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Applications of Polymer, Composite, and Coating Materials
Comprehensive Optical Strain Sensing Through the Use of Colloidal Quantum DotsClick to copy article linkArticle link copied!
- Michael D. SherburneMichael D. SherburneDepartment of Electrical and Computer Engineering, Air Force Institute of Technology, Dayton, Ohio 45433, United StatesMore by Michael D. Sherburne
- Candice R. RobertsCandice R. RobertsDepartment of Aeronautics and Astronautics, Air Force Institute of Technology, Dayton, Ohio 45433, United StatesMore by Candice R. Roberts
- John S. BrewerJohn S. BrewerDepartment of Aeronautics and Astronautics, Air Force Institute of Technology, Dayton, Ohio 45433, United StatesMore by John S. Brewer
- Thomas E. WeberThomas E. WeberPhysics Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, United StatesMore by Thomas E. Weber
- Tod V. LaurvickTod V. LaurvickDepartment of Electrical and Computer Engineering, Air Force Institute of Technology, Dayton, Ohio 45433, United StatesMore by Tod V. Laurvick
- Hengky Chandrahalim*Hengky Chandrahalim*E-mail: [email protected]Department of Electrical and Computer Engineering, Air Force Institute of Technology, Dayton, Ohio 45433, United StatesMore by Hengky Chandrahalim
Abstract
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The adaptation of colloidal quantum dots loaded within a polymer for use in nondestructive testing can be used as an optical strain gauge due to the nanomaterial’s strain sensing properties. In this paper, we utilized InP/ZnS colloidal quantum dots loaded within a polymer matrix applied onto the surface of a dog-bone foil precoated with an epoxy. By employing an empirical formula and a calibration factor, there is a propinquity between both the calculated optical strain and mechanical stress–strain reference data. Fluctuations are observed, which may be due to both additional strain responses not seen by the mechanical data and quantum dot blinking. These results and methods show the applied use of this novel optical nondestructive testing technique for a variety of structures, especially for structures that operate in harsh environments.
Copyright © 2020 American Chemical Society
1. Introduction
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Nondestructive testing (NDT) is carried out in a myriad of industries to ensure both the integrity and quality of their respective structures. (1−5) A pertinent example pushing the limits in the use of NDTs can be seen in the United States Air Force (USAF), where aircraft maintainers are facing unique NDT problems every day. NDT becomes more important as the USAF’s air fleet ages. (6) This issue encourages the development of novel NDT techniques since one of the main techniques used are eddy current probes that are inherently complicated to read. (7) A promising NDT technique can make use of newer nanotechnologies such as colloidal quantum dots (CQDs) to help address common NDT issues. A summary of well-established NDT methods compared to the work described in this paper can be seen in Table 1.
Table 1. Comparing the Pros and Cons of Presently Used NDT Methods to the One Presented in This Papera
| capability | ||||||
|---|---|---|---|---|---|---|
| NDT test | A | B | C | D | E | F |
| radiographic (X-rays) (8) | × | × | × | × | ||
| electromagnetic (9) | × | × | ||||
| acoustic emission (10) | × | × | × | × | ||
| laser methods (11) | × | × | ||||
| microwave (12,13) | × | × | ||||
| liquid penetrant (14) | × | × | ||||
| thermal/infrared (15−17) | × | × | ||||
| ultrasonic (18) | × | × | ||||
| this paper | × | × | × | × | ||
a
The different NDT capabilities within the table are the defined as: (A) sensitive to small cracks, (B) see through an airframe, (C) sense acoustic events, (D) high location accuracy, (E) applicable to any material, and (F) real-time testing.
Table 1 shows that an optical strain gauge approach using CQDs could address multiple NDT areas, making them more versatile for use in a variety of environments (e.g., weather, materials, and part sizes). Development shortfalls for near-field optical sensing of CQDs for measuring strain would be both seeing through an airframe and sensing acoustic cracks. Although the latter is both theoretically possible and demonstrated in a laboratory setting, it has not yet been applied as a tool for NDT. (19)
Previous investigations into the use of CQDs as optical strain gauges were only preliminary and without a written out calibration process for the optical strain data. In addition, these studies did not look into epoxy precoatings that would better emulate real-world conditions, especially for use as an aircraft NDT. (20,21) Epoxy-based primers (such as the Solvay BR 6747-1 used in this paper) and similar coatings are commonly used in aerospace applications to prevent corrosion and promote adhesion at adhesively bonded joints. This epoxy material is common for metal to metal and composite to metal bonds in new manufacturing and adhesively bonded repairs. The epoxy is designed to sustain forces that an aircraft would experience during the life of the aircraft. (22−27) As was seen in this paper, the epoxy precoating caused a unique spectral response not seen before in previous literature.
2. Theory
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CQDs are nanomaterials that emit a discrete wavelength dependent upon the diameter of the CQDs themselves. They can be excited with lower wavelengths under their emission wavelength. Due to their nanometer scale, they exhibit quantum confinement effects that allow for diagnostic applications such as temperature and magnetic field sensing. (28,29) CQDs have also been demonstrated to change their emission wavelength under strain in multiple studies, further motivating the development of a CQD optical strain gauge. (20,21,30−32)
The diameters of CQDs are usually in the range of sub-nanometers, and an example of a spherical CQD is seen in Figure 1. (33)
Figure 1
Figure 1. Graphic of a CQD where the inner core (pink), outer shell (yellow), and polymer ligands (black lines) can be seen. Sherburne, M. X-Ray Detection and Strain Sensing Applications of Colloidal Quantum Dots. M.S. Thesis, Air Force Institute of Technology, March 2020. (33)
From Figure 1, the CQDs are prevented from agglomerating due to their encapsulating organic ligands. These polymers allow CQDs to be dispersed within other organic and liquid media. CQDs are commonly sold in the commercial market as a core–shell, where the core contains the semiconducting material and the shell (usually made of ZnO) helps to smooth over defects around the core while protecting the semiconducting material from environmental degradation. (33)
CQDs are able to change their wavelength when experiencing either tensile or compressive strain, due to being made up of semiconducting material. This is also due to the interatomic spacing between the atoms within a CQD, which determines the relative energies of the electrons. (30) By changing the relative energy of the electrons, this would in turn change the discrete energy states and thus change the wavelength of emission. To be more specific, semiconducting materials contain both heavy holes and light holes that can change their respective locations on a E–k diagram depending upon the type of strain the material is experiencing. This in turn changes the material’s effective band gap, which shifts the wavelength of emission. (34,35)
3. Experimental Setup
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Testing was carried out in accordance with the American Society for Testing and Materials (ASTM) standard E345. (36) Per the standard, the sample (dog-bone foil) gauge length was used as the reference length and strain was calculated based on the head displacement as compared to the gauge length. The metal samples employed were made of 301 stainless steel. The dimensions of the neck of the dog-bone were: 83.312 mm × 12.7 mm × 0.1016 mm. An epoxy-based precoating (Solvay BR 6747-1) was applied as a surface treatment to the dog-bones. The surface roughness of the precoated dog-bone samples was measured with a profilometer at an average of 0.483 μm. This roughness helped the polymer better adhere to a metallic surface.
InP/ZnS CQDs were homogeneously loaded with a 10% concentration into a proprietary UV photocurable polymer (supplied by NN-Labs). We selected 530 nm for emission wavelength due to relatively high signal returns from optical imaging devices at this wavelength. The selection of InP/ZnS was chosen because of both cadmium and lead exposure concerns if used as a coating on aircraft. (37) The CQD-loaded polymer was then coated as a thin film onto the middle of the dog-bone across a 20 mm × 12.7 mm surface. The dog-bone sample was then placed in a convection oven and baked at 121.11 °C for 23 min and 30 s. A Leica DVM6 microscope was used to measure the thickness of the CQD-loaded polymer layer. The microscope settings used were: 0° tilt, Z-step size of 0.25 μm, and a FOV3.6 lens.
Figure 2
Figure 2. Three-dimensional surface model of the coated stainless steel dog-bone with the CQD polymer matrix applied. The left half of the image contained the CQD-loaded polymer matrix coating, while the right half was only the precoating (Solvay BR 6747-1) on top of the stainless steel. (a) Three-dimensional surface image of the dog-bone. (b) Two-dimensional (2D) cross-section through the CQD-loaded polymer and precoated polymer boundary.
The maximum/minimum thickness across the CQD-loaded polymer matrix and no CQD-loaded polymer matrix boundary were measured as 17.9 ± 0.125 and 4.33 ± 0.125 μm, respectively. The mean thickness across this section was 10.07 ± 0.177 μm. As seen in Figure 2, the application of CQD-loaded polymer did not cause a thicker surface. Instead, the CQD-loaded polymer matrix was applied within the grooves and valleys of the epoxy precoating on the surface of the sample.
A servo-hydraulic test frame (model: MTS Systems Corporation 370.02) was used to apply a tensile force to the sample. The test frame had the following specifications: rated capacity (25 kN), actuator force capacity (25 kN), actuator dynamic stroke (100 mm), actuator total stroke (114 mm), actuator rated flow (57 lpm), manifold rated flow (57 lpm), and bearing type (standard). Mechanical measurements were taken by a force transducer (model: MTS Systems Corporation 661.19H-04). Both axial displacement in mm and axial force in N were collected. The experimental setup can be seen in Figure 3.
Figure 3
Figure 3. (a) Illustration of the experimental setup. (b) Labeled photo of the experimental setup. Sherburne, M. X-Ray Detection and Strain Sensing Applications of Colloidal Quantum Dots. M.S. Thesis, Air Force Institute of Technology, March 2020. (33)
As seen in Figure 3, the spectrometer (model: Ocean Optics FLAME-S-VIS-NIR) with ≈1.5 nm full width at half-maximum (FWHM) optical resolution was secured to the load frame and fiber coupled to a collimator (model: Thorlabs ZC618APC-A). A standard blacklight was clamped to the load frame. The spectrometer was set to integrate light over 1 s increments across a spectral range of 350–1000 nm, which goes through the peak emission wavelength of interest at 530 nm. The start time between the load frame and the spectrometer acquisition was synchronized by two researchers (timing error of ±1 s). The experiment was displacement controlled at 8.7750 × 10–4 in/s over a period of 504 s (to failure of the sample). Two dog-bone samples were used to help the researchers dial down the correct settings and orientation of the blacklight and collimator. This resulted in only one dog-bone sample that resulted in useful collected values.
A digital imaging correlation (DIC) test was done using the same dog-bone fabrication recipe without the CQD-loaded polymer layer. The entire face of the dog-bone was white speckled for the ARAMIS 4M rev03 adjustable DIC camera to make stress–strain measurements. The complementary metal-oxide semiconductor (CMOS) camera resolution was 2400 × 1728 pixels with a strain accuracy of up to 0.01%. The displacement was controlled at the same rate at 8.7750 × 10–4.
4. Stress–Strain Calculations
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To calculate the stress–strain curve, first tensile stress is calculated by the following σ = F/A, where F is the axial force and A is the cross-sectional area in m2 perpendicular to the top surface of the dog-bone sample. The cross-sectional area is calculated to be 1.29032 × 10–6 m2. The axial force taken from the experiment would be divided by this cross-sectional area to get the tensile stress over time. The following equation is used to get the tensile strain 
, where ΔL is the change in axial displacement and L0 is the original gauge length of the dog-bone sample. (38) With both the tensile strain and tensile stress on hand, trends can be determined by jointly plotting both the mechanical stress–strain curve and the CQD photoluminescence (PL) spectra.
, where ΔL is the change in axial displacement and L0 is the original gauge length of the dog-bone sample. (38) With both the tensile strain and tensile stress on hand, trends can be determined by jointly plotting both the mechanical stress–strain curve and the CQD photoluminescence (PL) spectra.4.1. Calculating Percent Change of Relative Emission Intensity
Figure 4a shows the changing optical spectra due to continuously applied strain over time. The black dotted-dashed line represents the initial nonstrained spectra. As the sample is strained toward failure, the sides of the spectral peak collapse while the center point of the peak rises as a plateau. There was no clear blue or red shifting of wavelengths in contrast to what was reported in similar literature. An animation of the optical spectra changing can be seen in the Supporting Information.
Figure 4
Figure 4. This figure shows the three-step process from (a) collecting the spectral data from the experiment, (b) applying a calibration, and then (c) plotting the calibrated optical strain data in relation to the mechanical reference strain data.
To quantify strain measurements for this sample from the optical data, a %PL change was calculated as a percentage to get relative data at each moment in time. This %PL change was calculated as the percent difference between the average emission intensity values of the wavelength points contained on the plateau between ν3 and ν4 and the average emission intensity values of side reference points ν1 and ν2. This can be explained by the following relation
where κ(t) is the calculated averaged difference between the two sets of points described and κ0 is the same calculation at time zero. This is then multiplied by 100 to make it a percentage of change. Mathematically, κ(t) is described by the following formula
where I(ν, t) is the total amount of current collected by the spectrometer at wavelength ν and time t. More specifically, I(ν, t) is equivalent to the normalized counts of the PL spectra. The left side of this relationship represents the integrated average values between ν3: 542.88 nm and ν4: 545.39 nm and the right side represents the integrated average values between ν1: 536.79 nm and ν2: 539.29 nm. An average of values is needed because of the random fluctuations across both the plateau and reference regions. The measurement method described made it viable to use the optical spectra seen in this experiment as a way to optically measure strain.
(1)
(2)
4.2. Calibrating CQD Percent PL Intensity to Strain
Since the dog-bone sample had slack before loading, both the mechanical reference and CQD optical strain data had to be shifted to ensure that the linear region passed through the origin. Linear approximation of the linear elastic region was done by selecting points corresponding to 100 and 700 MPa. Due to fewer points in the CQD optical data, four reference points around both the 100 and 700 MPa points as seen in Figure 4b were averaged to be used for linearization. Then, the correction factor was determined by the intersection of this line with the X-axis. Finally, this correction factor was subtracted from each collected strain value such that the linear region passed through the origin. For the mechanical reference data, this correction was 9.934 × 10–4 (strain), and for the CQD optical data, this correction was 225 %PL shift.
With the corrected data for both the mechanical reference and CQD optical information, a calibration factor was determined by comparing the greatest CQD optical measured strain with the greatest mechanical reference strain value. For example, using corrected data, the greatest mechanical reference strain value was divided by the greatest CQD optical strain value. This was similar to how one would calibrate the lateral force response of an atomic force microscope (AFM). (39) In this case, that calibration factor was determined to be 2.905 × 10–4
. Further characterization of the strain properties of CQDs would enable a priori calibration. The calibrated optical data was plotted alongside the mechanical reference data in Figure 4c.
. Further characterization of the strain properties of CQDs would enable a priori calibration. The calibrated optical data was plotted alongside the mechanical reference data in Figure 4c.4.3. Calculating the Experiment’s Sensitivity
Characterizing the sensitivity of the optical strain gauge to the length of deformation of the sample under strain was a metric of interest. The sensitivity S with units in meters can be calculated through the following formula
where η is the absolute value maximum %PLchange change between data points, which in this case was 37.77 au. Additionally, Δ%PLchange is the absolute value change of %PLchange over a defined period of time, which is 1 s in this case. Finally, ΔL is the length of deformation over the same defined period of time as Δ%PLchange.
(3)
5. Results and Discussion
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Going back to Figure 4a, the rising plateau could be attributed to the CQD-loaded polymer experiencing both tensile and transverse strain due to the Poisson effect. However, this transverse strain was determined to be overall negligible to the tensile strain. This then led to the hypothesis that the compressive strain contribution within the rising plateau spectrum occurred due to both the nanoscale interactions between the CQD-loaded polymer and the surrounding epoxy precoating. The CQDs within the polymer could experience compression when being strained against the epoxy precoating and in addition Förster resonance energy transfer (FRET) may have also contributed to the rising plateau. FRET was already found in the same InP/ZnS CQD-loaded polymer material in another study. (33) From the 545 to 560 nm spectrum in Figure 4a, the steepening of the curve was less pronounced when compared to the 530–545 nm spectrum. This was due to cross-talk between the 545 and 560 nm emitting CQDs as they became closer (1/R6) energy transfer efficiency distance relationship to the CQDs with a smaller wavelength of emission. (40) A similar experiment conducted by Yin et al. showed both a shifting trend in wavelength and in relative PL intensity, but no optical spectral structures that this paper’s experiment had seen. (20) The fundamental difference between their experiment and this paper was no application of the epoxy precoating, which helped to corroborate the hypothesis that an additional interaction between the CQDs and the surrounding epoxy precoating in this paper’s experiment has caused the unique rising plateau structure.
As seen after calibration in Figure 4c, the optical data fits right alongside with the mechanical stress–strain curve. There were three noticeable deviations from the mechanical reference data: (1) the initial slack, (2) three separate trends along the elastic region, and (3) few data points available about the proportional limit and toward failure of the sample. For the first deviation, the initial slack can be explained by the 3D physical movement of the sample as strain was first applied. This would cause a lag and a difference in optical values until the sample began to stretch. This then led to the second deviation, where three separate trends were seen along the elastic region. Due to the CQD-loaded polymer being located in a localized area on the sample versus covering the entire sample, there would be localized changes seen in the optical data that the mechanical reference data would be unable to sense. This was further confirmed by the DIC data collected in Figure 5. In addition, the DIC data also answered the third deviation about the proportional limit since the localized strain would be changing at a different rate than the overall dog-bone structure.
Figure 5
Figure 5. DIC images showing the surface strains of a sample. The mechanical strains correlated for their respective DIC images were the following: (D1) 0.04, (D2) 0.08, (D3) 0.09, and (D4) 0.1. The orange dashed boxes showed, where the CQD-loaded polymer coating would be during the optical experiment.
The DIC data shown in Figure 5 can be related to the markers D1–D4 in Figure 4c. Initially in D1, the source of the majority of strain was along the localized area coated with the CQD-loaded polymer; however, as the sample was strained into the plastic region (as seen in the DIC data from D3–D4), the source of the majority of strain traveled to one end of the dog-bone. This led to a nonlinear trend in the optical strain data as the localized strain began to lessen in strain due to the fracture occurring at the bottom of the dog-bone. Overall, the DIC data helped to visualize why there were significant deviations between the optical data and the mechanical reference data at certain regions about the stress–strain curve.
Figure 4 shows different data collected for the final strain reading after the sample fractured. This disparity reflected the difference in measurement reference employed by each measurement system. The reference strain was based on the change in distance between the two grips of the test frame. In the case of this displacement controlled experiment, the grips continued to move apart as the sample fractured, until the displacement was halted. Thus, after fracture, the reference strain continued to positively increase. In contrast, the CQD-loaded polymer was measuring strain directly from the face of the sample. After fracture, the material was expected to recover the elastic deformation imparted by initially loading the sample at the same slope of the initial linear elastic behavior. In Figure 4, the expected path of this elastic recovery was denoted by the purple dashed line. When referencing the final calibrated CQD strain point, the value of strain showed more recovered deformation. This was attributed to the fact that the fracture of the sample dynamically released the stored strain energy and not only recovered the elastic deformation but caused a slight compressive strain. This was further shown by buckling appearing in the sample after fracture, which must have been caused by compressive strains.
It was observed that the sensitivity of the experiment described in this paper was lower at the beginning of the applied strain and became higher toward the failure of the sample. The sensitivity data showed a skewed distribution toward higher sensitivity; hence, the median would be the best way to describe the overall sensitivity instead of the average. The median sensitivity of this experimental setup was 1.88 μm with a maximum sensitivity of 1.34 μm and a minimum sensitivity of 6.79 μm.
6. Conclusions
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We have demonstrated that CQD-loaded polymer experienced a noticeable and measurable intensity shift in wavelength with a relatively simple equipment. From the experiment, a readable relative intensity change of the rising plateau peak of ≈690% was measured. Upon applying a calibration to the %PL data, there was an excellent correlation between the optical data and the mechanical stress–strain data. This optical data was also compared to several data points of DIC data to show how the CQDs measured a specific area of strain versus the overall structure, hence showing its potential for high-resolution strain imaging. Also observed in the data were fluctuations in the emission intensity signal over applied strain. This may be attributed to CQD blinking and could be mitigated using both oligo-(phenylene vinylene) (OPV) ligands and alloyed CQDs. (41−43) However, more than likely, the CQD strain diagnostic shown here was measuring additional mechanical changes that occurred in the sample than could be detected with a mechanical stress–strain device.
Due to being able to measure a localized area, the results show that there is a lot of promise in further developing this technology and making it useful as a next-gen NDT technique. Applications that can make use of this work can be the NDT of: aircraft, ground vehicles, and ships. In addition, the most near-term use of this technology could be the following: a new strain gauge for quality control, 3D printing, and in buildings/structures.
Supporting Information
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The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsami.0c12110.
Graphical animation of the optical spectra changing along the mechanical stress–strain curve (AVI)
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Author Information
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- Hengky Chandrahalim - Department of Electrical and Computer Engineering, Air Force Institute of Technology, Dayton, Ohio 45433, United States;
http://orcid.org/0000-0003-1930-1359;
Acknowledgments
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The authors thank C. Brasch from MITRE for his inspiration of pursuing the possible idea of using CQDs as a type of strain sensor for aircraft NDT applications. The authors also thank R. Aung for his smoothing code that allowed for creating a professional stress–strain profile. In addition, the authors thank B. Rothberg for his help in looking over the manuscript for technical correctness. This research was supported in part by the U.S. Dept. of Energy, National Nuclear Security Administration under grant NA000103. Approved for unlimited release, LA-UR-20-24430. The views expressed are those of the authors and do not reflect the official policy or position of the U.S. Air Force, Department of Defense, Department of Energy, or the U.S. government.
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- 15Roy, D.; Tuli, S. Applicability of LED-Based Excitation Source for Defect Depth Resolved Frequency Modulated Thermal Wave Imaging. IEEE Trans. Instrum. Meas. 2017, 66, 2658– 2665, DOI: 10.1109/TIM.2017.2711798Google ScholarThere is no corresponding record for this reference.
- 16Ahmed, J.; Gao, B.; Woo, W. L. Wavelet-Integrated Alternating Sparse Dictionary Matrix Decomposition in Thermal Imaging CFRP Defect Detection. IEEE Trans. Ind. Inf. 2019, 15, 4033– 4043, DOI: 10.1109/TII.2018.2881341Google ScholarThere is no corresponding record for this reference.
- 17He, Z.; Wang, H.; He, Y.; Zhang, G.; Wang, J.; Zou, G.; Chady, T. Joint Scanning Laser Thermography Defect Detection Method for Carbon Fiber Reinforced Polymer. IEEE Sens. J. 2020, 20, 328– 336, DOI: 10.1109/JSEN.2019.2941077Google Scholar17https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXht1ShsLbL&md5=e4aee33e40e8bc261b39dcb97b044276Joint scanning laser thermography defect detection method for carbon fiber reinforced polymerHe, Zhiyi; Wang, Hongjin; He, Yunze; Zhang, Guixiang; Wang, Jiazheng; Zou, Gaoyu; Chady, TomaszIEEE Sensors Journal (2020), 20 (1), 328-336CODEN: ISJEAZ; ISSN:1558-1748. (Institute of Electrical and Electronics Engineers)In this paper, a new inspection method, joint scanning laser thermog. (JSLT) as well as its data reconstruction and processing algorithm, is proposed. The new inspection method is utilized to detect and characterize the flat-bottom holes (FBH) in carbon fiber composites by using joint laser scanning scheme. By analyzing the nature of the thermal image sequences sampled under such a scanning scheme, a quick and simple reconstruction method is developed to characterize the buried depth of defects based on 1D heat conduction model. The processed thermal images are expected to get higher temporal resoln. and spatial resoln. It can inspect larger area within shorter acquisition time than the pulse thermog. Thus, the study solves the dilemma between the inspection speed and the inspection capacity. Later, a joint laser scanning thermog. test is set up to test the algorithm on a carbon fiber composite panel with defects buried at different depth. The exptl. results show that the reconstructed data almost behave as those under pulse excitation. The tendency of temp. to change in the logarithmic domain over time is similar to the curve in the TSR method. But, unlike the pulse thermog. data, the defect detection rate of PCA based on reconstructed data is higher than that of fast Fourier transform (FFT) amplitude image, independent component anal. (ICA) and FFT phase image. The JSLT system is used to detect FBHs and the diam.-depth ratio reached 3.33.
- 18Shen, Z.; Chen, S.; Zhang, L.; Yao, K.; Tan, C. Y. Direct-Write Piezoelectric Ultrasonic Transducers for Non-Destructive Testing of Metal Plates. IEEE Sens. J. 2017, 17, 3354– 3361, DOI: 10.1109/JSEN.2017.2694454Google Scholar18https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXkvVCltbs%253D&md5=ca4935e2946eb0643339e5fb732f3989Direct-write piezoelectric ultrasonic transducers for non-destructive testing of metal platesShen, Zhiyuan; Chen, Shuting; Zhang, Lei; Yao, Kui; Tan, Chin YawIEEE Sensors Journal (2017), 17 (11), 3354-3361CODEN: ISJEAZ; ISSN:1558-1748. (Institute of Electrical and Electronics Engineers)Current real time structural health monitoring is implemented by assembling multiple discrete sensors on a structure with each sensor providing only point measurement. The installation of the multiple sensors results in high global cost and low reliability. This paper reports the design, directwrite fabrication, and testing of ultrasonic transducers on a plate structure and a non-destructive testing method for detecting defects using the sensor array comprising the direct-write ultrasonic transducers. The transducers are made of piezoelec. poly(vinylidenefluoride/trifluoroethylene) (P(VDF/TrFE)) polymer coatings that are aerosol-spray deposited and patterned directly on the plate structure to be monitored. The ultrasonic transducers bearing annular array comb electrodes are designed for generating and selectively detecting fundamental antisym. Lamb-mode ultrasonic waves in the plate structure. The ultrasonic transducers can serve as both the actuators to generate ultrasonic waves and the sensors to detect ultrasonic waves. The ultrasonic waves propagating through the plate structure contain the information about the structural integrity. With copper bars of different thicknesses introduced at the plate center as mock defects of different severity, the correlation between the transducer response and the defect thickness and hence, the severity is verified. It is also demonstrated that four ultrasonic transducers located at the square plate (100 mm × 100 mm × 1.27 mm) corners forming a transducer array, which can locate the defect on the plate. A short time Fourier transform algorithm and an imaging algorithm are developed for processing signal of the pitch-catch ultrasonic wave spectra to det. the location of the defects, which is verified by exptl. results.
- 19Gulbahar, B.; Memisoglu, G. CSSTag: Optical Nanoscale Radar and Particle Tracking for In-Body and Microfluidic Systems With Vibrating Graphene and Resonance Energy Transfer. IEEE Trans. Nanobiosci. 2017, 16, 905– 916, DOI: 10.1109/TNB.2017.2785226Google ScholarThere is no corresponding record for this reference.
- 20Yin, S.; Zhao, Z.; Luan, W.; Tu, S.-T. In-Situ Strain Gauge: Based on Photoluminescence of Quantum Dots. Procedia Eng. 2015, 130, 1788– 1794, DOI: 10.1016/j.proeng.2015.12.335Google Scholar20https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XitVGrsA%253D%253D&md5=b9017f3bff873e3521c88ac56298c10aIn-Situ Strain Gauge: Based on Photoluminescence of Quantum DotsYin, S. F.; Zhao, Z. M.; Luan, W. L.; Tu, S.-T.Procedia Engineering (2015), 130 (), 1788-1794CODEN: PERNBE; ISSN:1877-7058. (Elsevier Ltd.)Due to that the spectra of CdSe/ZnS core/shell nanocrystals showed a wavelength shift when under external pressures, researches are conducted to design a wavelength shift-based strain or stress gauge. However, the spectrum's shift can only be subtly sensitive when the pressure applied to nanocrystals reaches GPa, which makes the gauge hard to be applied to practice. In this paper, it was found that the photoluminescence(PL) intensity of CdSe/ZnS core/shell quantum dots (QDs)epoxy resin composites changes significantly with strain. Meanwhile, the changes remains stable after 3-5 cycles. We coated the QDs-epoxy resin composites on the surface of metal tensile sample, the PL intensity and strain changes synchronously. In addn., it has been successfully proved that the variation of QDs' concns. along with the strain is the main reason for the photoluminescence intensity changing. This research has shown the possibility that this kind of nanocomposite can be designed as a new strain gauge to quant. detect stress or strain in-situ by being coated on the structure surface.
- 21Shauloff, N.; Bhattacharya, S.; Jelinek, R. Elastic Carbon Dot/Polymer Films for Fluorescent Tensile Sensing and Mechano-Optical Tuning. Carbon 2019, 152, 363– 371, DOI: 10.1016/j.carbon.2019.06.046Google Scholar21https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhtF2ku7rN&md5=e8fd8d531d0aae9af8d3093d738ddafaElastic carbon dot/polymer films for fluorescent tensile sensing and mechano-optical tuningShauloff, Nitzan; Bhattacharya, Sagarika; Jelinek, RazCarbon (2019), 152 (), 363-371CODEN: CRBNAH; ISSN:0008-6223. (Elsevier Ltd.)Development of simple, readily-applicable sensors for mech. deformation of polymers is highly sought albeit a formidable task. Here we demonstrate that composite films comprising carbon dots (C-dots) embedded in an elastic polymer host allow fluorescence-based quant. detn. of tensile modulation. Film stretching induced both blue shift in the C-dots' fluorescence peak positions and dramatic increase in fluorescence intensities. The phenomenon was demonstrated for different C-dots exhibiting distinct fluorescence emissions (e.g. colors). Importantly, the C-dot/polymer fluorescence intensity could be quant. correlated to tensile parameters, specifically film stress and strain. The direct correlation is ascribed to stretch-induced modulation of the av. distances among the polymer-embedded C-dots and concomitant modification of aggregation-induced self-quenching. We further exploited the tensile-dependent fluorescence modulation of the C-dot/polymer system to construct a tunable-intensity white light emitter, opening the way to innovative mech.-tuned optical device.
- 22Blohowiak, K. Improvements in Surface Preparation Methods for Adhesive Bonding SERDP/ESTCP Workshop. Def. Tech. Inf. Cent. 2008, A604688Google ScholarThere is no corresponding record for this reference.
- 23Mazza, J. J.; Avram, J. B.; Kuhbander, R. J. Grit-Blast/Silane (GBS) Aluminum Surface Preparation for Structural Adhesive Bonding. Def. Tech. Inf. Cent. 2003, ADA415239Google ScholarThere is no corresponding record for this reference.
- 24Mazza, J. J.; Gaskin, G. B.; De Piero, W. S.; Blohowiak, K. Y. Sol-Gel Technology for Low-Voc Nonchromated Adhesive Bonding Applications SERDP Project PP-1113, Task 1. Def. Tech. Inf. Cent. 2004, ADA423563Google ScholarThere is no corresponding record for this reference.
- 25Kleinschmidt, D.; James, M.; Jensen, R.; Jaworowski, M.; Zhang, W.; Stropki, J.; Gadkari, V.; Tienda, K.; Blohowiak, K.; Kutscha, E. Understanding Corrosion Protection Requirements for Adhesive Bond Primers. Def. Tech. Inf. Cent. 2016, AD1092341Google ScholarThere is no corresponding record for this reference.
- 26Blohowiak, K. Y.; Anderson, R. A.; Stephenson, R. R. Structure Technology and Analysis Program (STAP) Delivery Order 0010: Sol-Gel Technology for Surface Preparation of Metal Alloys for Adhesive Bonding and Sealing Operations. Def. Tech. Inf. Cent. 2001, ADA419256Google ScholarThere is no corresponding record for this reference.
- 27McCray, D. B. Nonmetals Test and Evaluation Delivery Order 0007: The Development of On-Aircraft Surface Preparations Utilizing Sol-Gel Coatings for Adhesive Bonding Aluminum Alloys. Def. Tech. Inf. Cent. 2001, ADA406628Google ScholarThere is no corresponding record for this reference.
- 28Li, S.; Zhang, K.; Yang, J.-M.; Lin, L.; Yang, H. Single Quantum Dots As Local Temperature Markers. Nano Lett. 2007, 7, 3102– 3105, DOI: 10.1021/nl071606pGoogle Scholar28https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXps1entr4%253D&md5=4d2265db98f7572680aac82641d1119dSingle Quantum Dots as Local Temperature MarkersLi, Sha; Zhang, Kai; Yang, Jui-Ming; Lin, Liwei; Yang, HawNano Letters (2007), 7 (10), 3102-3105CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)This work describes noncontact, local temp. measurements using wavelength shifts of CdSe quantum dots (QDs). Individual QDs are capable of sensing temp. variations and reporting temp. changes remotely through optical readout. Temp. profiles of a microheater under different input voltages are evaluated based on the spectral shift of QDs on the heater, and results are consistent with a 1-dimensional electrothermal model. The theor. resoln. of this technique could go down to the size of a single quantum dot using far-field optics for temp. characterizations of micro/nanostructures.
- 29Pietka, B. Excitonic Complexes in Natural Quantum Dots Formed in Type II GaAs/AlAs Structures. Ph.D. Thesis, Université Joseph-Fourier: Grenoble, 2007.Google ScholarThere is no corresponding record for this reference.
- 30Bryant, G. W.; Zieliński, M.; Malkova, N.; Sims, J.; Jaskólski, W.; Aizpurua, J. Effect of Mechanical Strain on the Optical Properties of Quantum Dots: Controlling Exciton Shape, Orientation, and Phase with a Mechanical Strain. Phys. Rev. Lett. 2010, 105. 067404 DOI: 10.1103/PhysRevLett.105.067404 .Google Scholar30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVyrsL%252FL&md5=ea396e8f2f840607c85ba6b55d94c38bEffect of mechanical strain on the optical properties of quantum dots: controlling exciton shape, orientation, and phase with a mechanical strainBryant, Garnett W.; Zielinski, M.; Malkova, Natalia; Sims, James; Jaskolski, W.; Aizpurua, JavierPhysical Review Letters (2010), 105 (6), 067404/1-067404/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We show how a nanomech. strain can be used to dynamically reengineer the optics of quantum dots, giving a tool to manipulate mechanoexciton shape, orientation, fine structure splitting, and optical transitions, transfer carriers between dots, and interact qubits for quantum processing. Most importantly, a nanomech. strain reengineers both the magnitude and phase of the exciton exchange coupling to tune exchange splittings, change the phase of spin mixing, and rotate the polarization of mechanoexcitons, providing phase and energy control of excitons.
- 31Kuo, M. K.; Lin, T. R.; Hong, K. B.; Liao, B. T.; Lee, H. T.; Yu, C. H. Two-Step Strain Analysis of Self-Assembled InAs/GaAs Quantum Dots. Semicond. Sci. Technol. 2006, 21, 626– 632, DOI: 10.1088/0268-1242/21/5/010Google Scholar31https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XntFeisr0%253D&md5=a2c522d33334afa9cf1aec7a970612a1Two-step strain analysis of self-assembled InAs/GaAs quantum dotsKuo, M. K.; Lin, T. R.; Hong, K. B.; Liao, B. T.; Lee, H. T.; Yu, C. H.Semiconductor Science and Technology (2006), 21 (5), 626-632CODEN: SSTEET; ISSN:0268-1242. (Institute of Physics Publishing)Strain effects on optical properties of self-assembled InAs/GaAs quantum dots grown by epitaxy are investigated. Since a capping layer is added after the self-assembly process of the quantum dots, it might be reasonable to assume that the capping layer neither experiences nor affects the induced deformation of quantum dots during the self-assembly process. A new two-step model is proposed to analyze the three-dimensional induced strain fields of quantum dots. The model is based on the theory of linear elasticity and takes into account the sequence of the fabrication process of quantum dots. In the first step, the heterostructure system of quantum dots without the capping layer is considered. The mismatch of lattice consts. between the wetting layer and the substrate is the driving source for the induced elastic strain. The strain field obtained in the first step is then treated as an initial strain for the whole heterostructure system, with the capping layer, in the second step. The strain from the two-step anal. is then incorporated into a steady-state effective-mass Schrodinger equation. The energy levels as well as the wavefunctions of both the electron and the hole are calcd. The numerical results show that the strain field from this new two-step model is significantly different from models where the sequence of the fabrication process is completely omitted. The calcd. optical wavelength from this new model agrees well with previous exptl. photoluminescence data from other studies. It seems reasonable to conclude that the proposed two-step strain anal. is crucial for future optical anal. and applications.
- 32Zhang, Y.; Chen, Y.; Mietschke, M.; Zhang, L.; Yuan, F.; Abel, S.; Hühne, R.; Nielsch, K.; Fompeyrine, J.; Ding, F.; Schmidt, O. G. Monolithically Integrated Microelectromechanical Systems for On-Chip Strain Engineering of Quantum Dots. Nano Lett. 2016, 16, 5785– 5791, DOI: 10.1021/acs.nanolett.6b02523Google Scholar32https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVektrzN&md5=b83b883b1aacfdda0700ef1367477238Monolithically Integrated Microelectromechanical Systems for On-Chip Strain Engineering of Quantum DotsZhang, Yang; Chen, Yan; Mietschke, Michael; Zhang, Long; Yuan, Feifei; Abel, Stefan; Huehne, Ruben; Nielsch, Kornelius; Fompeyrine, Jean; Ding, Fei; Schmidt, Oliver G.Nano Letters (2016), 16 (9), 5785-5791CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Elastic strain fields based on single crystal piezoelec. elements represent an effective way for engineering the quantum dot (QD) emission with unrivaled precision and technol. relevance. However, pioneering researches in this direction were mainly based on bulk piezoelec. substrates, which prevent the development of chip-scale devices. Here, we present a monolithically integrated Microelectromech. systems (MEMS) device with great potential for on-chip quantum photonic applications. High-quality epitaxial PMN-PT thin films have been grown on SrTiO3 buffered Si and show excellent piezoelec. responses. Dense arrays of MEMS with small footprints are then fabricated based on these films, forming an on-chip strain tuning platform. After transferring the QD-contg. nanomembranes onto these MEMS, the nonclassical emissions (e.g., single photons) from single QDs can be engineered by the strain fields. We envision that the strain tunable QD sources on the individually addressable and monolithically integrated MEMS pave the way toward complex quantum photonic applications on chip.
- 33Sherburne, M. X-Ray Detection and Strain Sensing Applications of Colloidal Quantum Dots. M.Sc. Thesis, Air Force Institute of Technology, 2020.Google ScholarThere is no corresponding record for this reference.
- 34Zhou, W.; Liu, Y.; Yang, Y.; Wu, P. Band Gap Engineering of SnO2 by Epitaxial Strain: Experimental and Theoretical Investigations. J. Phys. Chem. C 2014, 118, 6448– 6453, DOI: 10.1021/jp500546rGoogle Scholar34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXjsVSnt7Y%253D&md5=4c53ea015c64afc3158bba32887edcb9Band Gap Engineering of SnO2 by Epitaxial Strain: Experimental and Theoretical InvestigationsZhou, Wei; Liu, Yanyu; Yang, Yuzhe; Wu, PingJournal of Physical Chemistry C (2014), 118 (12), 6448-6453CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The effect of mis-match strain on the structural, electronic, and optical properties in SnO2 epitaxial thin films has been systematically investigated by the exptl. and theor. methods. Our results indicate that the tensile strain exists in the thin film and decreases with the thickness of epitaxial samples. Besides, the optical band gap significantly reduces with increasing the tensile strain in the bc plane. Our hybrid functional calcns. present that the narrowing of band gap of SnO2 under tensile strain is due to the weakening of bonding and antibonding split, which results from the disorder of SnO6 octahedra, and the biaxial strain is found to be more efficient than the uniaxial strain for tuning the band gap of SnO2.
- 35Yu, P. Y.; Cardona, M. Fundamentals of Semiconductors; Springer: Berlin, 2010; Chapter 3, pp 121– 127.Google ScholarThere is no corresponding record for this reference.
- 36Blake, A. J.; Kohlmeyer, R. R.; Drummy, L. F.; Gutiérrez-Kolar, J. S.; Carpena-Núñez, J.; Maruyama, B.; Shahbazian-Yassar, R.; Huang, H.; Durstock, M. F. Creasable Batteries: Understanding Failure Modes through Dynamic Electrochemical Mechanical Testing. ACS Appl. Mater. Interfaces 2016, 8, 5196– 5204, DOI: 10.1021/acsami.5b11175Google Scholar36https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjvFaksw%253D%253D&md5=b1f2c898a1fe066be259b29343519352Creasable Batteries: Understanding Failure Modes through Dynamic Electrochemical Mechanical TestingBlake, Aaron J.; Kohlmeyer, Ryan R.; Drummy, Lawrence F.; Gutierrez-Kolar, Jacob S.; Carpena-Nunez, Jennifer; Maruyama, Benji; Shahbazian-Yassar, Reza; Huang, Hong; Durstock, Michael F.ACS Applied Materials & Interfaces (2016), 8 (8), 5196-5204CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Thin-film batteries that can be folded, bent, and even repeatedly creased with minimal or no loss in electrochem. performance have been demonstrated and systematically evaluated using two dynamic mech. testing approaches for either controlled bending or creasing of flexible devices. The results show that mech. robust and flexible Li-ion batteries (Li4Ti5O12//LiFePO4) based on the use of a nonwoven multiwalled carbon nanotube (MWNT) mat as a current collector (CC) exhibited a 14-fold decrease in voltage fluctuation at a bending strain of 4.2%, as compared to cells using traditional metal foil CCs. More importantly, MWNT-based full-cells exhibited excellent mech. integrity through 288 crease cycles, whereas the foil full-cell exhibited continuously degraded performance with each fold and catastrophic fracture after only 94 folds. The enhancements due to MWNT CCs can be attributed to excellent interfacial properties as well as high mech. strength coupled with compliancy, which allow the batteries to easily conform during mech. abuse. These results quant. demonstrate the substantial enhancement offered in both mech. and electrochem. stability which can be realized with traditional processing approaches when an appropriate choice of a flexible and robust CC is utilized.
- 37Rocha, T. L.; Mestre, N. C.; Sabóia-Morais, S. M. T.; Bebianno, M. J. Environmental Behaviour and Ecotoxicity of Quantum Dots at Various Trophic Levels: A Review. Environ. Int. 2017, 98, 1– 17, DOI: 10.1016/j.envint.2016.09.021Google Scholar37https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1ygs7fK&md5=b989b5ade56cc5640892e376c1db1484Environmental behaviour and ecotoxicity of quantum dots at various trophic levels: A reviewRocha, Thiago Lopes; Mestre, Nelia C.; Saboia-Morais, Simone Maria Teixeira; Bebianno, Maria JoaoEnvironment International (2017), 98 (), 1-17CODEN: ENVIDV; ISSN:0160-4120. (Elsevier Ltd.)A review with many refs. Despite the wide application of quantum dots (QDs) in electronics, pharmacy and nanomedicine, limited data is available on their environmental health risk. To advance our current understanding of the environmental impact of these engineered nanomaterials, the aim of this review is to give a detailed insight on the existing information concerning the behavior, transformation and fate of QDs in the aquatic environment, as well as on its mode of action (MoA), ecotoxicity, trophic transfer and biomagnification at various trophic levels (micro-organisms, aquatic invertebrates and vertebrates). Data show that several types of Cd-based QDs, even at low concns. (< mg Cd L- 1), induce different toxic effects compared to their dissolved counterpart, indicating nano-specific ecotoxicity. QD ecotoxicity at different trophic levels is highly dependent on its physico-chem. properties, environmental conditions, concn. and exposure time, as well as, species, while UV irradn. increases its toxicity. The state of the art regarding the MoA of QDs according to taxonomic groups is summarised and illustrated. Accumulation and trophic transfer of QDs was obsd. in freshwater and seawater species, while limited biomagnification and detoxification processes were detected. Finally, current knowledge gaps are discussed and recommendations for future research identified. Overall, the knowledge available indicates that in order to develop sustainable nanotechnologies there is an urgent need to develop Cd-free QDs and new "core-shell-conjugate" QD structures.
- 38Roark, R. Roark’s Formulas for Stress and Strain; McGraw-Hill: New York, 2002; Chapter 2, pp 9– 15.Google ScholarThere is no corresponding record for this reference.
- 39Chung, K.-H.; Pratt, J. R.; Reitsma, M. G. Lateral Force Calibration: Accurate Procedures for Colloidal Probe Friction Measurements in Atomic Force Microscopy. Langmuir 2010, 26, 1386– 1394, DOI: 10.1021/la902488rGoogle Scholar39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXht1Kjtb%252FM&md5=c39cb42731d489d247007481e89e57f7Lateral Force Calibration: Accurate Procedures for Colloidal Probe Friction Measurements in Atomic Force MicroscopyChung, Koo-Hyun; Pratt, Jon R.; Reitsma, Mark G.Langmuir (2010), 26 (2), 1386-1394CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)The colloidal probe technique for at. force microscopy (AFM) has allowed the study of an extensive range of surface force phenomena, including the measurement of frictional (lateral) forces between numerous materials. The quant. accuracy of such friction measurements is often debated, in part due to a lack of confidence in existing calibration strategies. Here the authors compare three in situ AFM lateral force calibration techniques using a single colloidal probe, seeking to establish a foundation for quant. measurement by linking these techniques to accurate force refs. available at the National Institute of Stds. and Technol. The authors introduce a procedure for calibrating the AFM lateral force response to known electrostatic forces applied directly to the conductive colloidal probe. In a 2nd procedure, the authors apply known force directly to the colloidal probe using a precalibrated piezo-resistive ref. cantilever. The authors found agreement between these direct methods ∼2% (within random uncertainty for both measurements). In a 3rd procedure, the authors performed a displacement-based calibration using the piezo-resistive ref. cantilever as a stiffness ref. artifact. The method demonstrated agreement ∼7% with the direct force methods, with the difference attributed to an expected systematic uncertainty, caused by in-plane deflection in the cantilever during loading. The comparison establishes the existing limits of instrument accuracy and sets down a basis for selection criteria for materials and methods in colloidal probe friction (lateral) force measurements via at. force microscopy.
- 40Schaufele, F.; Demarco, I.; Day, R. N. Molecular Imaging; Elsevier Inc., 2005; pp 72– 94.Google ScholarThere is no corresponding record for this reference.
- 41Hammer, N. I.; Emrick, T.; Barnes, M. D. Quantum Dots Coordinated With Conjugated Organic Ligands: New Nanomaterials With Novel Photophysics. Nanoscale Res. Lett. 2007, 2, 282– 290, DOI: 10.1007/s11671-007-9062-8Google Scholar41https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXpslegsbo%253D&md5=3b2209692022bcbdc09fe576089ef922Quantum dots coordinated with conjugated organic ligands: new nanomaterials with novel photophysicsHammer, Nathan I.; Emrick, Todd; Barnes, Michael D.Nanoscale Research Letters (2007), 2 (6), 282-290CODEN: NRLAAD; ISSN:1556-276X. (Springer)A review. CdSe quantum dots functionalized with oligo-(phenylene vinylene) (OPV) ligands (CdSe-OPV nanostructures) represent a new class of composite nanomaterials with significantly modified photophysics relative to bulk blends or isolated components. Singlemol. spectroscopy on these species have revealed novel photophysics such as enhanced energy transfer, spectral stability, and strongly modified excited state lifetimes and blinking statistics. Here, we review the role of ligands in quantum dot applications and summarize some of our recent efforts probing energy and charge transfer in hybrid CdSe-OPV composite nanostructures.
- 42Bae, W. K.; Padilha, L. A.; Park, Y.-S.; McDaniel, H.; Robel, I.; Pietryga, J. M.; Klimov, V. I. Controlled Alloying of the Core–Shell Interface in CdSe/CdS Quantum Dots for Suppression of Auger Recombination. ACS Nano 2013, 7, 3411– 3419, DOI: 10.1021/nn4002825Google Scholar42https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXksVyhs70%253D&md5=de3c777c4d29ce406a4b3ed5411661a5Controlled Alloying of the Core-Shell Interface in CdSe/CdS Quantum Dots for Suppression of Auger RecombinationBae, Wan Ki; Padilha, Lazaro A.; Park, Young-Shin; McDaniel, Hunter; Robel, Istvan; Pietryga, Jeffrey M.; Klimov, Victor I.ACS Nano (2013), 7 (4), 3411-3419CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)The influence of a CdSexS1-x interfacial alloyed layer on the photophys. properties of core/shell CdSe/CdS nanocrystal quantum dots (QDs) is investigated by comparing ref. QDs with a sharp core/shell interface to alloyed structures with an intermediate CdSexS1-x layer at the core/shell interface. To fully realize the structural contrast, we have developed two novel synthetic approaches: a method for fast CdS-shell growth, which results in an abrupt core/shell boundary (no intentional or unintentional alloying), and a method for depositing a CdSexS1-x alloy layer of controlled compn. onto the CdSe core prior to the growth of the CdS shell. Both types of QDs possess similar size-dependent single-exciton properties (photoluminescence energy, quantum yield, and decay lifetime). However the alloyed QDs show a significantly longer biexciton lifetime and up to a 3-fold increase in the biexciton emission efficiency compared to the ref. samples. These results provide direct evidence that the structure of the QD interface has a significant effect on the rate of nonradiative Auger recombination, which dominates biexciton decay. We also observe that the energy gradient at the core-shell interface introduced by the alloyed layer accelerates hole trapping from the shell to the core states, which results in suppression of shell emission. This comparative study offers practical guidelines for controlling multicarrier Auger recombination without a significant effect on either spectral or dynamical properties of single excitons. The proposed strategy should be applicable to QDs of a variety of compns. (including, e.g., IR-emitting QDs) and can benefit numerous applications from light emitting diodes and lasers to photodetectors and photovoltaics.
- 43Selopal, G. S.; Zhao, H.; Liu, G.; Zhang, H.; Tong, X.; Wang, K.; Tang, J.; Sun, X.; Sun, S.; Vidal, F.; Wang, Y.; Wang, Z. M.; Rosei, F. Interfacial Engineering in Colloidal “Giant” Quantum Dots for High-Performance Photovoltaics. Nano Energy 2019, 55, 377– 388, DOI: 10.1016/j.nanoen.2018.11.001Google Scholar43https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1Cht7nL&md5=ede06a7227b1f2534fb76181df967999Interfacial engineering in colloidal "giant" quantum dots for high-performance photovoltaicsSelopal, Gurpreet S.; Zhao, Haiguang; Liu, Guiju; Zhang, Hui; Tong, Xin; Wang, Kanghong; Tang, Jie; Sun, Xuhui; Sun, Shuhui; Vidal, Francois; Wang, Yiqian; Wang, Zhiming M.; Rosei, FedericoNano Energy (2019), 55 (), 377-388CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)Colloidal quantum dots (QDs) are semiconductor nanocrystals which exhibit discrete energy levels. They are promising building blocks for optoelectronic devices, thanks to their tunable band structure. Here, we explore a nanoengineering approach to highlight the influence of an alloyed interface on the optical and electronic properties of CdSe/(CdS)6 "giant" core/shell (CS) QDs by introducing CdSexS1-x interfacial layers between core and shell. By incorporating of CdSexS1-x interfacial layers, CdSe/(CdSexS1-x)4/(CdS)2 (x = 0.5) core/shell (CSA1) QDs exhibit a broader absorption response towards longer wavelength and higher electron-hole transfer rate due to favorable electronic band alignment with respect to CS QDs, as confirmed by optical absorption, photoluminescence (PL) and transient fluorescence spectroscopic measurements. In addn., simulations of spatial probability distributions show that the interface layer enhances electron-hole spatial overlap. As a result, CSA1 QDs sensitized solar cells (QDSCs) yield a max. photoconversion efficiency (PCE) of 5.52%, which is 79% higher than QDSCs based on ref. CS QDs. To fully demonstrate the structural interface engineering approach, the CdSexS1-x interfacial layers were further engineered by tailoring the selenium (Se) and sulfur (S) molar ratios during in situ growth of each interfacial layer. This graded alloyed CdSe/(CdSexS1-x)5/(CdS)1 (x = 0.9-0.1) core/shell (CSA2) QDs show a further broadening of the absorption spectrum, higher carrier transport rate and modified confinement potential with respect to CSA1 QDs as well as ref. CS QDs, yielding a PCE of 7.14%. Our findings define a promising approach to improve the performance of QDSCs and other optoelectronic devices based on CS QDs.
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Abstract
Figure 1
Figure 1. Graphic of a CQD where the inner core (pink), outer shell (yellow), and polymer ligands (black lines) can be seen. Sherburne, M. X-Ray Detection and Strain Sensing Applications of Colloidal Quantum Dots. M.S. Thesis, Air Force Institute of Technology, March 2020. (33)
Figure 2
Figure 2. Three-dimensional surface model of the coated stainless steel dog-bone with the CQD polymer matrix applied. The left half of the image contained the CQD-loaded polymer matrix coating, while the right half was only the precoating (Solvay BR 6747-1) on top of the stainless steel. (a) Three-dimensional surface image of the dog-bone. (b) Two-dimensional (2D) cross-section through the CQD-loaded polymer and precoated polymer boundary.
Figure 3
Figure 3. (a) Illustration of the experimental setup. (b) Labeled photo of the experimental setup. Sherburne, M. X-Ray Detection and Strain Sensing Applications of Colloidal Quantum Dots. M.S. Thesis, Air Force Institute of Technology, March 2020. (33)
Figure 4
Figure 4. This figure shows the three-step process from (a) collecting the spectral data from the experiment, (b) applying a calibration, and then (c) plotting the calibrated optical strain data in relation to the mechanical reference strain data.
Figure 5
Figure 5. DIC images showing the surface strains of a sample. The mechanical strains correlated for their respective DIC images were the following: (D1) 0.04, (D2) 0.08, (D3) 0.09, and (D4) 0.1. The orange dashed boxes showed, where the CQD-loaded polymer coating would be during the optical experiment.
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- 18Shen, Z.; Chen, S.; Zhang, L.; Yao, K.; Tan, C. Y. Direct-Write Piezoelectric Ultrasonic Transducers for Non-Destructive Testing of Metal Plates. IEEE Sens. J. 2017, 17, 3354– 3361, DOI: 10.1109/JSEN.2017.269445418https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXkvVCltbs%253D&md5=ca4935e2946eb0643339e5fb732f3989Direct-write piezoelectric ultrasonic transducers for non-destructive testing of metal platesShen, Zhiyuan; Chen, Shuting; Zhang, Lei; Yao, Kui; Tan, Chin YawIEEE Sensors Journal (2017), 17 (11), 3354-3361CODEN: ISJEAZ; ISSN:1558-1748. (Institute of Electrical and Electronics Engineers)Current real time structural health monitoring is implemented by assembling multiple discrete sensors on a structure with each sensor providing only point measurement. The installation of the multiple sensors results in high global cost and low reliability. This paper reports the design, directwrite fabrication, and testing of ultrasonic transducers on a plate structure and a non-destructive testing method for detecting defects using the sensor array comprising the direct-write ultrasonic transducers. The transducers are made of piezoelec. poly(vinylidenefluoride/trifluoroethylene) (P(VDF/TrFE)) polymer coatings that are aerosol-spray deposited and patterned directly on the plate structure to be monitored. The ultrasonic transducers bearing annular array comb electrodes are designed for generating and selectively detecting fundamental antisym. Lamb-mode ultrasonic waves in the plate structure. The ultrasonic transducers can serve as both the actuators to generate ultrasonic waves and the sensors to detect ultrasonic waves. The ultrasonic waves propagating through the plate structure contain the information about the structural integrity. With copper bars of different thicknesses introduced at the plate center as mock defects of different severity, the correlation between the transducer response and the defect thickness and hence, the severity is verified. It is also demonstrated that four ultrasonic transducers located at the square plate (100 mm × 100 mm × 1.27 mm) corners forming a transducer array, which can locate the defect on the plate. A short time Fourier transform algorithm and an imaging algorithm are developed for processing signal of the pitch-catch ultrasonic wave spectra to det. the location of the defects, which is verified by exptl. results.
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- 29Pietka, B. Excitonic Complexes in Natural Quantum Dots Formed in Type II GaAs/AlAs Structures. Ph.D. Thesis, Université Joseph-Fourier: Grenoble, 2007.There is no corresponding record for this reference.
- 30Bryant, G. W.; Zieliński, M.; Malkova, N.; Sims, J.; Jaskólski, W.; Aizpurua, J. Effect of Mechanical Strain on the Optical Properties of Quantum Dots: Controlling Exciton Shape, Orientation, and Phase with a Mechanical Strain. Phys. Rev. Lett. 2010, 105. 067404 DOI: 10.1103/PhysRevLett.105.067404 .30https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3cXhtVyrsL%252FL&md5=ea396e8f2f840607c85ba6b55d94c38bEffect of mechanical strain on the optical properties of quantum dots: controlling exciton shape, orientation, and phase with a mechanical strainBryant, Garnett W.; Zielinski, M.; Malkova, Natalia; Sims, James; Jaskolski, W.; Aizpurua, JavierPhysical Review Letters (2010), 105 (6), 067404/1-067404/4CODEN: PRLTAO; ISSN:0031-9007. (American Physical Society)We show how a nanomech. strain can be used to dynamically reengineer the optics of quantum dots, giving a tool to manipulate mechanoexciton shape, orientation, fine structure splitting, and optical transitions, transfer carriers between dots, and interact qubits for quantum processing. Most importantly, a nanomech. strain reengineers both the magnitude and phase of the exciton exchange coupling to tune exchange splittings, change the phase of spin mixing, and rotate the polarization of mechanoexcitons, providing phase and energy control of excitons.
- 31Kuo, M. K.; Lin, T. R.; Hong, K. B.; Liao, B. T.; Lee, H. T.; Yu, C. H. Two-Step Strain Analysis of Self-Assembled InAs/GaAs Quantum Dots. Semicond. Sci. Technol. 2006, 21, 626– 632, DOI: 10.1088/0268-1242/21/5/01031https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD28XntFeisr0%253D&md5=a2c522d33334afa9cf1aec7a970612a1Two-step strain analysis of self-assembled InAs/GaAs quantum dotsKuo, M. K.; Lin, T. R.; Hong, K. B.; Liao, B. T.; Lee, H. T.; Yu, C. H.Semiconductor Science and Technology (2006), 21 (5), 626-632CODEN: SSTEET; ISSN:0268-1242. (Institute of Physics Publishing)Strain effects on optical properties of self-assembled InAs/GaAs quantum dots grown by epitaxy are investigated. Since a capping layer is added after the self-assembly process of the quantum dots, it might be reasonable to assume that the capping layer neither experiences nor affects the induced deformation of quantum dots during the self-assembly process. A new two-step model is proposed to analyze the three-dimensional induced strain fields of quantum dots. The model is based on the theory of linear elasticity and takes into account the sequence of the fabrication process of quantum dots. In the first step, the heterostructure system of quantum dots without the capping layer is considered. The mismatch of lattice consts. between the wetting layer and the substrate is the driving source for the induced elastic strain. The strain field obtained in the first step is then treated as an initial strain for the whole heterostructure system, with the capping layer, in the second step. The strain from the two-step anal. is then incorporated into a steady-state effective-mass Schrodinger equation. The energy levels as well as the wavefunctions of both the electron and the hole are calcd. The numerical results show that the strain field from this new two-step model is significantly different from models where the sequence of the fabrication process is completely omitted. The calcd. optical wavelength from this new model agrees well with previous exptl. photoluminescence data from other studies. It seems reasonable to conclude that the proposed two-step strain anal. is crucial for future optical anal. and applications.
- 32Zhang, Y.; Chen, Y.; Mietschke, M.; Zhang, L.; Yuan, F.; Abel, S.; Hühne, R.; Nielsch, K.; Fompeyrine, J.; Ding, F.; Schmidt, O. G. Monolithically Integrated Microelectromechanical Systems for On-Chip Strain Engineering of Quantum Dots. Nano Lett. 2016, 16, 5785– 5791, DOI: 10.1021/acs.nanolett.6b0252332https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XhsVektrzN&md5=b83b883b1aacfdda0700ef1367477238Monolithically Integrated Microelectromechanical Systems for On-Chip Strain Engineering of Quantum DotsZhang, Yang; Chen, Yan; Mietschke, Michael; Zhang, Long; Yuan, Feifei; Abel, Stefan; Huehne, Ruben; Nielsch, Kornelius; Fompeyrine, Jean; Ding, Fei; Schmidt, Oliver G.Nano Letters (2016), 16 (9), 5785-5791CODEN: NALEFD; ISSN:1530-6984. (American Chemical Society)Elastic strain fields based on single crystal piezoelec. elements represent an effective way for engineering the quantum dot (QD) emission with unrivaled precision and technol. relevance. However, pioneering researches in this direction were mainly based on bulk piezoelec. substrates, which prevent the development of chip-scale devices. Here, we present a monolithically integrated Microelectromech. systems (MEMS) device with great potential for on-chip quantum photonic applications. High-quality epitaxial PMN-PT thin films have been grown on SrTiO3 buffered Si and show excellent piezoelec. responses. Dense arrays of MEMS with small footprints are then fabricated based on these films, forming an on-chip strain tuning platform. After transferring the QD-contg. nanomembranes onto these MEMS, the nonclassical emissions (e.g., single photons) from single QDs can be engineered by the strain fields. We envision that the strain tunable QD sources on the individually addressable and monolithically integrated MEMS pave the way toward complex quantum photonic applications on chip.
- 33Sherburne, M. X-Ray Detection and Strain Sensing Applications of Colloidal Quantum Dots. M.Sc. Thesis, Air Force Institute of Technology, 2020.There is no corresponding record for this reference.
- 34Zhou, W.; Liu, Y.; Yang, Y.; Wu, P. Band Gap Engineering of SnO2 by Epitaxial Strain: Experimental and Theoretical Investigations. J. Phys. Chem. C 2014, 118, 6448– 6453, DOI: 10.1021/jp500546r34https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXjsVSnt7Y%253D&md5=4c53ea015c64afc3158bba32887edcb9Band Gap Engineering of SnO2 by Epitaxial Strain: Experimental and Theoretical InvestigationsZhou, Wei; Liu, Yanyu; Yang, Yuzhe; Wu, PingJournal of Physical Chemistry C (2014), 118 (12), 6448-6453CODEN: JPCCCK; ISSN:1932-7447. (American Chemical Society)The effect of mis-match strain on the structural, electronic, and optical properties in SnO2 epitaxial thin films has been systematically investigated by the exptl. and theor. methods. Our results indicate that the tensile strain exists in the thin film and decreases with the thickness of epitaxial samples. Besides, the optical band gap significantly reduces with increasing the tensile strain in the bc plane. Our hybrid functional calcns. present that the narrowing of band gap of SnO2 under tensile strain is due to the weakening of bonding and antibonding split, which results from the disorder of SnO6 octahedra, and the biaxial strain is found to be more efficient than the uniaxial strain for tuning the band gap of SnO2.
- 35Yu, P. Y.; Cardona, M. Fundamentals of Semiconductors; Springer: Berlin, 2010; Chapter 3, pp 121– 127.There is no corresponding record for this reference.
- 36Blake, A. J.; Kohlmeyer, R. R.; Drummy, L. F.; Gutiérrez-Kolar, J. S.; Carpena-Núñez, J.; Maruyama, B.; Shahbazian-Yassar, R.; Huang, H.; Durstock, M. F. Creasable Batteries: Understanding Failure Modes through Dynamic Electrochemical Mechanical Testing. ACS Appl. Mater. Interfaces 2016, 8, 5196– 5204, DOI: 10.1021/acsami.5b1117536https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XjvFaksw%253D%253D&md5=b1f2c898a1fe066be259b29343519352Creasable Batteries: Understanding Failure Modes through Dynamic Electrochemical Mechanical TestingBlake, Aaron J.; Kohlmeyer, Ryan R.; Drummy, Lawrence F.; Gutierrez-Kolar, Jacob S.; Carpena-Nunez, Jennifer; Maruyama, Benji; Shahbazian-Yassar, Reza; Huang, Hong; Durstock, Michael F.ACS Applied Materials & Interfaces (2016), 8 (8), 5196-5204CODEN: AAMICK; ISSN:1944-8244. (American Chemical Society)Thin-film batteries that can be folded, bent, and even repeatedly creased with minimal or no loss in electrochem. performance have been demonstrated and systematically evaluated using two dynamic mech. testing approaches for either controlled bending or creasing of flexible devices. The results show that mech. robust and flexible Li-ion batteries (Li4Ti5O12//LiFePO4) based on the use of a nonwoven multiwalled carbon nanotube (MWNT) mat as a current collector (CC) exhibited a 14-fold decrease in voltage fluctuation at a bending strain of 4.2%, as compared to cells using traditional metal foil CCs. More importantly, MWNT-based full-cells exhibited excellent mech. integrity through 288 crease cycles, whereas the foil full-cell exhibited continuously degraded performance with each fold and catastrophic fracture after only 94 folds. The enhancements due to MWNT CCs can be attributed to excellent interfacial properties as well as high mech. strength coupled with compliancy, which allow the batteries to easily conform during mech. abuse. These results quant. demonstrate the substantial enhancement offered in both mech. and electrochem. stability which can be realized with traditional processing approaches when an appropriate choice of a flexible and robust CC is utilized.
- 37Rocha, T. L.; Mestre, N. C.; Sabóia-Morais, S. M. T.; Bebianno, M. J. Environmental Behaviour and Ecotoxicity of Quantum Dots at Various Trophic Levels: A Review. Environ. Int. 2017, 98, 1– 17, DOI: 10.1016/j.envint.2016.09.02137https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28Xhs1ygs7fK&md5=b989b5ade56cc5640892e376c1db1484Environmental behaviour and ecotoxicity of quantum dots at various trophic levels: A reviewRocha, Thiago Lopes; Mestre, Nelia C.; Saboia-Morais, Simone Maria Teixeira; Bebianno, Maria JoaoEnvironment International (2017), 98 (), 1-17CODEN: ENVIDV; ISSN:0160-4120. (Elsevier Ltd.)A review with many refs. Despite the wide application of quantum dots (QDs) in electronics, pharmacy and nanomedicine, limited data is available on their environmental health risk. To advance our current understanding of the environmental impact of these engineered nanomaterials, the aim of this review is to give a detailed insight on the existing information concerning the behavior, transformation and fate of QDs in the aquatic environment, as well as on its mode of action (MoA), ecotoxicity, trophic transfer and biomagnification at various trophic levels (micro-organisms, aquatic invertebrates and vertebrates). Data show that several types of Cd-based QDs, even at low concns. (< mg Cd L- 1), induce different toxic effects compared to their dissolved counterpart, indicating nano-specific ecotoxicity. QD ecotoxicity at different trophic levels is highly dependent on its physico-chem. properties, environmental conditions, concn. and exposure time, as well as, species, while UV irradn. increases its toxicity. The state of the art regarding the MoA of QDs according to taxonomic groups is summarised and illustrated. Accumulation and trophic transfer of QDs was obsd. in freshwater and seawater species, while limited biomagnification and detoxification processes were detected. Finally, current knowledge gaps are discussed and recommendations for future research identified. Overall, the knowledge available indicates that in order to develop sustainable nanotechnologies there is an urgent need to develop Cd-free QDs and new "core-shell-conjugate" QD structures.
- 38Roark, R. Roark’s Formulas for Stress and Strain; McGraw-Hill: New York, 2002; Chapter 2, pp 9– 15.There is no corresponding record for this reference.
- 39Chung, K.-H.; Pratt, J. R.; Reitsma, M. G. Lateral Force Calibration: Accurate Procedures for Colloidal Probe Friction Measurements in Atomic Force Microscopy. Langmuir 2010, 26, 1386– 1394, DOI: 10.1021/la902488r39https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1MXht1Kjtb%252FM&md5=c39cb42731d489d247007481e89e57f7Lateral Force Calibration: Accurate Procedures for Colloidal Probe Friction Measurements in Atomic Force MicroscopyChung, Koo-Hyun; Pratt, Jon R.; Reitsma, Mark G.Langmuir (2010), 26 (2), 1386-1394CODEN: LANGD5; ISSN:0743-7463. (American Chemical Society)The colloidal probe technique for at. force microscopy (AFM) has allowed the study of an extensive range of surface force phenomena, including the measurement of frictional (lateral) forces between numerous materials. The quant. accuracy of such friction measurements is often debated, in part due to a lack of confidence in existing calibration strategies. Here the authors compare three in situ AFM lateral force calibration techniques using a single colloidal probe, seeking to establish a foundation for quant. measurement by linking these techniques to accurate force refs. available at the National Institute of Stds. and Technol. The authors introduce a procedure for calibrating the AFM lateral force response to known electrostatic forces applied directly to the conductive colloidal probe. In a 2nd procedure, the authors apply known force directly to the colloidal probe using a precalibrated piezo-resistive ref. cantilever. The authors found agreement between these direct methods ∼2% (within random uncertainty for both measurements). In a 3rd procedure, the authors performed a displacement-based calibration using the piezo-resistive ref. cantilever as a stiffness ref. artifact. The method demonstrated agreement ∼7% with the direct force methods, with the difference attributed to an expected systematic uncertainty, caused by in-plane deflection in the cantilever during loading. The comparison establishes the existing limits of instrument accuracy and sets down a basis for selection criteria for materials and methods in colloidal probe friction (lateral) force measurements via at. force microscopy.
- 40Schaufele, F.; Demarco, I.; Day, R. N. Molecular Imaging; Elsevier Inc., 2005; pp 72– 94.There is no corresponding record for this reference.
- 41Hammer, N. I.; Emrick, T.; Barnes, M. D. Quantum Dots Coordinated With Conjugated Organic Ligands: New Nanomaterials With Novel Photophysics. Nanoscale Res. Lett. 2007, 2, 282– 290, DOI: 10.1007/s11671-007-9062-841https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXpslegsbo%253D&md5=3b2209692022bcbdc09fe576089ef922Quantum dots coordinated with conjugated organic ligands: new nanomaterials with novel photophysicsHammer, Nathan I.; Emrick, Todd; Barnes, Michael D.Nanoscale Research Letters (2007), 2 (6), 282-290CODEN: NRLAAD; ISSN:1556-276X. (Springer)A review. CdSe quantum dots functionalized with oligo-(phenylene vinylene) (OPV) ligands (CdSe-OPV nanostructures) represent a new class of composite nanomaterials with significantly modified photophysics relative to bulk blends or isolated components. Singlemol. spectroscopy on these species have revealed novel photophysics such as enhanced energy transfer, spectral stability, and strongly modified excited state lifetimes and blinking statistics. Here, we review the role of ligands in quantum dot applications and summarize some of our recent efforts probing energy and charge transfer in hybrid CdSe-OPV composite nanostructures.
- 42Bae, W. K.; Padilha, L. A.; Park, Y.-S.; McDaniel, H.; Robel, I.; Pietryga, J. M.; Klimov, V. I. Controlled Alloying of the Core–Shell Interface in CdSe/CdS Quantum Dots for Suppression of Auger Recombination. ACS Nano 2013, 7, 3411– 3419, DOI: 10.1021/nn400282542https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC3sXksVyhs70%253D&md5=de3c777c4d29ce406a4b3ed5411661a5Controlled Alloying of the Core-Shell Interface in CdSe/CdS Quantum Dots for Suppression of Auger RecombinationBae, Wan Ki; Padilha, Lazaro A.; Park, Young-Shin; McDaniel, Hunter; Robel, Istvan; Pietryga, Jeffrey M.; Klimov, Victor I.ACS Nano (2013), 7 (4), 3411-3419CODEN: ANCAC3; ISSN:1936-0851. (American Chemical Society)The influence of a CdSexS1-x interfacial alloyed layer on the photophys. properties of core/shell CdSe/CdS nanocrystal quantum dots (QDs) is investigated by comparing ref. QDs with a sharp core/shell interface to alloyed structures with an intermediate CdSexS1-x layer at the core/shell interface. To fully realize the structural contrast, we have developed two novel synthetic approaches: a method for fast CdS-shell growth, which results in an abrupt core/shell boundary (no intentional or unintentional alloying), and a method for depositing a CdSexS1-x alloy layer of controlled compn. onto the CdSe core prior to the growth of the CdS shell. Both types of QDs possess similar size-dependent single-exciton properties (photoluminescence energy, quantum yield, and decay lifetime). However the alloyed QDs show a significantly longer biexciton lifetime and up to a 3-fold increase in the biexciton emission efficiency compared to the ref. samples. These results provide direct evidence that the structure of the QD interface has a significant effect on the rate of nonradiative Auger recombination, which dominates biexciton decay. We also observe that the energy gradient at the core-shell interface introduced by the alloyed layer accelerates hole trapping from the shell to the core states, which results in suppression of shell emission. This comparative study offers practical guidelines for controlling multicarrier Auger recombination without a significant effect on either spectral or dynamical properties of single excitons. The proposed strategy should be applicable to QDs of a variety of compns. (including, e.g., IR-emitting QDs) and can benefit numerous applications from light emitting diodes and lasers to photodetectors and photovoltaics.
- 43Selopal, G. S.; Zhao, H.; Liu, G.; Zhang, H.; Tong, X.; Wang, K.; Tang, J.; Sun, X.; Sun, S.; Vidal, F.; Wang, Y.; Wang, Z. M.; Rosei, F. Interfacial Engineering in Colloidal “Giant” Quantum Dots for High-Performance Photovoltaics. Nano Energy 2019, 55, 377– 388, DOI: 10.1016/j.nanoen.2018.11.00143https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXit1Cht7nL&md5=ede06a7227b1f2534fb76181df967999Interfacial engineering in colloidal "giant" quantum dots for high-performance photovoltaicsSelopal, Gurpreet S.; Zhao, Haiguang; Liu, Guiju; Zhang, Hui; Tong, Xin; Wang, Kanghong; Tang, Jie; Sun, Xuhui; Sun, Shuhui; Vidal, Francois; Wang, Yiqian; Wang, Zhiming M.; Rosei, FedericoNano Energy (2019), 55 (), 377-388CODEN: NEANCA; ISSN:2211-2855. (Elsevier Ltd.)Colloidal quantum dots (QDs) are semiconductor nanocrystals which exhibit discrete energy levels. They are promising building blocks for optoelectronic devices, thanks to their tunable band structure. Here, we explore a nanoengineering approach to highlight the influence of an alloyed interface on the optical and electronic properties of CdSe/(CdS)6 "giant" core/shell (CS) QDs by introducing CdSexS1-x interfacial layers between core and shell. By incorporating of CdSexS1-x interfacial layers, CdSe/(CdSexS1-x)4/(CdS)2 (x = 0.5) core/shell (CSA1) QDs exhibit a broader absorption response towards longer wavelength and higher electron-hole transfer rate due to favorable electronic band alignment with respect to CS QDs, as confirmed by optical absorption, photoluminescence (PL) and transient fluorescence spectroscopic measurements. In addn., simulations of spatial probability distributions show that the interface layer enhances electron-hole spatial overlap. As a result, CSA1 QDs sensitized solar cells (QDSCs) yield a max. photoconversion efficiency (PCE) of 5.52%, which is 79% higher than QDSCs based on ref. CS QDs. To fully demonstrate the structural interface engineering approach, the CdSexS1-x interfacial layers were further engineered by tailoring the selenium (Se) and sulfur (S) molar ratios during in situ growth of each interfacial layer. This graded alloyed CdSe/(CdSexS1-x)5/(CdS)1 (x = 0.9-0.1) core/shell (CSA2) QDs show a further broadening of the absorption spectrum, higher carrier transport rate and modified confinement potential with respect to CSA1 QDs as well as ref. CS QDs, yielding a PCE of 7.14%. Our findings define a promising approach to improve the performance of QDSCs and other optoelectronic devices based on CS QDs.
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Graphical animation of the optical spectra changing along the mechanical stress–strain curve (AVI)
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