The superconducting transition temperature and grain size of dc sputtered Nb films are systematically investigated. The results show that the superconductivity is closely related to the grain size, rather than to the ...The superconducting transition temperature and grain size of dc sputtered Nb films are systematically investigated. The results show that the superconductivity is closely related to the grain size, rather than to the scattering strength of electrons or the surface layer proximity effect of the films.展开更多
The photoluminescence(PL) properties of blue multiple InGaN/GaN quantum well(BMQW) and green multiple InGaN/GaN quantum well(GMQW) formed on a single sapphire substrate are investigated. The results indicate that the ...The photoluminescence(PL) properties of blue multiple InGaN/GaN quantum well(BMQW) and green multiple InGaN/GaN quantum well(GMQW) formed on a single sapphire substrate are investigated. The results indicate that the peak energy of GMQW-related emission(PG) exhibits more significant "S-shaped" dependence on temperature than that of BMQW-related emission(PB), and the excitation power-dependent carrier-scattering effect is observed only in the PG emission;the excitation power-dependent total blue-shift(narrowing) of peak position(line-width) for the PGemission is more significant than that for the PBemission;the GMQW shows a lower internal quantum efficiency than the BMQW. All of these results can be attributed to the fact that the GMQW has higher indium content than the BMQW due to its lower growth temperature and late growth, and the higher indium content in the GMQW induces a more significant compositional fluctuation, a stronger quantum confined Stark effect, and more non-radiative centers.展开更多
Four blue-violet light emitting InGaN/GaN multiple quantum well（MQW） structures with different well widths are grown by metal–organic chemical vapor deposition. The carrier localization effect in these samples is i...Four blue-violet light emitting InGaN/GaN multiple quantum well（MQW） structures with different well widths are grown by metal–organic chemical vapor deposition. The carrier localization effect in these samples is investigated mainly by temperature-dependent photoluminescence measurements. It is found that the localization effect is enhanced as the well width increases from 1.8 nm to 3.6 nm in our experiments. The temperature induced PL peak blueshift and linewidth variation increase with increasing well width, implying that a greater amplitude of potential fluctuation as well as more localization states exist in wider wells. In addition, it is noted that the broadening of the PL spectra always occurs mainly on the low-energy side of the PL spectra due to the temperature-induced band-gap shrinkage, while in the case of the widest well, a large extension of the spectral curve also occurs in the high energy sides due to the existence of more shallow localized centers.展开更多
文章利用分子束外延方法在蓝宝石衬底上制备Bi_2Se_3拓扑绝缘体薄膜,研究衬底温度对薄膜生长质量的影响。首先对370、380、390、400℃衬底温度下生长的Bi_2Se_3薄膜样品,利用反射高能电子衍射仪(reflection high-energy electron diffra...文章利用分子束外延方法在蓝宝石衬底上制备Bi_2Se_3拓扑绝缘体薄膜,研究衬底温度对薄膜生长质量的影响。首先对370、380、390、400℃衬底温度下生长的Bi_2Se_3薄膜样品,利用反射高能电子衍射仪(reflection high-energy electron diffraction,RHEED)、原子力显微镜(atomic force microscope,AFM)进行表面形貌的表征;利用X射线衍射仪(X-ray diffraction,XRD)和X射线能谱仪(energy dispersive X-ray spectroscopy,EDS)对样品的晶相和化学组分进行分析筛样。结果表明,衬底温度为390℃时制备的Bi_2Se_3薄膜表面平整、成分接近理想配比、结晶质量较好。最后利用综合物性测量系统测量了最佳衬底温度制备的样品的电学性质,表明样品为n型拓扑绝缘体薄膜。展开更多
Sampling principle and characteristics and edge effect of orthogonal wavelet transform of signals are researched. Two samples of signals and wavelet bases must be taken in wavelet transform. In the second sample sampl...Sampling principle and characteristics and edge effect of orthogonal wavelet transform of signals are researched. Two samples of signals and wavelet bases must be taken in wavelet transform. In the second sample sampling interval or sampling length in different frequency range will be automatically adjusted. Wavelet transform can detect singular points. Both ends of signals are singular points. Edge effect is not avoidable.展开更多
基金Supported by the National Basic Research Program of China (Grant No. 2006CB- 91304)the Knowledge Innovation Project of Chinese Academy of Sciences Contributed by ZHANG DianLin
文摘The superconducting transition temperature and grain size of dc sputtered Nb films are systematically investigated. The results show that the superconductivity is closely related to the grain size, rather than to the scattering strength of electrons or the surface layer proximity effect of the films.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51672163,51872167,and 61504044)the Major Research Plan of the National Natural Science Foundation of China(Grant No.91433112)
文摘The photoluminescence(PL) properties of blue multiple InGaN/GaN quantum well(BMQW) and green multiple InGaN/GaN quantum well(GMQW) formed on a single sapphire substrate are investigated. The results indicate that the peak energy of GMQW-related emission(PG) exhibits more significant "S-shaped" dependence on temperature than that of BMQW-related emission(PB), and the excitation power-dependent carrier-scattering effect is observed only in the PG emission;the excitation power-dependent total blue-shift(narrowing) of peak position(line-width) for the PGemission is more significant than that for the PBemission;the GMQW shows a lower internal quantum efficiency than the BMQW. All of these results can be attributed to the fact that the GMQW has higher indium content than the BMQW due to its lower growth temperature and late growth, and the higher indium content in the GMQW induces a more significant compositional fluctuation, a stronger quantum confined Stark effect, and more non-radiative centers.
基金supported by the National Key Research and Development Program of China(Grant No.2016YFB0401801)the National Natural Science Foundation of China(Grant Nos.61674138,61674139,61604145,61574135,61574134,61474142,61474110,61377020,and 61376089)+1 种基金Science Challenge Project,China(Grant No.JCKY2016212A503)One Hundred Person Project of the Chinese Academy of Sciences
文摘Four blue-violet light emitting InGaN/GaN multiple quantum well（MQW） structures with different well widths are grown by metal–organic chemical vapor deposition. The carrier localization effect in these samples is investigated mainly by temperature-dependent photoluminescence measurements. It is found that the localization effect is enhanced as the well width increases from 1.8 nm to 3.6 nm in our experiments. The temperature induced PL peak blueshift and linewidth variation increase with increasing well width, implying that a greater amplitude of potential fluctuation as well as more localization states exist in wider wells. In addition, it is noted that the broadening of the PL spectra always occurs mainly on the low-energy side of the PL spectra due to the temperature-induced band-gap shrinkage, while in the case of the widest well, a large extension of the spectral curve also occurs in the high energy sides due to the existence of more shallow localized centers.
文摘文章利用分子束外延方法在蓝宝石衬底上制备Bi_2Se_3拓扑绝缘体薄膜,研究衬底温度对薄膜生长质量的影响。首先对370、380、390、400℃衬底温度下生长的Bi_2Se_3薄膜样品,利用反射高能电子衍射仪(reflection high-energy electron diffraction,RHEED)、原子力显微镜(atomic force microscope,AFM)进行表面形貌的表征;利用X射线衍射仪(X-ray diffraction,XRD)和X射线能谱仪(energy dispersive X-ray spectroscopy,EDS)对样品的晶相和化学组分进行分析筛样。结果表明,衬底温度为390℃时制备的Bi_2Se_3薄膜表面平整、成分接近理想配比、结晶质量较好。最后利用综合物性测量系统测量了最佳衬底温度制备的样品的电学性质,表明样品为n型拓扑绝缘体薄膜。
文摘Sampling principle and characteristics and edge effect of orthogonal wavelet transform of signals are researched. Two samples of signals and wavelet bases must be taken in wavelet transform. In the second sample sampling interval or sampling length in different frequency range will be automatically adjusted. Wavelet transform can detect singular points. Both ends of signals are singular points. Edge effect is not avoidable.
