GaN epifilms are grown on the patterned sapphire substrates (PSS) (0001) and the conventional sapphire substrates (CSS) (0001) by metal-organic chemical vapor deposition (MOCVD) using a novel two-step growth. High res...GaN epifilms are grown on the patterned sapphire substrates (PSS) (0001) and the conventional sapphire substrates (CSS) (0001) by metal-organic chemical vapor deposition (MOCVD) using a novel two-step growth. High resolution X-ray diffraction (HR-XRD) is used to investigate the threading dislocation (TD) density of the GaN epifilms. The TD density is calculated from the ω-scans full width at half maximum (FWHM) results of HR-XRD. The edge dislocation destiny of GaN grown on the PSS is 2.7×108 cm-2, which is less than on the CSS. This is confirmed by the results of atomic force microscopy (AFM) measurement. The lower TD destiny indicates that the crystalline quality of the GaN epifilms grown on the PSS is improved compared to GaN epifilms grown on the CSS. The residual strains of GaN grown on the PSS and CSS are compared by Raman Scattering spectra. It is clearly seen that the residual strain in the GaN grown on PSS is lower than on the CSS.展开更多
InN film was grown on 4H-SiC （0001） substrate by RF plasma-assisted molecular beam epitaxy （RF- MBE）. Prior to the growth of InN film, an InN buffer layer with a thickness of ～5.5 nm was grown on the substrate. S...InN film was grown on 4H-SiC （0001） substrate by RF plasma-assisted molecular beam epitaxy （RF- MBE）. Prior to the growth of InN film, an InN buffer layer with a thickness of ～5.5 nm was grown on the substrate. Surface morphology, microstructure and structural quality of InN film were investigated. Micro-structural defects, such as stacking faults and anti-phase domain in InN film were carefully investigated using transmission electron microscopy （TEM）. The results show that a high density of line contrasts, parallel to the growth direction （c-axis）, was clearly observed in the grown InN film. Dark field TEM images recorded with diffraction vectors g = 1120 and g = 0002 revealed that such line contrasts evolved from a coalescence of the adjacent rnisoriented islands during the initial stage of the InN nucleation on the substrate surface. This InN nucleation also led to a generation of anti-phase domains.展开更多
In order to improve the threading stability and the head thickness precision in tandem hot rolling process, an adaptive threading strategy was proposed. The proposed strategy was realized by the rolling characteristic...In order to improve the threading stability and the head thickness precision in tandem hot rolling process, an adaptive threading strategy was proposed. The proposed strategy was realized by the rolling characteristics analysis, and factors which affect the rolling force and the final thickness were determined and analyzed based on the influence coefficients calculation process. An objective function consisting of the influenced factors was founded, and the disturbance quantity was obtained by minimizing the function with the Nelder-Mead simplex method, and the proposed adaptive threading strategy was realized based on the calculation results. The adaptive threading strategy has been applied to one 7-stand hot tandem mill successfully, actual statistics data show that the predicted rolling force prediction in the range of +/- 5.0% is improved to 97.8%, the head thickness precision in the range of +/- 35 mu m is improved to 98.5%, and the threading stability and the head thickness precision are enhanced to a high level.展开更多
基金support from the National Natural Science Foundation of China (Grant Nos. 60877006 and 50872146)
文摘GaN epifilms are grown on the patterned sapphire substrates (PSS) (0001) and the conventional sapphire substrates (CSS) (0001) by metal-organic chemical vapor deposition (MOCVD) using a novel two-step growth. High resolution X-ray diffraction (HR-XRD) is used to investigate the threading dislocation (TD) density of the GaN epifilms. The TD density is calculated from the ω-scans full width at half maximum (FWHM) results of HR-XRD. The edge dislocation destiny of GaN grown on the PSS is 2.7×108 cm-2, which is less than on the CSS. This is confirmed by the results of atomic force microscopy (AFM) measurement. The lower TD destiny indicates that the crystalline quality of the GaN epifilms grown on the PSS is improved compared to GaN epifilms grown on the CSS. The residual strains of GaN grown on the PSS and CSS are compared by Raman Scattering spectra. It is clearly seen that the residual strain in the GaN grown on PSS is lower than on the CSS.
基金supported by the Thailand Center of Excellence in Physics(Th EP)the King Mongkut’s University of Technology Thonburi under The National Research University Project+2 种基金supported by the National Research Council of Thailand(NRCT)the Thai Government Stimulus Package 2(TKK2555)the Project for Establishment of Comprehensive Center for Innovative Food,Health Products and Agriculture
文摘InN film was grown on 4H-SiC （0001） substrate by RF plasma-assisted molecular beam epitaxy （RF- MBE）. Prior to the growth of InN film, an InN buffer layer with a thickness of ～5.5 nm was grown on the substrate. Surface morphology, microstructure and structural quality of InN film were investigated. Micro-structural defects, such as stacking faults and anti-phase domain in InN film were carefully investigated using transmission electron microscopy （TEM）. The results show that a high density of line contrasts, parallel to the growth direction （c-axis）, was clearly observed in the grown InN film. Dark field TEM images recorded with diffraction vectors g = 1120 and g = 0002 revealed that such line contrasts evolved from a coalescence of the adjacent rnisoriented islands during the initial stage of the InN nucleation on the substrate surface. This InN nucleation also led to a generation of anti-phase domains.
基金Project(51504061)supported by the National Natural Science Foundation of China
文摘In order to improve the threading stability and the head thickness precision in tandem hot rolling process, an adaptive threading strategy was proposed. The proposed strategy was realized by the rolling characteristics analysis, and factors which affect the rolling force and the final thickness were determined and analyzed based on the influence coefficients calculation process. An objective function consisting of the influenced factors was founded, and the disturbance quantity was obtained by minimizing the function with the Nelder-Mead simplex method, and the proposed adaptive threading strategy was realized based on the calculation results. The adaptive threading strategy has been applied to one 7-stand hot tandem mill successfully, actual statistics data show that the predicted rolling force prediction in the range of +/- 5.0% is improved to 97.8%, the head thickness precision in the range of +/- 35 mu m is improved to 98.5%, and the threading stability and the head thickness precision are enhanced to a high level.
