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[IEEE 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Ottawa, ON, Canada (2019.7.8-2019.7.12)] 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Model Calibration of InGaAs/InP p-I-n Test Structures
摘要： Numerical calibration of InGaAs/InP double-heterostructure p-I-n junctions is performed at room temperature using guarded test structures of various areas and investigating the contributions from minority carrier diffusion, depletion region generation and finally perimeter (shunt) leakage. The perimeter leakage is determined to be 0.5 pA/cm, whereas the depletion region contributes 2.2 nA/cm2; the bulk diffusion contribution is excluded via the guard ring but can be computed analytically to be 2.0 nA/cm2. Reproducing the experimental test structures within the numerical modeling environment accurately reproduces the data based on calibrating the diffusion length and SRH lifetime.
关键词： dark current,III-V semiconductors,diffusion length,perimeter leakage,recombination
更新于2025-09-11 14:15:04
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Defect process and lithium diffusion in Li2TiO3
摘要： Lithium metatitanate, Li2TiO3, is a material that is being considered for the breeder blanket region of fusion reactors, and as a cathode material in lithium batteries. We employ atomistic simulations to study the point defect processes and lithium diffusion in Li2TiO3. It is calculated that the activation energy of migration of Li ions via the vacancy mechanism is 0.51 eV along the ab plane. The energetically favorable intrinsic defect type is Li Frenkel (1.25 eV/defect). This is important as the formation of Li vacancies is required as they act as vehicles for Li diffusion in the vacancy mechanism. The solution of trivalent dopants can contribute further Li vacancies, however, the synthesis routes should be determined experimentally.
关键词： Li diffusion,Li2TiO3,Defects,Dopants
更新于2025-09-11 14:15:04
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Multishot diffusion-prepared magnitude-stabilized balanced steady-state free precession sequence for distortion-free diffusion imaging
摘要： Purpose: To develop and evaluate a multishot diffusion‐prepared (DP) magnitude‐stabilized balanced steady‐state free precession (bSSFP) diffusion imaging sequence with improved geometric fidelity. Methods: A signal spoiler (magnitude stabilizer; MS) was implemented in a DP‐bSSFP diffusion sequence. Effects of magnitude stabilizers with respect to phase errors were simulated using Bloch simulation. Phantom study was conducted to compare the apparent diffusion coefficient (ADC) accuracy and geometric reliability, quantified using target registration error (TRE), with diffusion‐weighted single‐shot echo‐planar imaging (DW‐ssEPI). Six volunteers were recruited. DW‐ssEPI, DP‐bSSFP with and without ECG triggering, and DP‐MS‐bSSFP with and without ECG triggering were acquired 10 times with b = 500 s/mm2 in a single‐shot manner to evaluate magnitude variability. Diffusion trace images and diffusion tensor images were acquired using a 4‐shot DP‐MS‐bSSFP. Results: Simulation showed that the DP‐MS‐bSSFP approach is insensitive to phase errors. The DP‐MS‐bSSFP approach had satisfactory ADC accuracy on the phantom with <5% difference with DW‐ssEPI. The mean/max TRE for DW‐ssEPI was 2.31/4.29 mm and was 0.51/1.20 mm for DP‐MS‐bSSFP. In the repeated single‐shot study, DP‐bSSFP without ECG triggering had severe signal void artifacts and exhibited a nonrepeatable pattern, which can be partially mitigated by ECG triggering. Adding the MS provided stable signal magnitude across all repetitions. High‐quality ADC maps and color‐coded fractional anisotropy maps were generated using the 4‐shot DP‐MS‐bSSFP. The mean/max TRE was 2.89/10.80 mm for DW‐ssEPI and 0.59/1.69 mm for DP‐MS‐bSSFP. Good agreements of white matter ADC, cerebrospinal fluid ADC, and white matter fractional anisotropy value were observed between DP‐MS‐bSSFP and DW‐ssEPI. Conclusion: The proposed DP‐MS‐bSSFP approach provided high‐quality diffusion‐weighted and diffusion‐tensor images with minimal geometric distortion.
关键词： magnitude inconsistency,multishot diffusion,magnitude stabilizer,bSSFP,phase inconsistency,diffusion preparation
更新于2025-09-10 09:29:36
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A Depolarized Dynamic Light Scattering Method to Calculate Translational and Rotational Diffusion Coefficients of Nanorods
摘要： A new analysis of depolarized dynamic light scattering data is presented, which allows the unambiguous determination of rotational and translational diffusions coefficients of nanorods in suspension. By visualizing data scaling, purely translational diffusive motions can be isolated from vertically polarized scattering, allowing the unique determination of rotational diffusion from the depolarized scattering. The method is applied to nanorods with four different aspect ratios, and compared with theoretical predictions. Diffusion coefficients obtained show good agreement with calculations based on the direct measurements of rod length and diameter. Where the theories are shown to be valid, the method allows the measurement of statistically meaningful particle sizes and aspect ratios.
关键词： depolarized dynamic light scattering,gold nanorods,Brownian motion,translational diffusion,rotational diffusion
更新于2025-09-10 09:29:36
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Charge and thermal modeling of a semiconductor-based optical refrigerator
摘要： Despite multiple attempts to achieve optical refrigeration in very high (99.5%) external quantum efficiency (EQE) GaAs, no cooling has been observed to date. In this study, we investigate optical refrigeration in GaAs by numerically solving the transient drift-diffusion equation coupled to Poisson’s equation. The charge carrier distributions we obtain, together with the heat diffusion equation, allow us to observe the spatial and temporal evolution of cooling/heating within GaAs. Our results indicate that maximum cooling occurs at a laser intensity different from that which maximizes EQE. An 11-fold difference in intensity exists with a corresponding 6-fold difference in cooling power. We ultimately find that samples suspended in vacuum using a 250 lm SiO2 fiber cool to 88 K, starting from room temperature. These results emphasize the critical importance of choosing an appropriate laser excitation intensity to achieve optical refrigeration along with minimizing the conductive heat load on the refrigerator. Furthermore, results of this study are applicable towards analyzing the optical response of other optoelectronic systems where accurate charge and/or heat diffusion modeling is critical.
关键词： drift-diffusion equation,external quantum efficiency,Poisson’s equation,cooling power,optical refrigeration,heat diffusion equation,GaAs
更新于2025-09-10 09:29:36
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Inter-Diffusion of Iridium, Platinum, Palladium and Rhodium with Germanium
摘要： The down-scaling of nanoelectronic devices to ever smaller dimensions and greater performance has pushed silicon-based devices to their physical limits. Much effort is currently being invested in research to examine the feasibility of replacing Si by a higher mobility semiconductor, such as germanium, in niche high-performance metal oxide semiconductor (MOS) devices. Before Ge can be adopted in industry, a suitable contact material for the active areas of a transistor must be identified. It is proposed that platinum group metal (pgm) germanides be used for this purpose, in a similar manner as metal silicides are used in Si technology. Implementation of Ge-based technology requires a thorough understanding of the solid-state interactions in metal/Ge systems in order to foresee and avoid problems that may be encountered during integration. We present a systematic study of the solid-state interactions in germanide systems of four of the pgms: iridium, platinum, palladium and rhodium. Our approach was essentially twofold. Firstly, conventional thin film couples were used to study the sequence of phase formation in the germanide systems. Conventional thin film couples were also used to identify and monitor the dominant diffusing species during the formation of some of the germanides as these can influence the thermal stability of a device. Secondly, we observed and analysed several aspects of the lateral diffusion reactions in these four systems, including activation energies and diffusion mechanisms. Lateral diffusion couples were prepared by the deposition of thick rectangular islands of one material on to thin films of another material. Rutherford backscattering spectrometry (RBS) and microprobe-Rutherford backscattering spectrometry (μRBS) were used to analyse several aspects of the thin film and lateral diffusion interactions respectively. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were also employed.
关键词： nanoelectronic devices,solid-state interactions,germanium,platinum group metal germanides,lateral diffusion
更新于2025-09-10 09:29:36
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A New Analytical Charge Transfer Model for Time-of-Flight Image Sensors
摘要： A powerful tool for analyzing the performances of an image sensor designed for time-of-flight measurement purposes, the impulse response measurement (IRM), is presented. A way to measure the charges diffusion time (time for the photogenerated charges to be collected by the photodiode) using the analysis of an IRM is given. An unexpected phenomenon that occurs when performing a specific IRM is then showcased: performing two successive transfers, a short duration one followed by a long duration one is actually less efficient than performing a single transfer of long duration (same duration as the second transfer in the first case). Accordingly, a mathematical sufficient condition on the charge transfer efficiency function (CTEF) is enounced. A physical modeling based on thermionic emission theory and the influence of the potential barrier’s width on its effective height is presented. The model leads to a new CTEF expression that fulfills the mathematical requirement. Finally, a numerical simulation with the new CTEF fitting the experimental IRM data is performed.
关键词： time-of-flight (TOF),thermionic emission theory,Dirac-light pulse (DLP),diffusion time,impulse response measurement (IRM),Charge transfer efficiency function (CTEF),CMOS image sensor (CIS),light image detection and ranging (LIDAR),sense node (SN)
更新于2025-09-10 09:29:36
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Imaging the Microstructure of the Human Fetal Heart
摘要： Almost 50 years have elapsed since the seminal anatomic studies of Streeter et al1 showed that the fibers of the myocardium are arranged in a crossing helical pattern. During this time, numerous ex vivo studies of myocardial fiber architecture have been performed with magnetic resonance diffusion tensor imaging (DTI). In addition, recent advances in gradient strength and acceleration techniques now allow DTI of the entire heart to be performed in vivo.2,3 DTI also allows microstructural information to be integrated with magnetic resonance–derived metrics of myocardial strain, function, and viability.4–6
关键词： myocardium,magnetic resonance imaging,heart defects, congenital,heart,diffusion tensor imaging,Editorial
更新于2025-09-10 09:29:36
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Intermolecular Singlet Fission in Unsymmetrical Derivatives of Pentacene in Solution
摘要： Intermolecular singlet fission (SF) is an electronically coupled process between two chromophores, where distance dependences are decisive in terms of rates and yields. In the current work, a family of pentacene derivatives featuring different functional groups have been designed, synthesized, and probed with respect to intermolecular SF in the low, medium, and high concentration regimes rather than in the solid state. By means of advanced photophysical techniques, global analysis modeling, and ab initio calculations, a model for intermolecular SF is postulated. The model is based on an early key intermediate, which involves the diffusional encounter between one pentacene in its singlet excited-state with another one in its ground state and which features excimer characteristics. This is followed by a transformation into a coupled triplet excited-state. The role of the functional group appended to pentacene is analyzed with respect to steric shielding of the pentacene core as a means to prevent photophysical degradation, as well as control diffusional encounter and, subsequently, SF. The findings demonstrate the potential of new molecular materials for SF, especially in solution studies, as well as the challenges of implementing them in energy conversion schemes due to the appearance of photodegradation processes that compete with SF.
关键词： triplet diffusion,excitonic intermediates,singlet fission,unsymmetrical pentacene
更新于2025-09-10 09:29:36
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[IEEE 2018 24th International Conference on Pattern Recognition (ICPR) - Beijing, China (2018.8.20-2018.8.24)] 2018 24th International Conference on Pattern Recognition (ICPR) - A Novel ADCs-Based CNN Classification System for Precise Diagnosis of Prostate Cancer
摘要： This paper addresses the issue of early diagnosis of prostate cancer from diffusion-weighted magnetic resonance imaging (DWI) using a convolutional neural network (CNN) based computer-aided diagnosis (CAD) system. The proposed CNN-based CAD system first segments the prostate using a geometric deformable model. The evolution of this model is guided by a stochastic speed function that exploits first-and second-order appearance models besides shape prior. The fusion of these guiding criteria is accomplished using a nonnegative matrix factorization (NMF) model. Then, the apparent diffusion coefficients (ADCs) within the segmented prostate are calculated at each b-value. They are used as imaging markers for the blood diffusion of the scanned prostate. For the purpose of classification/diagnosis, a three dimensional CNN has been trained to extract the most discriminatory features of these ADC maps for distinguishing malignant from benign prostate tumors. The performance of the proposed CNN-based CAD system is evaluated using DWI datasets acquired from 45 patients (20 benign and 25 malignant) at seven different b-values. The acquisition of these DWI datasets is performed using two different scanners with different magnetic field strengths (1.5 Tesla and 3 Tesla). The conducted experiments on in-vivo data confirm that the use of ADCs makes the proposed system nonsensitive to the magnetic field strength.
关键词： Prostate Cancer,Convolutional Neural Networks,Apparent Diffusion Coefficients
更新于2025-09-10 09:29:36