Two strain-state samples of GaN, labelled the strain-relief sample and the quality-improved sample, were grown by hydride vapour phase epitaxy （HVPE）, and then characterized by high-resolution X-ray diffraction, pho...Two strain-state samples of GaN, labelled the strain-relief sample and the quality-improved sample, were grown by hydride vapour phase epitaxy （HVPE）, and then characterized by high-resolution X-ray diffraction, photoluminescence and optical microscopy. Two strain states of GaN in HVPE, like 3D and 2[） growth modes in metal-organic chemical vapour deposition （MOCVD）, provide an effective way to solve the heteroepitaxial problems of both strain relief and quality improvement. The gradual variation metbod （GVM）, developed based on the two strain states, is characterized by growth parameters＇ gradual variation alternating between the strain-relief growth conditions and the quality-improved growth conditions. In GVM, the introduction of the strain-relief amplitude, which is defined by the range from the quality-improved growth conditions to the strain-relief growth conditions, makes the strain-relief control concise and effective. The 300-μm thick bright and crack-free GaN film grown on a two-inch sapphire proves the effectiveness of GVM.展开更多
Thick GaN films were grown on the sapphire substrate by hydride vapour phase epitaxy. The properties of GaN films were found to be significantly influenced by the duration of exposing the sapphire substrate to ammonia...Thick GaN films were grown on the sapphire substrate by hydride vapour phase epitaxy. The properties of GaN films were found to be significantly influenced by the duration of exposing the sapphire substrate to ammonia prior to the GaN growth initiation. The crystalline quality of GaN films revealed by high resolution X-ray diffraction were strongly dependent on the nitridation time, which determined substrate surface topography. The different nitridation schemes strongly affected the morphology of GaN overlayers resulting in the blue shift of the main excitonic peak in photoluminescence spectra at room temperature.展开更多
The preparation of porous structure on the molecular beam epitaxy （MBE）-grown mixed-polarity GaN epilayers was reported by using the wet chemical etching method. The effect of this porous structure on the residual s...The preparation of porous structure on the molecular beam epitaxy （MBE）-grown mixed-polarity GaN epilayers was reported by using the wet chemical etching method. The effect of this porous structure on the residual stress of subsequent-growth GaN epilayers was studied by Raman and photoluminescence （PL） spectrum. Substantial decrease in the biaxial stresse can be achieved by employing the porous buffers in the hydride vapour phase epitaxy （HVPE） epilayer growth.展开更多
Boehmite was prepared under heat treatment in water vapour, and the phase transformation of gibbsite heat-treated at various temperatures was investigated. The sample was characterized by scanning electron microscopy(...Boehmite was prepared under heat treatment in water vapour, and the phase transformation of gibbsite heat-treated at various temperatures was investigated. The sample was characterized by scanning electron microscopy(SEM), X-ray diffraction (XRD), thermogravimetry and differential thermalanalysis (TG-DTA), fourier transform infrared (FTIR),and BET surface area.Effect of temperature on preparation was studied in the range of 155°–195°.With the increase in temperature, transformation of gibbsite into crystalline boehmites took place as indicated by the X-ray diffraction (XRD). The shape of the grains in the prepared sample was cube-like morphology.In water vapour gibbsite transform into boehmite by a dissolution - precipitation mechanism.展开更多
For the seventies, scientists focused their researches to find techniques to produce high quality films. One of the ideas, for example, was to generate an ionized cluster beam (ICB) formed by inert gas condensation (I...For the seventies, scientists focused their researches to find techniques to produce high quality films. One of the ideas, for example, was to generate an ionized cluster beam (ICB) formed by inert gas condensation (IGC) from evaporation of material. This method generates non-agglomerated nanoparticles to be deposited onto any substrate. However, the synthesis of spherical and well-dispersed nanoparticles remains, today, a major technological issue. Several trials have been performed with magnetron sputtering that has the advantage of producing very pure atomic vapour from a wide variety of solid materials or composites, and therefore in this configuration offers the possibility to synthesize nanoparticles in a gaz phase with potential numerous applications. In this paper, we describe several results of our laboratory and we show how it is possible to synthesize non-agglomerated nanoparticles with a narrow size distribution in the nm range. Detailed examples of Ag, TiO2, Au, Y, C, Co and Fe are given. We illustrate their current use in applications including catalyst to produce aligned Multi-Wall Carbon Nanotubes, seeding layer to promote anatase TiO2 crystallisation for photocatalytic material, superhydrophobic material and nanoparticle for nanomedecine.展开更多
Complex crystal aggregates from fluorspar vapor phase were grown at specific low-pressure/high-temperature conditions. The quasi-equilibrium of initiated crystal-chemical reactions at the proceeding vapour-crystal pha...Complex crystal aggregates from fluorspar vapor phase were grown at specific low-pressure/high-temperature conditions. The quasi-equilibrium of initiated crystal-chemical reactions at the proceeding vapour-crystal phase transformation was strongly dependent on the mass-transport inside an originally designed multicameral crucible, loaded by several portions of natural fluorite. By changing the temperature pressure over the already molten fluorspar portions as well as the gas-permeability of the channels connecting different sections in crucible interior to vacuum ambient, one may control the rate of gaseous-vapour diffusion and the degree of supper-saturation inside the peripheral crucible compartment wherein nucleation and crystal growing occurred. In this way, grown aggregates revealed a complicated habit formed during three-stage growing process provided by relevant thermodynamic and phase. Residual stresses were not observed in the aggregates whereas those in simultaneously grown boules from the non-vaporized melts in crucible cameras were clearly distinguished. The optical transmittance spectra of the boules were obtained considerably better, especially in the UV, comparing to those for crystal aggregates, both showing several peaks of specific light-absorption due to enhanced presence of rare-earth (RE) impurities. The aggregates manifest nearly full reflectivity from Vis to near IR region. The vapor phase growth mechanisms, when natural fluorite with some RE contents has been used, were explained on thermodynamic grounds that shown the manner of reliable control on the phenomenon. The results were anticipated to help for developing new perspective techniques for growth from vapor of several fluoride compounds with complex structure and composition and wide application. It was speculated that similar growth mechanisms of CaF2?crystals were possible on the moon in its very early period of formation.展开更多
This paper presents new experimental evidence of the PeTa effect—infrared characteristic radiation under first order phase transitions, especially the crystallization of melts and the deposition and condensation of v...This paper presents new experimental evidence of the PeTa effect—infrared characteristic radiation under first order phase transitions, especially the crystallization of melts and the deposition and condensation of vapours/gases. The PeTa effect describes the transient radiation that a particle (i.e., atom, molecule or/and cluster) emits transient radiation during a transition from a meta-stable higher energetic level (in a super-cooled melt or a super-saturated vapour) to the stable condensed lower level (in a crystal or a liquid). The radiation removes latent heat with photons of characteristic frequencies that are generated under this transition. The abbreviation “PeTa effect” means Perel’man-Tatartchenko’s effect.展开更多
This paper presents new experimental results concerning the PeTa effect—infrared characteristic radiation under first order phase transitions, especially during deposition and condensation of vapours/gases and the cr...This paper presents new experimental results concerning the PeTa effect—infrared characteristic radiation under first order phase transitions, especially during deposition and condensation of vapours/gases and the crystallisation of melts. The abbreviation “PeTa effect” means Perel’man-Tatartchenko’s effect. The nature of the PeTa effect is transient radiation that a particle (i.e., atom, molecule or/and cluster) emits during a transition from a meta-stable higher energetic level (in a super-cooled melt or super-saturated vapour) to the stable condensed lower level (in a crystal or liquid). The radiation removes latent heat with photons of characteristic frequencies that are generated under this transition. This paper is the second in a set describing the appearance of PeTa radiation under air cooling with deposition and condensation of air components. The radiation was recorded using an IR Fourier Spectrometer with a highly sensitive MCT detector. Certain peculiarities of the recorded radiation as well as its applications in the physics of the atmospheres of Earth and Jupiter are analysed.展开更多
Aim To study the relationship between the substrate temperature and the morphology and properties of GaN. Methods\ Applying the hydride chemical vapor deposition method, GaN films were deposited on different kinds of...Aim To study the relationship between the substrate temperature and the morphology and properties of GaN. Methods\ Applying the hydride chemical vapor deposition method, GaN films were deposited on different kinds of substrates, including sapphire, Si(111),Si(100),GaAs and GaP(111) both on the P face and the Ga face. The growth was performed at low temperatures of below 700℃. XRD, Hall measurement, cathodoluminescence (CL) and atomic force microscopy (AFM) were used to characterise the film properties. Results\ It was found that the temperature and the nature of substrate materials influence the layer morphology. Conclusion\ The analysis shows that no apparent relationship exists between the optical properties and layer morphology.展开更多
基金Project supported by the National Basic Research Program of China (Grant No.2007CB307004)the National High Technology Research and Development Program of China (Grant No.2009AA03A198)+1 种基金the National Natural Science Foundation of China (Grant Nos.60776041 61076012,60876063,and 60676032)the Science and Technology Fund of Beijing,China (Grant No.Z101103050410003)
文摘Two strain-state samples of GaN, labelled the strain-relief sample and the quality-improved sample, were grown by hydride vapour phase epitaxy （HVPE）, and then characterized by high-resolution X-ray diffraction, photoluminescence and optical microscopy. Two strain states of GaN in HVPE, like 3D and 2[） growth modes in metal-organic chemical vapour deposition （MOCVD）, provide an effective way to solve the heteroepitaxial problems of both strain relief and quality improvement. The gradual variation metbod （GVM）, developed based on the two strain states, is characterized by growth parameters＇ gradual variation alternating between the strain-relief growth conditions and the quality-improved growth conditions. In GVM, the introduction of the strain-relief amplitude, which is defined by the range from the quality-improved growth conditions to the strain-relief growth conditions, makes the strain-relief control concise and effective. The 300-μm thick bright and crack-free GaN film grown on a two-inch sapphire proves the effectiveness of GVM.
基金National"863"Project of China (2001AA311100 and 2002AA305304) Sino French Cooperation Project:CNRS/ASC Chine 2003 Project(14915)
文摘Thick GaN films were grown on the sapphire substrate by hydride vapour phase epitaxy. The properties of GaN films were found to be significantly influenced by the duration of exposing the sapphire substrate to ammonia prior to the GaN growth initiation. The crystalline quality of GaN films revealed by high resolution X-ray diffraction were strongly dependent on the nitridation time, which determined substrate surface topography. The different nitridation schemes strongly affected the morphology of GaN overlayers resulting in the blue shift of the main excitonic peak in photoluminescence spectra at room temperature.
基金supported by the National Natural Science Foundation of China under grant No.10574130.
文摘The preparation of porous structure on the molecular beam epitaxy （MBE）-grown mixed-polarity GaN epilayers was reported by using the wet chemical etching method. The effect of this porous structure on the residual stress of subsequent-growth GaN epilayers was studied by Raman and photoluminescence （PL） spectrum. Substantial decrease in the biaxial stresse can be achieved by employing the porous buffers in the hydride vapour phase epitaxy （HVPE） epilayer growth.
文摘Boehmite was prepared under heat treatment in water vapour, and the phase transformation of gibbsite heat-treated at various temperatures was investigated. The sample was characterized by scanning electron microscopy(SEM), X-ray diffraction (XRD), thermogravimetry and differential thermalanalysis (TG-DTA), fourier transform infrared (FTIR),and BET surface area.Effect of temperature on preparation was studied in the range of 155°–195°.With the increase in temperature, transformation of gibbsite into crystalline boehmites took place as indicated by the X-ray diffraction (XRD). The shape of the grains in the prepared sample was cube-like morphology.In water vapour gibbsite transform into boehmite by a dissolution - precipitation mechanism.
文摘For the seventies, scientists focused their researches to find techniques to produce high quality films. One of the ideas, for example, was to generate an ionized cluster beam (ICB) formed by inert gas condensation (IGC) from evaporation of material. This method generates non-agglomerated nanoparticles to be deposited onto any substrate. However, the synthesis of spherical and well-dispersed nanoparticles remains, today, a major technological issue. Several trials have been performed with magnetron sputtering that has the advantage of producing very pure atomic vapour from a wide variety of solid materials or composites, and therefore in this configuration offers the possibility to synthesize nanoparticles in a gaz phase with potential numerous applications. In this paper, we describe several results of our laboratory and we show how it is possible to synthesize non-agglomerated nanoparticles with a narrow size distribution in the nm range. Detailed examples of Ag, TiO2, Au, Y, C, Co and Fe are given. We illustrate their current use in applications including catalyst to produce aligned Multi-Wall Carbon Nanotubes, seeding layer to promote anatase TiO2 crystallisation for photocatalytic material, superhydrophobic material and nanoparticle for nanomedecine.
文摘Complex crystal aggregates from fluorspar vapor phase were grown at specific low-pressure/high-temperature conditions. The quasi-equilibrium of initiated crystal-chemical reactions at the proceeding vapour-crystal phase transformation was strongly dependent on the mass-transport inside an originally designed multicameral crucible, loaded by several portions of natural fluorite. By changing the temperature pressure over the already molten fluorspar portions as well as the gas-permeability of the channels connecting different sections in crucible interior to vacuum ambient, one may control the rate of gaseous-vapour diffusion and the degree of supper-saturation inside the peripheral crucible compartment wherein nucleation and crystal growing occurred. In this way, grown aggregates revealed a complicated habit formed during three-stage growing process provided by relevant thermodynamic and phase. Residual stresses were not observed in the aggregates whereas those in simultaneously grown boules from the non-vaporized melts in crucible cameras were clearly distinguished. The optical transmittance spectra of the boules were obtained considerably better, especially in the UV, comparing to those for crystal aggregates, both showing several peaks of specific light-absorption due to enhanced presence of rare-earth (RE) impurities. The aggregates manifest nearly full reflectivity from Vis to near IR region. The vapor phase growth mechanisms, when natural fluorite with some RE contents has been used, were explained on thermodynamic grounds that shown the manner of reliable control on the phenomenon. The results were anticipated to help for developing new perspective techniques for growth from vapor of several fluoride compounds with complex structure and composition and wide application. It was speculated that similar growth mechanisms of CaF2?crystals were possible on the moon in its very early period of formation.
文摘This paper presents new experimental evidence of the PeTa effect—infrared characteristic radiation under first order phase transitions, especially the crystallization of melts and the deposition and condensation of vapours/gases. The PeTa effect describes the transient radiation that a particle (i.e., atom, molecule or/and cluster) emits transient radiation during a transition from a meta-stable higher energetic level (in a super-cooled melt or a super-saturated vapour) to the stable condensed lower level (in a crystal or a liquid). The radiation removes latent heat with photons of characteristic frequencies that are generated under this transition. The abbreviation “PeTa effect” means Perel’man-Tatartchenko’s effect.
文摘This paper presents new experimental results concerning the PeTa effect—infrared characteristic radiation under first order phase transitions, especially during deposition and condensation of vapours/gases and the crystallisation of melts. The abbreviation “PeTa effect” means Perel’man-Tatartchenko’s effect. The nature of the PeTa effect is transient radiation that a particle (i.e., atom, molecule or/and cluster) emits during a transition from a meta-stable higher energetic level (in a super-cooled melt or super-saturated vapour) to the stable condensed lower level (in a crystal or liquid). The radiation removes latent heat with photons of characteristic frequencies that are generated under this transition. This paper is the second in a set describing the appearance of PeTa radiation under air cooling with deposition and condensation of air components. The radiation was recorded using an IR Fourier Spectrometer with a highly sensitive MCT detector. Certain peculiarities of the recorded radiation as well as its applications in the physics of the atmospheres of Earth and Jupiter are analysed.
文摘Aim To study the relationship between the substrate temperature and the morphology and properties of GaN. Methods\ Applying the hydride chemical vapor deposition method, GaN films were deposited on different kinds of substrates, including sapphire, Si(111),Si(100),GaAs and GaP(111) both on the P face and the Ga face. The growth was performed at low temperatures of below 700℃. XRD, Hall measurement, cathodoluminescence (CL) and atomic force microscopy (AFM) were used to characterise the film properties. Results\ It was found that the temperature and the nature of substrate materials influence the layer morphology. Conclusion\ The analysis shows that no apparent relationship exists between the optical properties and layer morphology.
