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Photoabsorption Spectrum and Optically Forbidden Transitions of Krypton by Electron Impact
YUAN Zhen-Sheng, ZHU Lin-Fan, LIU Xiao-Jing, LI Wen-Bin, CHENG Hua-Dong, XU Ke-Zun
Chin. Phys. Lett. 2002, 19 (4):
495-496
.
A high resolution fast electron energy loss spectrometer with
multi-channel energy analyse was employed. The maxima just above the threshold 4-1(2P1/2), which is regarded as a shape resonance, was obtained at 16.3 eV. The optically forbidden excitations of 4s electron were measured for the first time, and the energy positions are 23.75 eV(4s-15s), 25.66 eV(4-16s/4d) and 26.60 eV(4-17s/5d), respectively.
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Intracavity-Doubled Self-Q-Switched Nd,Cr:YAG 946/473 nm
Microchip Laser
LI De-Hua, WANG Ling, GAO Chun-Qing, ZHANG Zhi-Guo, FENG Bao-Hua, Volker Gaebler, LIU Bai-Ning, H. J. Eichler, ZHANG Shi-Wen, LIU An-Han, SHEN De-Zhong
Chin. Phys. Lett. 2002, 19 (4):
504-506
.
We carried out the operation of an intracavity frequency-doubled self-Q-switched Nd,Cr:YAG/KNbO3 946/473nm microchip laser pumped by a Ti:sapphire laser. The overall cavity length was about 4 mm. The maximum average blue power of 12 mW was achieved with a repetition rate of 13 kHz at an absorbed pump power of 545 mW. The pulses of 473 nm laser had duration of 7ns and peak power of 132 W at this pump level. The conversion efficiency was 2.2 % with respect to absorbed pump power of 808 nm laser.
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Structural Properties of Water by a Flexible Water Model
LIANG Yun-Feng, ZHU Zhen-Gang, LIU Chang-Song
Chin. Phys. Lett. 2002, 19 (4):
524-527
.
The structural properties of water at different temperatures have been investigated using a flexible water model in the isothermal-isobaric ensemble. With decreasing temperature, the tetrahedrality of the distribution of the water molecules around the central water molecule is enhanced, and the hydrogen bonds become more linear. By means of a conjugate gradient energy minimization, dynamical configurations at various temperatures have been mapped onto nearby potential-energy minima, the 50°-60°peak (P1) in the distribution function of the O-O-O angle of a trimer becomes far smaller. However there appears to be a small but observable temperature dependence of P1, i.e., the higher the temperature, the higher the P1 intensity.
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Interfacial Properties of AlN/Si(111) Grown by Metal-Organic
Chemical Vapor Deposition
XI Dong-Juan, ZHENG You-Dou, CHEN Peng, ZHAO Zuo-Ming, CHEN Ping, XIE Shi-Yong, JIANG Ruo-Lian, SHEN Bo, GU Shu-Lin, ZHANG Rong
Chin. Phys. Lett. 2002, 19 (4):
543-545
.
We have studied the interfacial structures of AlN/Si(111) grown by metal-organic 0chemical vapor deposition. X-ray photoelectron spectrum and Auger electron spectrum were employed to analyse the components and chemical structures of AlN/Si(111). The results indicated that a mix-crystal transition region, approximately 12nm, was present between AlN film and Si substrate and it was composed of AlN and Si3N4. After analysis we found the existence of Si3N4 could not be avoided in AlN/Si(111) interface because of strong diffusion at 1070°C. Even in AlN layer Si-N bonds, Si-Si bonds can be found.
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Schottky Barrier Height Inhomogeneity of Ti/n-GaAs Contact Studied by the I-V-T Technique
JIANG Yu-Long, RU Guo-Ping, LU Fang, QU Xin-Ping, LI Bing-Zong, LI Wei, LI Ai-Zhen
Chin. Phys. Lett. 2002, 19 (4):
553-556
.
The current-voltage characteristics of Ti/n-GaAs Schottky diodes measured over a temperature range of 78 to 299 K have been interpreted on the basis of thermionic emission across an inhomogeneous Schottky contact. The experiment shows that the apparent barrier height (Фap) increases from 0.437 eV at 78 K to 0.698 eV at room temperature. The plot of Фap versus 1/T does not exhibit a simple linear relationship over the whole temperature range, indicating that the barrier height distribution is more complicated than the frequently observed single Gaussian distribution. A new multi-Gaussian distribution model is developed. Our experimental results can be explained by a double Gaussian distribution of the barrier heights. The weight, the mean barrier height, and the standard deviation of the two Gaussian functions are 0.00001 and 0.99999, 0.721 and 0.696, 0.069 and 0.012eV, respectively.
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Improved Carrier Transfer in Red Organic Light Emitting Diodes
Doped with Rubrene
LIU Hong-Yu, GAO Wen-Bao, YANG Kai-Xia, LIU Shi-Yong
Chin. Phys. Lett. 2002, 19 (4):
572-574
.
A red organic light emitting diode doped with rubrene is constructed with the configuration of ITO/NPB/Alq3: rubrene: DCM/Alq3/LiF/Al. In the device, N,N'-bis-(1-naphthl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB) is used as the hole-transporting layer, tris(8-quinolinolato) aluminum (Alq3) as the electron-transporting layer and Alq3 doped with 5,6,11,12-tetraphenylnaphthacene (rubrene) and 4-dicyanomethylene-2-methyl-6- p-dimethyla- minostyryl)-4H-pyran (DCM) as the emitting layer. When the doping concentration of rubrene is 6% and that of DCM is 4%, red purity of the device is improved effectively. The experimental phenomena are explained as the result of the improved carrier transfer from rubrene to DCM.
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Influences of Annealing on the Opto-electronic Properties of
ZnO Films Grown by Plasma-Enhanced MOCVD
WANG Jin-Zhong, DU Guo-Tong, WANG Xin-Qiang, CHANG Yu-Chun, YAN Wei, YANG Shu-Ren, MA Yan, WANG Hai-Song, GAO Ding-San, LIU Xiang, CAO Hui, XU Jun-Ying, R. P. H. Chang
Chin. Phys. Lett. 2002, 19 (4):
581-583
.
ZnO thin films have been grown on C-plane sapphire substrates by plasma-enhanced metal-organic chemical vapor deposition. The samples are then annealed at a higher temperature. The resistivity, concentration of electron, mobility and optically pumped threshold of both as-grown and annealed films are investigated. Furthermore, their structural and optical properties are also examined with x-ray diffraction, emission spectra and optical transmission spectra. The results indicate that the quality of ZnO thin films can be improved by annealing.
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A Novel GaAs/InGaAs/AlGaAs Structure of Modulation-Doped Field-Effect Transistors with High Transconductances
CHANG Yu-Chun, Hailin Luo, Y. Wang, WANG Hai-Song, WANG Jian-Gang, DU Guo-Tong
Chin. Phys. Lett. 2002, 19 (4):
588-590
.
Novel structure GaAs/InGaAs/AlGaAs pseudomorphic modulation-doped field-effect transistors (MODFETs) with a buried p-i-n dipole layer and a 200 nm buffer layer have been fabricated. According to the calculation, the dipole buried layer not only results in the very thin buffer layer required, but also enhances the density of two-dimensional electron gas. The measured transconductances of these MODFETs, with a gate length of 2 μm and a drain-source spacing of 5 μm, are as high as 320 mS/mm and the measured maximum drain currents of the typical devices are higher than 500 mA/mm.
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Magnetocrystalline Anisotropy and Magnetoelasticity of Preferentially Oriented Martensitic Variants in Ni52Mn24Ga24 Single Crystals
QU Jing-Ping, WANG Wen-Hong, MENG Fan-Bin, LIU Bao-Dan, LIU Zhu-Hong, CHEN Jing-Lan, LI Yang-Xian, WU Guang-Heng
Chin. Phys. Lett. 2002, 19 (4):
591-594
.
The magnetocrystalline anisotropy and magnetoelasticity of preferentially oriented martensitic variants in an off-stoichiometric Ni52Mn24Ga24 single crystal were investigated. We found that the easy magnetization direction of the martensite phase is the [110] direction, and the hard magnetization exhibited in [001], the growth direction of single crystals. The temperature dependence of the anisotropy fields and constants of Ni52Mn24Ga24 have been determined. It was found that at martensite phase, the anisotropy field increases monotonically with decreasing temperature, but the anisotropy constant first increases rapidly and then the increasing rate become smaller and smaller. Based on a previous model, present results suggest that the competition between the Zeeman energy and the magnetocrystalline anisotropy energy is mainly responsible for the magnitude of magnetic-field-induced strain in this material.
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Mössbauer Evidence for Ferromagnetic Ordering in Copper-Iron
Cyanometallates
XIA Yuan-Fu, YU Zhi, SONG Yong, HUANG Hong-Bo, YOU Xiao-Zeng, X. Z. Zhou, Z. W. Li, H. P. Kunkel, Gwyn Williams
Chin. Phys. Lett. 2002, 19 (4):
595-598
.
A novel member of the Prussian blue family, CuII3 [FeIII (CN)6]2.3NH3.6H2O, was synthesized, in which NH3 ligands are in stochastic distribution. X-ray diffraction data, zero-field-cooled magnetization and field-cooled magnetization curves, Mössbauer spectra with/without an external field of 5 T and a structural model are presented. This Prussian blue analog displays considerable magnetic hardness below the magnetic transition temperature Tc, which is about 19.8 K. The coercive field determined from the magnetization hysteresis loop at 5 K was 2.76 kOe. The copper-iron cyanometallates have potential applications in the design of novel magnetic systems.
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Lattice Strain Induced by Ion Implantation in AlGaAs/AlGaInAs Quantum Well Samples
LIU Pi-Jun, XIA Yue-Yuan, LIU Xiang-Dong, YUAN Feng-Po, PAN Jiao-Qing, XUE Cheng-Shan, LI Yu-Guo, ZHAO Ming-Wen, MA Yu-Chen
Chin. Phys. Lett. 2002, 19 (4):
599-601
.
Si+ ions of 350 keV have been implanted into AlGaAs/AlGaInAs quantum well samples in the dose range from 5 x 1013cm-2 to 5 x 1014cm-2. The Raman spectra and high resolution x-ray diffraction (HRXRD) were measured from these implanted samples as well as the un-implanted one. In the implanted layers the average strain which was evaluated by HRXRD increases with the implantation doses and varies from 0.0011 to 0.0029. The quantum well interface intermixing effect and compositional modification also observed from HRXRD. At the higher doses, an abnormal annealing procedure takes place and it partly removes damage, but the strain is kept almost unchanged in the epilayers.
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Contribution of the Atmospheric Dynamics to the Sporadic Sodium Layer Formation
YANG Guo-Tao, WANG Jia-Min, LIU Bing-Mo, CHENG Xue-Wu, WAN Wei-Xing, GONG Shun-Sheng
Chin. Phys. Lett. 2002, 19 (4):
602-604
.
We report on a sporadic sodium layer (SSL) event observed by our Na fluorescence lidar at Wuhan, China (31°N, 114°E) on March 16, 1999, and we reveal some special behaviour. From careful analysis of various sodium content variations of the layer during the development of this SSL event, it is found that besides the sodium injection mechanism as expected, another mechanism we called the atmospheric dynamics also made a noticeable contribution to this SSL formation. Computer simulations conformed that under the combined action of a suitable sodium injection and a bi-direction vertical wind field, an SSL profile can be reproduced with a pronounced SSL
peak on normal sodium layer as we observed in this event. From these results, it is emphasized that atmospheric dynamics is important for the SSL formation.
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48 articles
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