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Colloidal Crystals of NaYF <sub/>4</sub> Upconversion Nanocrystals Studied by Small-Angle X-Ray Scattering (SAXS)
摘要： Spherical NaYF4 upconversion nanocrystals with mean radii of about 5 and 11 nm are observed to form colloidal crystals, i.e., 3D assemblies of the particles with long-range order. The colloidal crystals of the larger particles form directly in solution when dispersions of the particles in toluene are stored at room temperature for several weeks. Crystallization of the smaller particles takes place when their dispersions in hexane are slowly dried at elevated temperatures. The formation and the structure of the colloidal crystals are studied by small-angle X-ray scattering (SAXS). SAXS measurements show that the smaller as well as the larger particles assemble into a face-centered cubic lattice with unit cell dimensions of a = 18.7 nm and a = 35.5 nm, respectively. The SAXS data also show that the particles in the colloidal crystals still bear a layer of oleic acid on their surfaces. The thickness of this layer is 1.5–1.8 nm, as determined by comparing the unit cell dimensions of the colloidal crystals with the mean particle sizes. The latter could be very precisely determined from the distinct oscillations observed in the SAXS data of dilute colloidal dispersions of the nanocrystals.
关键词： upconversion,colloidal crystals,nanocrystals,small-angle X-ray scattering
更新于2025-09-09 09:28:46
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P-6.11: Sensor Technology - A new chance for low generation TFT production line
摘要： We analyzed several sensor technology which have good compatibility with current TFF process, including Digital X-Ray Detector, Glass-substrate Pressure Sensor, Glass-substrate Memory, Glass-substrate Antenna and Glass-substrate MEMS Devices. The above offers some directions for low generation TFT production line’s transition.
关键词： Glass-substrate Memory,Digital X-Ray Detector,Glass-substrate MEMS Devices,Glass-substrate Pressure Sensor,Glass-substrate Antenna
更新于2025-09-09 09:28:46
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Development of an ultra-fast photomultiplier tube for gamma-ray Cherenkov detectors at the National Ignition Facility (PD-PMT)
摘要： A new ultra-fast photomultiplier tube and associated drivers have been developed for use in the next generation of gamma-ray high pressure gas Cherenkov detectors for inertial con?nement fusion experiments at the National Ignition Facility. Pulse-dilation technology has been applied to a standard micro-channel-plate-based photomultiplier tube to improve the temporal response by about 10×. The tube has been packaged suitably for deployment on the National Ignition Facility, and remote electronics have been designed to deliver the required non-linear waveforms to the pulse dilation electrode. This is achieved with an avalanche pulse generator system capable of generating fast arbitrary waveforms over the useful parameter space. The pulse is delivered via fast impedance-matching transformers and isolators, allowing the cathode to be ramped on a sub-nanosecond time scale between two high voltages in a controlled non-linear manner. This results in near linear pulse dilation over several ns. The device has a built-in ?ducial system that allows easy calibration and testing with ?ber optic laser sources. Results are presented demonstrating the greatly improved response time and other parameters of the device.
关键词： inertial con?nement fusion,gamma-ray Cherenkov detectors,National Ignition Facility,ultra-fast photomultiplier tube,pulse-dilation technology
更新于2025-09-09 09:28:46
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Experimental determination of reference pulses for highly segmented HPGe detectors and application to Pulse Shape Analysis used in $\gamma$γ-ray tracking arrays
摘要： For the first time, bases of signals delivered by highly segmented HPGe detectors, for identified hit locations, have been determined in situ, that is in the actual accelerator-target-detection system conditions corresponding to data acquisition during a physics experiment. As a consequence, these bases include all the genuine features and alterations of the signals induced by the experimental setup, e.g. diaphony, electronic response, specificity of individual crystals. The present pulse shape bases were constructed using calibration source data taken at the beginning of the AGATA campaign at GANIL. An experiment performed at GANIL using the AGATA γ-ray detector together with the VAMOS spectrometer was used to validate the bases. The performance of the bases when used for pulse-shape analysis has been compared to the performance of the standard bases, composed of pulse shapes generated by a computer simulation used for AGATA. This is done by comparing the Doppler correction capability. The so-called Jacobian method used to generate the in situ bases also produces correlations that can be applied to locate in a direct way (no search algorithm) the location where a γ-ray interacted given that only one segment is hit. As about 50% of all pulse-shape analysis is performed on crystals with only one segment hit this will allow for a large reduction in the needed computer power. Different ways to improve the results of this prospective work are discussed.
关键词： HPGe detectors,Doppler correction,γ-ray tracking arrays,VAMOS spectrometer,Pulse Shape Analysis,AGATA
更新于2025-09-09 09:28:46
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Selenization of (Cu, In, Ga)/Se/Mo/Glass Thin Films: A Real-Time Synchrotron X-ray Scattering Study
摘要： The precursor selenization of (Cu, In, Ga)/Se/Mo/glass thin films during annealing without additional supply of Se was studied through a real-time synchrotron X-ray scattering experiment. At a lower temperature, the crystalline CIS, Cu2In, In2Se3, and Ga2Se3 phases were formed. By increasing the temperature, some parts of the crystalline CIS phase decomposed into Cu2In and In2Se3 phases. At a higher temperature, the crystalline CIGS phase was synthesized gradually by the reaction of the crystalline Cu2In, In2Se3, and Ga2Se3 phases, and not by direct crystallization of the amorphous precursor. The behavior of the integrated intensities and the crystal domain sizes were consistent with the changes in X-ray powder diffraction profiles. The high synthesis temperature in the CIGS phase was attributed to the high activation energy barrier for diffusion of Ga ions in the crystalline Ga2Se3 phase.
关键词： Real-Time Synchrotron X-ray Scattering,Synthesis of the CIGS Phase,Selenization During Annealing,(Cu, In, Ga)/Se/Mo/Glass Thin Films
更新于2025-09-09 09:28:46
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Particle size effect on the dielectric properties of ZnO nanoparticles
摘要： Zinc oxide (ZnO) nanoparticles with di?erent particle sizes were synthesized by thermal annealing T A of zinc hydroxide at various temperatures. X-ray di?raction measurements show that all nanoparticles possess a typical wurtzite structure and no other impurity phases are observed. The average particle size (d ) increases from 22 to 98 nm as T A increases from 100 to 850?C. The dielectric properties of nanocrystalline ZnO with various particle sizes were studied in the frequency range of 20 Hz to 1 MHz between 80 K and 320 K. Dielectric measurement indicates that the particle size of samples has great in?uence on the dielectric behavior of ZnO nanoparticles. The M ” curves show strong grain peaks in all ZnO nanoparticles, whereas only 22 nm and 98 nm particles show weak grain boundary peaks. In addition, the ac conductivity (σac) follows Jonscher,s power law for all ZnO nanoparticles, but two types of conduction mechanisms were observed. It is concluded that the σac behavior of 22-nm particles is well accounted by the correlated-barrier-hopping model (CBH), whereas the d >22-nm particles behavior is probably due to Quantum Tunneling Mechanism (QMT). The di?erent σac behavior can be attributed to the various defects in grain boundary and formation of inhomogeneous dielectric structures.
关键词： A. Oxide materials,C. Grain boundaries,B. Precipitation,D. X-ray di?raction,C. Dielectric response,A. Semiconductors
更新于2025-09-09 09:28:46
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Effect of CsI(Tl) micro-conical-frustums on the performance of the pixelated CsI(Tl) scintillation screen in X-ray imaging
摘要： The pixelated CsI(Tl) scintillation screen based on oxidized silicon micro-pore array template with CsI(Tl) micro-conical-frustums (CMCF) was proposed. The effect of the CMCF on the performance of the pixelated CsI(Tl) scintillation screen in X-ray imaging was studied by using Geant4 Monte Carlo simulation code. The variations of the light output (LO), modulation transfer function (MTF) and detective quantum efficiency (DQE) for the screen with the cone angle β of the CMCF in X-ray imaging were revealed. The results show that the LO of the pixelated scintillation screen with CMCF is superior to that of the screens with CsI(Tl) micro-cylinders (CMC) or with reversed CsI(Tl) micro-conical-frustums (RCMCF), but the spatial resolution of the X-ray imaging system by using the pixelated scintillation screen with RCMCF is better than that by using the screens with CMCF or with CMC. At low frequency, the cone angle β corresponding to DQEs from good to bad are 2.40°, 0.00° and -2.40°. But at high frequency, the cone angle β corresponding to DQEs from good to bad change to 2.40°, -2.40° and 0.00°. The reason is that, for a pixelated scintillation screen, the DQE for the screen not only depends on the efficiency of X-ray absorption, but also depends on the number of scintillation photons exiting the bottom the screen per interacting X-ray photon and its Poisson excess, and MTF. The simulated results of DQEs show that the comprehensive performance of the pixelated CsI(Tl) screen with CMCF in X-ray imaging is better than that of the screens with CMC or with CRMCF.
关键词： Shape of CsI(Tl) micro-conical-frustum,Performance in X-ray imaging,Oxidized silicon micro-pore array template,Pixelated CsI(Tl) scintillation screen
更新于2025-09-09 09:28:46
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Engineering the Palladium–WSe <sub/>2</sub> Interface Chemistry for Field Effect Transistors with High Performance Hole Contacts
摘要： Palladium has been widely employed as a hole contact to WSe2 and has enabled, at times, the highest WSe2 transistor performance. However, there are orders of magnitude variation across the literature in Pd–WSe2 contact resistance and ION/IOFF ratios with no true understanding of how to consistently achieve high–performance contacts. In this work, WSe2 transistors with impressive ION/IOFF ratios of 106 and Pd–WSe2 Schottky diodes with near–zero variability are demonstrated utilizing Ohmic–like Pd contacts through deliberate control of the interface chemistry. The increased concentration of a PdSex intermetallic is correlated with an Ohmic band alignment and concomitant defect passivation, which further reduces the contact resistance, variability, and barrier height inhomogeneity. The lowest contact resistance occurs when a 60 minute post metallization anneal at 400 °C in forming gas (FG) is performed. X-ray photoelectron spectroscopy indicates this FG anneal produces 3× the concentration of PdSex and an Ohmic band alignment, in contrast to that detected after annealing in ultra–high vacuum, during which a 0.2 eV hole Schottky barrier forms. Raman spectroscopy and scanning transmission electron microscopy highlight the necessity of the fabrication step to achieve high–performance contacts as no PdSex forms and WSe2 is unperturbed by room temperature Pd deposition. However, at least one WSe2 layer is consumed by the necessary interface reactions that form PdSex requiring strategic exploitation of a sacrificial WSe2 layer during device fabrication. The interface chemistry and structural properties are correlated with Pd–WSe2 diode and transistor performance and the recommended processing steps are provided to enable reliable high–performance contact formation.
关键词： annealing,palladium,WSe2,interface chemistry,X-ray photoelectron spectroscopy,transistor,metal contact
更新于2025-09-09 09:28:46
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Mathematical Modeling of Droplet Formation, Evaporation, and Film Growth to Study Crystallite Size and Film Thickness of Spray Pyrolysis Deposited TiO<sub>2</sub> Thin Films
摘要： The pure TiO2 thin films were successfully deposited onto a glass substrate by using modified spray pyrolysis system. The TiO2 thin films were deposited at temperature 350?C using Titanium trichloride precursor solutions of concentration 0.075 M, 0.1 M, and 0.125 M. Also, TiO2 thin films with precursor solutions of concentration 0.1 M were deposited at different deposition temperature 350?C, 400?C, and 450?C. The prepared samples were further annealed at 500?C for 2 h to improve crystallinity. The XRD study revealed that the deposited TiO2 thin films were polycrystalline and showed anatase phase with pre-dominant (101) peak. The crystallite size calculated from XRD was found to increase with increase in precursor solution concentration. The mathematical model to calculate crystallite size and film thickness were developed and the predicted results were compared with experimental results. The experimentally calculated crystallite size and thickness was in good agreement with the predicted results. The details of mathematical model and calculations TiO2 thin films for were discussed in detail.
关键词： Growth,Liquid phase epitaxy,Crystallization,Titanium oxide,X-ray diffraction,Semiconducting films
更新于2025-09-09 09:28:46
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Linear and Third Order Non-Linear Optical Properties of Urea Salicylic Acid Crystal
摘要： An organic non-linear optical crystal urea salicylic acid was grown by slow evaporation method using the mixed solvent of ethanol and water in equal ratio. The lattice parameters of urea salicylic acid crystal were obtained by single X-ray diffraction study. The optical transmittance study revealed the good transmission window of the urea-salicylic acid and its suitability for optical applications. The non-linear refractive index, n2, absorption coefficient, β and third order susceptibility, χ(3) have been measured through the Z-scan technique with He-Ne laser at 632.8 nm. The grown urea salicylic acid crystal exhibits two photon absorption and self-defocussing performance.
关键词： Crystal growth,X-ray diffraction,Optical properties
更新于2025-09-09 09:28:46