Porous silicon film is a capillary-like medium, which is able to reveal different meso-elastic modulus with porosity. During the preparation of porous silicon samples, the capillary force is a non-classic force relate...Porous silicon film is a capillary-like medium, which is able to reveal different meso-elastic modulus with porosity. During the preparation of porous silicon samples, the capillary force is a non-classic force related to the liquid evaporation which directly influences the evolution of residual stress. In this study, a non-linear relation of Raman shift to stress coefficient and the porosity is obtained from the elastic modulus measured with nano-indentation by Bellet et al. [J. Appl. Phys. 60 （1996） 3772] Dynamic capillarity during the drying process of porous silicon is investigated using micro-Raman spectroscopy, and the results reveal that the residual stress resulted from the capillarity increased rapidly. Indeed, the dynamic capillarity has a close relationship with a great deal of micro-pore structures of the porous silicon.展开更多
The electrical conductivity of molten olivine is studied up to 3720K and 13.2 GPa. The results indicate that the electrical conductivity of molten olivine exhibits the perfect Arrhenius behaviour. The activation energ...The electrical conductivity of molten olivine is studied up to 3720K and 13.2 GPa. The results indicate that the electrical conductivity of molten olivine exhibits the perfect Arrhenius behaviour. The activation energy as well as temperature effect is much smaller than that of the solid olivine. It is expected that the high conductivity zone in the mantle is almost independent of the melting based on our experimental data.展开更多
We perform the high-pressure energy dispersive x-ray diffraction experiments of nickel nanoparticle chain using a synchrotron source under quasi-hydrostatic compression up to 44.7GPa. There is no phase transition over...We perform the high-pressure energy dispersive x-ray diffraction experiments of nickel nanoparticle chain using a synchrotron source under quasi-hydrostatic compression up to 44.7GPa. There is no phase transition over the pressure range. The bulk modulus Ko, the first pressure derivative of bulk modulus K＇0 and the volume Vo are calculated from the pressure-volume data using the Birch-Murnaghan equation of state. A decrease of compressibility is observed, in agreement with the Hall-Perch effect.展开更多
Canti-bridged epitaxial lateral overgrowth （CBELO） of GaN is performed by metalorganic chemical vapour deposition （MOCVD） on maskless V-grooved sapphire substrates prepared by wet chemical etching with different m...Canti-bridged epitaxial lateral overgrowth （CBELO） of GaN is performed by metalorganic chemical vapour deposition （MOCVD） on maskless V-grooved sapphire substrates prepared by wet chemical etching with different mesa widths. The wing tilt usually observed in ELO is not found in the CBELO GaN with wide mesa widths, while it can be detected obviously in the GaN with narrow mesa widths. The wing tilt of CBELO GaN grown on a grooved sapphire substrate with narrow mesa can be controlled by adjusting the thickness of the nucleation layer. The dependence of the wing tilt on the nucleation layer thickness is studied. Cross-sectional scanning electron microscopy is used to characterize the geometry of the wing regions, and double crystal x-ray diffraction is used to analyse the structural characteristics and to measure the magnitude of the crystalline wing tilt. It is found that the crystalline wing tilt can be eliminated completely by first growth of a thin nucleation GaN layer then the CBELO GaN. Possible reason and the origin of the wing tilt in CBELO GaN films are also discussed.展开更多
A three-step growth process is developed for depositing high-quality aluminium-nitride （AlN） epilayers on （001） sapphire by low pressure metalorganic chemical vapour deposition （LP-MOCVD）. We adopt a low tempera...A three-step growth process is developed for depositing high-quality aluminium-nitride （AlN） epilayers on （001） sapphire by low pressure metalorganic chemical vapour deposition （LP-MOCVD）. We adopt a low temperature （LT） A1N nucleation layer （NL）, and two high temperature （HT） A1N layers with different V/Ⅲ ratios. Our results reveal that the optimal NL temperature is 840-880℃, and there exists a proper growth switching from low to high V/Ⅲ ratio for further reducing threading dislocations （TDs）. The screw-type TD density of the optimized AIN film is just 7.86×10^6 cm^-2, about three orders lower than its edge-type one of 2×10^9 cm^-2 estimated by high-resolution x-ray diffraction （HRXRD） and cross-sectional transmission electron microscopy （TEM）.展开更多
Kinetics of phase transformation from pseudocubic to tetragonal phase in Bi3NbO7 solid solution is studied by using the ac impedance method under isothermal conditions. Conductivity of the investigated compound is use...Kinetics of phase transformation from pseudocubic to tetragonal phase in Bi3NbO7 solid solution is studied by using the ac impedance method under isothermal conditions. Conductivity of the investigated compound is used to characterize the kinetic process of the transition. The Avrami exponent and the activation energy of phase transition are around 1.5 and 3.5eV, respectively. These kinetic parameters reveal that the pseudocubic-tetragonal transition in Bi3NbO7 .belongs to a three-dimensional diffusion-controlled growth with zero nucleation rate.展开更多
Two hexagonal GaN epilayers （samples A and B） with multiple buffer layers and single buffer layer are grown on Si （111） by metal-organic vapour phase epitaxy （MOVPE）. From the results of Rutherford backscatteri...Two hexagonal GaN epilayers （samples A and B） with multiple buffer layers and single buffer layer are grown on Si （111） by metal-organic vapour phase epitaxy （MOVPE）. From the results of Rutherford backscattering （RBS）/channeling and high resolution x-ray diffraction （HRXRD）, we obtain the lattice constant （a and c） of two GaN epilayers （aA = 0.3190 nm, cA = 0.5184 nm and aB = 0.3192 nm, CB = 0.5179 nm）, the crystal quality of two GaN epilayers （ ХminA=4.87%, ХminB =7.35% along 〈1-↑213〉 axis） and the tetragonal distortion eT of the two samples along depth （sample A is nearly fully relaxed, sample B is not relaxed enough）. Comparing the results with the two samples, it is indicated that sample A with multiple buffer layers have better crystal quality than sample B with a single buffer layer, and it is a good way to grow GaN epilayer on Si （111） substrates using multiple buffer layers to improve crystal quality and to reduce lattice mismatch.展开更多
AlxGa1-xN/GaN heterostructures are grown on c-sapphire with the Al composition x from 0.2 to 0.4 and thicknesses from 20nm to 30nm. The lattice parameters a and c are determined from 2θ/ω scan. The AIGaN layers are ...AlxGa1-xN/GaN heterostructures are grown on c-sapphire with the Al composition x from 0.2 to 0.4 and thicknesses from 20nm to 30nm. The lattice parameters a and c are determined from 2θ/ω scan. The AIGaN layers are found to be under tensile strain by using x-ray diffraction. Vegard＇s law induces a large deviation in Al composition determination by only considering the linear relationship between one lattice parameter （α or c） and Al composition. The accurate determination of Al composition is only possible with consideration of both the lattice parameters α and c, by assuming the tetragonal distortion in the AlGaN layer. Additionally, the results obtained from x-ray diffraction are verified by Rutherford backscattering.展开更多
Based on the 360° computing method of refractive angle for parallel beam diffraction enhanced imaging computed tomography （DE-CT） technique, a new algorithm used to calculate the refractive angle for fan-beam D...Based on the 360° computing method of refractive angle for parallel beam diffraction enhanced imaging computed tomography （DE-CT） technique, a new algorithm used to calculate the refractive angle for fan-beam DE-CT technique is developed. The refractive index gradient can be obtained by using the new algorithm with projection data of an object in the range of 0 - 360°, and the new algorithm only needs to set the analyser at half slope position of the rocking curve.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 10232030 and 10502014.
文摘Porous silicon film is a capillary-like medium, which is able to reveal different meso-elastic modulus with porosity. During the preparation of porous silicon samples, the capillary force is a non-classic force related to the liquid evaporation which directly influences the evolution of residual stress. In this study, a non-linear relation of Raman shift to stress coefficient and the porosity is obtained from the elastic modulus measured with nano-indentation by Bellet et al. [J. Appl. Phys. 60 （1996） 3772] Dynamic capillarity during the drying process of porous silicon is investigated using micro-Raman spectroscopy, and the results reveal that the residual stress resulted from the capillarity increased rapidly. Indeed, the dynamic capillarity has a close relationship with a great deal of micro-pore structures of the porous silicon.
基金Supported by the National Natural Science Foundation of China under Grant Nos 40473034, 40404007, 10574055 and 50532020, and the National Basic Research Programme of China under Grant No 2005CB724404.
文摘The electrical conductivity of molten olivine is studied up to 3720K and 13.2 GPa. The results indicate that the electrical conductivity of molten olivine exhibits the perfect Arrhenius behaviour. The activation energy as well as temperature effect is much smaller than that of the solid olivine. It is expected that the high conductivity zone in the mantle is almost independent of the melting based on our experimental data.
文摘We perform the high-pressure energy dispersive x-ray diffraction experiments of nickel nanoparticle chain using a synchrotron source under quasi-hydrostatic compression up to 44.7GPa. There is no phase transition over the pressure range. The bulk modulus Ko, the first pressure derivative of bulk modulus K＇0 and the volume Vo are calculated from the pressure-volume data using the Birch-Murnaghan equation of state. A decrease of compressibility is observed, in agreement with the Hall-Perch effect.
基金Supported by the National Key Basic Research Programme of China under Grant No 2002CB311900, and the National Natural Science Foundation of China under Grant Nos 10474126 and 10574148.
文摘Canti-bridged epitaxial lateral overgrowth （CBELO） of GaN is performed by metalorganic chemical vapour deposition （MOCVD） on maskless V-grooved sapphire substrates prepared by wet chemical etching with different mesa widths. The wing tilt usually observed in ELO is not found in the CBELO GaN with wide mesa widths, while it can be detected obviously in the GaN with narrow mesa widths. The wing tilt of CBELO GaN grown on a grooved sapphire substrate with narrow mesa can be controlled by adjusting the thickness of the nucleation layer. The dependence of the wing tilt on the nucleation layer thickness is studied. Cross-sectional scanning electron microscopy is used to characterize the geometry of the wing regions, and double crystal x-ray diffraction is used to analyse the structural characteristics and to measure the magnitude of the crystalline wing tilt. It is found that the crystalline wing tilt can be eliminated completely by first growth of a thin nucleation GaN layer then the CBELO GaN. Possible reason and the origin of the wing tilt in CBELO GaN films are also discussed.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10474126 and 10574148, the National High- Tech Research and Development Programme of China under Grant Nos 07K1031B21 and 07K1021B21, and the National Basic Research Programme of China under Grant No 2002CB311900.
文摘A three-step growth process is developed for depositing high-quality aluminium-nitride （AlN） epilayers on （001） sapphire by low pressure metalorganic chemical vapour deposition （LP-MOCVD）. We adopt a low temperature （LT） A1N nucleation layer （NL）, and two high temperature （HT） A1N layers with different V/Ⅲ ratios. Our results reveal that the optimal NL temperature is 840-880℃, and there exists a proper growth switching from low to high V/Ⅲ ratio for further reducing threading dislocations （TDs）. The screw-type TD density of the optimized AIN film is just 7.86×10^6 cm^-2, about three orders lower than its edge-type one of 2×10^9 cm^-2 estimated by high-resolution x-ray diffraction （HRXRD） and cross-sectional transmission electron microscopy （TEM）.
文摘Kinetics of phase transformation from pseudocubic to tetragonal phase in Bi3NbO7 solid solution is studied by using the ac impedance method under isothermal conditions. Conductivity of the investigated compound is used to characterize the kinetic process of the transition. The Avrami exponent and the activation energy of phase transition are around 1.5 and 3.5eV, respectively. These kinetic parameters reveal that the pseudocubic-tetragonal transition in Bi3NbO7 .belongs to a three-dimensional diffusion-controlled growth with zero nucleation rate.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10375004 and 10575007, and the Bilateral China-Belgium Cooperation under Grant No BIL04/05. The authors thank Dr K. Cheng for providing the GaN samples.
文摘Two hexagonal GaN epilayers （samples A and B） with multiple buffer layers and single buffer layer are grown on Si （111） by metal-organic vapour phase epitaxy （MOVPE）. From the results of Rutherford backscattering （RBS）/channeling and high resolution x-ray diffraction （HRXRD）, we obtain the lattice constant （a and c） of two GaN epilayers （aA = 0.3190 nm, cA = 0.5184 nm and aB = 0.3192 nm, CB = 0.5179 nm）, the crystal quality of two GaN epilayers （ ХminA=4.87%, ХminB =7.35% along 〈1-↑213〉 axis） and the tetragonal distortion eT of the two samples along depth （sample A is nearly fully relaxed, sample B is not relaxed enough）. Comparing the results with the two samples, it is indicated that sample A with multiple buffer layers have better crystal quality than sample B with a single buffer layer, and it is a good way to grow GaN epilayer on Si （111） substrates using multiple buffer layers to improve crystal quality and to reduce lattice mismatch.
基金Supported by the Key Laboratory of Heavy Ion Physics, Ministry of Education of China, and by the National Natural Science Foundation under Grant No 10375004.
文摘AlxGa1-xN/GaN heterostructures are grown on c-sapphire with the Al composition x from 0.2 to 0.4 and thicknesses from 20nm to 30nm. The lattice parameters a and c are determined from 2θ/ω scan. The AIGaN layers are found to be under tensile strain by using x-ray diffraction. Vegard＇s law induces a large deviation in Al composition determination by only considering the linear relationship between one lattice parameter （α or c） and Al composition. The accurate determination of Al composition is only possible with consideration of both the lattice parameters α and c, by assuming the tetragonal distortion in the AlGaN layer. Additionally, the results obtained from x-ray diffraction are verified by Rutherford backscattering.
基金Supported by the National Natural Science Foundation of China under Grant No 10702001, and the Foundation of Beijing Synchrotron Radiation Facility.
文摘Based on the 360° computing method of refractive angle for parallel beam diffraction enhanced imaging computed tomography （DE-CT） technique, a new algorithm used to calculate the refractive angle for fan-beam DE-CT technique is developed. The refractive index gradient can be obtained by using the new algorithm with projection data of an object in the range of 0 - 360°, and the new algorithm only needs to set the analyser at half slope position of the rocking curve.
