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Toward Two-Dimensional All-Carbon Heterostructures via Ion Beam Patterning of Single-Layer Graphene
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† †Faculty of Physics, PNM and ‡Faculty of Physics, VCQ, QuNaBioS, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria
§ ∥ §The Center for Nanosciences and Nanotechnology and ∥School of Chemistry, The Raymond and Beverly Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
*E-mail: [email protected]
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Nano Letters

Cite this: Nano Lett. 2015, 15, 9, 5944–5949
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https://doi.org/10.1021/acs.nanolett.5b02063
Published July 10, 2015

Copyright © 2015 American Chemical Society. This publication is licensed under CC-BY.

Abstract

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Graphene has many claims to fame: it is the thinnest possible membrane, it has unique electronic and excellent mechanical properties, and it provides the perfect model structure for studying materials science at the atomic level. However, for many practical studies and applications the ordered hexagon arrangement of carbon atoms in graphene is not directly suitable. Here, we show that the atoms can be locally either removed or rearranged into a random pattern of polygons using a focused ion beam (FIB). The atomic structure of the disordered regions is confirmed with atomic-resolution scanning transmission electron microscopy images. These structural modifications can be made on macroscopic scales with a spatial resolution determined only by the size of the ion beam. With just one processing step, three types of structures can be defined within a graphene layer: chemically inert graphene, chemically active amorphous 2D carbon, and empty areas. This, along with the changes in properties, gives promise that FIB patterning of graphene will open the way for creating all-carbon heterostructures to be used in fields ranging from nanoelectronics and chemical sensing to composite materials.

Copyright © 2015 American Chemical Society

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Graphene has received enormous attention since its introduction a decade ago. (1) Because of its two-dimensional (2D) nature, all atoms in graphene are directly exposed to external interactions through electric and magnetic fields or via chemical and physical processes. This provides a great opportunity for engineering its properties. It is well understood (2) that a controlled rearrangement of the atoms in graphene from the honeycomb pattern into other structures will affect the electronic properties of the material (for example, by introducing a band gap due to scattering of charge carriers (3)) and increase its chemical reactivity. (4) Also, nanocrystalline graphene manufactured from self-assembled molecular monolayers has been shown to be insulating (5) indicating the wide range of electronic properties accessible via manipulation of graphene. However, the considerable challenge of manipulating the atomic structure of a 2D object has so far limited the number of studies on this topic.
Perhaps the most versatile method for the manipulation of materials today is ion irradiation. Its application on the nanoscale, however, requires developing a detailed atomic level understanding on irradiation effects. This is because methods for estimating ion irradiation effects in bulk materials can rarely be directly used for low-dimensional structures, (6) and the optimal irradiation parameters change drastically from bulk to nanomaterials. For example, ion implantation of graphene only becomes possible when the energies are reduced to less than 100 eV, (7-9) which is orders of magnitude lower than in a typical implantation process.
Until now, only rarely has any atomic-level information been obtained for ion irradiation of 2D materials, either through atomistic simulations (6, 7, 10, 11, 13-15) or via direct atomic-scale imaging of resulting point defects. (9, 16-20) Instead, many studies have used nonlocal methods such as Raman spectroscopy to analyze the disorder. (21-28) Also, in most studies the irradiated structure was the interface between graphene and a substrate rather than suspended graphene. In this case, the underlying material always contributes to the observed changes. (13-15) So far, on SiO2 substrate, a transition from pristine graphene through a nanocrystallite structure into an amorphous material has been indirectly observed following Ga+ ion irradiation at 30 keV. (22) This is similar to what has been found during 100 keV electron irradiation of suspended graphene. (29, 30) Also the effect of swift heavy ion irradiation at grazing angles has been studied with graphene on a substrate. (31, 32) A recent study explored defects created via irradiation of suspended graphene with 30 keV He+ ions. At an angle of 30°, which was used in the study, such irradiation has been predicted to produce almost exclusively single vacancies. (10) Correspondingly, even at a fluence of ∼1016 ions/cm2, mostly individual point defects were observed.
Here, we show that perpendicular irradiation with a focused beam of Ga+ ions at 35 keV results in amorphization of suspended graphene at a dose of about 3.1 × 1015 ions/cm2. Doses three times as high lead to perforation of the membrane, allowing its use, for example, as the thinnest possible beam splitter for matter-wave interferometry. (33) As shown via atomic-resolution scanning transmission electron microscopy (STEM) medium angle angular dark field (MAADF) images, the amorphous areas remain two-dimensional and consist of a variety of carbon rings with sizes ranging from five to nine atoms (with occasional pores) and are similar to the amorphous 2D carbon structure created with electron irradiation of graphene. (29, 30) In contrast to transmission electron microscopy (TEM), focused ion beam (FIB) processing can be easily done for areas encompassing square millimeters. With the parameters used in this study, it allows writing pores and amorphized areas into graphene with spatial accuracy down to 35 nm.
The patterns were written into single-layer graphene that was grown via chemical vapor deposition and suspended on a holey SiNx substrate, using a focused beam of Ga+ ions with an energy of 35 keV. The substrate contains an array of circular holes that each have a diameter of about 2.5 μm, over which the graphene is suspended. Figure 1a shows an overview scanning electron microscopy (SEM) image of one pattern. A higher magnification TEM image of a pattern written on another sample with a higher dose of Ga+ is shown in Figure 1b. While the low-dose irradiation has not perforated the graphene, the higher dose has resulted in an array of holes.
To study the structure of the patterned areas at a smaller scale, we used STEM-MAADF imaging with the Nion UltraSTEM 100 (34) microscope at 60 kV. The combination of the low acceleration voltage and ultrahigh vacuum (10–9 mbar at the sample) ensures that no beam-induced damage will occur even at the irradiated areas, although the kinetic energy of the imaging electrons still suffices to rotate bonds at defects in graphene. (20, 35) An overview STEM-MAADF image of a pattern written with the lower dose is shown in Figure 1c. The image in Figure 1d shows a closer view of another low-dose region, which allows measuring the width of the written structures (Figure 1e) to be about 35 nm. This corresponds to the estimated beam size of 20–30 nm of the FIB. The same image also shows that the hydrocarbon contamination on top of graphene is continuous over the pattern and has a similar appearance everywhere. This can be seen in Figure 1f, where a blurred version of the image is subtracted from the original image to bring out the contamination pattern, which at this length scale looks like noise. However, the small dark areas actually correspond to areas where noncontaminated parts of the sample were found.

Figure 1

Figure 1. Overview images of the structures patterned into graphene with a focused ion beam. (a) SEM overview image of the SiNx TEM grid showing an array of holes with a diameter of 2.5 μm. Graphene covers the complete area and is suspended over the holes. The pattern written with the FIB at a dose of 4.96 pC/nm2 is visible as dark stripes on the suspended membranes. (b) TEM image of a pattern written at a dose of 15.2 pC/nm2. The white areas correspond to completely removed graphene. (c) STEM-MAADF image of a low-dose pattern (darker areas correspond to lower amount of matter). (d) Higher-magnification STEM-MAADF image of structures written with the lower dose. (e) Line profile from the area marked in panel (d) showing the width of the patterns to be approximately 35 nm. (f) Same image as in panel (d) with the effect of the FIB patterning hidden by subtracting a blurred image (Gaussian blur with radius of 20 px). The resulting image shows only the features of the hydrocarbon contamination on the sample.

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Contamination is one of the hardest challenges in working with suspended graphene membranes. In our case, the situation is further worsened by the additional deposition of contamination that occurs during SEM imaging. However, a small fraction of the sample surface remained clean enough to image the atomic structure. Atomic resolution images of the irradiated but not perforated areas are shown in Figure 2a–c and pristine graphene in the nonpatterned part of the same hole in Figure 2d. In every clean area of the irradiated graphene, we found nonhexagonal carbon rings indicating irradiation-induced structural changes with occasional Si atoms incorporated into the nonhexagonal rings (see Figure 2a). Analysis of all of the imaged amorphized areas resulted in the following fractions for the different ring sizes: (5) 22.5%, (6) 63.2%, (7) 13.1%, (8) 0.9%, and (9) 0.4% (in total 818 rings were identified from the images). As in ref 30, we define the crystallinity as the number of hexagons divided by the total number of rings. In the present irradiated material, a crystallinity of 63% is found, while in ref 30 it was 51%. Hence, the amorphization here is close but not quite as strong as in ref 30 although the material is already a random network structure with no nanometer-scale crystalline areas.

Figure 2

Figure 2. Atomic-resolution images of amorphized graphene areas. (a–d) Example STEM-MAADF images from the amorphized areas (a–c) and a pristine area (d). A deconvolution with the beam profile, modeled as a sum of two Gaussians, has been applied as described in ref 36, followed by a Gaussian blur for panels (a–c) with a radius of 2–3 pixels. (e–h) Same images after the application of a minimum filter with a radius of 10 pixels to enhance the visibility of the nonhexagonal rings with the size of each ring marked on top of the rings. The marked atoms in panel (a) were identified as Si based on the contrast in the MAADF images. The bright areas around the atomically thin structures are covered by hydrocarbon contamination. All scale bars are 1 nm. Each pair of images is colored uniquely to ease the comparison.

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A rough estimation for the number of carbon atoms removed from the amorphized areas during ion irradiation can be obtained from the ratios of average intensities (irradiated versus nonirradiated area) in annular dark field images (with background subtracted). This yields a ratio of 91%, which indicates that the amorphized areas have approximately 9% density deficit as compared to pristine graphene. Comparing this number with earlier estimations of electron irradiation-amorphization of graphene (30) shows that such deficit is close to the completely disordered material, as is consistent with our atomic-resolution images. It is also an almost exact match with the density deficit at which the electron-beam-amorphized graphene has a crystallinity value of about 63% (30) (the value calculated above for the current material). This serves as an independent validation for the estimated 9% density deficit.
The dose that was sufficient to amorphize graphene was about 4.96 pC/nm2, which corresponds to ϕam ≈ 31 ions/nm2 (or, 3.1 × 1015 ions/cm2). To put this dose into perspective, it can be compared with the fact that a square nanometer of graphene has about 38.2 atoms. For cutting graphene, a three times higher dose was required (ϕcut ≈ 95 ions/nm2, or 9.5 × 1015 ions/cm2). Ion beam effects for bulk materials are typically estimated based on the concept of stopping power. In the case of 35 keV Ga+ irradiation of a carbon material, the nuclear stopping power is estimated to be 142 eV/Å and the electronic stopping power 24 eV/Å. (37) For a dose of 31 ions/nm2, such deposited energy is orders of magnitude more than what is needed to completely disintegrate a single layer of graphene. So, clearly this approach is not directly useful for 2D materials. A better understanding can be reached through a binary collision approximation. Numerical estimate using an empirical repulsive potential (38) leads to a limiting impact parameter of 0.83 Å for a collision that transfers enough kinetic energy from a 35 keV Ga+ ion to a carbon atom to cause a displacement in graphene (about 23 eV (39)). This is more than half of the bond length in graphene and corresponds to a probability of 83% for an ion to displace at least one of the target atoms, taking into account the area each carbon atom occupies in the graphene lattice.
Atomistic simulations (6) predict that under our experimental conditions defects will be created with a ratio of approximately 1:1:2 for single vacancies, amorphization events (no atoms sputtered), and complex vacancies (more than one atom sputtered), respectively. The calculated sputtering yield is about 0.55 atoms/ion, which is somewhat lower than what could be expected from the binary collision estimate. This is consistent with the assumption that for perpendicular irradiation the atoms are typically scattered in the plane and not necessarily removed from it. For a more accurate estimate of the number of sputtered atoms, we need to take into account the increasing vacancy concentration in the structure during irradiation, (11) which leads to an approximation formula for low vacancy concentrations (12)(1)where ϕ is the irradiation dose (ions/nm2), n ≈ 38.2 atoms/nm2 the density of graphene, Y0 ≈ 0.55 sputtering yield at cv = 0 and γ a constant that can be obtained through simulations. (11) On the basis of data for Ar+ and Xe+ irradiation at 30 keV, γ can be expected to be between 0.5 and 0.8 for Ga+ irradiation of graphene at 35 keV. For γ = 0.65, we get cv(ϕam) ≈ 35% and cv(ϕcut) > 70%. In contrast to 35% density deficit in the amorphized structure, the two independent estimates described above yielded a value of 9%. This discrepancy is most likely caused by the increased chemical reactivity of vacancies that attract carbon (and occasionally silicon) atoms from the contamination.
The ultrahigh vacuum column of the microscope reduces chemical etching to practically zero, simplifying the analysis of dynamical processes. However, at the same time all beneficial chemical reactions due to water (and other) molecules cracked by the imaging electrons, which could reduce the hydrocarbon contamination, are also prevented. To test both how the contamination is bound to the graphene and how amorphization affects the chemical inertness of graphene, we let air into the microscope column after initial imaging by opening a leak valve. We exposed the structure to a parallel electron beam while increasing the pressure in the objective from 5.3 × 10–9 to 1.1 × 10–6 mbar over an hour. The results of this treatment are shown in Figure 3. The contamination decreased dramatically and several clean areas appeared in the nonirradiated area of the sample, whereas holes grew in the irradiated areas. This demonstrates that controlled amorphization of graphene will activate it chemically. Because we were able to clean parts of the contamination, it cannot be covalently bound to the sample. Therefore, one possible way to overcome the contamination problem could be high-temperature vacuum annealing, which can be expected to remove most of the floating hydrocarbons.

Figure 3

Figure 3. Chemical etching of the amorphous pattern. (a) STEM-MAADF close-up image of a patterned area of the sample before and (b) after an exposure of about 1 h to a parallel electron beam while air was leaked to the objective area of the microscope column (pressure increase from ca. 5.3 × 10–9 to 1.1 × 10–6 mbar). The approximate area exposed to the beam corresponds to the darkened circular shape seen in panel (b). Partial overlay on the left-hand-side of panel (a) highlights the structure of the pattern (“ml+cont” corresponds to nonirradiated graphene and contamination, whereas “am+cont” refers to amorphized areas). Circles with solid and dashed lines mark the same hole and metal contamination, respectively, in both images to ease the comparison. A higher magnification of the area marked with a rectangle in panel (b) is shown in panel (c) to ease distinguishing holes and clean graphene from each other.

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As a conclusion, we have shown that the regular hexagon pattern of single-layer graphene can be selectively either sputtered or transformed into a random pattern of polygons ranging from pentagons to octagons and nine-membered carbon rings in a controlled manner using a focused Ga+ ion beam at 35 keV. This allows defining three different kinds of areas into a graphene layer with just one processing step with the FIB: chemically inert highly conductive graphene, chemically active, presumably less conductive, amorphous 2D carbon, and empty holes. The smallest demonstrated feature size was about 35 nm. A dose of ϕam ≈ 30 ions/nm2 was found to nearly completely amorphize graphene, whereas ϕcut ≈ 100 ions/nm2 leads to its perforation. The amorphous areas showed a density deficit of about 9% in discrepancy with an expected value of about 35%. This discrepancy is likely due to filling of the vacancies from the hydrocarbon contamination covering the graphene sheet. This point is supported by the observation of Si atoms immersed into the defected structures. The amorphized regions have a crystallinity value of 63%. The chemical activation gives promise to the application of selectively amorphized graphene in fields ranging from chemical sensing (4) to functionalized membranes and composite materials, while the predicted introduction of a band gap (3) allows their utilization in all-carbon electronics.

Methods

Samples

We used commercial single-layer graphene samples (Ted Pella Inc., Redding/CA 21712-5 PELCO) grown with chemical vapor deposition and deposited on SiNx transmission electron microscopy grids with a regular pattern of holes with an approximate diameter of 2.5 μm.

Focused Ion Beam

Fully and partially sputtered areas were written on different single-layer graphene samples using a focused beam of 35 keV Ga+ ions (Raith Ionline FIB). The beam size was approximately 20–30 nm, and the writing was performed in a linelike fashion with a step size of 1 nm and a dwell time of 0.0179 ms for the partially sputtered areas, which were later confirmed to be amorphized. The corresponding line dose was 1240 pC/cm. For fully sputtered areas, the dose was 3800 pC/cm (dwell time of 0.0482 ms). For the sample with the lower dose, a pattern of 27 × 6 slits, each 500 nm long, and separated 100 nm from each other, was designed to completely cover the 2.5 μm substrate holes in an area fully covered by graphene. This pattern was duplicated with the same hexagonal periodicity as the circular holes. The whole pattern was milled into the holes by taking a FIB image of a 30 × 30 μm2 area covered with graphene (with as short as possible exposure to the beam to avoid additional damage to the graphene) and fitting the pattern onto the holes. Milling such a pattern takes about 1 min.

Electron Microscopy

The SEM image in Figure 1a was recorded with Jeol 6700F SEM and the TEM image in Figure 1b with a table top Delong Instruments LVEM5 microscope. High-resolution imaging was carried out with a Nion UltraSTEM 100. The device is equipped with a cold field emission gun, which was operated at 60 kV in ultrahigh vacuum (5.3 × 10–9 mbar at the sample). A medium angle annular dark-field detector was used to record the images. At the end of the experiment, we let air into the microscope column under a parallel electron beam to partially remove the contamination and to test the chemical reactivity. The pressure was increased over a period of an hour to 1.1 × 10–6 mbar. In nonirradiated areas, this procedure uncovered pristine graphene. In the amorphized parts, the chemical processes lead additionally to the appearance of pores.

Author Information

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  • Corresponding Author
    • Jani Kotakoski - †Faculty of Physics, PNM and ‡Faculty of Physics, VCQ, QuNaBioS, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria;  §The Center for Nanosciences and Nanotechnology and ∥School of Chemistry, The Raymond and Beverly Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel;  Email: [email protected]
  • Authors
    • Christian Brand - †Faculty of Physics, PNM and ‡Faculty of Physics, VCQ, QuNaBioS, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria;  §The Center for Nanosciences and Nanotechnology and ∥School of Chemistry, The Raymond and Beverly Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
    • Yigal Lilach - †Faculty of Physics, PNM and ‡Faculty of Physics, VCQ, QuNaBioS, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria;  §The Center for Nanosciences and Nanotechnology and ∥School of Chemistry, The Raymond and Beverly Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
    • Ori Cheshnovsky - †Faculty of Physics, PNM and ‡Faculty of Physics, VCQ, QuNaBioS, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria;  §The Center for Nanosciences and Nanotechnology and ∥School of Chemistry, The Raymond and Beverly Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
    • Clemens Mangler - †Faculty of Physics, PNM and ‡Faculty of Physics, VCQ, QuNaBioS, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria;  §The Center for Nanosciences and Nanotechnology and ∥School of Chemistry, The Raymond and Beverly Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
    • Markus Arndt - †Faculty of Physics, PNM and ‡Faculty of Physics, VCQ, QuNaBioS, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria;  §The Center for Nanosciences and Nanotechnology and ∥School of Chemistry, The Raymond and Beverly Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
    • Jannik C. Meyer - †Faculty of Physics, PNM and ‡Faculty of Physics, VCQ, QuNaBioS, University of Vienna, Boltzmanngasse 5, A-1090 Vienna, Austria;  §The Center for Nanosciences and Nanotechnology and ∥School of Chemistry, The Raymond and Beverly Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978, Israel
  • Notes
    The authors declare no competing financial interest.

Acknowledgment

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We acknowledge funding from the Austrian Science Fund (FWF) projects M 1481-N20 and P 25721-N20, Wiener Wissenschafts-, Forschungs- und Technologiefonds (WWTF) project MA14-009, European Research Council (ERC) Projects No. 336453-PICOMAT and No. 320694, and European Union Commission Project No. 304886-NANOQUESTFIT. C.B. acknowledges financial support by the Alexander von Humboldt foundation.

References

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    Using atomistic computer simulations based on anal. potential and d.-functional theory models, we study effects of ion irradn. on graphene. We identify the types and concns. of defects which appear in graphene under impacts of various ions with energies ranging from tens of eV to mega-eV. For two-dimensional targets, defects beyond single and double vacancies are formed via in-plane recoils. We demonstrate that the conventional approach based on binary-collision approxn. and stochastic algorithms developed for bulk solids cannot be applied to graphene and other low-dimensional systems. Finally, taking into account the gas-holding capacity of graphene, we suggest the use of graphene as the ultimate membrane for ion-beam anal. of gases and other volatile systems which cannot be put in the high vacuum required for the operation of ion beams.
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  7. 7
    Åhlgren, E.; Kotakoski, J.; Krasheninnikov, A. Atomistic simulations of the implantation of low-energy boron and nitrogen ions into graphene Phys. Rev. B: Condens. Matter Mater. Phys. 2011, 83, 115424 DOI: 10.1103/PhysRevB.83.115424
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  8. 8
    Xu, Y.; Zhang, K.; Brüsewitz, C.; Wu, X.; Hofsäss, H. C. Investigation of the effect of low energy ion beam irradiation on mono-layer graphene AIP Adv. 2013, 3, 072120 DOI: 10.1063/1.4816715
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    8
    Investigation of the effect of low energy ion beam irradiation on mono-layer graphene
    Xu, Yijun; Zhang, Kun; Brusewitz, Christoph; Wu, Xuemei; Hofsass, Hans Christian
    AIP Advances (2013), 3 (7), 072120/1-072120/11CODEN: AAIDBI; ISSN:2158-3226. (American Institute of Physics)
    In this paper, the effect of low energy irradn. on mono-layer graphene was studied. Mono-layer graphene films were irradiated with B, N and F ions at different energy and fluence. XPS indicates that foreign ions implanted at ion energies below 35 eV could dope into the graphene lattice and form new chem. bonds with carbon atoms. The results of Raman measurement indicate that ion beam irradn. causes defects and disorder to the graphene crystal structure, and the level of defects increases with increasing of ion energy and fluence. Surface morphol. images also prove that ion beam irradn. creates damages to graphene film. The expt. results suggest that low-energy irradn. with energies of about 30 eV and fluences up to 5 · 1014 cm-2 could realize small amt. of doping, while introducing weak damage to graphene. Low energy ion beam irradn., provides a promising approach for controlled doping of graphene. (c) 2013 American Institute of Physics.
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  9. 9
    Bangert, U. Ion implantation of graphene - towards IC compatible technologies Nano Lett. 2013, 13, 4902– 4907 DOI: 10.1021/nl402812y
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    9
    Ion Implantation of Graphene-Toward IC Compatible Technologies
    Bangert, U.; Pierce, W.; Kepaptsoglou, D. M.; Ramasse, Q.; Zan, R.; Gass, M. H.; Van den Berg, J. A.; Boothroyd, C. B.; Amani, J.; Hofsass, H.
    Nano Letters (2013), 13 (10), 4902-4907CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    Doping of graphene via low energy ion implantation could open possibilities for fabrication of nanometer-scale patterned graphene-based devices as well as for graphene functionalization compatible with large-scale integrated semiconductor technol. Using advanced electron microscopy/spectroscopy methods, the authors show for the 1st time directly that graphene can be doped with B and N via ion implantation and that the retention is in good agreement with predictions from calcn.-based literature values. Atomic resoln. high-angle dark field imaging (HAADF) combined with single-atom electron energy loss (EEL) spectroscopy reveals that for sufficiently low implantation energies ions are predominantly substitutionally incorporated into the graphene lattice with a very small fraction residing in defect-related sites.
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  10. 10
    Lehtinen, O.; Kotakoski, J.; Krasheninnikov, A. V.; Keinonen, J. Cutting and controlled modification of graphene with ion beams Nanotechnology 2011, 22, 175306 DOI: 10.1088/0957-4484/22/17/175306
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    10
    Cutting and controlled modification of graphene with ion beams
    Lehtinen, O.; Kotakoski, J.; Krasheninnikov, A. V.; Keinonen, J.
    Nanotechnology (2011), 22 (17), 175306/1-175306/8CODEN: NNOTER; ISSN:1361-6528. (Institute of Physics Publishing)
    Using atomistic computer simulations, we study how ion irradn. can be used to alter the morphol. of a graphene monolayer, by introducing defects of specific type, and to cut graphene sheets. Based on the results of our anal. potential mol. dynamics simulations, a kinetic Monte Carlo code is developed for modeling morphol. changes in a graphene monolayer under irradn. at macroscopic time scales. Impacts of He, Ne, Ar, Kr, Xe, and Ga ions with kinetic energies ranging from tens of eV to 10 MeV and angles of incidence between 0° and 88° are studied. Our results provide microscopic insights into the response of graphene to ion irradn. and can directly be used for the optimization of graphene cutting and patterning with focused ion beams.
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  11. 11
    Åhlgren, E. H.; Kotakoski, J.; Lehtinen, O.; Krasheninnikov, A. V. Ion irradiation tolerance of graphene as studied by atomistic simulations Appl. Phys. Lett. 2012, 100, 233108 DOI: 10.1063/1.4726053
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  12. 12

    The formula has been established for low cv and shows asymptotically wrong behaviour for cv → 1. It can therefore only be trusted for cv ≪ 1.

    There is no corresponding record for this reference.
  13. 13
    Standop, S.; Lehtinen, O.; Herbig, C.; Lewes-Malandrakis, G.; Craes, F.; Kotakoski, J.; Michely, T.; Krasheninnikov, A. V.; Busse, C. Ion Impacts on Graphene/Ir(111): Interface Channeling, Vacancy Funnels, and a Nanomesh Nano Lett. 2013, 13, 1948– 1955 DOI: 10.1021/nl304659n
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    13
    Ion impacts on graphene/Ir(111): Interface channeling, vacancy funnels, and nanomesh
    Standop, Sebastian; Lehtinen, Ossi; Herbig, Charlotte; Lewes-Malandrakis, Georgia; Craes, Fabian; Kotakoski, Jani; Michely, Thomas; Krasheninnikov, Arkady V.; Busse, Carsten
    Nano Letters (2013), 13 (5), 1948-1955CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
    By combining ion beam expts. and atomistic simulations we study the prodn. of defects in graphene on Ir(111) under grazing incidence of low energy Xe ions. We demonstrate that the ions are channeled in between graphene and the substrate, giving rise to chains of vacancy clusters with their edges bending down toward the substrate. These clusters self-organize to a graphene nanomesh via thermally activated diffusion as their formation energy varies within the graphene moire supercell.
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  14. 14
    Åhlgren, E. H.; Hämäläinen, S. K.; Lehtinen, O.; Liljeroth, P.; Kotakoski, J. Structural manipulation of the graphene/metal interface with Ar+ irradiation Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 155419 DOI: 10.1103/PhysRevB.88.155419
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    Herbig, C.; Åhlgren, E. H.; Jolie, W.; Busse, C.; Kotakoski, J.; Krasheninnikov, A. V.; Michely, T. Interfacial Carbon Nanoplatelet Formation by Ion Irradiation of Graphene on Ir(111) ACS Nano 2014, 8, 12208– 12218 DOI: 10.1021/nn503874n
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    Tapasztó, L.; Dobrik, G.; Nemes-Incze, P.; Vertesy, G.; Lambin, Ph.; Biró, L. P. Tuning the electronic structure of graphene by ion irradiation Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 78, 233407 DOI: 10.1103/PhysRevB.78.233407
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    Tuning the electronic structure of graphene by ion irradiation
    Tapaszto, L.; Dobrik, G.; Nemes-Incze, P.; Vertesy, G.; Lambin, Ph.; Biro, L. P.
    Physical Review B: Condensed Matter and Materials Physics (2008), 78 (23), 233407/1-233407/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    Mech. exfoliated graphene layers deposited on SiO2 substrate were irradiated with Ar+ ions in order to exptl. study the effect of at. scale defects and disorder on the low-energy electronic structure of graphene. The irradiated samples were investigated by scanning tunneling microscopy and spectroscopy measurements, which reveal that defect sites, besides acting as scattering centers for electrons through local modification of the on-site potential, also induce disorder in the hopping amplitudes. The most important consequence of the induced disorder is the substantial redn. in the Fermi velocity, revealed by bias-dependent imaging of electron-d. oscillations obsd. near defect sites.
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  17. 17
    Ugeda, M. M.; Brihuega, I.; Guinea, F.; Gómez-Rodríguez, J. M. Missing Atom as a Source of Carbon Magnetism Phys. Rev. Lett. 2010, 104, 096804 DOI: 10.1103/PhysRevLett.104.096804
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    17
    Missing atom as a source of carbon magnetism
    Ugeda, M. M.; Brihuega, I.; Guinea, F.; Gomez-Rodriguez, J. M.
    Physical Review Letters (2010), 104 (9), 096804/1-096804/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    Atomic vacancies have a strong impact in the mech., electronic, and magnetic properties of graphenelike materials. By artificially generating isolated vacancies on a graphite surface and measuring their local d. of states on the at. scale, single vacancies modify the electronic properties of this graphenelike system. The authors' scanning tunneling microscopy expts., complemented by tight-binding calcns., reveal a sharp electronic resonance at the Fermi energy around each single graphite vacancy, which can be assocd. with the formation of local magnetic moments and implies a dramatic redn. of the charge carriers' mobility. While vacancies in single layer graphene lead to magnetic couplings of arbitrary sign, the authors' results show the possibility of inducing a macroscopic ferrimagnetic state in multilayered graphene just by randomly removing single C atoms.
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  18. 18
    Ugeda, M. M.; Fernández-Torre, D.; Brihuega, I.; Pou, P.; Martínez-Galera, A. J.; Pérez, R.; Gómez-Rodríguez, J. M. Point defects on graphene on metals Phys. Rev. Lett. 2011, 107, 116803 DOI: 10.1103/PhysRevLett.107.116803
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    18
    Point defects on graphene on metals
    Ugeda, M. M.; Fernandez-Torre, D.; Brihuega, I.; Pou, P.; Martinez-Galera, A. J.; Perez, Ruben; Gomez-Rodriguez, J. M.
    Physical Review Letters (2011), 107 (11), 116803/1-116803/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
    Understanding the coupling of graphene with its local environment is crit. to be able to integrate it in tomorrow's electronic devices. Here we show how the presence of a metallic substrate affects the properties of an atomically tailored graphene layer. We have deliberately introduced single C vacancies on a graphene monolayer grown on a Pt(111) surface and investigated its impact in the electronic, structural, and magnetic properties of the graphene layer. Our low temp. scanning tunneling microscopy studies, complemented by d. functional theory, show the existence of a broad electronic resonance above the Fermi energy assocd. with the vacancies. Vacancy sites become reactive leading to an increase of the coupling between the graphene layer and the metal substrate at these points; this gives rise to a rapid decay of the localized state and the quenching of the magnetic moment assocd. with C vacancies in freestanding graphene layers.
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  19. 19
    Ugeda, M. M.; Brihuega, I.; Hiebel, F.; Mallet, P.; Veuillen, J.-Y.; Gómez-Rodríguez, J. M.; Ynduráin, F. Electronic and structural characterization of divacancies in irradiated graphene Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 85, 121402 DOI: 10.1103/PhysRevB.85.121402
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    19
    Electronic and structural characterization of divacancies in irradiated graphene
    Ugeda, Miguel M.; Brihuega, Ivan; Hiebel, Fanny; Mallet, Pierre; Veuillen, Jean-Yves; Gomez-Rodriguez, Jose M.; Yndurain, Felix
    Physical Review B: Condensed Matter and Materials Physics (2012), 85 (12), 121402/1-121402/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
    We provide a thorough study of a carbon divacancy, a point defect expected to have a large impact on the properties of graphene. Low-temp. scanning tunneling microscopy imaging of irradiated graphene on different substrates enabled us to identify a common twofold symmetry point defect. Our first-principles calcns. reveal that the structure of this type of defect accommodates two adjacent missing atoms in a rearranged at. network formed by two pentagons and one octagon, with no dangling bonds. Scanning tunneling spectroscopy measurements on divacancies generated in nearly ideal graphene show an electronic spectrum dominated by an empty-states resonance, which is ascribed to a nearly flat, spin-degenerated band of π-electron nature. While the calcd. electronic structure rules out the formation of a magnetic moment around the divacancy, the generation of an electronic resonance near the Fermi level reveals divacancies as key point defects for tuning electron transport properties in graphene systems.
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  20. 20
    Pan, C.-T.; Hinks, J. A.; Ramasse, Q. M.; Greaves, G.; Bangert, U.; Donnelly, S. E.; Haigh, S. J. In-situ observation and atomic resolution imaging of the ion irradiation induced amorphisation of graphene Sci. Rep. 2014, 4, 6334 DOI: 10.1038/srep06334
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    20
    In-situ observation and atomic resolution imaging of the ion irradiation induced amorphization of graphene
    Pan, C.-T.; Hinks, J. A.; Ramasse, Q. M.; Greaves, G.; Bangert, U.; Donnelly, S. E.; Haigh, S. J.
    Scientific Reports (2014), 4 (), 6334CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
    Ion irradn. has been obsd. to induce a macroscopic flattening and in-plane shrinkage of graphene sheets without a complete loss of crystallinity. Electron diffraction studies performed during simultaneous in-situ ion irradn. have allowed identification of the fluence at which the graphene sheet loses long-range order. This approach has facilitated complementary ex-situ investigations, allowing the first at. resoln. scanning transmission electron microscopy images of ion-irradn. induced graphene defect structures together with quant. anal. of defect densities using Raman spectroscopy.
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  21. 21
    Compagnini, G.; Giannazzo, F.; Sonde, S.; Raineri, V.; Rimini, E. Ion irradiation and defect formation in single layer graphene Carbon 2009, 47, 3201– 3207 DOI: 10.1016/j.carbon.2009.07.033
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    21
    Ion irradiation and defect formation in single layer graphene
    Compagnini, Giuseppe; Giannazzo, Filippo; Sonde, Sushant; Raineri, Vito; Rimini, Emanuele
    Carbon (2009), 47 (14), 3201-3207CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
    Ion irradn. by 500 keV C+ ions was used to introduce defects into graphene sheets deposited on SiO2 in a controlled way. The combined use of Raman spectroscopy and at. force microscopy (AFM) allowed one to clarify the mechanisms of disorder formation in single layers, bilayers and multi-layers of graphene. The ratio between the D and G peak intensities in the Raman spectra of single layers is higher than for bilayers and multi-layers, indicating a higher amt. of disorder. This cannot be only ascribed to point defects, originating from direct C+-C collisions, but also the different interactions of single layers and few layers with the substrate plays a crucial role. As demonstrated by AFM, for irradn. at fluences higher than 5 × 1013 cm-2, the morphol. of single layers becomes fully conformed to that of the SiO2 substrate, i.e. graphene ripples are completely suppressed, while ripples are still present on bilayer and multi-layers. The stronger interaction of a single layer with the substrate roughness leads to the obsd. larger amt. of disorder.
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  22. 22
    Zhou, Y.-B.; Liao, Z.-M.; Wang, Y.-F.; Duesberg, G. S.; Xu, J.; Fu, Q.; Wu, X.-S.; Yu, D.-P. Ion irradiation induced structural and electrical transition in graphene J. Chem. Phys. 2010, 133, 234703 DOI: 10.1063/1.3518979
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    Compagnini, G.; Forte, G.; Giannazzo, F.; Raineri, V.; La Magna, A.; Deretzis, I. Ion beam induced defects in graphene: Raman spectroscopy and DFT calculations J. Mol. Struct. 2011, 993, 506– 509 DOI: 10.1016/j.molstruc.2010.12.065
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    Kalbac, M.; Lehtinen, O.; Krasheninnikov, A. V.; Keinonen, J. Ion-Irradiation-Induced Defects in Isotopically-Labeled Two Layered Graphene: Enhanced In-Situ Annealing of the Damage Adv. Mater. 2013, 25, 1004– 1009 DOI: 10.1002/adma.201203807
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    24
    Ion-Irradiation-Induced Defects in Isotopically-Labeled Two Layered Graphene: Enhanced In-Situ Annealing of the Damage
    Kalbac, Martin; Lehtinen, Ossi; Krasheninnikov, Arkady V.; Keinonen, Juhani
    Advanced Materials (Weinheim, Germany) (2013), 25 (7), 1004-1009CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
    The effect of 100 keV Ar+ ion irradn. on isotopically labeled single and two-layer graphene has been studied using Raman spectra and atomistic simulations. The no. of defects in both of the graphene layers increased with increasing irradn. fluence, but the rate of defect accumulation was significantly different in the layers, with the final defect d. in the bottom layer being lower than that in the top layer. This observation was explained via the anal. of the final locations of interstitial carbon atoms produced by sputtering by the energetic ion in the atomistic simulations. A significantly higher no. of interstitials was produced in between the bottom layer and the substrate. As these interstitials are expected to be mobile at room temp., they can recombine with vacancies in the bottom layer resulting in the redn. of total damage.
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  25. 25
    Wang, Q.; Mao, W.; Ge, D.; Zhang, Y.; Shao, Y.; Ren, N. Effects of Ga ion-beam irradiation on monolayer graphene Appl. Phys. Lett. 2013, 103, 073501 DOI: 10.1063/1.4818458
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    25
    Effects of Ga ion-beam irradiation on monolayer graphene
    Wang, Quan; Mao, Wei; Ge, Daohan; Zhang, Yanmin; Shao, Ying; Ren, Naifei
    Applied Physics Letters (2013), 103 (7), 073501/1-073501/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    The effects of Ga ion on the single layer graphene (SLG) were studied by Raman spectroscopy (RS), SEM, and field-effect characterization. Under vacuum conditions, Ga ion-irradn. can induce disorders and cause red shift of 2D band of RS, rather than lattice damage in high quality SLG. The compressive strain induced by Ga ion decreases the cryst. size in SLG, which is responsible for the variation of Raman scattering and elec. properties. Nonlinear out-put characteristic and resistance increased are also found in the I-V measurement. The results have important implications during CVD graphene characterization and related device fabrication. (c) 2013 American Institute of Physics.
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  26. 26
    Zeng, J.; Yao, H. J.; Zhang, S. X.; Zhai, P. F.; Duan, J. L.; Sun, Y. M.; Li, G. P.; Liu, J. Swift heavy ions induced irradiation effects in monolayer graphene and highly oriented pyrolytic graphite Nucl. Instrum. Methods Phys. Res., Sect. B 2014, 330, 18– 23 DOI: 10.1016/j.nimb.2014.03.019
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    26
    Swift heavy ions induced irradiation effects in monolayer graphene and highly oriented pyrolytic graphite
    Zeng, J.; Yao, H. J.; Zhang, S. X.; Zhai, P. F.; Duan, J. L.; Sun, Y. M.; Li, G. P.; Liu, J.
    Nuclear Instruments & Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms (2014), 330 (), 18-23CODEN: NIMBEU; ISSN:0168-583X. (Elsevier B.V.)
    Monolayer graphene and highly oriented pyrolytic graphite (HOPG) were irradiated by swift heavy ions (209Bi and 112Sn) with the fluence between 1011 and 1014 ions/cm2. Both pristine and irradiated samples were investigated by Raman spectroscopy. It was found that D and D' peaks appear after irradn., which indicated the ion irradn. introduced damage both in the graphene and graphite lattice. Due to the special single at. layer structure of graphene, the irradn. fluence threshold Φth of the D band of graphene is significantly lower (<1 × 1011 ions/cm2) than that (2.5 × 1012 ions/cm2) of HOPG. The larger defect d. in graphene than in HOPG indicates that the monolayer graphene is much easier to be damaged than bulk graphite by swift heavy ions. Moreover, different defect types in graphene and HOPG were detected by the different values of ID/ID'. For the irradn. with the same electronic energy loss, the velocity effect was found in HOPG. However, in this expt., the velocity effect was not obsd. in graphene samples irradiated by swift heavy ions.
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    Mathew, S. Mega-electron-volt proton irradiation on supported and suspended graphene: A Raman spectroscopic layer dependent study J. Appl. Phys. 2011, 110, 084309 DOI: 10.1063/1.3647781
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    27
    Mega-electron-volt proton irradiation on supported and suspended graphene: A Raman spectroscopic layer dependent study
    Mathew, S.; Chan, T. K.; Zhan, D.; Gopinadhan, K.; Roy Barman, A.; Breese, M. B. H.; Dhar, S.; Shen, Z. X.; Venkatesan, T.; Thong, John T. L.
    Journal of Applied Physics (2011), 110 (8), 084309/1-084309/9CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
    Graphene samples with 1, 2, and 4 layers and 1 + 1 folded bi-layers and graphite were irradiated with 2 MeV protons at fluences ranging from 1 × 1015 to 6 × 1018 ions/cm2. The samples were characterized using visible and UV Raman spectroscopy and Raman microscopy. The ion-induced defects decrease with increasing no. of layers. Graphene samples suspended over etched holes in SiO2 were fabricated and used to study the influence of the substrate SiO2 for defect creation in graphene. While Raman vibrational modes at 1460 cm-1 and 1555 cm-1 were obsd. in the visible Raman spectra of substantially damaged graphene samples, these modes were absent in the irradiated-suspended monolayer graphene. (c) 2011 American Institute of Physics.
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  28. 28
    Kumar, S.; Tripathi, A.; Khan, S. A.; Pannu, C.; Avasthi, D. K. Radiation stability of graphene under extreme conditions Appl. Phys. Lett. 2014, 105, 133107 DOI: 10.1063/1.4897004
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    28
    Radiation stability of graphene under extreme conditions
    Kumar, Sunil; Tripathi, Ambuj; Khan, Saif A.; Pannu, Compesh; Avasthi, Devesh K.
    Applied Physics Letters (2014), 105 (13), 133107/1-133107/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
    We report radiation stability of graphene under extreme condition of high energy d. generated by 150 MeV Au ion irradn. The expt. reveals that graphene is radiation resistant for irradn. at 1014 ions/cm2 of 150 MeV Au ions. Annealing effects are obsd. at lower fluences whereas defect prodn. occurs at higher fluences but significant crystallinity is retained. Our results demonstrate applicability of graphene based devices in radiation environment and space applications. (c) 2014 American Institute of Physics.
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  29. 29
    Kotakoski, J.; Krasheninnikov, A. V.; Kaiser, U.; Meyer, J. C. From Point Defects in Graphene to Two-Dimensional Amorphous Carbon Phys. Rev. Lett. 2011, 106, 105505 DOI: 10.1103/PhysRevLett.106.105505
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    29
    From point defects in graphene to two-dimensional amorphous carbon
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    Physical Review Letters (2011), 106 (10), 105505/1-105505/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
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Cite this: Nano Lett. 2015, 15, 9, 5944–5949
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https://doi.org/10.1021/acs.nanolett.5b02063
Published July 10, 2015

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  • Abstract

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    Figure 1

    Figure 1. Overview images of the structures patterned into graphene with a focused ion beam. (a) SEM overview image of the SiNx TEM grid showing an array of holes with a diameter of 2.5 μm. Graphene covers the complete area and is suspended over the holes. The pattern written with the FIB at a dose of 4.96 pC/nm2 is visible as dark stripes on the suspended membranes. (b) TEM image of a pattern written at a dose of 15.2 pC/nm2. The white areas correspond to completely removed graphene. (c) STEM-MAADF image of a low-dose pattern (darker areas correspond to lower amount of matter). (d) Higher-magnification STEM-MAADF image of structures written with the lower dose. (e) Line profile from the area marked in panel (d) showing the width of the patterns to be approximately 35 nm. (f) Same image as in panel (d) with the effect of the FIB patterning hidden by subtracting a blurred image (Gaussian blur with radius of 20 px). The resulting image shows only the features of the hydrocarbon contamination on the sample.

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    Figure 2

    Figure 2. Atomic-resolution images of amorphized graphene areas. (a–d) Example STEM-MAADF images from the amorphized areas (a–c) and a pristine area (d). A deconvolution with the beam profile, modeled as a sum of two Gaussians, has been applied as described in ref 36, followed by a Gaussian blur for panels (a–c) with a radius of 2–3 pixels. (e–h) Same images after the application of a minimum filter with a radius of 10 pixels to enhance the visibility of the nonhexagonal rings with the size of each ring marked on top of the rings. The marked atoms in panel (a) were identified as Si based on the contrast in the MAADF images. The bright areas around the atomically thin structures are covered by hydrocarbon contamination. All scale bars are 1 nm. Each pair of images is colored uniquely to ease the comparison.

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    Figure 3

    Figure 3. Chemical etching of the amorphous pattern. (a) STEM-MAADF close-up image of a patterned area of the sample before and (b) after an exposure of about 1 h to a parallel electron beam while air was leaked to the objective area of the microscope column (pressure increase from ca. 5.3 × 10–9 to 1.1 × 10–6 mbar). The approximate area exposed to the beam corresponds to the darkened circular shape seen in panel (b). Partial overlay on the left-hand-side of panel (a) highlights the structure of the pattern (“ml+cont” corresponds to nonirradiated graphene and contamination, whereas “am+cont” refers to amorphized areas). Circles with solid and dashed lines mark the same hole and metal contamination, respectively, in both images to ease the comparison. A higher magnification of the area marked with a rectangle in panel (b) is shown in panel (c) to ease distinguishing holes and clean graphene from each other.

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      Bangert, U.; Pierce, W.; Kepaptsoglou, D. M.; Ramasse, Q.; Zan, R.; Gass, M. H.; Van den Berg, J. A.; Boothroyd, C. B.; Amani, J.; Hofsass, H.
      Nano Letters (2013), 13 (10), 4902-4907CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      Doping of graphene via low energy ion implantation could open possibilities for fabrication of nanometer-scale patterned graphene-based devices as well as for graphene functionalization compatible with large-scale integrated semiconductor technol. Using advanced electron microscopy/spectroscopy methods, the authors show for the 1st time directly that graphene can be doped with B and N via ion implantation and that the retention is in good agreement with predictions from calcn.-based literature values. Atomic resoln. high-angle dark field imaging (HAADF) combined with single-atom electron energy loss (EEL) spectroscopy reveals that for sufficiently low implantation energies ions are predominantly substitutionally incorporated into the graphene lattice with a very small fraction residing in defect-related sites.
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    10. 10
      Lehtinen, O.; Kotakoski, J.; Krasheninnikov, A. V.; Keinonen, J. Cutting and controlled modification of graphene with ion beams Nanotechnology 2011, 22, 175306 DOI: 10.1088/0957-4484/22/17/175306
      10
      Cutting and controlled modification of graphene with ion beams
      Lehtinen, O.; Kotakoski, J.; Krasheninnikov, A. V.; Keinonen, J.
      Nanotechnology (2011), 22 (17), 175306/1-175306/8CODEN: NNOTER; ISSN:1361-6528. (Institute of Physics Publishing)
      Using atomistic computer simulations, we study how ion irradn. can be used to alter the morphol. of a graphene monolayer, by introducing defects of specific type, and to cut graphene sheets. Based on the results of our anal. potential mol. dynamics simulations, a kinetic Monte Carlo code is developed for modeling morphol. changes in a graphene monolayer under irradn. at macroscopic time scales. Impacts of He, Ne, Ar, Kr, Xe, and Ga ions with kinetic energies ranging from tens of eV to 10 MeV and angles of incidence between 0° and 88° are studied. Our results provide microscopic insights into the response of graphene to ion irradn. and can directly be used for the optimization of graphene cutting and patterning with focused ion beams.
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    11. 11
      Åhlgren, E. H.; Kotakoski, J.; Lehtinen, O.; Krasheninnikov, A. V. Ion irradiation tolerance of graphene as studied by atomistic simulations Appl. Phys. Lett. 2012, 100, 233108 DOI: 10.1063/1.4726053
      There is no corresponding record for this reference.
    12. 12

      The formula has been established for low cv and shows asymptotically wrong behaviour for cv → 1. It can therefore only be trusted for cv ≪ 1.

      There is no corresponding record for this reference.
    13. 13
      Standop, S.; Lehtinen, O.; Herbig, C.; Lewes-Malandrakis, G.; Craes, F.; Kotakoski, J.; Michely, T.; Krasheninnikov, A. V.; Busse, C. Ion Impacts on Graphene/Ir(111): Interface Channeling, Vacancy Funnels, and a Nanomesh Nano Lett. 2013, 13, 1948– 1955 DOI: 10.1021/nl304659n
      13
      Ion impacts on graphene/Ir(111): Interface channeling, vacancy funnels, and nanomesh
      Standop, Sebastian; Lehtinen, Ossi; Herbig, Charlotte; Lewes-Malandrakis, Georgia; Craes, Fabian; Kotakoski, Jani; Michely, Thomas; Krasheninnikov, Arkady V.; Busse, Carsten
      Nano Letters (2013), 13 (5), 1948-1955CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)
      By combining ion beam expts. and atomistic simulations we study the prodn. of defects in graphene on Ir(111) under grazing incidence of low energy Xe ions. We demonstrate that the ions are channeled in between graphene and the substrate, giving rise to chains of vacancy clusters with their edges bending down toward the substrate. These clusters self-organize to a graphene nanomesh via thermally activated diffusion as their formation energy varies within the graphene moire supercell.
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    14. 14
      Åhlgren, E. H.; Hämäläinen, S. K.; Lehtinen, O.; Liljeroth, P.; Kotakoski, J. Structural manipulation of the graphene/metal interface with Ar+ irradiation Phys. Rev. B: Condens. Matter Mater. Phys. 2013, 88, 155419 DOI: 10.1103/PhysRevB.88.155419
      There is no corresponding record for this reference.
    15. 15
      Herbig, C.; Åhlgren, E. H.; Jolie, W.; Busse, C.; Kotakoski, J.; Krasheninnikov, A. V.; Michely, T. Interfacial Carbon Nanoplatelet Formation by Ion Irradiation of Graphene on Ir(111) ACS Nano 2014, 8, 12208– 12218 DOI: 10.1021/nn503874n
      There is no corresponding record for this reference.
    16. 16
      Tapasztó, L.; Dobrik, G.; Nemes-Incze, P.; Vertesy, G.; Lambin, Ph.; Biró, L. P. Tuning the electronic structure of graphene by ion irradiation Phys. Rev. B: Condens. Matter Mater. Phys. 2008, 78, 233407 DOI: 10.1103/PhysRevB.78.233407
      16
      Tuning the electronic structure of graphene by ion irradiation
      Tapaszto, L.; Dobrik, G.; Nemes-Incze, P.; Vertesy, G.; Lambin, Ph.; Biro, L. P.
      Physical Review B: Condensed Matter and Materials Physics (2008), 78 (23), 233407/1-233407/4CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      Mech. exfoliated graphene layers deposited on SiO2 substrate were irradiated with Ar+ ions in order to exptl. study the effect of at. scale defects and disorder on the low-energy electronic structure of graphene. The irradiated samples were investigated by scanning tunneling microscopy and spectroscopy measurements, which reveal that defect sites, besides acting as scattering centers for electrons through local modification of the on-site potential, also induce disorder in the hopping amplitudes. The most important consequence of the induced disorder is the substantial redn. in the Fermi velocity, revealed by bias-dependent imaging of electron-d. oscillations obsd. near defect sites.
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    17. 17
      Ugeda, M. M.; Brihuega, I.; Guinea, F.; Gómez-Rodríguez, J. M. Missing Atom as a Source of Carbon Magnetism Phys. Rev. Lett. 2010, 104, 096804 DOI: 10.1103/PhysRevLett.104.096804
      17
      Missing atom as a source of carbon magnetism
      Ugeda, M. M.; Brihuega, I.; Guinea, F.; Gomez-Rodriguez, J. M.
      Physical Review Letters (2010), 104 (9), 096804/1-096804/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Atomic vacancies have a strong impact in the mech., electronic, and magnetic properties of graphenelike materials. By artificially generating isolated vacancies on a graphite surface and measuring their local d. of states on the at. scale, single vacancies modify the electronic properties of this graphenelike system. The authors' scanning tunneling microscopy expts., complemented by tight-binding calcns., reveal a sharp electronic resonance at the Fermi energy around each single graphite vacancy, which can be assocd. with the formation of local magnetic moments and implies a dramatic redn. of the charge carriers' mobility. While vacancies in single layer graphene lead to magnetic couplings of arbitrary sign, the authors' results show the possibility of inducing a macroscopic ferrimagnetic state in multilayered graphene just by randomly removing single C atoms.
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    18. 18
      Ugeda, M. M.; Fernández-Torre, D.; Brihuega, I.; Pou, P.; Martínez-Galera, A. J.; Pérez, R.; Gómez-Rodríguez, J. M. Point defects on graphene on metals Phys. Rev. Lett. 2011, 107, 116803 DOI: 10.1103/PhysRevLett.107.116803
      18
      Point defects on graphene on metals
      Ugeda, M. M.; Fernandez-Torre, D.; Brihuega, I.; Pou, P.; Martinez-Galera, A. J.; Perez, Ruben; Gomez-Rodriguez, J. M.
      Physical Review Letters (2011), 107 (11), 116803/1-116803/5CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      Understanding the coupling of graphene with its local environment is crit. to be able to integrate it in tomorrow's electronic devices. Here we show how the presence of a metallic substrate affects the properties of an atomically tailored graphene layer. We have deliberately introduced single C vacancies on a graphene monolayer grown on a Pt(111) surface and investigated its impact in the electronic, structural, and magnetic properties of the graphene layer. Our low temp. scanning tunneling microscopy studies, complemented by d. functional theory, show the existence of a broad electronic resonance above the Fermi energy assocd. with the vacancies. Vacancy sites become reactive leading to an increase of the coupling between the graphene layer and the metal substrate at these points; this gives rise to a rapid decay of the localized state and the quenching of the magnetic moment assocd. with C vacancies in freestanding graphene layers.
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    19. 19
      Ugeda, M. M.; Brihuega, I.; Hiebel, F.; Mallet, P.; Veuillen, J.-Y.; Gómez-Rodríguez, J. M.; Ynduráin, F. Electronic and structural characterization of divacancies in irradiated graphene Phys. Rev. B: Condens. Matter Mater. Phys. 2012, 85, 121402 DOI: 10.1103/PhysRevB.85.121402
      19
      Electronic and structural characterization of divacancies in irradiated graphene
      Ugeda, Miguel M.; Brihuega, Ivan; Hiebel, Fanny; Mallet, Pierre; Veuillen, Jean-Yves; Gomez-Rodriguez, Jose M.; Yndurain, Felix
      Physical Review B: Condensed Matter and Materials Physics (2012), 85 (12), 121402/1-121402/5CODEN: PRBMDO; ISSN:1098-0121. (American Physical Society)
      We provide a thorough study of a carbon divacancy, a point defect expected to have a large impact on the properties of graphene. Low-temp. scanning tunneling microscopy imaging of irradiated graphene on different substrates enabled us to identify a common twofold symmetry point defect. Our first-principles calcns. reveal that the structure of this type of defect accommodates two adjacent missing atoms in a rearranged at. network formed by two pentagons and one octagon, with no dangling bonds. Scanning tunneling spectroscopy measurements on divacancies generated in nearly ideal graphene show an electronic spectrum dominated by an empty-states resonance, which is ascribed to a nearly flat, spin-degenerated band of π-electron nature. While the calcd. electronic structure rules out the formation of a magnetic moment around the divacancy, the generation of an electronic resonance near the Fermi level reveals divacancies as key point defects for tuning electron transport properties in graphene systems.
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    20. 20
      Pan, C.-T.; Hinks, J. A.; Ramasse, Q. M.; Greaves, G.; Bangert, U.; Donnelly, S. E.; Haigh, S. J. In-situ observation and atomic resolution imaging of the ion irradiation induced amorphisation of graphene Sci. Rep. 2014, 4, 6334 DOI: 10.1038/srep06334
      20
      In-situ observation and atomic resolution imaging of the ion irradiation induced amorphization of graphene
      Pan, C.-T.; Hinks, J. A.; Ramasse, Q. M.; Greaves, G.; Bangert, U.; Donnelly, S. E.; Haigh, S. J.
      Scientific Reports (2014), 4 (), 6334CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      Ion irradn. has been obsd. to induce a macroscopic flattening and in-plane shrinkage of graphene sheets without a complete loss of crystallinity. Electron diffraction studies performed during simultaneous in-situ ion irradn. have allowed identification of the fluence at which the graphene sheet loses long-range order. This approach has facilitated complementary ex-situ investigations, allowing the first at. resoln. scanning transmission electron microscopy images of ion-irradn. induced graphene defect structures together with quant. anal. of defect densities using Raman spectroscopy.
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    21. 21
      Compagnini, G.; Giannazzo, F.; Sonde, S.; Raineri, V.; Rimini, E. Ion irradiation and defect formation in single layer graphene Carbon 2009, 47, 3201– 3207 DOI: 10.1016/j.carbon.2009.07.033
      21
      Ion irradiation and defect formation in single layer graphene
      Compagnini, Giuseppe; Giannazzo, Filippo; Sonde, Sushant; Raineri, Vito; Rimini, Emanuele
      Carbon (2009), 47 (14), 3201-3207CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)
      Ion irradn. by 500 keV C+ ions was used to introduce defects into graphene sheets deposited on SiO2 in a controlled way. The combined use of Raman spectroscopy and at. force microscopy (AFM) allowed one to clarify the mechanisms of disorder formation in single layers, bilayers and multi-layers of graphene. The ratio between the D and G peak intensities in the Raman spectra of single layers is higher than for bilayers and multi-layers, indicating a higher amt. of disorder. This cannot be only ascribed to point defects, originating from direct C+-C collisions, but also the different interactions of single layers and few layers with the substrate plays a crucial role. As demonstrated by AFM, for irradn. at fluences higher than 5 × 1013 cm-2, the morphol. of single layers becomes fully conformed to that of the SiO2 substrate, i.e. graphene ripples are completely suppressed, while ripples are still present on bilayer and multi-layers. The stronger interaction of a single layer with the substrate roughness leads to the obsd. larger amt. of disorder.
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    22. 22
      Zhou, Y.-B.; Liao, Z.-M.; Wang, Y.-F.; Duesberg, G. S.; Xu, J.; Fu, Q.; Wu, X.-S.; Yu, D.-P. Ion irradiation induced structural and electrical transition in graphene J. Chem. Phys. 2010, 133, 234703 DOI: 10.1063/1.3518979
      There is no corresponding record for this reference.
    23. 23
      Compagnini, G.; Forte, G.; Giannazzo, F.; Raineri, V.; La Magna, A.; Deretzis, I. Ion beam induced defects in graphene: Raman spectroscopy and DFT calculations J. Mol. Struct. 2011, 993, 506– 509 DOI: 10.1016/j.molstruc.2010.12.065
      There is no corresponding record for this reference.
    24. 24
      Kalbac, M.; Lehtinen, O.; Krasheninnikov, A. V.; Keinonen, J. Ion-Irradiation-Induced Defects in Isotopically-Labeled Two Layered Graphene: Enhanced In-Situ Annealing of the Damage Adv. Mater. 2013, 25, 1004– 1009 DOI: 10.1002/adma.201203807
      24
      Ion-Irradiation-Induced Defects in Isotopically-Labeled Two Layered Graphene: Enhanced In-Situ Annealing of the Damage
      Kalbac, Martin; Lehtinen, Ossi; Krasheninnikov, Arkady V.; Keinonen, Juhani
      Advanced Materials (Weinheim, Germany) (2013), 25 (7), 1004-1009CODEN: ADVMEW; ISSN:0935-9648. (Wiley-VCH Verlag GmbH & Co. KGaA)
      The effect of 100 keV Ar+ ion irradn. on isotopically labeled single and two-layer graphene has been studied using Raman spectra and atomistic simulations. The no. of defects in both of the graphene layers increased with increasing irradn. fluence, but the rate of defect accumulation was significantly different in the layers, with the final defect d. in the bottom layer being lower than that in the top layer. This observation was explained via the anal. of the final locations of interstitial carbon atoms produced by sputtering by the energetic ion in the atomistic simulations. A significantly higher no. of interstitials was produced in between the bottom layer and the substrate. As these interstitials are expected to be mobile at room temp., they can recombine with vacancies in the bottom layer resulting in the redn. of total damage.
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    25. 25
      Wang, Q.; Mao, W.; Ge, D.; Zhang, Y.; Shao, Y.; Ren, N. Effects of Ga ion-beam irradiation on monolayer graphene Appl. Phys. Lett. 2013, 103, 073501 DOI: 10.1063/1.4818458
      25
      Effects of Ga ion-beam irradiation on monolayer graphene
      Wang, Quan; Mao, Wei; Ge, Daohan; Zhang, Yanmin; Shao, Ying; Ren, Naifei
      Applied Physics Letters (2013), 103 (7), 073501/1-073501/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      The effects of Ga ion on the single layer graphene (SLG) were studied by Raman spectroscopy (RS), SEM, and field-effect characterization. Under vacuum conditions, Ga ion-irradn. can induce disorders and cause red shift of 2D band of RS, rather than lattice damage in high quality SLG. The compressive strain induced by Ga ion decreases the cryst. size in SLG, which is responsible for the variation of Raman scattering and elec. properties. Nonlinear out-put characteristic and resistance increased are also found in the I-V measurement. The results have important implications during CVD graphene characterization and related device fabrication. (c) 2013 American Institute of Physics.
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    26. 26
      Zeng, J.; Yao, H. J.; Zhang, S. X.; Zhai, P. F.; Duan, J. L.; Sun, Y. M.; Li, G. P.; Liu, J. Swift heavy ions induced irradiation effects in monolayer graphene and highly oriented pyrolytic graphite Nucl. Instrum. Methods Phys. Res., Sect. B 2014, 330, 18– 23 DOI: 10.1016/j.nimb.2014.03.019
      26
      Swift heavy ions induced irradiation effects in monolayer graphene and highly oriented pyrolytic graphite
      Zeng, J.; Yao, H. J.; Zhang, S. X.; Zhai, P. F.; Duan, J. L.; Sun, Y. M.; Li, G. P.; Liu, J.
      Nuclear Instruments & Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms (2014), 330 (), 18-23CODEN: NIMBEU; ISSN:0168-583X. (Elsevier B.V.)
      Monolayer graphene and highly oriented pyrolytic graphite (HOPG) were irradiated by swift heavy ions (209Bi and 112Sn) with the fluence between 1011 and 1014 ions/cm2. Both pristine and irradiated samples were investigated by Raman spectroscopy. It was found that D and D' peaks appear after irradn., which indicated the ion irradn. introduced damage both in the graphene and graphite lattice. Due to the special single at. layer structure of graphene, the irradn. fluence threshold Φth of the D band of graphene is significantly lower (<1 × 1011 ions/cm2) than that (2.5 × 1012 ions/cm2) of HOPG. The larger defect d. in graphene than in HOPG indicates that the monolayer graphene is much easier to be damaged than bulk graphite by swift heavy ions. Moreover, different defect types in graphene and HOPG were detected by the different values of ID/ID'. For the irradn. with the same electronic energy loss, the velocity effect was found in HOPG. However, in this expt., the velocity effect was not obsd. in graphene samples irradiated by swift heavy ions.
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    27. 27
      Mathew, S. Mega-electron-volt proton irradiation on supported and suspended graphene: A Raman spectroscopic layer dependent study J. Appl. Phys. 2011, 110, 084309 DOI: 10.1063/1.3647781
      27
      Mega-electron-volt proton irradiation on supported and suspended graphene: A Raman spectroscopic layer dependent study
      Mathew, S.; Chan, T. K.; Zhan, D.; Gopinadhan, K.; Roy Barman, A.; Breese, M. B. H.; Dhar, S.; Shen, Z. X.; Venkatesan, T.; Thong, John T. L.
      Journal of Applied Physics (2011), 110 (8), 084309/1-084309/9CODEN: JAPIAU; ISSN:0021-8979. (American Institute of Physics)
      Graphene samples with 1, 2, and 4 layers and 1 + 1 folded bi-layers and graphite were irradiated with 2 MeV protons at fluences ranging from 1 × 1015 to 6 × 1018 ions/cm2. The samples were characterized using visible and UV Raman spectroscopy and Raman microscopy. The ion-induced defects decrease with increasing no. of layers. Graphene samples suspended over etched holes in SiO2 were fabricated and used to study the influence of the substrate SiO2 for defect creation in graphene. While Raman vibrational modes at 1460 cm-1 and 1555 cm-1 were obsd. in the visible Raman spectra of substantially damaged graphene samples, these modes were absent in the irradiated-suspended monolayer graphene. (c) 2011 American Institute of Physics.
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    28. 28
      Kumar, S.; Tripathi, A.; Khan, S. A.; Pannu, C.; Avasthi, D. K. Radiation stability of graphene under extreme conditions Appl. Phys. Lett. 2014, 105, 133107 DOI: 10.1063/1.4897004
      28
      Radiation stability of graphene under extreme conditions
      Kumar, Sunil; Tripathi, Ambuj; Khan, Saif A.; Pannu, Compesh; Avasthi, Devesh K.
      Applied Physics Letters (2014), 105 (13), 133107/1-133107/5CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      We report radiation stability of graphene under extreme condition of high energy d. generated by 150 MeV Au ion irradn. The expt. reveals that graphene is radiation resistant for irradn. at 1014 ions/cm2 of 150 MeV Au ions. Annealing effects are obsd. at lower fluences whereas defect prodn. occurs at higher fluences but significant crystallinity is retained. Our results demonstrate applicability of graphene based devices in radiation environment and space applications. (c) 2014 American Institute of Physics.
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    29. 29
      Kotakoski, J.; Krasheninnikov, A. V.; Kaiser, U.; Meyer, J. C. From Point Defects in Graphene to Two-Dimensional Amorphous Carbon Phys. Rev. Lett. 2011, 106, 105505 DOI: 10.1103/PhysRevLett.106.105505
      29
      From point defects in graphene to two-dimensional amorphous carbon
      Kotakoski, J.; Krasheninnikov, A. V.; Kaiser, U.; Meyer, J. C.
      Physical Review Letters (2011), 106 (10), 105505/1-105505/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      While cryst. two-dimensional materials have become an exptl. reality during the past few years, an amorphous 2-dimensional material was not reported before. Here, using electron irradn. the authors create an sp2-hybridized 1-atom-thick flat C membrane with a random arrangement of polygons, including four-membered C rings. The transformation occurs step by step by nucleation and growth of low-energy multivacancy structures constructed of rotated hexagons and other polygons. The authors' observations, along with 1st-principles calcns., provide new insights to the bonding behavior of C and dynamics of defects in graphene. The created domains possess a band gap, which may open new possibilities for engineering graphene-based electronic devices.
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    30. 30
      Eder, F. R.; Kotakoski, J.; Kaiser, U.; Meyer, J. C. A journey from order to disorder Atom by atom transformation from graphene to a 2d carbon glass Sci. Rep. 2014, 4, 4060 DOI: 10.1038/srep04060
      30
      A journey from order to disorder - Atom by atom transformation from graphene to a 2D carbon glass
      Eder, Franz R.; Kotakoski, Jani; Kaiser, Ute; Meyer, Jannik C.
      Scientific Reports (2014), 4 (), 4060/1-4060/6CODEN: SRCEC3; ISSN:2045-2322. (Nature Publishing Group)
      One of the most interesting questions in solid state theory is the structure of glass, which has eluded researchers since the early 1900's. Since then, two competing models, the random network theory and the crystallite theory, have both gathered exptl. support. Here, we present a direct, at.-level structural anal. during a crystal-to-glass transformation, including all intermediate stages. We introduce disorder on a 2D crystal, graphene, gradually, utilizing the electron beam of a transmission electron microscope, which allows us to capture the at. structure at each step. The change from a crystal to a glass happens suddenly, and at a surprisingly early stage. Right after the transition, the disorder manifests as a vitreous network sepg. individual crystallites, similar to the modern version of the crystallite theory. However, upon increasing disorder, the vitreous areas grow on the expense of the crystallites and the structure turns into a random network. Thereby, our results show that, at least in the case of a 2D structure, both of the models can be correct, and can even describe the same material at different degrees of disorder.
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    31. 31
      Ochedowski, O.; Akcöltekin, S.; Ban d’Etat, B.; Lebius, H.; Schleberger, M. Detecting swift heavy ion irradiation effects with graphene Nucl. Instrum. Methods Phys. Res., Sect. B 2013, 314, 18– 20 DOI: 10.1016/j.nimb.2013.03.063
      31
      Detecting swift heavy ion irradiation effects with graphene
      Ochedowski, O.; Akcoeltekin, S.; Ban-d'Etat, B.; Lebius, H.; Schleberger, M.
      Nuclear Instruments & Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms (2013), 314 (), 18-20CODEN: NIMBEU; ISSN:0168-583X. (Elsevier B.V.)
      In this paper we show how single layer graphene can be utilized to study swift heavy ion (SHI) modifications on various substrates. The samples were prepd. by mech. exfoliation of bulk graphite onto SrTiO3, NaCl and Si(1 1 1), resp. SHI irradiations were performed under glancing angles of incidence and the samples were analyzed by means of at. force microscopy in ambient conditions. We show that graphene can be used to check whether the irradn. was successful or not, to det. the nominal ion fluence and to locally mark SHI impacts. In case of samples prepd. in situ, graphene is shown to be able to catch material which would otherwise escape from the surface.
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      https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXnvValtLk%253D&md5=cf86d10d1bdbbede74c2ec67d6b084e7
    32. 32
      Ochedowski, O.; Kleine Bussmann, B.; Ban d’Etat, B.; Lebius, H.; Schleberger, M. Manipulation of the graphene surface potential by ion irradiation Appl. Phys. Lett. 2013, 102, 153103 DOI: 10.1063/1.4801973
      32
      Manipulation of the graphene surface potential by ion irradiation
      Ochedowski, O.; Kleine Bussmann, B.; Ban d'Etat, B.; Lebius, H.; Schleberger, M.
      Applied Physics Letters (2013), 102 (15), 153103/1-153103/4CODEN: APPLAB; ISSN:0003-6951. (American Institute of Physics)
      The work function of exfoliated single layer graphene can be modified by irradn. with swift (Ekin = 92 MeV) heavy ions under glancing angles of incidence. Upon ion impact individual surface tracks are created in graphene on SiC. Due to the very localized energy deposition characteristic for ions in this energy range, the surface area which is structurally altered is limited to ≈0.01 μm2 per track. Kelvin probe force microscopy reveals that those surface tracks consist of electronically modified material and that a few tracks suffice to shift the surface potential of the whole single layer flake by ≈400 meV. Thus, the irradn. turns the initially n-doped graphene into p-doped graphene with a hole d. of 8.5 × 1012 holes/cm2. This doping effect persists even after heating the irradiated samples to 500°. Therefore, this charge transfer is not due to adsorbates but must instead be attributed to implanted atoms. The method presented here opens up a way to efficiently manipulate the charge carrier concn. of graphene. (c) 2013 American Institute of Physics.
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    33. 33
      Brand, C.; Sclafani, M.; Knobloch, C.; Lilach, Y.; Juffmann, T.; Kotakoski, J.; Mangler, C.; Winter, A.; Turchanin, A.; Meyer, J. C.; Cheshnovsky, O.; Arndt, M. An atomically thin matter-wave beam splitter Nature Nanotech. in press, 2015.
      There is no corresponding record for this reference.
    34. 34
      Krivanek, O. L.; Corbin, G. J.; Dellby, N.; Elston, B. F.; Keyse, R. J.; Murfitt, M. F.; Own, C. S.; Szilagyi, Z. S.; Woodruff, J. W. An electron microscope for the aberration-corrected era Ultramicroscopy 2008, 108, 179– 195 DOI: 10.1016/j.ultramic.2007.07.010
      34
      An electron microscope for the aberration-corrected era
      Krivanek, O. L.; Corbin, G. J.; Dellby, N.; Elston, B. F.; Keyse, R. J.; Murfitt, M. F.; Own, C. S.; Szilagyi, Z. S.; Woodruff, J. W.
      Ultramicroscopy (2008), 108 (3), 179-195CODEN: ULTRD6; ISSN:0304-3991. (Elsevier B.V.)
      Improved resoln. made possible by aberration correction has greatly increased the demands on the performance of all parts of high-end electron microscopes. In order to meet these demands, we have designed and built an entirely new scanning transmission electron microscope (STEM). The microscope includes a flexible illumination system that allows the properties of its probe to be changed on-the-fly, a third-generation aberration corrector which corrects all geometric aberrations up to fifth order, an ultra-responsive yet stable five-axis sample stage, and a flexible configuration of optimized detectors. The microscope features many innovations, such as a modular column assembled from building blocks that can be stacked in almost any order, in situ storage and cleaning facilities for up to five samples, computer-controlled loading of samples into the column, and self-diagnosing electronics. The microscope construction is described, and examples of its capabilities are shown.
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    35. 35
      Kotakoski, J.; Mangler, C.; Meyer, J. C. Imaging atomic-level random walk of a point defect in graphene Nat. Commun. 2014, 5, 4991 DOI: 10.1038/ncomms4991
      There is no corresponding record for this reference.
    36. 36
      Krivanek, O. L. Atom-by-atom structural and chemical analysis by annular dark-field electron microscopy Nature 2010, 464, 571– 574 DOI: 10.1038/nature08879
      36
      Atom-by-atom structural and chemical analysis by annular dark-field electron microscopy
      Krivanek, Ondrej L.; Chisholm, Matthew F.; Nicolosi, Valeria; Pennycook, Timothy J.; Corbin, George J.; Dellby, Niklas; Murfitt, Matthew F.; Own, Christopher S.; Szilagyi, Zoltan S.; Oxley, Mark P.; Pantelides, Sokrates T.; Pennycook, Stephen J.
      Nature (London, United Kingdom) (2010), 464 (7288), 571-574CODEN: NATUAS; ISSN:0028-0836. (Nature Publishing Group)
      Direct imaging and chem. identification of all the atoms in a material with unknown three-dimensional structure would constitute a very powerful general anal. tool. Transmission electron microscopy should in principle be able to fulfil this role, as many scientists including Feynman realized early on. It images matter with electrons that scatter strongly from individual atoms and whose wavelengths are about 50 times smaller than an atom. Recently the technique has advanced greatly owing to the introduction of aberration-cor. optics. However, neither electron microscopy nor any other exptl. technique has yet been able to resolve and identify all the atoms in a non-periodic material consisting of several at. species. Here we show that annular dark-field imaging in an aberration-cor. scanning transmission electron microscope optimized for low voltage operation can resolve and identify the chem. type of every atom in monolayer hexagonal boron nitride that contains substitutional defects. Three types of at. substitutions were found and identified: carbon substituting for boron, carbon substituting for nitrogen, and oxygen substituting for nitrogen. The substitutions caused in-plane distortions in the boron nitride monolayer of about 0.1 Å magnitude, which were directly resolved, and verified by d. functional theory calcns. The results demonstrate that atom-by-atom structural and chem. anal. of all radiation-damage-resistant atoms present in, and on top of, ultra-thin sheets has now become possible.
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    37. 37

      Calculated with the approach introduced in ref 38 and implemented in the code TRIM.

      There is no corresponding record for this reference.
    38. 38
      Ziegler, J. F.; Biersack, J. P.; Littmark, U. The Stopping and Range of Ions in Solids; Pergamon: New York, 1985.
      There is no corresponding record for this reference.
    39. 39
      Meyer, J. C. Accurate Measurement of Electron Beam Induced Displacement Cross Sections for Single-Layer Graphene Phys. Rev. Lett. 2012, 108, 196102 DOI: 10.1103/PhysRevLett.108.196102
      39
      Accurate measurement of electron beam induced displacement cross sections for single-layer graphene
      Meyer, Jannik C.; Eder, Franz; Kurasch, Simon; Skakalova, Viera; Kotakoski, Jani; Park, Hye Jin; Roth, Siegmar; Chuvilin, Andrey; Eyhusen, Soeren; Benner, Gerd; Krasheninnikov, Arkady V.; Kaiser, Ute
      Physical Review Letters (2012), 108 (19), 196102/1-196102/6CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)
      We present an accurate measurement and a quant. anal. of electron-beam-induced displacements of carbon atoms in single-layer graphene. We directly measure the at. displacement ("knock-on") cross section by counting the lost atoms as a function of the electron-beam energy and applied dose. Further, we sep. knock-on damage (originating from the collision of the beam electrons with the nucleus of the target atom) from other radiation damage mechanisms (e.g., ionization damage or chem. etching) by the comparison of ordinary (12C) and heavy (13C) graphene. Our anal. shows that a static lattice approxn. is not sufficient to describe knock-on damage in this material, while a very good agreement between calcd. and exptl. cross sections is obtained if lattice vibrations are taken into account.
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