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Dependence of h-BN film thickness as grown on nickel single crystal substrates of different orientation
摘要： Chemical vapor deposition of 2D materials has been an active area of research in recent years because it is a scalable process for obtaining thin films that can be used to fabricate devices. The growth mechanism for hexagonal boron nitride (h-BN) on metal catalyst substrates has been described to be either surface energy driven or diffusion driven. In this work, h-BN is grown in a CVD system on Ni single crystal substrates as a function of Ni crystallographic orientation to clarify the competing forces acting on the growth mechanism. We observed that the thickness of the h-BN film depends on the Ni substrate orientation, with the growth rate increasing from the (100) surface to the (111) surface, and the highest on the (110) surface. We associate the observed results with surface reactivity and diffusivity differences for different Ni orientations. Boron and nitrogen diffuse and precipitate from the Ni bulk to form thin multilayer h-BN. Our results serve to clarify the h-BN CVD growth mechanism which has been previously ascribed to a surface energy-driven growth mechanism.
关键词： surface diffusion,electron backscatter diffraction,growth mechanism,hexagonal boron nitride
更新于2025-09-23 15:21:01
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Influence of Oxygen Vacancy Behaviors in Cooling Process on Semiconductor Gas Sensors: A Numerical Analysis
摘要： The in?uence of oxygen vacancy behaviors during a cooling process in semiconductor gas sensors is discussed by the numerical analysis method based on the gradient-distributed oxygen vacancy model. A diffusion equation is established to describe the behaviors of oxygen vacancies, which follows the effects of diffusion and exclusion in the cooling process. Numerical analysis is introduced to ?nd the accurate solutions of the diffusion equation. The solutions illustrate the oxygen vacancy distribution pro?les, which are dependent on the cooling rate as well as the temperature interval of the cooling process. The gas-sensing characteristics of reduced resistance and response are calculated. Both of them, together with oxygen vacancy distribution, show the grain size effects and the re-annealing effect. It is found that the properties of gas sensors can be controlled or adjusted by the designed cooling process. The proposed model provides a possibility for sensor characteristics simulations, which may be bene?cial for the design of gas sensors. A quantitative interpretation on the gas-sensing mechanism of semiconductors has been contributed.
关键词： numerical analysis,oxygen vacancy,gas sensor,semiconductor,diffusion equation
更新于2025-09-23 15:21:01
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Influence of Film Morphology on Transient Photocurrent Pulse Shape in Organic Thin Films: A Monte Carlo Study
摘要： The in?uence of ?lm morphology on the broadening of the time-of-?ight transient photo-current pulse is investigated using Monte Carlo simulation. Simulation of the time-of-?ight transient photo-current pulse shape is carried out for homogeneous and inhomogeneous organic thin ?lms by varying the overall energetic disorder. In homogeneous system, the value of the tail broadening parameter (W) of the photocurrent pulse is found to decrease upon decreasing the energetic disorder, which can be attributed to the variation in the non-thermal ?eld assisted diffusion. Interestingly, in the case of inhomogeneous system, upon decreasing the overall energetic disorder of the system the value of W initially attains a maximum value before it starts decreasing. This observation is explained in terms of the morphology dependent carrier diffusion. This study asserts the importance of the in?uence of the morphology dependent carrier diffusion on the charge transport in disordered systems and the related experimental measurements.
关键词： Polycrystalline organic thin ?lms,Charge transport,Tail broadening,Diffusion,Time of ?ight photoconductivity,Film Morphology
更新于2025-09-23 15:21:01
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Prediction of recurrent glioblastoma after laser interstitial thermal therapy: The role of diffusion imaging
摘要： Background. Evaluate the utility of diffusion-weighted imaging (DWI) for the assessment of local recurrence of glioblastoma (GBM) on imaging performed 24?h following MRI-guided laser interstitial thermal therapy (LITT). We hypothesize that microscopic peritumoral infiltration correlates with early subtle variations on DWI images and apparent diffusion coefficient (ADC) maps. Methods. Of 64 patients with GBM treated with LITT, 39 had MRI scans within 24?h after undergoing LITT. Patterns on DWI images and ADC maps 24?h following LITT were correlated with areas of future GBM recurrence identified through coregistration of subsequent MRI examinations. In the areas of suspected recurrence within the periphery of post-LITT lesions, signal intensity values on ADC maps were recorded and compared with the remaining peritumoral ring. Results. Thirty-nine patients with GBM met the inclusion criteria. For predicting recurrent GBM, areas of decreased DWI signal and increased signal on ADC maps within the expected peritumoral ring of restricted diffusion identified 24? h following LITT showed 86.1% sensitivity, 75.2% specificity, and high correlation (r? =? 0.53) with future areas of GBM recurrence (P < .01). Areas of future recurrence demonstrated a 37% increase in the ADC value (P < .001), compared with findings in the surrounding treated peritumoral region. A?significantly greater area under the receiver operating characteristics curve was determined for ADC values (P < .01). Conclusions. DWI obtained 24?h following LITT can help predict the location of GBM recurrence months before the development of abnormal enhancement. This may alter future treatment planning, perhaps suggesting areas that may be targeted for additional therapy.
关键词： apparent diffusion coefficient,MRI-guided laser interstitial thermal therapy,laser interstitial thermal therapy,diffusion-weighted image,glioblastoma
更新于2025-09-23 15:19:57
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Diffusion and Kinetica??Controlled Electrochemical Reactions for Improving the Performance of Solutiona??based Electrochemiluminescence Devices
摘要： Electrochemiluminescence (ECL) refers to the generation of light at an excited state owing to an electron transfer reaction between the electrochemically generated species located around the electrode. The ECL controlled by varying the potential has attracted attention for application in various fields, such as chemical analysis, immunoassay, and optoelectronic devices. Among them, ECL devices (ECLDs) have recently been considered as promising next-generation displays due to their low energy consumption, simple fabrication process, and ability to function in direct current (DC) and alternating current (AC). Most ECLDs have a single active layer, in which the ECL luminophore and electrolyte are mixed between two electrodes, acting as the anode and the cathode in a sandwich-type ECLD. Thus, the working mechanism of ECLDs differs from those of conventional light-emitting diodes (LEDs). This is due to the electrochemical system driven by the mass transfer of the mobile counter ions and luminophore present in the active layer. When external force such as current or voltage is applied to the ECLDs, the electrolyte ions acting as the mobile counter ions is redistributed to each electrode, after which the electrochemical double layers (EDLs) form at the electrode/active layer interface, leading to the generating of a high electric field. As a result, the electron transfer reaction between the electrode and the ECL luminophore occurs effectively, and an electric circuit, through which a faradaic current flows, is formed. Consequently, the redox species encounter each other in the ECLDs to form an excited state through electron exchange, followed by a self-terminating ECL. The ECL is affected both by the electron transfer rate (ko) between the ECL luminophore and electrode and by the diffusion-limited reaction associated with the mass transfer of the ECL luminophore. These factors are determined by the operational method, and the type and concentration of the electrolyte. Although several studies related to this subject have been reported, the dynamics of the electrochemical reactions involving the ko and the diffusion-limited reactions in ECLDs have not been properly elucidated.
关键词： Diffusion-limited reaction,Redox species,Electrode transfer reaction,Electrochemical reaction,Electrochemiluminescence
更新于2025-09-23 15:19:57
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Measurement and Theoretical Interpretation of Exciton Diffusion as a Function of Intermolecular Separation for Squaraines Targeted for Bulk Heterojunction Solar Cells
摘要： The efficiency of bulk heterojunction (BHJ) organic photovoltaic (OPV) devices depends significantly upon absorption of photons and the migration of the photogenerated excited state to the heterojunction interface between the electron donor and electron acceptor. Within anilino-squaraine, molecules known for their successful use in the active layer of OPV devices, electronic aggregation strongly influences the absorption spectrum, energy transfer (EnT), and exciton migration to this heterojunction interface. Therefore, the long-range transition dipole coupling and the relative populations of the associated excited states dictate the general effectiveness of these materials in optoelectronic devices. This work presents subpicosecond transient absorption (TA) data that probe the excited-state photophysics of samples with a continuum of intermolecular separation, from monomers in solution to high-concentration solid solution thin films analogous to OPV active layers. EnT times are calculated for each squaraine concentration, and pump-power dependence provides evidence for significant EnT despite a high preponderance of H-aggregation. Theoretical modeling of essential states supports the interpretation from TA spectra that excited states relax into more tightly packed H-aggregates. This work prompts further questions regarding a far-reaching mechanistic EnT bottleneck for molecular and polymeric BHJ devices.
关键词： H-aggregation,squaraine,organic photovoltaic,bulk heterojunction,exciton diffusion,energy transfer
更新于2025-09-23 15:19:57
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AIP Conference Proceedings [AIP Publishing 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Fes, Morocco (25–27 March 2019)] 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Towards all screen printed back-contact back-junction silicon solar cells
摘要： We report recent progress in the adoption of an optimized screen-printable boron dopant material, which enables the cost-competitive fabrication of novel n-type silicon solar cells such as “nPERT” and “IBC” cells. We manufactured first “IBC” devices with an early version of our dopant material, a co-diffusion approach and evaporated electrodes, achieving an efficiency of 20.9 % in 2016. Since then we optimized the dopant material and co-diffusion processes, as reported in this work. These optimizations now enable a long-term printing of the dopant material, suited for mass production, while maintaining crucial performance parameters. Moreover, we demonstrate a co-diffusion setup with POCl3, which does not require any additional dopant sources and can instead be adjusted with a wet chemical etch back. Combined with new commercially available electrode pastes, which have been evaluated with regard to simultaneous contacting of n- and p-type dopings, all screen printed n-type solar cells become a mass market possibility in the near future.
关键词： screen-printable boron dopant material,co-diffusion,POCl3,electrode pastes,n-type silicon solar cells,wet chemical etch back
更新于2025-09-23 15:19:57
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The influence of electrode for electroluminescence devices based on all-inorganic halide perovskite CsPbBr<sub>3</sub>
摘要： Electroluminescence devices based all-inorganic halide perovskite material with the excellent luminescence performance have been studied extensively in recent years. However, the important role for the electrodes of electroluminescence devices is payed few attention by theoretical and experimental studies. Appropriate electrodes can reduce the Schottky barrier height to decrease the energy loss, and prevent the metal impurities from diffusing into the perovskite material to generate deep traps levels, which improves the luminous efficiency and lifetime of devices. In this paper, not only the interface effects between CsPbBr3 and common metal electrode (Ag, Au, Ni, Cu and Pt) are studied by first-principle calculations, but also the diffusion effects of metal electrode atom into the CsPbBr3 layer are also explored by nudged elastic band calculations. The calculated results show the metal Ag is more suitable for the cathode for CsPbBr3 electroluminescence devices, while the metal Pt is more applicable for the anode. Based on the overall consideration about the interface effects and diffusion effects of the CsPbBr3-metal electrode junctions, the essential principle provide a valuable reference how to select the suitable electrodes for other electroluminescence devices.
关键词： electroluminescence devices,diffusion effects,Schottky barrier height,CsPbBr3,all-inorganic halide perovskite,metal electrodes
更新于2025-09-23 15:19:57
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Extraction of the minority carrier transport properties of solar cells using the Hovel model and genetic algorithms
摘要： In this paper, a quick and accurate method for extraction of the minority carrier transport properties of p-n or n-p junction solar cells, such as diffusion lengths and surface recombination velocities, is presented. The knowledge of these parameters is essential to investigate factors that limit the performance of photovoltaic devices. The proposed method, based on genetic algorithms and the analytical Hovel model, is used to fit the external quantum efficiency (EQE) curves of solar cells with different emitter thicknesses. As a demonstrative example of application of the procedure carried out in this work, theoretical and experimental EQE curves of n-p GaAs solar cells under the standard AM1.5G spectrum have been used in order to extract the desired parameters. Errors less than 2.4% have been obtained, which shows the ability of the developed tool. An analysis of the total number of iterations is presented. Results obtained can be used to improve the design, optimization and manufacturing process of high efficiency photovoltaic devices.
关键词： diffusion length,surface recombination velocity,Hovel model and genetic algorithms,solar cells
更新于2025-09-23 15:19:57
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Development of laser speckle blood flowmeter for evaluating the physiological function of skin
摘要： Objective: We developed and demonstrated laser speckle ?owgraphy (LSFG) for two-dimensional (2D) skin blood ?ow (SBF) measurements to facilitate the noninvasive comparisons of SBF between individuals. Approach: By using morphing technology with a face mesh to compare SBF spatial distributions among individuals, we examined the practicability of SBF measurement with LSFG. Main results: (1) The uniformity of SBF measurement was demonstrated by examinations at different distances and angles for healthy subjects. (2) Mean blur rate (MBR)—a blood ?ow index of LSFG—exhibited signi?cant correlation with the thermal diffusion method (TDM)—an established blood ?ow measurement method—suggesting that MBR is an effective index of SBF. (3) Blowout time, the half-width duration/duration of one cardiac cycle, exhibited signi?cant negative correlation with age and positive correlation with stratum corneum hydration. Signi?cance: These results suggest that LSFG is useful for evaluating SBF-related skin properties, and it has signi?cant potential in medicine and cosmetology.
关键词： aging,stratum corneum hydration,skin blood ?ow,laser speckle ?owgraphy,morphing,strain-gauge plethysmography,thermal diffusion
更新于2025-09-23 15:19:57