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Numerical Analysis of Thermal Stress in Semi-Transparent Oxide Crystals Grown by Czochralski and EFG Methods
摘要： Crystal growth of oxides is generally difficult since large curvatures of the growth interface in these systems generate high thermal stress, dislocations and crystal cracking. Three-dimensional numerical modeling is applied to investigate thermal stress distribution in sapphire and langatate La3Ta0.5Ga5.5O14 (LGT) semi-transparent crystals grown by Czochralski (Cz) and Edge-defined Film-fed Growth (EFG) techniques. The analysis of thermal stress distribution in a sapphire ingot grown in a Czochralski furnace shows high von Mises stresses distributed almost symmetrically on large areas in the crystal. Thermal stress computations for piezoelectric langatate crystals grown in a Czochralski configuration show non-symmetrical von Mises distribution with higher stress on one side of the ingot. These numerical results are in agreement with experimental results showing non-symmetrical cracking at the outer surface of the crystal. 3D modeling of multi-die EFG growth of white sapphire ribbons shows that the von Mises stress is almost constant when the number of ribbons is increased from two to ten. Two models are applied to simulate the internal radiative heat transfer in the sapphire crystals: P1 approximation and the Rosseland radiation model. Numerical results show that applying Rosseland formula introduces significant errors in temperature field calculations especially in the case of the EFG configuration.
关键词： computer simulation,Czochralski,sapphire,single crystal growth,stresses
更新于2025-09-23 15:22:29
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[IEEE 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Kyoto, Japan (2018.7.9-2018.7.13)] 2018 31st International Vacuum Nanoelectronics Conference (IVNC) - Electron sources based on diamond pin-diodes
摘要： Efficient electron sources are of ongoing interest in particular for space and terrestrial power telecommunications and radar applications. With conventional cathode technology based on thermionic- and field electron emission a novel approach for direct electron emission is realized through a diamond pin diode. Electrons injected into the conduction band of the intrinsic layer of the diode can be released into vacuum with a negative electron affinity surface of the i-layer. The diamond pin diodes were prepared on boron doped (p-type) substrates with (111) surface orientation. A high purity intrinsic and a phosphorus doped diamond layer (n-type, ~400nm thickness) were deposited in dedicated PECVD systems, respectively. An additional contact layer comprised of nanostructured carbon was grown in a dedicated PECVD. The layered device was processed by lithography utilizing an aluminum hard mask to etch mesa structures with diameters ranging from 50μm to 200μm. The final devices were treated in a pure hydrogen plasma to induce the negative electron affinity properties of the i-layer. After an annealing step in high vacuum individual pin diodes were biased in forward current and voltages up to 20V. The observation of light from the diode was attributed to the UV exciton state and indicated bipolar transport. At a diode current of about 80mA an electron emission current of 25μA was observed from a single 200μm diameter diode.
关键词： Diamond,solid state electronics,doping,phosphorus,electron emission,plasma-enhanced chemical vapor deposition,nanostructured carbon,pin diode,single crystal
更新于2025-09-23 15:21:21
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Designing Large Area Single Crystal Perovskite Solar Cells
摘要： Organic-inorganic halide single-crystal perovskite solar cells (PSCs) are promising for higher efficiency and better stability, while their development lags far behind polycrystalline counterpart. In particular, low efficiency (<5%) of large-area devices makes it challenging to be an alternative perovskite photovoltaic technology. In this perspective, we highlight the optimization of crystal growth and reduction of crystal thickness are keys to improve performance of the large-area single-crystal PSCs. After analyzing the characteristics of perovskite crystal growth methods and efficiency evolution of single-crystal PSCs, we conclude the low efficiency of large-area devices is due to conflict between low crystal quality and large crystal thickness. Then, we propose methods to grow high-quality perovskite single crystals and possible strategy to reduce the crystal thickness. Finally, investigation of key factors and exploration of large-area application are suggested to be conducted in parallel for future development of single-crystal PSCs.
关键词： large area,perovskite solar cells,single crystal,thickness reduction,crystal growth
更新于2025-09-23 15:21:01
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Phase formation and crystal growth of Ca <sub/>3</sub> TaAl <sub/>3</sub> Si <sub/>2</sub> O <sub/>14</sub> piezoelectric single crystal
摘要： Ca3TaAl3Si2O14 (CTAS) piezoelectric powders were sintered at various temperatures to investigate phase formation. The CTAS powder sintered at 1350 °C was composed of a main phase with a langasite-type structure in addition to two secondary phases, whereas the main phases of the CTAS powders sintered at 1200 and 1300 °C were the secondary phases in X-ray di?raction patterns. CTAS single crystals with a diameter of 1 in. were grown by a Czochralski method using the sintered powders, and CTAS single crystals without impurity phases could be grown using the powder sintered at 1350 °C. A higher sintering temperature of starting materials contributes to the creation of CTAS single crystals without impurity phases.
关键词： Ca3TaAl3Si2O14,piezoelectric,crystal growth,phase formation,single crystal
更新于2025-09-23 15:21:01
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Growth of high purity zone-refined Boron Carbide single crystals by Laser Diode Floating Zone method
摘要： We report the growth of 4 mm diameter x 50 mm long Boron Carbide (B4C) with large single crystal regions using a Laser Diode Floating Zone (LDFZ) method at varying growth rates of 5-20 mm/hr. These materials were grown using polycrystalline B4C as a seed. Microstructural characterization shows the presence of a significant number of twinning-boundaries along the growth direction ([001]h) oriented in the (1210)h plane. At faster growth rates >10 mm/hr, the crystal orientation was reproducible, suggesting a twin-plane mediated growth mechanism. On the contrary, at slower growth rates <10 mm/hr the crystal orientation was not reproducible, suggesting a critical rate for twin-plane mediated growth to dominate. Zone refinement of these crystals led to a significant reduction of trace impurities to better than 99.999 wt % purity, at the expense of increased twinning. Powder x-ray diffraction confirms that the bulk is rhombohedral B4C, consistent with the microstructural analysis. The X-ray reciprocal space maps reveal the growth direction to be close to the [001]h direction, and the corresponding ω-rocking curve width is ~530arcsec. The rocking curve consisted of 3 distinct peaks, indicating in-plane mosaicism, consistent with the twinning observed. Berkovich nano-indentation of the key (001)h plane showed 41 ± 1 GPa hardness, with a Young’s modulus of 520 ± 14 GPa, comparable to literature reports.
关键词： A2. Single crystal growth,A1. Defects,A1. X-ray diffraction,A1. Characterization,A2. Growth from melt
更新于2025-09-23 15:21:01
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Temperature dependence of scintillation responses in rare-earth-ions-doped LiCaAlF6 single crystals
摘要： We have tested high-temperature responses of prototype neutron detectors equipping Ce-doped lithium silicate glass (GS20), LiCaAlF6:Ce, LiCaAlF6:Eu, LiCaAlF6:Ce, Na, and LiCaAlF6:Eu, Na. These detectors were prepared by coupling of the scintillators to a photomultiplier tube (PMT) for high-temperature environments (R1288, Hamamatsu). In the pulse height spectra under thermal neutron irradiation in the temperature range from 25°C to 150°C, peak heights of all the samples decreased with increasing temperatures. The decreasing rates for the peak heights of LiCaAlF6 scintillators were lower than that of GS20. The LiCaAlF6 scintillators can be used in the temperature range from 25°C to 150°C.
关键词： fluoride,scintillator,neutron,single crystal
更新于2025-09-23 15:21:01
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From 1D to 3D: Fabrication of CH <sub/>3</sub> NH <sub/>3</sub> PbI <sub/>3</sub> Perovskite Solar Cell Thin Films from (Pyrrolidinium)PbI <sub/>3</sub> via Organic Cation Exchange Approach
摘要： A new crystal form of one-dimentional (1D) perovskite (pyrrolidinium)PbI3 is synthesized and characterized. The 1D perovskite has a good film formability by solution spin coating, and can be in situ transformed to three-dimensional (3D) CH3NH3PbI3 via organic cation exchange approach under CH3NH2 atmosphere, which is dense and uniform. The converted 3D perovskite film is employed as a light absorber, and the corresponding perovskite solar cell shows a power conversion efficiency of up to 19.2% under simulated one-sun AM 1.5G illumination (100 mW cm-2).
关键词： three-dimensional,one-dimensional,perovskite,solar cell,single crystal
更新于2025-09-23 15:21:01
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Novel report on structural, optical and electrical investigation into brucinium 4-methyl-3-nitrobenzoate 0.5 hydrate single crystal: a promising material for high-power laser, ultrahigh cooling, sensor and detector applications
摘要： A new brucinium 4-methyl-3-nitrobenzoate 0.5 hydrate (B4M3NB0.5H) NLO single crystal was harvested from saturated solution by solvent evaporation method. Crystal system and symmetric type of B4M3NB0.5H compound were analyzed by structure analysis. Linear optical parameters of title compound were discussed in detail by UV–visible analysis. Lifetime values of the molecule were quanti?ed by ?uorescence study, and it con?rms the good crystalline perfection of the grown crystal. The SHG ef?ciency is 5.11 times superior to the KDP material. By utilizing Nd:YAG laser as an input, SLDT measurement of the crystal was done. The grown crystal has good crystalline nature which is analyzed by HRXRD study. Dielectric behavior of B4M3NB0.5H crystal was discussed in detail. With the help of theoretical approach, few of the solid-state parameters were calculated and listed. Piezoelectric charge coef?cient and piezovoltage were calculated to be 4.5 p C/N and 0.0417 p V m/N, respectively. The TGA and DTA spectrum con?rms that the title compound is thermally stable up to 101 °C.
关键词： piezoelectric charge coefficient,brucinium 4-methyl-3-nitrobenzoate,fluorescence study,solvent evaporation method,SHG efficiency,HRXRD study,NLO single crystal,Nd:YAG laser,dielectric behavior,UV–visible analysis,TGA and DTA spectrum
更新于2025-09-23 15:21:01
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72.3 W 1064 nm Nd:YAG Single Crystal Fiber Laser and Intracavity Double Frequency Generation
摘要： As a bridge between crystal and fiber, the single crystal fiber (SCF) can combine the advantages of the two materials and show great potential in high-power lasers. In this paper, we select a Nd:YAG SCF as the gain medium in a diode-end-pumped linear cavity. The Nd:YAG SCF with the dimensions of ? = 1 mm × 50 mm was manufactured using the micro-pulling-down technique. At an incident pump power of 153.0 W, the maximum output power of the 1064 nm laser was 72.3 W. To the best of our knowledge, this is the highest power obtained in Nd:YAG SCF lasers. In addition, using a second-type phase-matched KTP crystal, the 10 W continuous wave green laser was obtained with an intracavity double-frequency structure.
关键词： single crystal fiber,high power,diode-end-pumped laser,double frequency
更新于2025-09-23 15:21:01
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Reactive ion etching of single crystal diamond by inductively coupled plasma: State of the art and catalog of recipes
摘要： Significant technology advances in the growth of single crystal diamond (SCD) have over the past decade led to commercial offerings of high quality SCD substrates, typically available in the form of well specified plates of several square millimeters in size [1]. At the same time, the cost of such plates has considerably decreased [2], which has triggered important research and development efforts aiming to exploit the exceptional optical [3], thermal [4] and mechanical properties [5] of SCD for a variety of applications in electronics [6], photonics [7–10], optics and opto-mechanics [11] and quantum technologies [12].
关键词： Single Crystal Diamond,State of the Art,Reactive Ion Etching,Catalog of Recipes,Inductively Coupled Plasma
更新于2025-09-23 15:21:01