of its future applications.
Methods
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Sample Synthesis
Sample graphite films were prepared as follows. Highly orientated PDMA/ODA (PDMA: 3,3′,4,4′-biphenyltetracarboxylic dianhydride; ODA: 4,4′-diaminodiphenyl ether) type PI films were used as raw materials. First, carbonization was performed by heating the films at ∼1000 °C in a nitrogen flow and then hollowed by using a graphite heater with the temperature increased to 3300 °C in an argon flow (heating rate: 20 °C/min; retention time at 3300 °C: 5 min).(21,22)
Sample Preparation for Cross-Sectional STP
First, after the vapor deposition of 200 nm thick gold (Au) along the ab-plane on both sides of a graphite sample, the sample was cut into a rectangular shape (∼0.5 × 1.5 mm2), and a 0.3 mm thick copper (Cu) plate of approximately the same size was adhered to each 200 nm thick Au layer, using a conductive silver (Ag) epoxy paste (resistivity ≤4 μΩ·m). At the same time, an insulating epoxy paste was applied to the edge of the graphite to prevent a short circuit between the Cu plates on both sides and the graphite edges and to accurately maintain the thickness of the graphite sample contributing to the measurement. Subsequently, the sample was cut roughly with a diamond cutter, and then a flat cross-sectional surface was formed by Ar ion sputtering (6 kV acceleration voltage, 10–5 Pa) by using a cross-sectional polisher (IM 4000 PLUS, Hitachi High-Technologies Corp.). A deep groove was observed between the graphite and the silver epoxy on the left side, as shown in Figure 3a–e, which was formed because of the shrinkage of the silver epoxy caused by the heat generated during the sputtering with the Ar beam.
ARTICLE SECTIONS
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsaelm.9b00298.
Electron backscattered diffraction pattern (EBSD) image, SEM image (PDF)
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Author Information
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- Hidemi Shigekawa - Faculty of Pure and Applied Sciences, University of Tsukuba, Tsukuba 305-8573, Japan;
http://orcid.org/0000-0001-9550-5148;
H.M., T.B., and A.T. performed the experiments. M.M. and Y.K. developed the PP method to grow high quality graphite sample films. M.Y. evaluated the sample quality by Raman spectroscopy and the EBSD method. S.Y. and O.T. provided technical advice. H.S. organized and supervised the project and edited the paper with H.M. and the other authors.
The authors declare no competing financial interest.
Acknowledgments
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H.S. acknowledges the financial support of a Grant-in-Aid for Scientific Research (17H06088) from Japan Society for the Promotion of Science. This work was supported in part by University of Tsukuba Nanofabrication Platform and the AIST Nano-Processing Facility in the “Nanotechnology Platform Project” sponsored by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.
References
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This article references 47 other publications.
- 1Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666– 669,[Crossref], [PubMed], [CAS], Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXos1Kqt70%253D&md5=488da13500bf24e8fc419052dc1a9e84Electric Field Effect in Atomically Thin Carbon FilmsNovoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A.Science (Washington, DC, United States) (2004), 306 (5696), 666-669CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)The authors describe monocryst. graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar elec. field effect such that electrons and holes in concns. up to 1013 per square centimeter and with room-temp. mobilities of ∼10,000 square centimeters per V-second can be induced by applying gate voltage.
- 2Wei, H.; Xiao, J.; Yang, Y.; Lv, S.; Shi, J.; Xu, X.; Dong, J.; Luo, Y.; Li, D.; Meng, Q. Free-Standing Flexible Carbon Electrode for Highly Efficient Hole-Conductor-Free Perovskite Solar Cells. Carbon 2015, 93, 861– 868,[Crossref], [CAS], Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXovVCisrY%253D&md5=f0df3ae12066694503ba926074a4f960Free-standing flexible carbon electrode for highly efficient hole conductor-free perovskite solar cellsWei, Huiyun; Xiao, Junyan; Yang, Yueyong; Lv, Songtao; Shi, Jiangjian; Xu, Xin; Dong, Juan; Luo, Yanhong; Li, Dongmei; Meng, QingboCarbon (2015), 93 (), 861-868CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)A free-standing thermoplastic C film with good flexibility and cond. was developed and introduced in perovskite solar cells for the 1st time. Due to its thermoplasticity, this free-standing C film can be directly hot pressed onto the perovskite layer as counter electrode. By optimization toward the components of C films and hot-pressing pressure, the back contact between the perovskite and C films was significantly improved. Up to 13.53% of power conversion efficiency was achieved, which is one of the highest efficiencies for hole transporting material-free perovskite solar cells. This kind of flexible C electrodes with the advantages of low-cost, simple and low-temp. (<100°) prepn. process and high efficiency, show great potential application in perovskite solar cells.
- 3Xu, Y.; Yu, H.; Wang, C.; Cao, J.; Chen, Y.; Ma, Z.; You, Y.; Wan, J.; Fang, X.; Chen, X. Multilayer Graphene with Chemical Modification as Transparent Conducting Electrodes in Organic Light-Emitting Diode. Nanoscale Res. Lett. 2017, 12, 254,[Crossref], [PubMed], [CAS], Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1cvltlOktA%253D%253D&md5=1d29aa4d78e38d89be7648639b85b176Multilayer Graphene with Chemical Modification as Transparent Conducting Electrodes in Organic Light-Emitting DiodeXu Yilin; Yu Haojian; Chen Yigang; Xu Yilin; Wang Cong; You Ying; Wan Jixiang; Fang Xiaohong; Chen Xiaoyuan; Yu Haojian; Cao Jin; Ma Zhongquan; You Ying; Wan Jixiang; Chen XiaoyuanNanoscale research letters (2017), 12 (1), 254 ISSN:1931-7573.Graphene is a promising candidate for the replacement of the typical transparent electrode indium tin oxide in optoelectronic devices. Currently, the application of polycrystalline graphene films grown by chemical vapor deposition is limited for their low electrical conductivity due to the poor transfer technique. In this work, we developed a new method of preparing tri-layer graphene films with chemical modification and explored the influence of doping and patterning process on the performance of the graphene films as transparent electrodes. In order to demonstrate the application of the tri-layer graphene films in optoelectronics, we fabricated the organic light-emitting diodes (OLEDs) based on them and found that plasma etching is feasible with certain influence on the quality of the graphene films and the performance of the OLEDs.
- 4Anagnostopoulos, G.; Pappas, P. N.; Li, Z.; Kinloch, I. A.; Young, R. J.; Novoselov, K. S.; Lu, C. Y.; Pugno, N.; Parthenios, J.; Galiotis, C.; Papagelis, K. Mechanical Stability of Flexible Graphene-Based Displays. ACS Appl. Mater. Interfaces 2016, 8, 22605– 22614,[ACS Full Text
], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht12jtr3I&md5=5923dc8b9c9abf3d76008fb4a319215dMechanical Stability of Flexible Graphene-Based DisplaysAnagnostopoulos, George; Pappas, Panagiotis-Nektarios; Li, Zheling; Kinloch, Ian A.; Young, Robert J.; Novoselov, Kostya S.; Lu, Ching Yu; Pugno, Nicola; Parthenios, John; Galiotis, Costas; Papagelis, KonstantinosACS Applied Materials & Interfaces (2016), 8 (34), 22605-22614CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)The mech. behavior of a prototype touch panel display, which consists of two layers of CVD graphene embedded into PET films, is investigated in tension and under contact-stress dynamic loading. In both cases, laser Raman spectroscopy was employed to assess the stress transfer efficiency of the embedded graphene layers. The tensile behavior was found to be governed by the "island-like" microstructure of the CVD graphene, and the stress transfer efficiency was dependent on the size of graphene "islands" but also on the yielding behavior of PET at relatively high strains. Finally, the fatigue tests, which simulate real operation conditions, showed that the max. temp. gradient developed at the point of "finger" contact after 80,000 cycles does not exceed the glass transition temp. of the PET matrix. The effect of these results on future product development and the design of new graphene-based displays are discussed. - 5Kim, J. Y.; Cho, N. S.; Cho, S.; Kim, K.; Cheon, S.; Kim, K.; Kang, S. Y.; Cho, S. M.; Lee, J. I.; Oh, J.; Kim, Y. H.; Ryu, H.; Hwang, C. S.; Kim, S.; Ah, C. S.; Kim, T. Y. Graphene Electrode Enabling Electrochromic Approaches for Daylight-Dimming Applications. Sci. Rep. 2018, 8, 3944,[Crossref], [PubMed], [CAS], Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1Mrnt1KrsA%253D%253D&md5=cdfddf43ec9a17feae320d5f6dae1b32Graphene Electrode Enabling Electrochromic Approaches for Daylight-Dimming ApplicationsKim Joo Yeon; Cheon Sanghoon; Cho Seong M; Kim Yong-Hae; Ryu Hojun; Hwang Chi-Sun; Kim Sujung; Ah Chil Seong; Kim Tae-Youb; Cho Nam Sung; Kang Seung-Youl; Oh Ji-Young; Cho Seungmin; Kim Kisoo; Cho Seungmin; Kim Kisoo; Kim Kyuwon; Lee Jeong-IkScientific reports (2018), 8 (1), 3944 ISSN:.For environmental reason, buildings increasingly install smart windows, which can dim incoming daylight based on active electrochromic devices (ECDs). In this work, multi-layered graphene (MLG) was investigated as an ECD window electrode, to minimize carbon dioxide (CO2) emissions by decreasing the electricity consumption for building space cooling and heating and as an alternative to the transparent conductor tin-doped indium oxide (ITO) in order to decrease dependence on it. Various MLG electrodes with different numbers of graphene layers were prepared with environmentally friendly poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) to produce ECD cells. Tests demonstrated the reproducibility and uniformity in optical performance, as well as the flexibility of the ECD fabrication. With the optimized MLG electrode, the ECD cells exhibited a very fast switching response for optical changes from transparent to dark states of a few hundred msec.
- 6Bae, S.; Kim, H.; Lee, Y.; Xu, X.; Park, J. S.; Zheng, Y.; Balakrishnan, J.; Lei, T.; Ri Kim, H.; Song, Y. Il; Kim, Y. J.; Kim, K. S.; Özyilmaz, B.; Ahn, J. H.; Hong, B. H.; Iijima, S. Roll-to-Roll Production of 30-Inch Graphene Films for Transparent Electrodes. Nat. Nanotechnol. 2010, 5, 574– 578,[Crossref], [PubMed], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXpvVSrur0%253D&md5=120e7e960a958f851c4b4049eaf90b19Roll-to-roll production of 30-inch graphene films for transparent electrodesBae, Sukang; Kim, Hyeongkeun; Lee, Youngbin; Xu, Xiangfan; Park, Jae-Sung; Zheng, Yi; Balakrishnan, Jayakumar; Lei, Tian; Kim, Hye Ri; Song, Young Il; Kim, Young-Jin; Kim, Kwang S.; Oezyilmaz, Barbaros; Ahn, Jong-Hyun; Hong, Byung Hee; Iijima, SumioNature Nanotechnology (2010), 5 (8), 574-578CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)The outstanding elec., mech. and chem. properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll prodn. and wet-chem. doping of predominantly monolayer 30-in. graphene films grown by chem. vapor deposition onto flexible copper substrates. The films have sheet resistances as low as ∼125 Ω .box.-1 with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as ∼30 Ω .box.-1 at ∼90% transparency, which is superior to com. transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.
- 7Yazami, R.; Touzain, P. A Reversible Graphite-Lithium Negative Electrode for Electrochemical Generators. J. Power Sources 1983, 9, 365– 371,[Crossref], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXktVyhu7k%253D&md5=b7a253d6bada57ee2ba6677ba114623eA reversible graphite-lithium anode for batteriesYazami, R.; Touzain, P.Journal of Power Sources (1983), 9 (3-4), 365-71CODEN: JPSODZ; ISSN:0378-7753.Li intercalation compds. in graphite were obtained by electrochem. methods using a solid org. electrolyte (polyethylene oxide with LiClO4). Intermittent electrochem. techniques enabled the kinetics (diffusion coeff.) and thermodn. (enthalpy) values to be calcd. Some secondary battery cycling tests using Li-graphite anodes are reported.
- 8Blomquist, N.; Wells, T.; Andres, B.; Bäckström, J.; Forsberg, S.; Olin, H. Metal-Free Supercapacitor with Aqueous Electrolyte and Low-Cost Carbon Materials. Sci. Rep. 2017, 7, 39836,[Crossref], [PubMed], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmsVClsw%253D%253D&md5=964116a5bf7c1242642ae69400c6433fMetal-free supercapacitor with aqueous electrolyte and low-cost carbon materialsBlomquist, Nicklas; Wells, Thomas; Andres, Britta; Baeckstroem, Joakim; Forsberg, Sven; Olin, HaakanScientific Reports (2017), 7 (), 39836CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)Elec. double-layer capacitors (EDLCs) or supercapacitors (SCs) are fast energy storage devices with high pulse efficiency and superior cyclability, which makes them useful in various applications including electronics, vehicles and grids. Aq. SCs are considered to be more environmentally friendly than those based on org. electrolytes. Because of the corrosive nature of the aq. environment, however, expensive electrochem. stable materials are needed for the current collectors and electrodes in aq. SCs. This results in high costs for a given energy-storage capacity. To address this, we developed a novel low-cost aq. SC using graphite foil as the current collector and a mix of graphene, nanographite, simple water-purifn. carbons and nanocellulose as electrodes. The electrodes were coated directly onto the graphite foil by using casting frames and the SCs were assembled in a pouch cell design. With this approach, we achieved a material cost redn. of greater than 90% while maintaining approx. one-half of the specific capacitance of a com. unit, thus demonstrating that the proposed SC can be an environmentally friendly, low-cost alternative to conventional SCs.
- 9Yu, A.; Roes, I.; Davies, A.; Chen, Z. Ultrathin, Transparent, and Flexible Graphene Films for Supercapacitor Application. Appl. Phys. Lett. 2010, 96, 253105,[Crossref], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXnvFShsrY%253D&md5=e3ad6104fc553414b3e858b605e1ea36Ultrathin, transparent, and flexible graphene films for supercapacitor applicationYu, Aiping; Roes, Isaac; Davies, Aaron; Chen, ZhongweiApplied Physics Letters (2010), 96 (25), 253105/1-253105/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)This study reports the prepn. of ultrathin, transparent graphene films for use in supercapacitor applications. The surface morphol. of the films was investigated by SEM and transmission electron microscopy, revealing a very homogeneous surface with intimate contact between graphene sheets. Electrochem. characterization demonstrated nearly ideal elec. double layer capacitive behavior. The capacitance obtained from charge-discharge anal. is 135 F/g for a film of ∼25 nm which has a transmittance of 70% at 550 nm and a high power d. of 7200 W/kg in 2M KCl electrolyte. (c) 2010 American Institute of Physics.
- 10Hannay, N. B.; Geballe, T. H.; Matthias, B. T.; Andres, K.; Schmidt, P.; MacNair, D. Superconductivity in Graphitic Compounds. Phys. Rev. Lett. 1965, 14, 225– 226,[Crossref], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF2MXlsF2ntg%253D%253D&md5=83a89930ac96e63ea1093e65905ded32Superconductivity in graphite compoundsHannay, N. B.; Geballe, T. H.; Matthias, B. T.; Andres, K.; Schmidt, P.; MacNair, D.Physical Review Letters (1965), 14 (7), 225-6CODEN: PRLTAO; ISSN:0031-9007.Supercond. was studied in intercalation compds. of graphite with alkali metals (K, Rb, or Cs). The transition temps. observed were 0.020-0.135°K. for Cs, 0.023-0.151°K. in the Rb system, and ≤0.55°K. in the K system. The width for any given transition is of the order of several millidegrees. The structure of these compds. is anisotropic.
- 11Belash, I.; Zharikov, O.; Palnichenko, A. Superconductivity of GIC with Li, Na and K. Synth. Met. 1989, 34, 455– 460,
- 12Larkins, G.; Vlasov, Y.; Holland, K. Evidence of Superconductivity in Doped Graphite and Graphene. Supercond. Sci. Technol. 2016, 29, 015015,[Crossref], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xjt1Kmsb4%253D&md5=ae152258300f7fd93425f002f303e5bdEvidence of superconductivity in doped graphite and graphemeLarkins, Grover; Vlasov, Yuriy; Holland, KiarSuperconductor Science and Technology (2016), 29 (1), 015015/1-015015/10CODEN: SUSTEF; ISSN:0953-2048. (IOP Publishing Ltd.)We have obsd. evidence of supercond. at temps. in the vicinity of 260 K in phosphorus-doped graphite and graphene. This evidence includes transport current, magnetic susceptibility, Hall effect and (pancake) vortex state measurements. All of these measurements indicate a transition which is that of a type II superconductor with no type I phase until below the limits of our measurement capabilities. Vortex states are inferred from periodically repeated steps in the resistance vs. temp. characteristics of highly oriented pyrolytic graphite and exfoliated doped multilayer graphene. Magnetic susceptibility measurements have shown results qual. similar to those expected (and exptl. obsd. by others) for ultra-thin (thickness « λL) films. The magnetization is neg. for field-cooled and zero-field-cooled measurements. The magnetization for field cooled and zero-field-cooled measurements begin to diverge at approx. 260 K. Hall effect measurements show a sign reversal in the Hall voltage as the temp. is reduced from 300 K to 78 K.
- 13Cui, X.; Lee, G. H.; Kim, Y. D.; Arefe, G.; Huang, P. Y.; Lee, C. H.; Chenet, D. A.; Zhang, X.; Wang, L.; Ye, F.; Pizzocchero, F.; Jessen, B. S.; Watanabe, K.; Taniguchi, T.; Muller, D. A.; Low, T.; Kim, P.; Hone, J. Multi-Terminal Transport Measurements of MoS2 Using a van Der Waals Heterostructure Device Platform. Nat. Nanotechnol. 2015, 10, 534– 540,[Crossref], [PubMed], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXnvFSlurw%253D&md5=52f54b0a75a286916e5084d4bd008758Multi-terminal transport measurements of MoS2 using a van der Waals heterostructure device platformCui, Xu; Lee, Gwan-Hyoung; Kim, Young Duck; Arefe, Ghidewon; Huang, Pinshane Y.; Lee, Chul-Ho; Chenet, Daniel A.; Zhang, Xian; Wang, Lei; Ye, Fan; Pizzocchero, Filippo; Jessen, Bjarke S.; Watanabe, Kenji; Taniguchi, Takashi; Muller, David A.; Low, Tony; Kim, Philip; Hone, JamesNature Nanotechnology (2015), 10 (6), 534-540CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Atomically thin two-dimensional semiconductors such as MoS2 hold great promise for elec., optical and mech. devices and display novel phys. phenomena. However, the electron mobility of mono- and few-layer MoS2 has so far been substantially below theor. predicted limits, which has hampered efforts to observe its intrinsic quantum transport behaviors. Potential sources of disorder and scattering include defects such as sulfur vacancies in the MoS2 itself as well as extrinsic sources such as charged impurities and remote optical phonons from oxide dielecs. To reduce extrinsic scattering, we have developed here a van der Waals heterostructure device platform where MoS2 layers are fully encapsulated within hexagonal boron nitride and elec. contacted in a multi-terminal geometry using gate-tunable graphene electrodes. Magneto-transport measurements show dramatic improvements in performance, including a record-high Hall mobility reaching 34,000 cm2 V-1 s-1 for six-layer MoS2 at low temp., confirming that low-temp. performance in previous studies was limited by extrinsic interfacial impurities rather than bulk defects in the MoS2. We also obsd. Shubnikov-de Haas oscillations in high-mobility monolayer and few-layer MoS2. Modeling of potential scattering sources and quantum lifetime anal. indicate that a combination of short-range and long-range interfacial scattering limits the low-temp. mobility of MoS2.
- 14Hishiyama, Y.; Kaburagi, Y. Electrical Resistivity of Highly Crystallized Kish Graphite. Carbon 1992, 30, 483– 486,[Crossref], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XkvVSkurw%253D&md5=10ed48d785926d1efdb6edc70dd0a7d9Electrical resistivity of highly crystallized kish graphiteHishiyama, Yoshihiro; Kaburagi, YutakaCarbon (1992), 30 (3), 483-6CODEN: CRBNAH; ISSN:0008-6223.Large and highly crystd. kish graphite flakes were obtained and the temp. dependence was detd. of the in-plane elec. resistivity for the specimens with the ρ300/ρ4.2K values of 56 and 106 at temps. between 1.28 and 300 K. The temp.-dependent component of the resistivity ρT was examd. precisely, particularly at low temps. Below about 5 K, ρT is proportional to T2, then increases faster to nearly T1 (ρT .varies. T2.7) to ∼15 K with increasing T. This is the intrinsic behavior of ρT for graphite crystal because of high crystallinity of the present specimens. The T2.7 dependence at 5-15 K is due to the scattering of carriers by the out-of-plane phonons, whereas the T2 dependence at temps. below about 5 K is attributed to the electron-hole scattering.
- 15Moore, A. W. Highly Oriented Pyrolytic Graphite. Chem. Phys. Carbon 1973, 11, 69– 187[CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXnslyg&md5=716d5c7a3c2dd8959d4323820f5a8128Highly oriented pyrolytic graphiteMoore, A. W.Chemistry and Physics of Carbon (1973), 11 (), 69-187CODEN: CPHCAY; ISSN:0069-3138.A review with 256 refs. on the structure, properties, and applications of highly oriented graphite obtained by the severe thermal annealing or stress annealing of pyrolytic carbons.
- 16Spain, I. L.; Ubbelohde, A. R.; Young, D. A. Electronic Properties of Well Oriented Graphite. Philos. Trans. R. Soc., A 1967, 262, 345– 386,[Crossref], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1cXksFGhtb8%253D&md5=263e720c96c3a2b848ffca01c46b7e92Electronic properties of well oriented graphiteSpain, I. L.; Ubbelohde, A. R.; Young, D. A.Philosophical Transactions of the Royal Society of London, Series A: Mathematical, Physical and Engineering Sciences (1967), 262 (1128), 345-86CODEN: PTRMAD; ISSN:1364-503X.A range of dense well-oriented graphites of high chem. purity was prepd. by stress recrystn. of pyrolytic material. Systematic trends in the galvanomagnetic and thermoelec. properties were investigated in these samples, in relation to c-axis distribution function, crystallite size, and basal-plane dislocation concn., at temps. from 300 to 1.2°K. and magnetic fields ≤6700 gauss. Basal plane properties of ideal graphite were evaluated in terms of the trends observed. The electronic properties were measured parallel to the c-axis for corresponding graphites with a range of defect concns. From the trends established, est. were made of various properties of ideal defect-free graphite in the c-axis direction, and of anisotropy ratios. The effects of neutrons irradn. on some of the electronic properties were also studied. The results are discussed in terms of multicarrier models.
- 17Murakami, M.; Nishiki, N.; Nakamura, K.; Ehara, J.; Okada, H.; Kouzaki, T.; Watanabe, K.; Hoshi, T.; Yoshimura, S. High-Quality and Highly Oriented Graphite Block from Polycondensation Polymer Films. Carbon 1992, 30, 255– 262,[Crossref], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38Xhsl2lsLc%253D&md5=0123850791b924fe8f1a36509e8822deHigh-quality and highly oriented graphite block from polycondensation polymer filmsMurakami, M.; Nishiki, N.; Nakamura, K.; Ehara, J.; Okada, H.; Kouzaki, T.; Watanabe, K.; Hoshi, T.; Yoshimura, S.Carbon (1992), 30 (2), 255-62CODEN: CRBNAH; ISSN:0008-6223.High-quality and highly oriented graphite was produced in the form of a thick block having phys. properties close to those of single-crystal graphite. It was prepd. from 25-μm-thick polyimide films with high mol. orientation. A sheath of the films was heat treated in an Ar atm. at ≤1000° (carbonization) and then heated for graphitization up to 3000° under a pressure between 100 and 300 kg/cm2. Graphite blocks as large as 150 × 50 × 13 mm3 were prepd., and the mosaic spread (the degree of preferred orientation) attained was 0.4°.
- 18Murakami, M.; Yoshimura, S. Highly Conductive Pyropolymer and High-Quality Graphite from Polyoxadiazole. Synth. Met. 1987, 18, 509– 514,[Crossref], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXhs1Kqurk%253D&md5=2a4e2b3b39172ea4ee14e34d630e0a4aHighly conductive pyropolymer and high-quality graphite from polyoxadiazoleMurakami, M.; Yoshimura, S.Synthetic Metals (1987), 18 (1-3), 509-14CODEN: SYMEDZ; ISSN:0379-6779.High-temp. heat treatment of a heat-resistant condensation polymer, polyoxadiazole, POD, yielded a large-area, flexible film composed of highly oriented and nearly ideal graphite crystallites. The graphitic behavior for POD heat-treated above 2800° was exemplified by the (002) lattice spacing of 3.354 Å, elec. cond. along the basal plane of 12,000-18,000 S/cm, laser Raman spectra, and TEM observations. Intercalation compds. of HNO3-GPOD (graphitized POD) showed the highest cond. of 3.2 × 105 S/cm with fairly good stability in air.
- 19Murakami, M.; Watanabe, K.; Yoshimura, S. High quality Pyrographite Films. Appl. Phys. Lett. 1986, 48, 1594– 1596,[Crossref], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28Xktleitb0%253D&md5=2760c0f089c9b3cf6dcb964d02bb8b09High-quality pyrographite filmsMurakami, Mutsuaki; Watanabe, Kazuhiro; Yoshimura, SusumuApplied Physics Letters (1986), 48 (23), 1594-6CODEN: APPLAB; ISSN:0003-6951.High-temp. heat treatment of a heat-resistant, condensation polymer poly(p-phenylene-1,3,4-oxadiazole) yielded a large-area, flexible film composed of highly oriented and nearly ideal graphite crystallites. The graphitic behavior was exemplified by both the (002) lattice spacing of 3.354 Å and extremely small full width at half-max. intensity of the (002) reflection, 0.16-0.17°, for the films heat treated above 2800°.
- 20Kaneka Corp.; http://www.kaneka.co.jp/en/.Google ScholarThere is no corresponding record for this reference.
- 21Kaburagi, Y.; Hishiyama, Y. Highly Crystallized Graphite Films Prepared by High-Temperature Heat Treatment from Carbonized Aromatic Polyimide Films. Carbon 1995, 33, 773– 777,[Crossref], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXms1ahsrg%253D&md5=b464d930f514a0f45614c903ce92de43Highly crystallized graphite films prepared by high-temperature heat treatment from carbonized aromatic polyimide filmsKaburagi, Yutaka; Hishiyama, YoshihiroCarbon (1995), 33 (6), 773-7CODEN: CRBNAH; ISSN:0008-6223. (Elsevier)Highly crystd. graphite films were prepd. by successive heat treatments at 3100°C for 40 min and then 3200°C for 23 min under atm. pressure of pure argon gas from thin carbonized polyimide films. The starting polyimide films were a com. available Kapton and a lab. prepd. high-modulus-polyimide film formed via polyamic acid gel. The crystallinity of the graphite films obtained was examd. by the measurements of interlayer spacing d002, mosaic spread MS, elec. cond. σ at 300 and 77 K, residual resistivity ratio RRR, and max. transverse magnetoresistance (Δρ/ρ)max, mean magnetoresistance anisotropy ratio r, and Hall coeff. RH at 77 K. The present graphite films exhibit the highest crystallinity as graphite films obtained from polyimide films (i.e., the values of d002, MS, σ at 300 K, RRR, and (Δρ/ρ)max and r in the field of 1 T at 77 K were 0.3354 nm, 1.7-2.3°, 1.80-2.14 × 106 S/m, 13.49-17.26 and 0.0040-0.0086, resp., and small pos. values of RH in fields around 0.2 T at 77 K were obsd.).
- 22Murakami, M.; Tatami, A.; Tachibana, M. Fabrication of High Quality and Large Area Graphite Thin Films by Pyrolysis and Graphitization of Polyimides. Carbon 2019, 145, 23– 30,[Crossref], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVars7s%253D&md5=7fbb23ee4b073252bacd043e13140c43Fabrication of high quality and large area graphite thin films by pyrolysis and graphitization of polyimidesMurakami, Mutsuaki; Tatami, Atsushi; Tachibana, MasamitsuCarbon (2019), 145 (), 23-30CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)We have developed large-area, high-quality graphite thin films that are 0.5-3 μm thick. To prep. the graphite films, we used pyrolysis and graphitization of polyimide up to temps. in the range 2900 °C-3300 °C, which is applicable to industrial-prodn. processing. Given that the graphite layers of the films are highly oriented in the surface plane, they have good phys. properties. The resulting elec. cond. of graphite film of thickness 1.4 μm and area 10 × 10 cm2 that was treated at 3200 °C is 24,800 S/cm, and the elec. cond. showed metallic temp. dependence. The carrier mobility of the film is 11,700 V/cm2, and the carrier concns. of electrons (Ne) and holes (Nh) are 6.98 × 1018 cm-3 and 5.90 × 1018 cm-3, resp. We consider the high elec. cond. and mobility to have been derived from the homogeneous, highly oriented graphite layers. We found that graphitization of films less than 3 μm thick progresses uniformly throughout the film, and the resulting graphite films have structures with uniform, highly oriented layers. The produced graphite thin films have excellent phys. properties and can be easily handled, so we believe that many industrial applications are possible.
- 23Ohashi, Y.; Koizumi, T.; Yoshikawa, T.; Shiiki, T.; Hironaka, K. Size Effect Inthe Thin Electrical Crystals Resistivity of Very Graphite. Tanso 1997, 180, 235– 238,[Crossref], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXhtlKku7g%253D&md5=62647d9534457ffbc73306c9ab05d877Size effect in the in-plane electrical resistivity of very thin graphite crystalsOhashi, Y.; Koizumi, T.; Yoshikawa, T.; Hironaka, T.; Shiiki, K.Tanso (1997), 180 (), 235-238CODEN: TASOA3; ISSN:0371-5345. (Tanso Zairyo Gakkai)To investigate the effect of film thickness of thin graphite crystals on the elec. properties, we prepd. thin graphite films by cleaving a kish graphite (KG) crystal with the rrr value of 32.3. The values of the thickness of the graphite films were 300-1000 Å. Keeping these graphite films free from strain, we measured the temp. dependence of the in-plane resistivity between liq. helium and room temps. The exptl. results could be expressed by a simple two band model and the Sugihara's theory for lattice vibration in thin-carbon films. By using these expressions, we estd. the overlap E0 of conduction and valence bands for the thin graphite films with various thicknesses. It was found that E0 decreases with decreasing film thickness. We also estd. the reciprocal of the relaxation time due to lattice defects or surface scattering 1/τi and that due to lattice vibration 1/τi for the thin films with various thicknesses. Consequently, it was found that the effect of 1/τi and that due to lattice vibration 1/τi for the thin films with various thicknesses. Consequently, it was found that the effect of 1/τi increases rapidly, as the film thickness decreases.
- 24Venugopal, G.; Kim, S. J. Temperature Dependence of Planar-Type Graphite Structures. J. Korean Phys. Soc. 2009, 55, 1102– 1105,[Crossref], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtlSkurrN&md5=856a634669fed3cea9da2f26f957331bTemperature dependence of planar-type graphite structuresVenugopal, Gunasekaran; Kim, Sang-JaeJournal of the Korean Physical Society (2009), 55 (3, Pt. 1), 1102-1105CODEN: JKPSDV; ISSN:0374-4884. (Korean Physical Society)We have characterized the temp. dependence of the transport behavior for planar-type structures along ab-plane fabricated in micron-scale graphite layers. The planar-type structures of graphite layers were fabricated by using a focused ion beam (FIB) etching method. In-plane areas of 10 μm × 10 μm, 6 μm × 5 μm, 6 μm × 2 μm, and 1 μm × 1 μm exhibit semi-conducting behaviors which is contradictory to conventional metallic behavior of graphite flakes and show a small drop in resistance around 49 K. The origin of this effect is suspected from Ga+ ion damage during FIB fabrication. The fabricated planar-type structures show a transition in the current (I) - voltage (V) curves from diode-like characteristics around 30 K to an Ohmic behavior around 300 K.
- 25Berger, C.; Song, Z.; Li, T.; Li, X.; Ogbazghi, A. Y.; Feng, R.; Dai, Z.; Marchenkov, A. N.; Conrad, E. H.; First, P. N.; de Heer, W. A. Ultrathin Epitaxial Graphite: 2D Electron Gas Properties and a Route toward Graphene-Based Nanoelectronics. J. Phys. Chem. B 2004, 108, 19912– 19916,[ACS Full Text], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXhtVegtb7I&md5=a720c4bfb799b6b35cec80d2c32a08fbUltrathin epitaxial graphite: two-dimensional electron gas properties and a route toward graphene-based nanoelectronicsBerger, Claire; Song, Zhimin; Li, Tianbo; Li, Xuebin; Ogbazghi, Asmerom Y.; Feng, Rui; Dai, Zhenting; Marchenkov, Alexei N.; Conrad, Edward H.; First, Phillip N.; de Heer, Walt A.Journal of Physical Chemistry B (2004), 108 (52), 19912-19916CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)The authors have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically three graphene sheets, were grown by thermal decompn. on the (0001) surface of 6H-SiC, and characterized by surface science techniques. The low-temp. conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kΩ to 225 kΩ at 4 K, with pos. magnetoconductance). Low-resistance samples show characteristics of weak localization in two dimensions, from which the authors est. elastic and inelastic mean free paths. At low fields, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of d. 1012 cm-2 per graphene sheet. The most highly ordered sample exhibits Shubnikov-de Haas oscillations that correspond to nonlinearities obsd. in the Hall resistance, indicating a potential new quantum Hall system. The authors show that the high-mobility films can be patterned via conventional lithog. techniques, and they demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nanopatterned epitaxial graphene (NPEG), with the potential for large-scale integration.
- 26Tsang, D. Z.; Dresselhaus, M. S. The C-Axis Electrical Conductivity of Kish Graphite. Carbon 1976, 14, 43– 46,[Crossref], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE28XlslSiurk%253D&md5=74c79d6b421cff98419eeacdaac54cd8The c-axis electrical conductivity of kish graphiteTsang, D. Z.; Dresselhaus, M. S.Carbon (1976), 14 (1), 43-6CODEN: CRBNAH; ISSN:0008-6223.The magnitude and temp. dependence of the x-axis d.c. cond. in kish graphite were similar to those in single crystal graphite but qual. different from those in pyrolytic graphite. Because of differences in the impurity and defect d. between kish and single crystal graphite, the present results supported a band conduction model for c-axis conduction in graphite.
- 27Primak, W.; Fuchs, L. H. Electrical Conductivities of Natural Graphite Crystals. Phys. Rev. 1954, 95, 22– 30,
- 28Valdes, L. Resistivity Measurements on Germanium for Transistors. Proc. IRE 1954, 42, 420– 427,
- 29Muralt, P.; Pohl, D. W. Scanning Tunneling Potentiometry. Appl. Phys. Lett. 1986, 48, 514– 516,[Crossref], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XhsVSiur8%253D&md5=ee0634e61db06979200649c6ab3d50e9Scanning tunneling potentiometryMuralt, P.; Pohl, D. W.Applied Physics Letters (1986), 48 (8), 514-16CODEN: APPLAB; ISSN:0003-6951.In certain problems of elec. transport through condensed matter, it is important to know the potential distribution with microscope resoln., e.g., at interfaces (Schottky barriers) or pn junctions. Scanning tunneling potentiometry, a new application of scanning tunneling microscopy, is capable of providing this information. The tunnel current is used for simultaneously sensing probe-to-sample distance and local potential. The method was tested with a Au-island metal-insulator-metal structure.
- 30Lüpke, F.; Korte, S.; Cherepanov, V.; Voigtländer, B. Scanning Tunneling Potentiometry Implemented into a Multi-Tip Setup by Software. Rev. Sci. Instrum. 2015, 86, 123701,[Crossref], [PubMed], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFemt73E&md5=56b461b96c5bd66551400158a94412f9Scanning tunneling potentiometry implemented into a multi-tip setup by softwareLuepke, F.; Korte, S.; Cherepanov, V.; Voigtlaender, B.Review of Scientific Instruments (2015), 86 (12), 123701/1-123701/7CODEN: RSINAK; ISSN:0034-6748. (American Institute of Physics)The authors present a multi-tip scanning tunneling potentiometry technique that can be implemented into existing multi-tip scanning tunneling microscopes without installation of addnl. hardware. The resulting setup allows flexible in situ contacting of samples under UHV conditions and subsequent measurement of the sample topog. and local elec. potential with resoln. down to Å and μV, resp. The performance of the potentiometry feedback is demonstrated by thermovoltage measurements on the Ag/Si(111) - (√(3) × √(3))R30o surface by resolving a standing wave pattern. Subsequently, the ability to map the local transport field as a result of a lateral current through the sample surface is shown on Ag/Si(111) - (√(3) × √(3))R30o and Si(111) - (7 × 7) surfaces. (c) 2015 American Institute of Physics.
- 31van der Pauw, L. J. A Method of Measuring Specific Resistivity and Hall Eeffect of Discs of Arbitrary Shape. Philips Res. Rep. 1958, 13, 1– 9Google ScholarThere is no corresponding record for this reference.
- 32Yoshida, A.; Hishiyama, Y. Electron Channeling Effect on Highly Oriented Graphites-Size Evaluation and Oriented Mapping of Crystals. J. Mater. Res. 1992, 7, 1400– 1405,[Crossref], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XksF2ls7g%253D&md5=01fe94a61c40d8c3f44eb26a54f87068Electron channeling effect on highly oriented graphites - size evaluation and oriented mapping of crystalsYoshida, Akira; Hishiyama, YoshihiroJournal of Materials Research (1992), 7 (6), 1400-5CODEN: JMREEE; ISSN:0884-2914.Structural studies on kish graphite and highly oriented pyrolytic graphite were performed using electron channeling patterns and micrographs in SEM. The av. crystal size and orientation were detd.
- 33Kaburagi, Y.; Yoshida, A.; Hishiyama, Y. Microtexture of Highly Crystallized Graphite as Studied by Galvanomagnetic Properties and Electron Channeling Contrast Effect. J. Mater. Res. 1996, 11, 769– 778,[Crossref], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XhsFejtrk%253D&md5=8a04ecce7c855b57f686525a6e21f4baMicrotexture of highly crystallized graphite as studied by galvanomagnetic properties and electron channeling contrast effectKaburagi, Yutaka; Yoshida, Akira; Hishiyama, YoshihiroJournal of Materials Research (1996), 11 (3), 769-78CODEN: JMREEE; ISSN:0884-2914. (Materials Research Society)The relationship between microtexture and crystallinity of highly crystd. graphites with the residual resistivity ratio ρ300K/ρ4.2K of 3.45-5.50 was investigated. The graphite crystals studied were kish graphite (KG), highly oriented pyrolytic graphite (HOPG), and highly crystd. graphite films prepd. from carbonized arom. polyimide films. The study was made by the observation of an electron channeling pattern and electron channeling contrast image (ECI) under scanning electron microscope and the measurements of x-ray diffraction, magnetoresistance, and Hall coeff. The values of the mean free path of the carriers λ, which approximates the mean crystal grain size, were estd. to be 2.6-6.1 μm from the magnetoresistance at 4.2 K for the highly crystd. graphites. The values of the av. crystal grain diam. D in the basal plane evaluated from ECI were several hundred microns or more for KG, 60 μm for HOPG, and 6 and 12 μm for the graphite films. The difference between the values of λ and D for each crystd. graphite was discussed in relation to other results obtained.
- 34Zhang, Y.; Small, J. P.; Pontius, W. V.; Kim, P. Fabrication and Electric-Field-Dependent Transport Measurements of Mesoscopic Graphite Devices. Appl. Phys. Lett. 2005, 86, 073104,[Crossref], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXit1ent7s%253D&md5=e99e0d56d953a6e42f310516b2791352Fabrication and electric-field-dependent transport measurements of mesoscopic graphite devicesZhang, Yuanbo; Small, Joshua P.; Pontius, William V.; Kim, PhilipApplied Physics Letters (2005), 86 (7), 073104/1-073104/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)The authors have developed a unique micromech. method to ext. extremely thin graphite samples. Graphite crystallites with thicknesses ranging from 10 to 100 nm and lateral size ∼2 μm are extd. from the bulk. Mesoscopic graphite devices are fabricated from these samples for elec. field-dependent conductance measurements. Strong conductance modulation as a function of gate voltage is obsd. in the thinner crystallite devices. The temp.-dependent resistivity measurements show more boundary scattering contribution in the thinner graphite samples.
- 35Miccoli, I.; Edler, F.; Pfnür, H.; Tegenkamp, C. The 100th Anniversary of the Four-Point Probe Technique: The Role of Probe Geometries in Isotropic and Anisotropic Systems. J. Phys.: Condens. Matter 2015, 27, 223201,[Crossref], [PubMed], [CAS], Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2MfkvFOktQ%253D%253D&md5=d147689a00ac6b6c1f3d3b2e91ca77f1The 100th anniversary of the four-point probe technique: the role of probe geometries in isotropic and anisotropic systemsMiccoli I; Edler F; Pfnur H; Tegenkamp CJournal of physics. Condensed matter : an Institute of Physics journal (2015), 27 (22), 223201 ISSN:.The electrical conductivity of solid-state matter is a fundamental physical property and can be precisely derived from the resistance measured via the four-point probe technique excluding contributions from parasitic contact resistances. Over time, this method has become an interdisciplinary characterization tool in materials science, semiconductor industries, geology, physics, etc, and is employed for both fundamental and application-driven research. However, the correct derivation of the conductivity is a demanding task which faces several difficulties, e.g. the homogeneity of the sample or the isotropy of the phases. In addition, these sample-specific characteristics are intimately related to technical constraints such as the probe geometry and size of the sample. In particular, the latter is of importance for nanostructures which can now be probed technically on very small length scales. On the occasion of the 100th anniversary of the four-point probe technique, introduced by Frank Wenner, in this review we revisit and discuss various correction factors which are mandatory for an accurate derivation of the resistivity from the measured resistance. Among others, sample thickness, dimensionality, anisotropy, and the relative size and geometry of the sample with respect to the contact assembly are considered. We are also able to derive the correction factors for 2D anisotropic systems on circular finite areas with variable probe spacings. All these aspects are illustrated by state-of-the-art experiments carried out using a four-tip STM/SEM system. We are aware that this review article can only cover some of the most important topics. Regarding further aspects, e.g. technical realizations, the influence of inhomogeneities or different transport regimes, etc, we refer to other review articles in this field.
- 36Wasscher, J. D. Note on Four-Point Resistivity Measurements on Anisotropic Conductors. Philips Res. Rep. 1946, 157, 301– 306Google ScholarThere is no corresponding record for this reference.
- 37van der Pauw, L. J. Determination of Resistivity Tensor and Hall Tensor of Anisotropic Conductors. Philips Res. Rep. 1961, 16, 187– 195Google ScholarThere is no corresponding record for this reference.
- 38Shiraki, I.; Tanabe, F.; Hobara, R.; Nagao, T.; Hasegawa, S. Independently Driven Four-Tip Probes for Conductivity Measurements in Ultrahigh Vacuum. Surf. Sci. 2001, 493, 633– 643,[Crossref], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXnsVGgur4%253D&md5=ae3d3d6e6bbd7daf021e9264e497012cIndependently driven four-tip probes for conductivity measurements in ultrahigh vacuumShiraki, I.; Tanabe, F.; Hobara, R.; Nagao, T.; Hasegawa, S.Surface Science (2001), 493 (1-3), 633-643CODEN: SUSCAS; ISSN:0039-6028. (Elsevier Science B.V.)To measure elec. cond. of materials in scales ranging from nanometer to millimeter, a four-point probe system was developed and installed in an ultrahigh-vacuum scanning electron microscope (UHV-SEM). Each probe, made of a W tip, was independently driven with piezoelec. actuators and a scanner in XYZ directions to achieve precise positioning in nanometer scales. The SEM was used for observing the tips for positioning, as well as the sample surface together with scanning reflection-high-energy electron diffraction capability. This four-point probe system has two kinds of special devices. One is octupole tube-type scanners for tip scanning parallel to the sample surface with negligible displacements normal to the surface. Another is a pre-amplifier which can be switched in current measurement mode between tunnel contact for scanning tunneling microscopy and direct contact for four-point probe method. The elec. resistance of a silicon crystal with a Si(1 1 1)-7×7 clean surface was measured with this machine as a function of probe spacing between 1 mm and 1 μm. The result clearly showed an enhancement of surface sensitivity in resistance measurement by reducing the probe spacing.
- 39Albers, J.; Berkowitz, H. L. An Alternative Approach to the Calculation of Four-Probe Resistances on Nonuniform Structures. J. Electrochem. Soc. 1985, 132, 2453– 2456,
- 40Simonis, P.; Goffaux, C.; Thiry, P.; Biro, L.; Lambin, P.; Meunier, V. STM Study of a Grain Boundary in Graphite. Surf. Sci. 2002, 511, 319– 322,[Crossref], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XksVeltbk%253D&md5=dc672ed4e2e8fa1e2b2104ad265b8532STM study of a grain boundary in graphiteSimonis, P.; Goffaux, C.; Thiry, P. A.; Biro, L. P.; Lambin, Ph.; Meunier, V.Surface Science (2002), 511 (1-3), 319-322CODEN: SUSCAS; ISSN:0039-6028. (Elsevier Science B.V.)A grain boundary in highly oriented pyrolytic graphite was investigated by scanning tunneling microscopy (STM). Along the boundary, a periodic structure was obsd. Crystallog. models were constructed to explain the bonding between the 2 grains and STM theor. simulations were carried out. They conclude to the probable presence of pentagon-heptagon chains at the boundary.
- 41Ma, R.; Huan, Q.; Wu, L.; Yan, J. J.; Guo, W.; Zhang, Y.; Wang, S.; Bao, L.; Liu, Y.; Du, S.; Pantelides, S. T.; Gao, H. Direct Four-Probe Measurement of Grain-Boundary Resistivity and Mobility in Millimeter-Sized Graphene. Nano Lett. 2017, 17, 5291– 5296,[ACS Full Text], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1ylsr%252FI&md5=a2c0fc3f602c3ae121cfb8f62b0750d2Direct four-probe measurement of grain-boundary resistivity and mobility in millimeter-sized grapheneMa, Ruisong; Huan, Qing; Wu, Liangmei; Yan, Jiahao; Guo, Wei; Zhang, Yu-Yang; Wang, Shuai; Bao, Lihong; Liu, Yunqi; Du, Shixuan; Pantelides, Sokrates T.; Gao, Hong-JunNano Letters (2017), 17 (9), 5291-5296CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Grain boundaries (GBs) in polycryst. graphene scatter charge carriers, which reduces carrier mobility and limits graphene applications in high-speed electronics. Here we report the extn. of the resistivity of GBs and the effect of GBs on carrier mobility by direct four-probe measurements on millimeter-sized graphene bicrystals grown by chem. vapor deposition (CVD). To ext. the GB resistivity and carrier mobility from direct four-probe intragrain and intergrain measurements, an electronically equiv. extended 2D GB region is defined based on Ohm's law. Measurements on seven representative GBs find that the max. resistivities are in the range of several kΩ·μm to more than 100 kΩ·μm. Furthermore, the mobility in these defective regions is reduced to 0.4-5.9‰ of the mobility of single-crystal, pristine graphene. Similarly, the effect of wrinkles on carrier transport can also be derived. The present approach provides a reliable way to directly probe charge-carrier scattering at GBs and can be further applied to evaluate the GB effect of other two-dimensional polycryst. materials, such as transition-metal dichalcogenides (TMDCs).
- 42Cummings, A. W.; Duong, D. L.; Nguyen, V. L.; Van Tuan, D.; Kotakoski, J.; Barrios Vargas, J. E.; Lee, Y. H.; Roche, S. Charge Transport in Polycrystalline Graphene: Challenges and Opportunities. Adv. Mater. 2014, 26, 5079– 5094,[Crossref], [PubMed], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXptlKqtbg%253D&md5=265d34018132d44b098e4efe2cdea021Charge transport in polycrystalline graphene: challenges and opportunitiesCummings, Aron W.; Duong, Dinh Loc; Nguyen, Van Luan; Tuan, Dinh Van; Kotakoski, Jani; Barrios Vargas, Jose Eduardo; Lee, Young Hee; Roche, StephanAdvanced Materials (Weinheim, Germany) (2014), 26 (30), 5079-5094CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. Graphene has attracted significant interest both for exploring fundamental science and for a wide range of technol. applications. Chem. vapor deposition (CVD) is currently the only working approach to grow graphene at wafer scale, which is required for industrial applications. Unfortunately, CVD graphene is intrinsically polycryst., with pristine graphene grains stitched together by disordered grain boundaries, which can be either a blessing or a curse. On the one hand, grain boundaries are expected to degrade the elec. and mech. properties of polycryst. graphene, rendering the material undesirable for many applications. On the other hand, they exhibit an increased chem. reactivity, suggesting their potential application to sensing or as templates for synthesis of one-dimensional materials. Therefore, it is important to gain a deeper understanding of the structure and properties of graphene grain boundaries. Here, we review exptl. progress on identification and elec. and chem. characterization of graphene grain boundaries. We use numerical simulations and transport measurements to demonstrate that elec. properties and chem. modification of graphene grain boundaries are strongly correlated. This not only provides guidelines for the improvement of graphene devices, but also opens a new research area of engineering graphene grain boundaries for highly sensitive electro-biochem. devices.
- 43Yu, Q.; Jauregui, L. A.; Wu, W.; Colby, R.; Tian, J.; Su, Z.; Cao, H.; Liu, Z.; Pandey, D.; Wei, D.; Chung, T. F.; Peng, P.; Guisinger, N. P.; Stach, E. A.; Bao, J.; Pei, S. S.; Chen, Y. P. Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapour Deposition. Nat. Mater. 2011, 10, 443– 449,[Crossref], [PubMed], [CAS], Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXlvVagsr8%253D&md5=6cf7121d4628ce7fc8a0aedfd57524f8Control and characterization of individual grains and grain boundaries in graphene grown by chemical vapour depositionYu, Qingkai; Jauregui, Luis A.; Wu, Wei; Colby, Robert; Tian, Jifa; Su, Zhihua; Cao, Helin; Liu, Zhihong; Pandey, Deepak; Wei, Dongguang; Chung, Ting Fung; Peng, Peng; Guisinger, Nathan P.; Stach, Eric A.; Bao, Jiming; Pei, Shin-Shem; Chen, Yong P.Nature Materials (2011), 10 (6), 443-449CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)The strong interest in graphene has motivated the scalable prodn. of high-quality graphene and graphene devices. As the large-scale graphene films synthesized so far are typically polycryst., it is important to characterize and control grain boundaries, generally believed to degrade graphene quality. Here we study single-crystal graphene grains synthesized by ambient CVD on polycryst. Cu, and show how individual boundaries between coalescing grains affect graphene's electronic properties. The graphene grains show no definite epitaxial relationship with the Cu substrate, and can cross Cu grain boundaries. The edges of these grains are found to be predominantly parallel to zigzag directions. We show that grain boundaries give a significant Raman D' peak, impede elec. transport, and induce prominent weak localization indicative of intervalley scattering in graphene. Finally, we demonstrate an approach using pre-patterned growth seeds to control graphene nucleation, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.
- 44Tsen, A. W.; Brown, L.; Levendorf, M. P.; Ghahari, F.; Huang, P. Y.; Havener, R. W.; Ruiz-Vargas, C. S.; Muller, D. A.; Kim, P.; Park, J. Tailoring Electrical Transport Across Grain Boundaries in Polycrystalline Graphene. Science 2012, 336, 1143– 1146,[Crossref], [PubMed], [CAS], Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XnsFOrt7c%253D&md5=c492162777c98896ea74b673b1985ccdTailoring electrical transport across grain boundaries in polycrystalline grapheneTsen, Adam W.; Brown, Lola; Levendorf, Mark P.; Ghahari, Fereshte; Huang, Pinshane Y.; Havener, Robin W.; Ruiz-Vargas, Carlos S.; Muller, David A.; Kim, Philip; Park, JiwoongScience (Washington, DC, United States) (2012), 336 (6085), 1143-1146CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Graphene produced by CVD is polycryst., and scattering of charge carriers at grain boundaries (GBs) could degrade its performance relative to exfoliated, single-crystal graphene. However, the elec. properties of GBs have so far been addressed indirectly without simultaneous knowledge of their locations and structures. We present elec. measurements on individual GBs in CVD graphene 1st imaged by TEM. Unexpectedly, the elec. conductance improves by 1 order of magnitude for GBs with better interdomain connectivity. Our study suggests that polycryst. graphene with good stitching may allow for uniformly high elec. performance rivaling that of exfoliated samples, which we demonstrate using optimized growth conditions and device geometry.
- 45Mogi, H.; Wang, Z. H.; Kikuchi, R.; Yoon, C. H.; Yoshida, S.; Takeuchi, O.; Shigekawa, H. Externally Triggerable Optical Pump-Probe Scanning Tunneling Microscopy. Appl. Phys. Express 2019, 12, 025005,[Crossref], [CAS], Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXotlKjtLw%253D&md5=a260204f582e13816906aff2791214d3Externally triggerable optical pump-probe scanning tunneling microscopyMogi, Hiroyuki; Wang, Zi-han; Kikuchi, Ryusei; Yoon, Cheul Hyun; Yoshida, Shoji; Takeuchi, Osamu; Shigekawa, HidemiApplied Physics Express (2019), 12 (2), 025005/1-025005/4CODEN: APEPC4; ISSN:1882-0786. (IOP Publishing Ltd.)Optical pump-probe scanning tunneling microscopy (OPP-STM) has enabled the measurement of ultrafast dynamics in real space. However, the use of a pulse picker to ext. selected laser pulses to realize delay-time modulation, which efficiently suppresses the thermal expansion problems, limits the availability of time-resolved measurement. Here, we present a more applicable type of OPP-STM that we have developed. Two externally triggerable pulse lasers were used to produce pump and probe pulses, and wide-range delay-time modulation was simply realized by adjusting the timing of the pulses. The performance of this new type of OPP-STM was demonstrated by measuring the carrier dynamics in WSe2.
- 46Mogi, H.; Wang, Z. H.; Bamba, T.; Takaguchi, Y.; Endo, T.; Yoshida, S.; Taninaka, A.; Oigawa, H.; Miyata, Y.; Takeuchi, O.; Shigekawa, H. Development of Laser-Combined Scanning Multiprobe Spectroscopy and Application to Analysis of WSe2/MoSe2 in-Plane Heterostructure. Appl. Phys. Express 2019, 12, 045002,[Crossref], [CAS], Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXps12is7Y%253D&md5=fbef832ce1ac24d468a1a1aab2380b08Development of laser-combined scanning multiprobe spectroscopy and application to analysis of WSe2/MoSe2 in-plane heterostructureMogi, Hiroyuki; Wang, Zi-Han; Bamba, Takafumi; Takaguchi, Yuhei; Endo, Takahiko; Yoshida, Shoji; Taninaka, Atsushi; Oigawa, Haruhiro; Miyata, Yasumitsu; Takeuchi, Osamu; Shigekawa, HidemiApplied Physics Express (2019), 12 (4), 45002CODEN: APEPC4; ISSN:1882-0786. (IOP Publishing Ltd.)By combining scanning multiprobe (MP) microscopy with optical methods such as light-modulated spectroscopy (LMS) and optical pump-probe (OPP) method, we have succeeded in developing a microscopy method for measuring electronic structures and photoinduced carrier dynamics in microscopic structures. We demonstrated its performance by analyzing the electronic structures in a monolayer island of a WSe2/MoSe2 in-plane heterostructure grown on a SiO2/Si substrate. By observing the field-effect transistor characteristics and photocurrent mapping over the heterostructure by LMS, we were able to visualize the band structure. Positional dependence of carrier dynamics was also successfully probed by OPP-MP spectroscopy.
- 47Soule, D. E. Magnetic Field Dependence of the Hall Effect and Magnetoresistance in Graphite Single Crystals. Phys. Rev. 1958, 112, 698– 707,[Crossref], [CAS], Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaG1MXjvVSrsA%253D%253D&md5=ec330e65785082a78b111592fc18d414Magnetic field dependence of the Hall effect and magnetoresistance in graphite single crystalsSoule, D. E.Physical Review (1958), 112 (), 698-707CODEN: PHRVAO; ISSN:0031-899X.cf. C.A. 52, 12473h. Hall coeff. and magnetoresistance in 99.995% purified natural graphite single crystals with 25-25,000-gauss fields oriented parallel to the hexagonal axis, were measured at 4.2, 77, and 298°K. Fast minority carriers from Fermi-surface warp were evident in low-field Hall coeff. Even where it changes sign, the Hall coeff. is sensitive to temp., impurities, and field, because of compensating effect between majority electron and hole ds. (total 2-5 × 1018/cc.; 1.0-1.15 electrons/hole) and mobilities (0.15-13 × 105 sq. cm./v.-sec.; electron/hole mobility is 0.79-1.10). Room-temp. magnetoresistance, quadratic at low field, progresses at higher fields to an impurity-sensitive 1.78 power-of-the field dependence. The large magnetoresistance ratio, 105 at 4.2°K. and 23 kilogausses, and de Haas-van Alphen oscillation, demonstrate the small effective masses (0.03 and 0.06 m0) and long relaxation times (2.5 × 10-11 sec.) at 4.2°K. Mobility follows a T-1.2 law in lattice-scatter below 50°K. Low-temp. carrier d.-mobility sensitivity to impurities substantiates sample purity.
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Abstract
Figure 1
Figure 1. Sample conditions and schematic illustrations of measurements. (a) Cross-sectional TEM image of a graphite sample. (b) Secondary electron microscopy (SEM) image. (c) Raman spectra obtained before and after exfoliation. The D peak corresponds to defects. The G peak, which corresponds to other factors such as strain and the dopant used, is shown for comparison with the D peak in intensity. (d) FIB–SEM system used to produce a cross section of graphite film and a SEM image of the obtained sample. (e) Setup of the MP-STP measurement. (f) Measurement sequence.
Figure 2
Figure 2. Results of MP-STM measurement in the ab-plane. (a) Optical microscopy image of the four probes during the measurement. (b) Topography image on which the grid measurement method was performed (1.5 × 1.5 μm2, tip bias Vt = 20 mV, and set-point current It = 30 pA). (c) 2D map of ΔΦ/Isample obtained over the surface in (b). The black arrow indicates the line corresponding to the green line in (b). (d) ΔΦ–Isample plot acquired in the black rectangles in (c). (e) Line profile of ΔΦ/Isample along the green line in (b). (f) Line profile of the topographic image along the green line in (b).
Figure 3
Figure 3. Results of cross-sectional MP-STM measurement. (a) Setup of the MP-STP measurement over the cross section. (b) Optical microscopy image of the upper side of the structure shown in (a). (c) Tapping AFM topographic image of the surface shown in (b). (d) Amplitude image (differential image) of the topographic image shown in (c). (e) Line profile along the blue line shown in the topography image in (c). (f) 2D distribution of ΔΦ/Isample obtained by the grid measurement over a scanning range of 800 × 800 nm2. (g) Line profile of ΔΦ/Isample along the x-direction, in which ΔΦ/Isample was averaged in the y-direction.
Figure 4
Figure 4. Experimental and calculated results ρab. (a) Histogram of ρab calculated using ΔΦ/Isample obtained at each grid point in Figure 2c. (b) Scaling model from the original structure with high anisotropic resistivity (left) to the structure with isotropic resistivity. (c) 2D distribution of ΔΦ/Isample shown in Figure 2c. (d) ΔΦ/Isample obtained by calculation.
Figure 5
Figure 5. Effect of wrinkles on the resistance of ρab. (a) Optical image of the wrinkles of the sample. (b) Optical image of the measured area with a wrinkle. (c) Optical image of the same area in (b) with a different light angle to make the wrinkle more visible. (d) Measurement area including a wrinkle. (e) Measurement area without wrinkle. (f) ΔΦ/Isample as a function of the position of tip 2. A and B correspond to those in (d). (g) ΔΦ/Isample as a function of the position of tip 2. C and D correspond to those in (e). Blue solid lines in (f) and (g) show the fitting curves obtained by using ρab as a parameter while retaining ρc constant.
References
ARTICLE SECTIONSThis article references 47 other publications.
- 1Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric Field Effect in Atomically Thin Carbon Films. Science 2004, 306, 666– 669,[Crossref], [PubMed], [CAS], Google Scholar1https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXos1Kqt70%253D&md5=488da13500bf24e8fc419052dc1a9e84Electric Field Effect in Atomically Thin Carbon FilmsNovoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A.Science (Washington, DC, United States) (2004), 306 (5696), 666-669CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)The authors describe monocryst. graphitic films, which are a few atoms thick but are nonetheless stable under ambient conditions, metallic, and of remarkably high quality. The films are a two-dimensional semimetal with a tiny overlap between valence and conductance bands, and they exhibit a strong ambipolar elec. field effect such that electrons and holes in concns. up to 1013 per square centimeter and with room-temp. mobilities of ∼10,000 square centimeters per V-second can be induced by applying gate voltage.
- 2Wei, H.; Xiao, J.; Yang, Y.; Lv, S.; Shi, J.; Xu, X.; Dong, J.; Luo, Y.; Li, D.; Meng, Q. Free-Standing Flexible Carbon Electrode for Highly Efficient Hole-Conductor-Free Perovskite Solar Cells. Carbon 2015, 93, 861– 868,[Crossref], [CAS], Google Scholar2https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXovVCisrY%253D&md5=f0df3ae12066694503ba926074a4f960Free-standing flexible carbon electrode for highly efficient hole conductor-free perovskite solar cellsWei, Huiyun; Xiao, Junyan; Yang, Yueyong; Lv, Songtao; Shi, Jiangjian; Xu, Xin; Dong, Juan; Luo, Yanhong; Li, Dongmei; Meng, QingboCarbon (2015), 93 (), 861-868CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)A free-standing thermoplastic C film with good flexibility and cond. was developed and introduced in perovskite solar cells for the 1st time. Due to its thermoplasticity, this free-standing C film can be directly hot pressed onto the perovskite layer as counter electrode. By optimization toward the components of C films and hot-pressing pressure, the back contact between the perovskite and C films was significantly improved. Up to 13.53% of power conversion efficiency was achieved, which is one of the highest efficiencies for hole transporting material-free perovskite solar cells. This kind of flexible C electrodes with the advantages of low-cost, simple and low-temp. (<100°) prepn. process and high efficiency, show great potential application in perovskite solar cells.
- 3Xu, Y.; Yu, H.; Wang, C.; Cao, J.; Chen, Y.; Ma, Z.; You, Y.; Wan, J.; Fang, X.; Chen, X. Multilayer Graphene with Chemical Modification as Transparent Conducting Electrodes in Organic Light-Emitting Diode. Nanoscale Res. Lett. 2017, 12, 254,[Crossref], [PubMed], [CAS], Google Scholar3https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1cvltlOktA%253D%253D&md5=1d29aa4d78e38d89be7648639b85b176Multilayer Graphene with Chemical Modification as Transparent Conducting Electrodes in Organic Light-Emitting DiodeXu Yilin; Yu Haojian; Chen Yigang; Xu Yilin; Wang Cong; You Ying; Wan Jixiang; Fang Xiaohong; Chen Xiaoyuan; Yu Haojian; Cao Jin; Ma Zhongquan; You Ying; Wan Jixiang; Chen XiaoyuanNanoscale research letters (2017), 12 (1), 254 ISSN:1931-7573.Graphene is a promising candidate for the replacement of the typical transparent electrode indium tin oxide in optoelectronic devices. Currently, the application of polycrystalline graphene films grown by chemical vapor deposition is limited for their low electrical conductivity due to the poor transfer technique. In this work, we developed a new method of preparing tri-layer graphene films with chemical modification and explored the influence of doping and patterning process on the performance of the graphene films as transparent electrodes. In order to demonstrate the application of the tri-layer graphene films in optoelectronics, we fabricated the organic light-emitting diodes (OLEDs) based on them and found that plasma etching is feasible with certain influence on the quality of the graphene films and the performance of the OLEDs.
- 4Anagnostopoulos, G.; Pappas, P. N.; Li, Z.; Kinloch, I. A.; Young, R. J.; Novoselov, K. S.; Lu, C. Y.; Pugno, N.; Parthenios, J.; Galiotis, C.; Papagelis, K. Mechanical Stability of Flexible Graphene-Based Displays. ACS Appl. Mater. Interfaces 2016, 8, 22605– 22614,[ACS Full Text], [CAS], Google Scholar4https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xht12jtr3I&md5=5923dc8b9c9abf3d76008fb4a319215dMechanical Stability of Flexible Graphene-Based DisplaysAnagnostopoulos, George; Pappas, Panagiotis-Nektarios; Li, Zheling; Kinloch, Ian A.; Young, Robert J.; Novoselov, Kostya S.; Lu, Ching Yu; Pugno, Nicola; Parthenios, John; Galiotis, Costas; Papagelis, KonstantinosACS Applied Materials & Interfaces (2016), 8 (34), 22605-22614CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)The mech. behavior of a prototype touch panel display, which consists of two layers of CVD graphene embedded into PET films, is investigated in tension and under contact-stress dynamic loading. In both cases, laser Raman spectroscopy was employed to assess the stress transfer efficiency of the embedded graphene layers. The tensile behavior was found to be governed by the "island-like" microstructure of the CVD graphene, and the stress transfer efficiency was dependent on the size of graphene "islands" but also on the yielding behavior of PET at relatively high strains. Finally, the fatigue tests, which simulate real operation conditions, showed that the max. temp. gradient developed at the point of "finger" contact after 80,000 cycles does not exceed the glass transition temp. of the PET matrix. The effect of these results on future product development and the design of new graphene-based displays are discussed.
- 5Kim, J. Y.; Cho, N. S.; Cho, S.; Kim, K.; Cheon, S.; Kim, K.; Kang, S. Y.; Cho, S. M.; Lee, J. I.; Oh, J.; Kim, Y. H.; Ryu, H.; Hwang, C. S.; Kim, S.; Ah, C. S.; Kim, T. Y. Graphene Electrode Enabling Electrochromic Approaches for Daylight-Dimming Applications. Sci. Rep. 2018, 8, 3944,[Crossref], [PubMed], [CAS], Google Scholar5https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC1Mrnt1KrsA%253D%253D&md5=cdfddf43ec9a17feae320d5f6dae1b32Graphene Electrode Enabling Electrochromic Approaches for Daylight-Dimming ApplicationsKim Joo Yeon; Cheon Sanghoon; Cho Seong M; Kim Yong-Hae; Ryu Hojun; Hwang Chi-Sun; Kim Sujung; Ah Chil Seong; Kim Tae-Youb; Cho Nam Sung; Kang Seung-Youl; Oh Ji-Young; Cho Seungmin; Kim Kisoo; Cho Seungmin; Kim Kisoo; Kim Kyuwon; Lee Jeong-IkScientific reports (2018), 8 (1), 3944 ISSN:.For environmental reason, buildings increasingly install smart windows, which can dim incoming daylight based on active electrochromic devices (ECDs). In this work, multi-layered graphene (MLG) was investigated as an ECD window electrode, to minimize carbon dioxide (CO2) emissions by decreasing the electricity consumption for building space cooling and heating and as an alternative to the transparent conductor tin-doped indium oxide (ITO) in order to decrease dependence on it. Various MLG electrodes with different numbers of graphene layers were prepared with environmentally friendly poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) to produce ECD cells. Tests demonstrated the reproducibility and uniformity in optical performance, as well as the flexibility of the ECD fabrication. With the optimized MLG electrode, the ECD cells exhibited a very fast switching response for optical changes from transparent to dark states of a few hundred msec.
- 6Bae, S.; Kim, H.; Lee, Y.; Xu, X.; Park, J. S.; Zheng, Y.; Balakrishnan, J.; Lei, T.; Ri Kim, H.; Song, Y. Il; Kim, Y. J.; Kim, K. S.; Özyilmaz, B.; Ahn, J. H.; Hong, B. H.; Iijima, S. Roll-to-Roll Production of 30-Inch Graphene Films for Transparent Electrodes. Nat. Nanotechnol. 2010, 5, 574– 578,[Crossref], [PubMed], [CAS], Google Scholar6https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXpvVSrur0%253D&md5=120e7e960a958f851c4b4049eaf90b19Roll-to-roll production of 30-inch graphene films for transparent electrodesBae, Sukang; Kim, Hyeongkeun; Lee, Youngbin; Xu, Xiangfan; Park, Jae-Sung; Zheng, Yi; Balakrishnan, Jayakumar; Lei, Tian; Kim, Hye Ri; Song, Young Il; Kim, Young-Jin; Kim, Kwang S.; Oezyilmaz, Barbaros; Ahn, Jong-Hyun; Hong, Byung Hee; Iijima, SumioNature Nanotechnology (2010), 5 (8), 574-578CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)The outstanding elec., mech. and chem. properties of graphene make it attractive for applications in flexible electronics. However, efforts to make transparent conducting films from graphene have been hampered by the lack of efficient methods for the synthesis, transfer and doping of graphene at the scale and quality required for applications. Here, we report the roll-to-roll prodn. and wet-chem. doping of predominantly monolayer 30-in. graphene films grown by chem. vapor deposition onto flexible copper substrates. The films have sheet resistances as low as ∼125 Ω .box.-1 with 97.4% optical transmittance, and exhibit the half-integer quantum Hall effect, indicating their high quality. We further use layer-by-layer stacking to fabricate a doped four-layer film and measure its sheet resistance at values as low as ∼30 Ω .box.-1 at ∼90% transparency, which is superior to com. transparent electrodes such as indium tin oxides. Graphene electrodes were incorporated into a fully functional touch-screen panel device capable of withstanding high strain.
- 7Yazami, R.; Touzain, P. A Reversible Graphite-Lithium Negative Electrode for Electrochemical Generators. J. Power Sources 1983, 9, 365– 371,[Crossref], [CAS], Google Scholar7https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXktVyhu7k%253D&md5=b7a253d6bada57ee2ba6677ba114623eA reversible graphite-lithium anode for batteriesYazami, R.; Touzain, P.Journal of Power Sources (1983), 9 (3-4), 365-71CODEN: JPSODZ; ISSN:0378-7753.Li intercalation compds. in graphite were obtained by electrochem. methods using a solid org. electrolyte (polyethylene oxide with LiClO4). Intermittent electrochem. techniques enabled the kinetics (diffusion coeff.) and thermodn. (enthalpy) values to be calcd. Some secondary battery cycling tests using Li-graphite anodes are reported.
- 8Blomquist, N.; Wells, T.; Andres, B.; Bäckström, J.; Forsberg, S.; Olin, H. Metal-Free Supercapacitor with Aqueous Electrolyte and Low-Cost Carbon Materials. Sci. Rep. 2017, 7, 39836,[Crossref], [PubMed], [CAS], Google Scholar8https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXmsVClsw%253D%253D&md5=964116a5bf7c1242642ae69400c6433fMetal-free supercapacitor with aqueous electrolyte and low-cost carbon materialsBlomquist, Nicklas; Wells, Thomas; Andres, Britta; Baeckstroem, Joakim; Forsberg, Sven; Olin, HaakanScientific Reports (2017), 7 (), 39836CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)Elec. double-layer capacitors (EDLCs) or supercapacitors (SCs) are fast energy storage devices with high pulse efficiency and superior cyclability, which makes them useful in various applications including electronics, vehicles and grids. Aq. SCs are considered to be more environmentally friendly than those based on org. electrolytes. Because of the corrosive nature of the aq. environment, however, expensive electrochem. stable materials are needed for the current collectors and electrodes in aq. SCs. This results in high costs for a given energy-storage capacity. To address this, we developed a novel low-cost aq. SC using graphite foil as the current collector and a mix of graphene, nanographite, simple water-purifn. carbons and nanocellulose as electrodes. The electrodes were coated directly onto the graphite foil by using casting frames and the SCs were assembled in a pouch cell design. With this approach, we achieved a material cost redn. of greater than 90% while maintaining approx. one-half of the specific capacitance of a com. unit, thus demonstrating that the proposed SC can be an environmentally friendly, low-cost alternative to conventional SCs.
- 9Yu, A.; Roes, I.; Davies, A.; Chen, Z. Ultrathin, Transparent, and Flexible Graphene Films for Supercapacitor Application. Appl. Phys. Lett. 2010, 96, 253105,[Crossref], [CAS], Google Scholar9https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXnvFShsrY%253D&md5=e3ad6104fc553414b3e858b605e1ea36Ultrathin, transparent, and flexible graphene films for supercapacitor applicationYu, Aiping; Roes, Isaac; Davies, Aaron; Chen, ZhongweiApplied Physics Letters (2010), 96 (25), 253105/1-253105/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)This study reports the prepn. of ultrathin, transparent graphene films for use in supercapacitor applications. The surface morphol. of the films was investigated by SEM and transmission electron microscopy, revealing a very homogeneous surface with intimate contact between graphene sheets. Electrochem. characterization demonstrated nearly ideal elec. double layer capacitive behavior. The capacitance obtained from charge-discharge anal. is 135 F/g for a film of ∼25 nm which has a transmittance of 70% at 550 nm and a high power d. of 7200 W/kg in 2M KCl electrolyte. (c) 2010 American Institute of Physics.
- 10Hannay, N. B.; Geballe, T. H.; Matthias, B. T.; Andres, K.; Schmidt, P.; MacNair, D. Superconductivity in Graphitic Compounds. Phys. Rev. Lett. 1965, 14, 225– 226,[Crossref], [CAS], Google Scholar10https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF2MXlsF2ntg%253D%253D&md5=83a89930ac96e63ea1093e65905ded32Superconductivity in graphite compoundsHannay, N. B.; Geballe, T. H.; Matthias, B. T.; Andres, K.; Schmidt, P.; MacNair, D.Physical Review Letters (1965), 14 (7), 225-6CODEN: PRLTAO; ISSN:0031-9007.Supercond. was studied in intercalation compds. of graphite with alkali metals (K, Rb, or Cs). The transition temps. observed were 0.020-0.135°K. for Cs, 0.023-0.151°K. in the Rb system, and ≤0.55°K. in the K system. The width for any given transition is of the order of several millidegrees. The structure of these compds. is anisotropic.
- 11Belash, I.; Zharikov, O.; Palnichenko, A. Superconductivity of GIC with Li, Na and K. Synth. Met. 1989, 34, 455– 460,
- 12Larkins, G.; Vlasov, Y.; Holland, K. Evidence of Superconductivity in Doped Graphite and Graphene. Supercond. Sci. Technol. 2016, 29, 015015,[Crossref], [CAS], Google Scholar12https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xjt1Kmsb4%253D&md5=ae152258300f7fd93425f002f303e5bdEvidence of superconductivity in doped graphite and graphemeLarkins, Grover; Vlasov, Yuriy; Holland, KiarSuperconductor Science and Technology (2016), 29 (1), 015015/1-015015/10CODEN: SUSTEF; ISSN:0953-2048. (IOP Publishing Ltd.)We have obsd. evidence of supercond. at temps. in the vicinity of 260 K in phosphorus-doped graphite and graphene. This evidence includes transport current, magnetic susceptibility, Hall effect and (pancake) vortex state measurements. All of these measurements indicate a transition which is that of a type II superconductor with no type I phase until below the limits of our measurement capabilities. Vortex states are inferred from periodically repeated steps in the resistance vs. temp. characteristics of highly oriented pyrolytic graphite and exfoliated doped multilayer graphene. Magnetic susceptibility measurements have shown results qual. similar to those expected (and exptl. obsd. by others) for ultra-thin (thickness « λL) films. The magnetization is neg. for field-cooled and zero-field-cooled measurements. The magnetization for field cooled and zero-field-cooled measurements begin to diverge at approx. 260 K. Hall effect measurements show a sign reversal in the Hall voltage as the temp. is reduced from 300 K to 78 K.
- 13Cui, X.; Lee, G. H.; Kim, Y. D.; Arefe, G.; Huang, P. Y.; Lee, C. H.; Chenet, D. A.; Zhang, X.; Wang, L.; Ye, F.; Pizzocchero, F.; Jessen, B. S.; Watanabe, K.; Taniguchi, T.; Muller, D. A.; Low, T.; Kim, P.; Hone, J. Multi-Terminal Transport Measurements of MoS2 Using a van Der Waals Heterostructure Device Platform. Nat. Nanotechnol. 2015, 10, 534– 540,[Crossref], [PubMed], [CAS], Google Scholar13https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXnvFSlurw%253D&md5=52f54b0a75a286916e5084d4bd008758Multi-terminal transport measurements of MoS2 using a van der Waals heterostructure device platformCui, Xu; Lee, Gwan-Hyoung; Kim, Young Duck; Arefe, Ghidewon; Huang, Pinshane Y.; Lee, Chul-Ho; Chenet, Daniel A.; Zhang, Xian; Wang, Lei; Ye, Fan; Pizzocchero, Filippo; Jessen, Bjarke S.; Watanabe, Kenji; Taniguchi, Takashi; Muller, David A.; Low, Tony; Kim, Philip; Hone, JamesNature Nanotechnology (2015), 10 (6), 534-540CODEN: NNAABX; ISSN:1748-3387. (Nature Publishing Group)Atomically thin two-dimensional semiconductors such as MoS2 hold great promise for elec., optical and mech. devices and display novel phys. phenomena. However, the electron mobility of mono- and few-layer MoS2 has so far been substantially below theor. predicted limits, which has hampered efforts to observe its intrinsic quantum transport behaviors. Potential sources of disorder and scattering include defects such as sulfur vacancies in the MoS2 itself as well as extrinsic sources such as charged impurities and remote optical phonons from oxide dielecs. To reduce extrinsic scattering, we have developed here a van der Waals heterostructure device platform where MoS2 layers are fully encapsulated within hexagonal boron nitride and elec. contacted in a multi-terminal geometry using gate-tunable graphene electrodes. Magneto-transport measurements show dramatic improvements in performance, including a record-high Hall mobility reaching 34,000 cm2 V-1 s-1 for six-layer MoS2 at low temp., confirming that low-temp. performance in previous studies was limited by extrinsic interfacial impurities rather than bulk defects in the MoS2. We also obsd. Shubnikov-de Haas oscillations in high-mobility monolayer and few-layer MoS2. Modeling of potential scattering sources and quantum lifetime anal. indicate that a combination of short-range and long-range interfacial scattering limits the low-temp. mobility of MoS2.
- 14Hishiyama, Y.; Kaburagi, Y. Electrical Resistivity of Highly Crystallized Kish Graphite. Carbon 1992, 30, 483– 486,[Crossref], [CAS], Google Scholar14https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XkvVSkurw%253D&md5=10ed48d785926d1efdb6edc70dd0a7d9Electrical resistivity of highly crystallized kish graphiteHishiyama, Yoshihiro; Kaburagi, YutakaCarbon (1992), 30 (3), 483-6CODEN: CRBNAH; ISSN:0008-6223.Large and highly crystd. kish graphite flakes were obtained and the temp. dependence was detd. of the in-plane elec. resistivity for the specimens with the ρ300/ρ4.2K values of 56 and 106 at temps. between 1.28 and 300 K. The temp.-dependent component of the resistivity ρT was examd. precisely, particularly at low temps. Below about 5 K, ρT is proportional to T2, then increases faster to nearly T1 (ρT .varies. T2.7) to ∼15 K with increasing T. This is the intrinsic behavior of ρT for graphite crystal because of high crystallinity of the present specimens. The T2.7 dependence at 5-15 K is due to the scattering of carriers by the out-of-plane phonons, whereas the T2 dependence at temps. below about 5 K is attributed to the electron-hole scattering.
- 15Moore, A. W. Highly Oriented Pyrolytic Graphite. Chem. Phys. Carbon 1973, 11, 69– 187[CAS], Google Scholar15https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2cXnslyg&md5=716d5c7a3c2dd8959d4323820f5a8128Highly oriented pyrolytic graphiteMoore, A. W.Chemistry and Physics of Carbon (1973), 11 (), 69-187CODEN: CPHCAY; ISSN:0069-3138.A review with 256 refs. on the structure, properties, and applications of highly oriented graphite obtained by the severe thermal annealing or stress annealing of pyrolytic carbons.
- 16Spain, I. L.; Ubbelohde, A. R.; Young, D. A. Electronic Properties of Well Oriented Graphite. Philos. Trans. R. Soc., A 1967, 262, 345– 386,[Crossref], [CAS], Google Scholar16https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaF1cXksFGhtb8%253D&md5=263e720c96c3a2b848ffca01c46b7e92Electronic properties of well oriented graphiteSpain, I. L.; Ubbelohde, A. R.; Young, D. A.Philosophical Transactions of the Royal Society of London, Series A: Mathematical, Physical and Engineering Sciences (1967), 262 (1128), 345-86CODEN: PTRMAD; ISSN:1364-503X.A range of dense well-oriented graphites of high chem. purity was prepd. by stress recrystn. of pyrolytic material. Systematic trends in the galvanomagnetic and thermoelec. properties were investigated in these samples, in relation to c-axis distribution function, crystallite size, and basal-plane dislocation concn., at temps. from 300 to 1.2°K. and magnetic fields ≤6700 gauss. Basal plane properties of ideal graphite were evaluated in terms of the trends observed. The electronic properties were measured parallel to the c-axis for corresponding graphites with a range of defect concns. From the trends established, est. were made of various properties of ideal defect-free graphite in the c-axis direction, and of anisotropy ratios. The effects of neutrons irradn. on some of the electronic properties were also studied. The results are discussed in terms of multicarrier models.
- 17Murakami, M.; Nishiki, N.; Nakamura, K.; Ehara, J.; Okada, H.; Kouzaki, T.; Watanabe, K.; Hoshi, T.; Yoshimura, S. High-Quality and Highly Oriented Graphite Block from Polycondensation Polymer Films. Carbon 1992, 30, 255– 262,[Crossref], [CAS], Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38Xhsl2lsLc%253D&md5=0123850791b924fe8f1a36509e8822deHigh-quality and highly oriented graphite block from polycondensation polymer filmsMurakami, M.; Nishiki, N.; Nakamura, K.; Ehara, J.; Okada, H.; Kouzaki, T.; Watanabe, K.; Hoshi, T.; Yoshimura, S.Carbon (1992), 30 (2), 255-62CODEN: CRBNAH; ISSN:0008-6223.High-quality and highly oriented graphite was produced in the form of a thick block having phys. properties close to those of single-crystal graphite. It was prepd. from 25-μm-thick polyimide films with high mol. orientation. A sheath of the films was heat treated in an Ar atm. at ≤1000° (carbonization) and then heated for graphitization up to 3000° under a pressure between 100 and 300 kg/cm2. Graphite blocks as large as 150 × 50 × 13 mm3 were prepd., and the mosaic spread (the degree of preferred orientation) attained was 0.4°.
- 18Murakami, M.; Yoshimura, S. Highly Conductive Pyropolymer and High-Quality Graphite from Polyoxadiazole. Synth. Met. 1987, 18, 509– 514,[Crossref], [CAS], Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXhs1Kqurk%253D&md5=2a4e2b3b39172ea4ee14e34d630e0a4aHighly conductive pyropolymer and high-quality graphite from polyoxadiazoleMurakami, M.; Yoshimura, S.Synthetic Metals (1987), 18 (1-3), 509-14CODEN: SYMEDZ; ISSN:0379-6779.High-temp. heat treatment of a heat-resistant condensation polymer, polyoxadiazole, POD, yielded a large-area, flexible film composed of highly oriented and nearly ideal graphite crystallites. The graphitic behavior for POD heat-treated above 2800° was exemplified by the (002) lattice spacing of 3.354 Å, elec. cond. along the basal plane of 12,000-18,000 S/cm, laser Raman spectra, and TEM observations. Intercalation compds. of HNO3-GPOD (graphitized POD) showed the highest cond. of 3.2 × 105 S/cm with fairly good stability in air.
- 19Murakami, M.; Watanabe, K.; Yoshimura, S. High quality Pyrographite Films. Appl. Phys. Lett. 1986, 48, 1594– 1596,[Crossref], [CAS], Google Scholar19https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28Xktleitb0%253D&md5=2760c0f089c9b3cf6dcb964d02bb8b09High-quality pyrographite filmsMurakami, Mutsuaki; Watanabe, Kazuhiro; Yoshimura, SusumuApplied Physics Letters (1986), 48 (23), 1594-6CODEN: APPLAB; ISSN:0003-6951.High-temp. heat treatment of a heat-resistant, condensation polymer poly(p-phenylene-1,3,4-oxadiazole) yielded a large-area, flexible film composed of highly oriented and nearly ideal graphite crystallites. The graphitic behavior was exemplified by both the (002) lattice spacing of 3.354 Å and extremely small full width at half-max. intensity of the (002) reflection, 0.16-0.17°, for the films heat treated above 2800°.
- 20Kaneka Corp.; http://www.kaneka.co.jp/en/.Google ScholarThere is no corresponding record for this reference.
- 21Kaburagi, Y.; Hishiyama, Y. Highly Crystallized Graphite Films Prepared by High-Temperature Heat Treatment from Carbonized Aromatic Polyimide Films. Carbon 1995, 33, 773– 777,[Crossref], [CAS], Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK2MXms1ahsrg%253D&md5=b464d930f514a0f45614c903ce92de43Highly crystallized graphite films prepared by high-temperature heat treatment from carbonized aromatic polyimide filmsKaburagi, Yutaka; Hishiyama, YoshihiroCarbon (1995), 33 (6), 773-7CODEN: CRBNAH; ISSN:0008-6223. (Elsevier)Highly crystd. graphite films were prepd. by successive heat treatments at 3100°C for 40 min and then 3200°C for 23 min under atm. pressure of pure argon gas from thin carbonized polyimide films. The starting polyimide films were a com. available Kapton and a lab. prepd. high-modulus-polyimide film formed via polyamic acid gel. The crystallinity of the graphite films obtained was examd. by the measurements of interlayer spacing d002, mosaic spread MS, elec. cond. σ at 300 and 77 K, residual resistivity ratio RRR, and max. transverse magnetoresistance (Δρ/ρ)max, mean magnetoresistance anisotropy ratio r, and Hall coeff. RH at 77 K. The present graphite films exhibit the highest crystallinity as graphite films obtained from polyimide films (i.e., the values of d002, MS, σ at 300 K, RRR, and (Δρ/ρ)max and r in the field of 1 T at 77 K were 0.3354 nm, 1.7-2.3°, 1.80-2.14 × 106 S/m, 13.49-17.26 and 0.0040-0.0086, resp., and small pos. values of RH in fields around 0.2 T at 77 K were obsd.).
- 22Murakami, M.; Tatami, A.; Tachibana, M. Fabrication of High Quality and Large Area Graphite Thin Films by Pyrolysis and Graphitization of Polyimides. Carbon 2019, 145, 23– 30,[Crossref], [CAS], Google Scholar22https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtVars7s%253D&md5=7fbb23ee4b073252bacd043e13140c43Fabrication of high quality and large area graphite thin films by pyrolysis and graphitization of polyimidesMurakami, Mutsuaki; Tatami, Atsushi; Tachibana, MasamitsuCarbon (2019), 145 (), 23-30CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)We have developed large-area, high-quality graphite thin films that are 0.5-3 μm thick. To prep. the graphite films, we used pyrolysis and graphitization of polyimide up to temps. in the range 2900 °C-3300 °C, which is applicable to industrial-prodn. processing. Given that the graphite layers of the films are highly oriented in the surface plane, they have good phys. properties. The resulting elec. cond. of graphite film of thickness 1.4 μm and area 10 × 10 cm2 that was treated at 3200 °C is 24,800 S/cm, and the elec. cond. showed metallic temp. dependence. The carrier mobility of the film is 11,700 V/cm2, and the carrier concns. of electrons (Ne) and holes (Nh) are 6.98 × 1018 cm-3 and 5.90 × 1018 cm-3, resp. We consider the high elec. cond. and mobility to have been derived from the homogeneous, highly oriented graphite layers. We found that graphitization of films less than 3 μm thick progresses uniformly throughout the film, and the resulting graphite films have structures with uniform, highly oriented layers. The produced graphite thin films have excellent phys. properties and can be easily handled, so we believe that many industrial applications are possible.
- 23Ohashi, Y.; Koizumi, T.; Yoshikawa, T.; Shiiki, T.; Hironaka, K. Size Effect Inthe Thin Electrical Crystals Resistivity of Very Graphite. Tanso 1997, 180, 235– 238,[Crossref], [CAS], Google Scholar23https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXhtlKku7g%253D&md5=62647d9534457ffbc73306c9ab05d877Size effect in the in-plane electrical resistivity of very thin graphite crystalsOhashi, Y.; Koizumi, T.; Yoshikawa, T.; Hironaka, T.; Shiiki, K.Tanso (1997), 180 (), 235-238CODEN: TASOA3; ISSN:0371-5345. (Tanso Zairyo Gakkai)To investigate the effect of film thickness of thin graphite crystals on the elec. properties, we prepd. thin graphite films by cleaving a kish graphite (KG) crystal with the rrr value of 32.3. The values of the thickness of the graphite films were 300-1000 Å. Keeping these graphite films free from strain, we measured the temp. dependence of the in-plane resistivity between liq. helium and room temps. The exptl. results could be expressed by a simple two band model and the Sugihara's theory for lattice vibration in thin-carbon films. By using these expressions, we estd. the overlap E0 of conduction and valence bands for the thin graphite films with various thicknesses. It was found that E0 decreases with decreasing film thickness. We also estd. the reciprocal of the relaxation time due to lattice defects or surface scattering 1/τi and that due to lattice vibration 1/τi for the thin films with various thicknesses. Consequently, it was found that the effect of 1/τi and that due to lattice vibration 1/τi for the thin films with various thicknesses. Consequently, it was found that the effect of 1/τi increases rapidly, as the film thickness decreases.
- 24Venugopal, G.; Kim, S. J. Temperature Dependence of Planar-Type Graphite Structures. J. Korean Phys. Soc. 2009, 55, 1102– 1105,[Crossref], [CAS], Google Scholar24https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXhtlSkurrN&md5=856a634669fed3cea9da2f26f957331bTemperature dependence of planar-type graphite structuresVenugopal, Gunasekaran; Kim, Sang-JaeJournal of the Korean Physical Society (2009), 55 (3, Pt. 1), 1102-1105CODEN: JKPSDV; ISSN:0374-4884. (Korean Physical Society)We have characterized the temp. dependence of the transport behavior for planar-type structures along ab-plane fabricated in micron-scale graphite layers. The planar-type structures of graphite layers were fabricated by using a focused ion beam (FIB) etching method. In-plane areas of 10 μm × 10 μm, 6 μm × 5 μm, 6 μm × 2 μm, and 1 μm × 1 μm exhibit semi-conducting behaviors which is contradictory to conventional metallic behavior of graphite flakes and show a small drop in resistance around 49 K. The origin of this effect is suspected from Ga+ ion damage during FIB fabrication. The fabricated planar-type structures show a transition in the current (I) - voltage (V) curves from diode-like characteristics around 30 K to an Ohmic behavior around 300 K.
- 25Berger, C.; Song, Z.; Li, T.; Li, X.; Ogbazghi, A. Y.; Feng, R.; Dai, Z.; Marchenkov, A. N.; Conrad, E. H.; First, P. N.; de Heer, W. A. Ultrathin Epitaxial Graphite: 2D Electron Gas Properties and a Route toward Graphene-Based Nanoelectronics. J. Phys. Chem. B 2004, 108, 19912– 19916,[ACS Full Text], [CAS], Google Scholar25https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXhtVegtb7I&md5=a720c4bfb799b6b35cec80d2c32a08fbUltrathin epitaxial graphite: two-dimensional electron gas properties and a route toward graphene-based nanoelectronicsBerger, Claire; Song, Zhimin; Li, Tianbo; Li, Xuebin; Ogbazghi, Asmerom Y.; Feng, Rui; Dai, Zhenting; Marchenkov, Alexei N.; Conrad, Edward H.; First, Phillip N.; de Heer, Walt A.Journal of Physical Chemistry B (2004), 108 (52), 19912-19916CODEN: JPCBFK; ISSN:1520-6106. (American Chemical Society)The authors have produced ultrathin epitaxial graphite films which show remarkable 2D electron gas (2DEG) behavior. The films, composed of typically three graphene sheets, were grown by thermal decompn. on the (0001) surface of 6H-SiC, and characterized by surface science techniques. The low-temp. conductance spans a range of localization regimes according to the structural state (square resistance 1.5 kΩ to 225 kΩ at 4 K, with pos. magnetoconductance). Low-resistance samples show characteristics of weak localization in two dimensions, from which the authors est. elastic and inelastic mean free paths. At low fields, the Hall resistance is linear up to 4.5 T, which is well-explained by n-type carriers of d. 1012 cm-2 per graphene sheet. The most highly ordered sample exhibits Shubnikov-de Haas oscillations that correspond to nonlinearities obsd. in the Hall resistance, indicating a potential new quantum Hall system. The authors show that the high-mobility films can be patterned via conventional lithog. techniques, and they demonstrate modulation of the film conductance using a top-gate electrode. These key elements suggest electronic device applications based on nanopatterned epitaxial graphene (NPEG), with the potential for large-scale integration.
- 26Tsang, D. Z.; Dresselhaus, M. S. The C-Axis Electrical Conductivity of Kish Graphite. Carbon 1976, 14, 43– 46,[Crossref], [CAS], Google Scholar26https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE28XlslSiurk%253D&md5=74c79d6b421cff98419eeacdaac54cd8The c-axis electrical conductivity of kish graphiteTsang, D. Z.; Dresselhaus, M. S.Carbon (1976), 14 (1), 43-6CODEN: CRBNAH; ISSN:0008-6223.The magnitude and temp. dependence of the x-axis d.c. cond. in kish graphite were similar to those in single crystal graphite but qual. different from those in pyrolytic graphite. Because of differences in the impurity and defect d. between kish and single crystal graphite, the present results supported a band conduction model for c-axis conduction in graphite.
- 27Primak, W.; Fuchs, L. H. Electrical Conductivities of Natural Graphite Crystals. Phys. Rev. 1954, 95, 22– 30,
- 28Valdes, L. Resistivity Measurements on Germanium for Transistors. Proc. IRE 1954, 42, 420– 427,
- 29Muralt, P.; Pohl, D. W. Scanning Tunneling Potentiometry. Appl. Phys. Lett. 1986, 48, 514– 516,[Crossref], [CAS], Google Scholar29https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XhsVSiur8%253D&md5=ee0634e61db06979200649c6ab3d50e9Scanning tunneling potentiometryMuralt, P.; Pohl, D. W.Applied Physics Letters (1986), 48 (8), 514-16CODEN: APPLAB; ISSN:0003-6951.In certain problems of elec. transport through condensed matter, it is important to know the potential distribution with microscope resoln., e.g., at interfaces (Schottky barriers) or pn junctions. Scanning tunneling potentiometry, a new application of scanning tunneling microscopy, is capable of providing this information. The tunnel current is used for simultaneously sensing probe-to-sample distance and local potential. The method was tested with a Au-island metal-insulator-metal structure.
- 30Lüpke, F.; Korte, S.; Cherepanov, V.; Voigtländer, B. Scanning Tunneling Potentiometry Implemented into a Multi-Tip Setup by Software. Rev. Sci. Instrum. 2015, 86, 123701,[Crossref], [PubMed], [CAS], Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2MXhvFemt73E&md5=56b461b96c5bd66551400158a94412f9Scanning tunneling potentiometry implemented into a multi-tip setup by softwareLuepke, F.; Korte, S.; Cherepanov, V.; Voigtlaender, B.Review of Scientific Instruments (2015), 86 (12), 123701/1-123701/7CODEN: RSINAK; ISSN:0034-6748. (American Institute of Physics)The authors present a multi-tip scanning tunneling potentiometry technique that can be implemented into existing multi-tip scanning tunneling microscopes without installation of addnl. hardware. The resulting setup allows flexible in situ contacting of samples under UHV conditions and subsequent measurement of the sample topog. and local elec. potential with resoln. down to Å and μV, resp. The performance of the potentiometry feedback is demonstrated by thermovoltage measurements on the Ag/Si(111) - (√(3) × √(3))R30o surface by resolving a standing wave pattern. Subsequently, the ability to map the local transport field as a result of a lateral current through the sample surface is shown on Ag/Si(111) - (√(3) × √(3))R30o and Si(111) - (7 × 7) surfaces. (c) 2015 American Institute of Physics.
- 31van der Pauw, L. J. A Method of Measuring Specific Resistivity and Hall Eeffect of Discs of Arbitrary Shape. Philips Res. Rep. 1958, 13, 1– 9Google ScholarThere is no corresponding record for this reference.
- 32Yoshida, A.; Hishiyama, Y. Electron Channeling Effect on Highly Oriented Graphites-Size Evaluation and Oriented Mapping of Crystals. J. Mater. Res. 1992, 7, 1400– 1405,[Crossref], [CAS], Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK38XksF2ls7g%253D&md5=01fe94a61c40d8c3f44eb26a54f87068Electron channeling effect on highly oriented graphites - size evaluation and oriented mapping of crystalsYoshida, Akira; Hishiyama, YoshihiroJournal of Materials Research (1992), 7 (6), 1400-5CODEN: JMREEE; ISSN:0884-2914.Structural studies on kish graphite and highly oriented pyrolytic graphite were performed using electron channeling patterns and micrographs in SEM. The av. crystal size and orientation were detd.
- 33Kaburagi, Y.; Yoshida, A.; Hishiyama, Y. Microtexture of Highly Crystallized Graphite as Studied by Galvanomagnetic Properties and Electron Channeling Contrast Effect. J. Mater. Res. 1996, 11, 769– 778,[Crossref], [CAS], Google Scholar33https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK28XhsFejtrk%253D&md5=8a04ecce7c855b57f686525a6e21f4baMicrotexture of highly crystallized graphite as studied by galvanomagnetic properties and electron channeling contrast effectKaburagi, Yutaka; Yoshida, Akira; Hishiyama, YoshihiroJournal of Materials Research (1996), 11 (3), 769-78CODEN: JMREEE; ISSN:0884-2914. (Materials Research Society)The relationship between microtexture and crystallinity of highly crystd. graphites with the residual resistivity ratio ρ300K/ρ4.2K of 3.45-5.50 was investigated. The graphite crystals studied were kish graphite (KG), highly oriented pyrolytic graphite (HOPG), and highly crystd. graphite films prepd. from carbonized arom. polyimide films. The study was made by the observation of an electron channeling pattern and electron channeling contrast image (ECI) under scanning electron microscope and the measurements of x-ray diffraction, magnetoresistance, and Hall coeff. The values of the mean free path of the carriers λ, which approximates the mean crystal grain size, were estd. to be 2.6-6.1 μm from the magnetoresistance at 4.2 K for the highly crystd. graphites. The values of the av. crystal grain diam. D in the basal plane evaluated from ECI were several hundred microns or more for KG, 60 μm for HOPG, and 6 and 12 μm for the graphite films. The difference between the values of λ and D for each crystd. graphite was discussed in relation to other results obtained.
- 34Zhang, Y.; Small, J. P.; Pontius, W. V.; Kim, P. Fabrication and Electric-Field-Dependent Transport Measurements of Mesoscopic Graphite Devices. Appl. Phys. Lett. 2005, 86, 073104,[Crossref], [CAS], Google Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2MXit1ent7s%253D&md5=e99e0d56d953a6e42f310516b2791352Fabrication and electric-field-dependent transport measurements of mesoscopic graphite devicesZhang, Yuanbo; Small, Joshua P.; Pontius, William V.; Kim, PhilipApplied Physics Letters (2005), 86 (7), 073104/1-073104/3CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)The authors have developed a unique micromech. method to ext. extremely thin graphite samples. Graphite crystallites with thicknesses ranging from 10 to 100 nm and lateral size ∼2 μm are extd. from the bulk. Mesoscopic graphite devices are fabricated from these samples for elec. field-dependent conductance measurements. Strong conductance modulation as a function of gate voltage is obsd. in the thinner crystallite devices. The temp.-dependent resistivity measurements show more boundary scattering contribution in the thinner graphite samples.
- 35Miccoli, I.; Edler, F.; Pfnür, H.; Tegenkamp, C. The 100th Anniversary of the Four-Point Probe Technique: The Role of Probe Geometries in Isotropic and Anisotropic Systems. J. Phys.: Condens. Matter 2015, 27, 223201,[Crossref], [PubMed], [CAS], Google Scholar35https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BC2MfkvFOktQ%253D%253D&md5=d147689a00ac6b6c1f3d3b2e91ca77f1The 100th anniversary of the four-point probe technique: the role of probe geometries in isotropic and anisotropic systemsMiccoli I; Edler F; Pfnur H; Tegenkamp CJournal of physics. Condensed matter : an Institute of Physics journal (2015), 27 (22), 223201 ISSN:.The electrical conductivity of solid-state matter is a fundamental physical property and can be precisely derived from the resistance measured via the four-point probe technique excluding contributions from parasitic contact resistances. Over time, this method has become an interdisciplinary characterization tool in materials science, semiconductor industries, geology, physics, etc, and is employed for both fundamental and application-driven research. However, the correct derivation of the conductivity is a demanding task which faces several difficulties, e.g. the homogeneity of the sample or the isotropy of the phases. In addition, these sample-specific characteristics are intimately related to technical constraints such as the probe geometry and size of the sample. In particular, the latter is of importance for nanostructures which can now be probed technically on very small length scales. On the occasion of the 100th anniversary of the four-point probe technique, introduced by Frank Wenner, in this review we revisit and discuss various correction factors which are mandatory for an accurate derivation of the resistivity from the measured resistance. Among others, sample thickness, dimensionality, anisotropy, and the relative size and geometry of the sample with respect to the contact assembly are considered. We are also able to derive the correction factors for 2D anisotropic systems on circular finite areas with variable probe spacings. All these aspects are illustrated by state-of-the-art experiments carried out using a four-tip STM/SEM system. We are aware that this review article can only cover some of the most important topics. Regarding further aspects, e.g. technical realizations, the influence of inhomogeneities or different transport regimes, etc, we refer to other review articles in this field.
- 36Wasscher, J. D. Note on Four-Point Resistivity Measurements on Anisotropic Conductors. Philips Res. Rep. 1946, 157, 301– 306Google ScholarThere is no corresponding record for this reference.
- 37van der Pauw, L. J. Determination of Resistivity Tensor and Hall Tensor of Anisotropic Conductors. Philips Res. Rep. 1961, 16, 187– 195Google ScholarThere is no corresponding record for this reference.
- 38Shiraki, I.; Tanabe, F.; Hobara, R.; Nagao, T.; Hasegawa, S. Independently Driven Four-Tip Probes for Conductivity Measurements in Ultrahigh Vacuum. Surf. Sci. 2001, 493, 633– 643,[Crossref], [CAS], Google Scholar38https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3MXnsVGgur4%253D&md5=ae3d3d6e6bbd7daf021e9264e497012cIndependently driven four-tip probes for conductivity measurements in ultrahigh vacuumShiraki, I.; Tanabe, F.; Hobara, R.; Nagao, T.; Hasegawa, S.Surface Science (2001), 493 (1-3), 633-643CODEN: SUSCAS; ISSN:0039-6028. (Elsevier Science B.V.)To measure elec. cond. of materials in scales ranging from nanometer to millimeter, a four-point probe system was developed and installed in an ultrahigh-vacuum scanning electron microscope (UHV-SEM). Each probe, made of a W tip, was independently driven with piezoelec. actuators and a scanner in XYZ directions to achieve precise positioning in nanometer scales. The SEM was used for observing the tips for positioning, as well as the sample surface together with scanning reflection-high-energy electron diffraction capability. This four-point probe system has two kinds of special devices. One is octupole tube-type scanners for tip scanning parallel to the sample surface with negligible displacements normal to the surface. Another is a pre-amplifier which can be switched in current measurement mode between tunnel contact for scanning tunneling microscopy and direct contact for four-point probe method. The elec. resistance of a silicon crystal with a Si(1 1 1)-7×7 clean surface was measured with this machine as a function of probe spacing between 1 mm and 1 μm. The result clearly showed an enhancement of surface sensitivity in resistance measurement by reducing the probe spacing.
- 39Albers, J.; Berkowitz, H. L. An Alternative Approach to the Calculation of Four-Probe Resistances on Nonuniform Structures. J. Electrochem. Soc. 1985, 132, 2453– 2456,
- 40Simonis, P.; Goffaux, C.; Thiry, P.; Biro, L.; Lambin, P.; Meunier, V. STM Study of a Grain Boundary in Graphite. Surf. Sci. 2002, 511, 319– 322,[Crossref], [CAS], Google Scholar40https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD38XksVeltbk%253D&md5=dc672ed4e2e8fa1e2b2104ad265b8532STM study of a grain boundary in graphiteSimonis, P.; Goffaux, C.; Thiry, P. A.; Biro, L. P.; Lambin, Ph.; Meunier, V.Surface Science (2002), 511 (1-3), 319-322CODEN: SUSCAS; ISSN:0039-6028. (Elsevier Science B.V.)A grain boundary in highly oriented pyrolytic graphite was investigated by scanning tunneling microscopy (STM). Along the boundary, a periodic structure was obsd. Crystallog. models were constructed to explain the bonding between the 2 grains and STM theor. simulations were carried out. They conclude to the probable presence of pentagon-heptagon chains at the boundary.
- 41Ma, R.; Huan, Q.; Wu, L.; Yan, J. J.; Guo, W.; Zhang, Y.; Wang, S.; Bao, L.; Liu, Y.; Du, S.; Pantelides, S. T.; Gao, H. Direct Four-Probe Measurement of Grain-Boundary Resistivity and Mobility in Millimeter-Sized Graphene. Nano Lett. 2017, 17, 5291– 5296,[ACS Full Text], [CAS], Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXht1ylsr%252FI&md5=a2c0fc3f602c3ae121cfb8f62b0750d2Direct four-probe measurement of grain-boundary resistivity and mobility in millimeter-sized grapheneMa, Ruisong; Huan, Qing; Wu, Liangmei; Yan, Jiahao; Guo, Wei; Zhang, Yu-Yang; Wang, Shuai; Bao, Lihong; Liu, Yunqi; Du, Shixuan; Pantelides, Sokrates T.; Gao, Hong-JunNano Letters (2017), 17 (9), 5291-5296CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Grain boundaries (GBs) in polycryst. graphene scatter charge carriers, which reduces carrier mobility and limits graphene applications in high-speed electronics. Here we report the extn. of the resistivity of GBs and the effect of GBs on carrier mobility by direct four-probe measurements on millimeter-sized graphene bicrystals grown by chem. vapor deposition (CVD). To ext. the GB resistivity and carrier mobility from direct four-probe intragrain and intergrain measurements, an electronically equiv. extended 2D GB region is defined based on Ohm's law. Measurements on seven representative GBs find that the max. resistivities are in the range of several kΩ·μm to more than 100 kΩ·μm. Furthermore, the mobility in these defective regions is reduced to 0.4-5.9‰ of the mobility of single-crystal, pristine graphene. Similarly, the effect of wrinkles on carrier transport can also be derived. The present approach provides a reliable way to directly probe charge-carrier scattering at GBs and can be further applied to evaluate the GB effect of other two-dimensional polycryst. materials, such as transition-metal dichalcogenides (TMDCs).
- 42Cummings, A. W.; Duong, D. L.; Nguyen, V. L.; Van Tuan, D.; Kotakoski, J.; Barrios Vargas, J. E.; Lee, Y. H.; Roche, S. Charge Transport in Polycrystalline Graphene: Challenges and Opportunities. Adv. Mater. 2014, 26, 5079– 5094,[Crossref], [PubMed], [CAS], Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXptlKqtbg%253D&md5=265d34018132d44b098e4efe2cdea021Charge transport in polycrystalline graphene: challenges and opportunitiesCummings, Aron W.; Duong, Dinh Loc; Nguyen, Van Luan; Tuan, Dinh Van; Kotakoski, Jani; Barrios Vargas, Jose Eduardo; Lee, Young Hee; Roche, StephanAdvanced Materials (Weinheim, Germany) (2014), 26 (30), 5079-5094CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)A review. Graphene has attracted significant interest both for exploring fundamental science and for a wide range of technol. applications. Chem. vapor deposition (CVD) is currently the only working approach to grow graphene at wafer scale, which is required for industrial applications. Unfortunately, CVD graphene is intrinsically polycryst., with pristine graphene grains stitched together by disordered grain boundaries, which can be either a blessing or a curse. On the one hand, grain boundaries are expected to degrade the elec. and mech. properties of polycryst. graphene, rendering the material undesirable for many applications. On the other hand, they exhibit an increased chem. reactivity, suggesting their potential application to sensing or as templates for synthesis of one-dimensional materials. Therefore, it is important to gain a deeper understanding of the structure and properties of graphene grain boundaries. Here, we review exptl. progress on identification and elec. and chem. characterization of graphene grain boundaries. We use numerical simulations and transport measurements to demonstrate that elec. properties and chem. modification of graphene grain boundaries are strongly correlated. This not only provides guidelines for the improvement of graphene devices, but also opens a new research area of engineering graphene grain boundaries for highly sensitive electro-biochem. devices.
- 43Yu, Q.; Jauregui, L. A.; Wu, W.; Colby, R.; Tian, J.; Su, Z.; Cao, H.; Liu, Z.; Pandey, D.; Wei, D.; Chung, T. F.; Peng, P.; Guisinger, N. P.; Stach, E. A.; Bao, J.; Pei, S. S.; Chen, Y. P. Control and Characterization of Individual Grains and Grain Boundaries in Graphene Grown by Chemical Vapour Deposition. Nat. Mater. 2011, 10, 443– 449,[Crossref], [PubMed], [CAS], Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3MXlvVagsr8%253D&md5=6cf7121d4628ce7fc8a0aedfd57524f8Control and characterization of individual grains and grain boundaries in graphene grown by chemical vapour depositionYu, Qingkai; Jauregui, Luis A.; Wu, Wei; Colby, Robert; Tian, Jifa; Su, Zhihua; Cao, Helin; Liu, Zhihong; Pandey, Deepak; Wei, Dongguang; Chung, Ting Fung; Peng, Peng; Guisinger, Nathan P.; Stach, Eric A.; Bao, Jiming; Pei, Shin-Shem; Chen, Yong P.Nature Materials (2011), 10 (6), 443-449CODEN: NMAACR; ISSN:1476-1122. (Nature Publishing Group)The strong interest in graphene has motivated the scalable prodn. of high-quality graphene and graphene devices. As the large-scale graphene films synthesized so far are typically polycryst., it is important to characterize and control grain boundaries, generally believed to degrade graphene quality. Here we study single-crystal graphene grains synthesized by ambient CVD on polycryst. Cu, and show how individual boundaries between coalescing grains affect graphene's electronic properties. The graphene grains show no definite epitaxial relationship with the Cu substrate, and can cross Cu grain boundaries. The edges of these grains are found to be predominantly parallel to zigzag directions. We show that grain boundaries give a significant Raman D' peak, impede elec. transport, and induce prominent weak localization indicative of intervalley scattering in graphene. Finally, we demonstrate an approach using pre-patterned growth seeds to control graphene nucleation, opening a route towards scalable fabrication of single-crystal graphene devices without grain boundaries.
- 44Tsen, A. W.; Brown, L.; Levendorf, M. P.; Ghahari, F.; Huang, P. Y.; Havener, R. W.; Ruiz-Vargas, C. S.; Muller, D. A.; Kim, P.; Park, J. Tailoring Electrical Transport Across Grain Boundaries in Polycrystalline Graphene. Science 2012, 336, 1143– 1146,[Crossref], [PubMed], [CAS], Google Scholar44https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC38XnsFOrt7c%253D&md5=c492162777c98896ea74b673b1985ccdTailoring electrical transport across grain boundaries in polycrystalline grapheneTsen, Adam W.; Brown, Lola; Levendorf, Mark P.; Ghahari, Fereshte; Huang, Pinshane Y.; Havener, Robin W.; Ruiz-Vargas, Carlos S.; Muller, David A.; Kim, Philip; Park, JiwoongScience (Washington, DC, United States) (2012), 336 (6085), 1143-1146CODEN: SCIEAS; ISSN:0036-8075. (American Association for the Advancement of Science)Graphene produced by CVD is polycryst., and scattering of charge carriers at grain boundaries (GBs) could degrade its performance relative to exfoliated, single-crystal graphene. However, the elec. properties of GBs have so far been addressed indirectly without simultaneous knowledge of their locations and structures. We present elec. measurements on individual GBs in CVD graphene 1st imaged by TEM. Unexpectedly, the elec. conductance improves by 1 order of magnitude for GBs with better interdomain connectivity. Our study suggests that polycryst. graphene with good stitching may allow for uniformly high elec. performance rivaling that of exfoliated samples, which we demonstrate using optimized growth conditions and device geometry.
- 45Mogi, H.; Wang, Z. H.; Kikuchi, R.; Yoon, C. H.; Yoshida, S.; Takeuchi, O.; Shigekawa, H. Externally Triggerable Optical Pump-Probe Scanning Tunneling Microscopy. Appl. Phys. Express 2019, 12, 025005,[Crossref], [CAS], Google Scholar45https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXotlKjtLw%253D&md5=a260204f582e13816906aff2791214d3Externally triggerable optical pump-probe scanning tunneling microscopyMogi, Hiroyuki; Wang, Zi-han; Kikuchi, Ryusei; Yoon, Cheul Hyun; Yoshida, Shoji; Takeuchi, Osamu; Shigekawa, HidemiApplied Physics Express (2019), 12 (2), 025005/1-025005/4CODEN: APEPC4; ISSN:1882-0786. (IOP Publishing Ltd.)Optical pump-probe scanning tunneling microscopy (OPP-STM) has enabled the measurement of ultrafast dynamics in real space. However, the use of a pulse picker to ext. selected laser pulses to realize delay-time modulation, which efficiently suppresses the thermal expansion problems, limits the availability of time-resolved measurement. Here, we present a more applicable type of OPP-STM that we have developed. Two externally triggerable pulse lasers were used to produce pump and probe pulses, and wide-range delay-time modulation was simply realized by adjusting the timing of the pulses. The performance of this new type of OPP-STM was demonstrated by measuring the carrier dynamics in WSe2.
- 46Mogi, H.; Wang, Z. H.; Bamba, T.; Takaguchi, Y.; Endo, T.; Yoshida, S.; Taninaka, A.; Oigawa, H.; Miyata, Y.; Takeuchi, O.; Shigekawa, H. Development of Laser-Combined Scanning Multiprobe Spectroscopy and Application to Analysis of WSe2/MoSe2 in-Plane Heterostructure. Appl. Phys. Express 2019, 12, 045002,[Crossref], [CAS], Google Scholar46https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXps12is7Y%253D&md5=fbef832ce1ac24d468a1a1aab2380b08Development of laser-combined scanning multiprobe spectroscopy and application to analysis of WSe2/MoSe2 in-plane heterostructureMogi, Hiroyuki; Wang, Zi-Han; Bamba, Takafumi; Takaguchi, Yuhei; Endo, Takahiko; Yoshida, Shoji; Taninaka, Atsushi; Oigawa, Haruhiro; Miyata, Yasumitsu; Takeuchi, Osamu; Shigekawa, HidemiApplied Physics Express (2019), 12 (4), 45002CODEN: APEPC4; ISSN:1882-0786. (IOP Publishing Ltd.)By combining scanning multiprobe (MP) microscopy with optical methods such as light-modulated spectroscopy (LMS) and optical pump-probe (OPP) method, we have succeeded in developing a microscopy method for measuring electronic structures and photoinduced carrier dynamics in microscopic structures. We demonstrated its performance by analyzing the electronic structures in a monolayer island of a WSe2/MoSe2 in-plane heterostructure grown on a SiO2/Si substrate. By observing the field-effect transistor characteristics and photocurrent mapping over the heterostructure by LMS, we were able to visualize the band structure. Positional dependence of carrier dynamics was also successfully probed by OPP-MP spectroscopy.
- 47Soule, D. E. Magnetic Field Dependence of the Hall Effect and Magnetoresistance in Graphite Single Crystals. Phys. Rev. 1958, 112, 698– 707,[Crossref], [CAS], Google Scholar47https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaG1MXjvVSrsA%253D%253D&md5=ec330e65785082a78b111592fc18d414Magnetic field dependence of the Hall effect and magnetoresistance in graphite single crystalsSoule, D. E.Physical Review (1958), 112 (), 698-707CODEN: PHRVAO; ISSN:0031-899X.cf. C.A. 52, 12473h. Hall coeff. and magnetoresistance in 99.995% purified natural graphite single crystals with 25-25,000-gauss fields oriented parallel to the hexagonal axis, were measured at 4.2, 77, and 298°K. Fast minority carriers from Fermi-surface warp were evident in low-field Hall coeff. Even where it changes sign, the Hall coeff. is sensitive to temp., impurities, and field, because of compensating effect between majority electron and hole ds. (total 2-5 × 1018/cc.; 1.0-1.15 electrons/hole) and mobilities (0.15-13 × 105 sq. cm./v.-sec.; electron/hole mobility is 0.79-1.10). Room-temp. magnetoresistance, quadratic at low field, progresses at higher fields to an impurity-sensitive 1.78 power-of-the field dependence. The large magnetoresistance ratio, 105 at 4.2°K. and 23 kilogausses, and de Haas-van Alphen oscillation, demonstrate the small effective masses (0.03 and 0.06 m0) and long relaxation times (2.5 × 10-11 sec.) at 4.2°K. Mobility follows a T-1.2 law in lattice-scatter below 50°K. Low-temp. carrier d.-mobility sensitivity to impurities substantiates sample purity.
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