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Volume 8 Issue 8
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Original Articles
Quantum Molecular Dynamics and Coarse Graind VUU
LI Zhuxia, WU Xizhen, ZHUO yizhong*
Chin. Phys. Lett. 1991, 8 (8): 384-387 .  
Abstract   PDF(pc) (197KB) ( 405 )
The theoretical foundation of Quantum Molecular Dynamics (QMD) is investigated in the framework of the Husimi representation. The kinetic equation in Husimi representation is derived and it is demonstrated that its ħ→0 limit is just the QMD or, in other words, QMD is the coarse grained Vlasov-Uehling-Uhlenbeck theory(VUU).
Ground State Transition of (p,t) Reactions on Ni Isotopes
YANG Jinqing, JIANG Dazhen, ZHANG Yingji, ZHANG Jie, HE Jianhua, CHENG Xiaowu
Chin. Phys. Lett. 1991, 8 (8): 388-391 .  
Abstract   PDF(pc) (181KB) ( 498 )
Angular distributions of 58,60,62,64Ni(p,t) ground state transitions at Ep = 25MeV have been measured and compared with distorted wave Born approximation predictions. Relative enhancement factors for four Ni isotopes have been extracted. Comparison between the enhancement factors and the predictions of interacting boson approximation model has been made. It is found that a value of Ωv = 6 is needed to describe the experimental result in SU(5) calculation.
Influence of Beam Equilibrium Self-fields on Linear Gain for a Free Electron Laser
YU Junsheng, LIU Shenggang
Chin. Phys. Lett. 1991, 8 (8): 392-395 .  
Abstract   PDF(pc) (154KB) ( 420 )
The small-signal linear gain for a combined electromagnetic wiggler and an axial-guide magnetic field free electron laser is derived within the presence of beam equilibrium self-fields. The numerical results show that the gain is reduced as the self-fields increase.
Dynamic Critical Behavior of Sierpinski Gasket Type Fractal
WANG Xiaomin, TAO Ruibao*
Chin. Phys. Lett. 1991, 8 (8): 396-399 .  
Abstract   PDF(pc) (179KB) ( 553 )
We have applied the exact real space renormalisation group method to analyse the critical dynamics of Heisenberg spin system at the percolation threshold embedded in the two dimensional Sierpinski Gasket type fractal. Our analysis yields the dynamic critical exponent Z and the scaling behaviors of response function and characteristic frequency. We aha show that the scaling exponent relation is accurately satisfied by the values of the Z and two other exponents.
Combined Use of Differential Scanning Calorimetry and Cross-Sectional Transmission Electron Microscopy for Characterization of Thin-Film Reactions
Chin. Phys. Lett. 1991, 8 (8): 400-403 .  
Abstract   PDF(pc) (231KB) ( 547 )
We demonstrate that the combined use of differential scanning calorimetry (DSC) and cross-sectional transmission electron microscopy (XTEM) is a powerful technique in the quantitative investigation of the nucleation and growth of metastable and equilibrium phases during thin-film interdiffusion reactions. The Various approaches and advantages of the DSC/XTEM technique in obtaining a variety of kinetic and thermodynamic data are discussed. Explosive reactions, as opposed to conventionally controlled reactions, may occur in thin films where the multilayer geometry is used.
CO on Cu{001}c(2 x 2)-Pd Studied by High Resolution Electron Energy Loss Spectroscopy
YAO Jun, LIU Guoliang, LIU Fengqin, LÜ, Sihua, WU Sicheng,
Chin. Phys. Lett. 1991, 8 (8): 404-407 .  
Abstract   PDF(pc) (244KB) ( 611 )
The adsorption of CO on Cu{001}c(2 x 2)-Pd surface has been studies by electron energy loss spectroscopy. At 240 K, CO molecules are Linearly bonded on the top of Pd atoms only. At 135 K, CO adsorbed both on the top position of Pd and Cu atoms which occupied preferably on Pd top position. Another possible dissociative adsorption phase of CO, which exists at room temperature, has been discussed also.
Aggregation Process in the Ion Irradiated Solid Films
WANG Jian, CAI Jun, WU Xingfang, LIU Baixin, FANG Zhengzhi
Chin. Phys. Lett. 1991, 8 (8): 408-411 .  
Abstract   PDF(pc) (209KB) ( 521 )
A fractal aggregation process in the ion irradiated films was recognized. The process was intrinsic of interaction of ions with solids and sincerely modelled by the cluster diffusion-limited-aggregation model. The energetic ions not only drive the atoms and clusters in the area of collision cascade in motion which may be modelled as random walks, but also create vacancies and voids which contribute to the aggregation process. The process was also of percolation characteristic with a fractal dimension 1.82 at the critical point.

Thermopower of YBa2 Cu3 O7 Superconductor Prepared by Melt-Textured Growth Method
JIANG Lianhua, MA Hong, REN Hongtao*, XIAO Lin*, HE Qing*, YU Qishan, HUANG Zhijun, YAN Shousheng
Chin. Phys. Lett. 1991, 8 (8): 412-415 .  
Abstract   PDF(pc) (175KB) ( 459 )
The results of thermopower measurements in a high Jc melt-textured growth (MTG) YBa2 Cu3 O7 bulk sample above 80K are reported, its behavior is strongly anisotropic. The small value in c-direction indicates the existence of an imperfection in the alignment of ab-planes and low resistance channels along the c-axis, which may be important for the high Jc value of the sample. Described by a two order tensor, the orientational dependence of thermopower can also be explained.
Preparation and Critical Current Measurements of Laser Ablated YBCO Superconducting Thin Films
ZHANG Yaogang, SEII Changqing, FAN Shoushan, CUI Changgeng*, LI Shanlin*, LI Jun*, LIU Mingxiong*
Chin. Phys. Lett. 1991, 8 (8): 416-419 .  
Abstract   PDF(pc) (171KB) ( 519 )
High Tc superconducting YBCO films have been fabricated by in-situ pulsed laser ablation method. The substrates used were SrTiO3 (100) and were heated to 650°C during deposition. X-ray diffraction results indicate that the as-deposited 6lms are highly oriented with c-axis perpendicular to the film surfaces. The critical currents were measured at 77.5 K under different magnetic fields from 0 up to 7 T by using dc four point method. The zero resistance temperature was 89 K and the highest critical current density was 2.5 x 106 A/cm2 at 77.5 K under zero field.
Self-collapse of Dumbbell Domains in Garnet Bubble Films
NIE Xiangfu, TANG Guide, HAN Baoshan*
Chin. Phys. Lett. 1991, 8 (8): 420-423 .  
Abstract   PDF(pc) (190KB) ( 588 )
The self-collapse phenomenon of dumbbell domains was studied experimentally. The coincidence of the bias field region of self-collapse with that of collapse for both the first and second kinds of dumbbells manifests that two necessary conditions for self-collapse are: (1) sufficiently high number of vertical Bloch lines (VBLs) in their walls and (2) these VBLs are in high compression, and there exists the similarity between self-collapse and collapse in mechanism.

Magneto-optical Kerr Effect of NdFe Films and NdFe/ Cu(A1) Bilayers
ZHOU Shiming, LU Mu, ZHAI Hongru, WANG Hao, XU Yongbing, Huang Haibo*
Chin. Phys. Lett. 1991, 8 (8): 424-427 .  
Abstract   PDF(pc) (142KB) ( 512 )
In this paper single layer NdFe film, bilayer NdFe/Cu and NdFe/Al films made by vacuum evaporation were studied. The magneto-optical Kerr effect(MOKE) and reflectivity spectra were measured. The following results were found: the contribution of Nd to MOKE is mainly at short wavelengths, for NdFe/Al the MOKE enhancement locates in the short wavelength range and for NdFe/Cu the enhancement peak locates near the absorption edge of reflector Cu, and in the MOKE spectra of bilayer NdFe/Cu film with some compositions, sign reversals were observed.
Power Dependence of the Recombination Processes in the InxGa1-xAs/GaAs Single Quantum Well
QIAN Shixiong, WU Jianyao, YUAN Shu, LI Yufen, Thorwald G. Andersson, CHEN Zonggui, PENG Wenji, SHE Weilong, YU Zhenxin
Chin. Phys. Lett. 1991, 8 (8): 428-431 .  
Abstract   PDF(pc) (199KB) ( 472 )
We have measured the power dependence of the photoluminesence spectra from a set of strained InxGa1-xAs/GaAs single quantum wells. The result shows that the excitation power has important effect on the carrier recombination processes. When the power increases from 0.5 to 14mW, the photoluminescence from the barrier becomes more intense than that from the well and the trapping efficiency decreases. At high excitation level, the ratio of the radiative recombination rate to the nonradiative recombination rate of the barrier increases ten times than that at lower excitation level, while it only doubles for the well.
Subband Optical Transitions in a-Si:H Quantum Well Structures
CHEN Kunji, XU Jun, ZHOU Lin, JIANG Jiangong, LI Zhifeng, DU Jiafang
Chin. Phys. Lett. 1991, 8 (8): 432-435 .  
Abstract   PDF(pc) (206KB) ( 386 )
The hydrogenated amorphous silicon (a-Si:H)/silicon carbide (a-SiCx:H) quantum well (QW) and superlattice structures were fabricated by glow discharge deposition. Wavelength differential absorption spectroscopy has been applied to study the subband transition in a-Si:H/a-SiCx:H Q W, and derivative spectra change clearly from a linear to a step-like form when a-Si:H well-layer thickness has decreased below 40Å. These results indicate that three-dimensional parabolic band transition is turned into subband transition in the a-Si:H QW.

Amorphization of Co-Nb Magnetic Alloys by Mechanical Alloying
MA Xueming, YUE Lanping, DONG Yuanda
Chin. Phys. Lett. 1991, 8 (8): 436-438 .  
Abstract   PDF(pc) (142KB) ( 499 )
Formation of amorphous Co-Nb system by mechanical alloying (MA) in the composition range of Co25Nb75-Co70Nb30 was studied by X-ray diffraction. Magnetic properties of the mechanically alloyed Co70Nb30 powder were measured. The variation in Hc curve with milling time can be explained by two-stage mechanism involved in the milling process. The results show that the amorphous powder prepared by MA is of good soft magnetic properties.
14 articles