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Thermally annealed wafer-scale h-BN films grown on sapphire substrate by molecular beam epitaxy
摘要： The effect of high temperature annealing (HTA) on crystalline quality improvement of h-BN films grown on sapphire substrates has been investigated. It is found that BN grown using conventional molecular beam epitaxy is disordered due to the growth temperature below 1000 °C. By annealing at a temperature of 1700 °C, thermodynamically stable crystalline h-BN could be obtained at wafer scale, where diffusion of atoms in the as-grown BN film is enhanced and the structural defect density decreases. The crystalline h-BN has been confirmed by x-ray diffraction, Raman scattering, and atomic force microscopy measurements. This work demonstrates that HTA is a simple and effective way to achieve wafer-scale crystalline h-BN films, which have numerous potential applications in next-generation two-dimensional devices and flexible III-nitride optoelectronic devices.
关键词： crystalline quality,molecular beam epitaxy,sapphire substrate,h-BN films,high temperature annealing
更新于2025-09-19 17:13:59
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Enhancing the performance of photovoltaic operating under harsh conditions using carbon-nanotube thermoelectric harvesters
摘要： This paper proposes a novel configuration for enhancing the efficiency of photovoltaics (PV) operating in high-temperature environment using a nano-thermoelectric carbon nanotube-based harvester attached to the backside of the solar cell (SC). The attached harvester will not only extract heat energy from the cell but will also convert this wasted heat energy into electrical energy. The proposed configuration has been fabricated and tested experimentally, where I–V measurements have been conducted. An overall enhancement in SC efficiency of 50%, with respect to reference cell, has been achieved using the proposed harvester. In addition, the harvester itself provided a power in the range of hundreds of microwatts that can be utilized in various low-power applications.
关键词： High-temperature environment,Thermoelectric harvester,Solar cell efficiency,Photovoltaics,Carbon nanotubes
更新于2025-09-19 17:13:59
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Thermal modelling and design of dynamically-controlled heater plates for high temperature processing of 300 mm wafers
摘要： The temperature uniformity of heater plates (HPs) should be sustained due to critical dimension uniformity and robust operation in high temperature processing of 300 mm wafers. It is very challenging to maintain the temperature uniformity of the HP despite the dynamic control of power inputs and temperatures. The packaged power terminals (PPTs) of the HPs may considerably affect their thermal reliability. Hence, the sophisticated thermal modellings and designs of the HPs and the PPTs are necessary. In this study, the finite element analysis (FEA) thermal models of the HP and the PPT were generated, experimentally validated, and employed for the analysis and the design. The influences of the heating element width, the heating element gap, and the zone gap on the thermal performance of the HP were investigated. The parametric influences of the substrate thickness on the thermal performance of the PPT were also explored. The results show that the effect of the heating element width on the temperature of the HP is almost negligible. The results have found that a sophisticated design of the heating elements may reduce the radial temperature difference of the HP by 56 % compared with the baseline case. The results suggest that the sophisticated design may enable both the simplified structure and the enhanced temperature uniformity of the HP.
关键词： Temperature uniformity,Packaged power terminal,High temperature processing,300 mm wafer,Heater plate
更新于2025-09-16 10:30:52
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High pressure and high temperature induced polymerization of C<sub>60</sub> quantum dots
摘要： We synthesized C60 quantum dots (QDs) with a uniform size by a modified ultrasonic process and studied its polymerization under high pressure and high temperature (HPHT). Raman spectroscopy showed that a phase assemblage of a dimer (D) phase (62 vol %) and one-dimensional chain with an orthorhombic (O) phase (38 vol %) was observed at 1.5 GPa and 300°C. At 2.0 GPa and 430°C, the proportion of the O phase increases to 46 vol %, while the corresponding D phase decreases to 54 vol %. Compared with bulk and nanosized C60, C60 QDs cannot easily form a high-dimensional polymeric structure. This fact is probably caused by the small particle size, orientation of the disordered structure of C60 QDs and the barrier of oxide function groups between C60 molecules. Our studies enhance understanding the polymerization behavior of low-dimension C60 nanomaterials under HPHT conditions.
关键词： high pressure and high temperature,C60 quantum dots,fullerene polymer
更新于2025-09-16 10:30:52
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Laser heating setup for diamond anvil cells for <i>in situ</i> synchrotron and in house high and ultra-high pressure studies
摘要： The diamond anvil cell (DAC) technique combined with laser heating is one of the major methods for studying materials at high pressure and high temperature conditions. In this work, we present a transferable double-sided laser heating setup for DACs with in situ temperature determination. The setup allows precise heating of samples inside a DAC at pressures above 200 GPa and could be combined with synchrotron beamline equipment. It can be applied to X-ray diffraction and X-ray transmission microscopy experiments. In the setup, we use high-magnification and low working distance infinity corrected laser focusing objectives that enable us to decrease the size of the laser beam to less than 5 μm and achieve the maximum optical magnification of 320 times. All optical components of the setup were chosen to minimize chromatic and spatial aberrations for accurate in situ temperature determination by multiwavelength spectroscopy in the 570–830 nm spectral range. Flexible design of our setup allows simple interchange of laser sources and focusing optics for application in different types of studies. The setup was successfully tested in house and at the high-pressure diffraction beamline ID15B at the European Synchrotron Radiation Facility. We demonstrate an example of application of the setup for the high pressure–high temperature powder diffraction study of PdH and X-ray transmission microscopy of platinum at 22(1) GPa as a novel method of melting detection in DACs.
关键词： high pressure,diamond anvil cell,X-ray transmission microscopy,X-ray diffraction,synchrotron,laser heating,high temperature
更新于2025-09-16 10:30:52
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In situ TEM observation of controlled growth of two-dimensional WS2 with vertically aligned layers and high-temperature stability
摘要： Layered transition metal dichalcogenides with vertically aligned morphology show great potentials in energy conversion and storage due to the high density of exposed edge sites which have enhanced electrochemical reactivity. In this letter, through in situ heating investigations in a transmission electron microscope, the controlled growth of vertically aligned WS2 with high-temperature stability has been achieved through the thermolysis of solid precursor K2WS4. It is found that the growth of vertically aligned WS2 layers employs hybrid growth modes, in which the growth of new WS2 slab is initiated at old ones from either the middle part or edge part. These vertically aligned WS2 layers show great stability at high temperature of 900°C. Our detailed investigations and theoretical calculations indicate that potassium element in the solid precursor plays a critical role in the growth and evolution of vertically aligned WS2. This method is also applicable to the controlled growth of vertically aligned MoS2 with high-temperature stability through the decomposition of K2MoS4. These findings pave a way for tailored design and fabrication of materials with optimized structure to achieve their superior properties.
关键词： Vertical growth,In situ,High-temperature stability,Transition metal dichalcogenides,TEM
更新于2025-09-16 10:30:52
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From bulk to porous GaN crystal: precise structural control and its application in ultraviolet photodetectors
摘要： Porous GaN has many unique merits, such as a large specific surface area, adjustable bandgap and excellent optical performance. Here, we develop a simple and effective method for preparing porous GaN single crystals through high temperature annealing. The effects of different annealing temperatures on the porous structure, crystal quality and optical properties of GaN are investigated. The relationship model of annealing temperatures, times and GaN porous structures is summarized. An ultraviolet (UV) photodetector based on porous GaN is fabricated. The effects of porous structures on the performance of the GaN UV photodetector are investigated for the first time. We found that the appropriate GaN porous structure can improve the performance of the photodetector. A possible performance enhancement mechanism has been proposed. Based on the high performance and simple fabrication process, porous GaN crystal can be an excellent candidate for UV photodetectors.
关键词： optical properties,crystal quality,UV photodetector,high temperature annealing,porous GaN
更新于2025-09-16 10:30:52
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Versitile X-ray diagnostics of laser-produced high-temperature plasmas using an ultra-high luminosity spectrometer
摘要： Versitile diagnostics of high-temperature magnesium laser-produced plasmas is performed using an ultra-high luminosity X-ray focusing crystal spectrometer. The plasmas are produced by focusing nanosecond laser pulses (0.53 mm, 1 J, 2 ns) on a massive magnesium target. The absolute intensities and X-ray yields are measured for the resonance lines of H- and He-like ions (spectral range: D?l = 8 –10 ?), the electron temperature of plasmas is determined (range: Te = 200 – 550 eV), and the behaviour of these parameters is established in a broad range of laser pulse energy EL (10 mJ – 1 J). This approach permits the parameters of laser-plasma radiation sources to be monitored in real time in a wide intensity range (difference in intensity: over 104) and in a broad range of plasma parameters.
关键词： laser-produced plasmas,X-ray spectrometers,high-temperature plasma diagnostics,X-ray spectroscopy and metrology,multiply charged ions
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Design and simulation of etched physical structure fiber Bragg grating for fabricating high temperature sensors
摘要： Side-polishing single-mode fiber (SP-SMF) to the D-fiber and etch the physical structure Grating into the polishing flat surface. The simulation results of SP-SMF by COMSOL software show that the electric field contour lines at the air-cladding interface is continuous when the fiber cladding is polished to closer the core. Using Rsoft software to simulate the side-polished and etched fiber Bragg grating（SP-EFBG） and obtained the structural parameters of SP-EFBG, when the grating period and grating length and grating depth of the simulated SP-EFBG are 775nm and 10000μm and 150nm respectively, obtain the central wavelength and bandwidth and peak reflectivity is 1550nm and 0.2044nm and 90.79% respectively.
关键词： Rsoft Simulation,Side-polished fiber Bragg grating,High-temperature,COMSOL Simulation,Etched fiber Bragg grating
更新于2025-09-16 10:30:52
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Radiation-resistant optical fiber Fabry-Perot interferometer used for high-temperature sensing
摘要： An optical fiber Fabry-Perot interferometer based on sapphire wafer for high-temperature sensing under Co-60 γ irradiation is designed. The sensing probe is composed by a thin sapphire wafer and a pure silica multi-mode fiber. In the experiment, the interferometer is exposed under the Co-60 γ irradiation with different irradiation time and absorbed dose rate. The irradiated optical fiber sensor underwent three temperature cycle tests up to 800°C and demonstrated excellent sensing performance at high temperature. The whole sensing system has the capability to survive in high temperature environment that surpasses 800°C. The interferometer can achieve the high sensitivity of 29.9 pm/oC at the wavelength around 1340 nm when the temperature is 800°C. The proposed sensor and sensing system has great potential to be applied under strong irradiation and high temperature.
关键词： optical fiber sensor,high temperature,sapphire wafer,radiation,Fabry-Perot interferometer
更新于2025-09-16 10:30:52