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Volume 11 Issue 11
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Original Articles
Factorial Cumulant Moments and Short Range Correlation in P-P Collisions at 400GeV/c
WANG Shaoshun, ZHANG Jie, XIAO Chenguo, YE Yunxiu, ZHONG Yu
Chin. Phys. Lett. 1994, 11 (11): 657-660 .  
Abstract   PDF(pc) (201KB) ( 443 )
The pseudorapidity distribution of charged particles produced in p-p collisions at 400GeV/c was measured by using the Lexan bubble chamber films offered by the CERN NA27 collaboration. The scaled factorial cumulant moments have been calculated. The results show that the second order cumulants have positive values, while the cumulants of higher order are consistent with zero except for the case with nch≥4 events, where the third-order cumulants have small positive values beyond the statistical uncertainties. From Monte Carlo events with the same single particle spectrum and no correlations, we observed that for broad mixed-multiplicity distributions, a significant part of K2 is coming from the single-particle fluctuation due to the fluctuation multiplicity.
Calculation of Process t → Wbgg
YU Zenghui, SUN Lazhen, MA Wengan, LIU Yaoyang
Chin. Phys. Lett. 1994, 11 (11): 661-664 .  
Abstract   PDF(pc) (138KB) ( 436 )
We presented the calculation of the decay width for the massive top quark accompanied by a emission of two hard gluons. It is shown that the top quark decay channel with two-gluon bremsstrahlung increases its total width by 2% to 7%, so that this contribution is non-negligible and should be included in considering top decay.
Quark Deconfinement of a Hadron in Ultrarelativistic Nucleus-Nucleus Collisions
HE Zejun, CHEN Junfeng, XU Xiaoming, QIU Xijun
Chin. Phys. Lett. 1994, 11 (11): 665-668 .  
Abstract   PDF(pc) (199KB) ( 365 )
The temperature dependent energy and corresponding internal pressure of the hadron are obtained by taking Fermi weighted sums over internal discrete energy levels. We find that beyond the critical temperature, the solution of the hadron radius determined from the balance relation between the internal and external pressures of the hadron disappears, which shows that the quark deconfinement transition has occured. In addition, it is shown that the heat bath plays role in delaying the deconfinement process.

High-Contrast Doppler-Free Collinear Polarization Spectroscopy
LIU Zidong
Chin. Phys. Lett. 1994, 11 (11): 669-672 .  
Abstract   PDF(pc) (217KB) ( 373 )
High-Contrast Doppler-free collinear polarization spectroscopy has been studied in a novel optically stabilized diode laser scheme using Rb vapor cell immersed in a zero external magnetic field. The experimental results are in good agreement with recent theoretical calculations.
Radiation Characteristics of Laser Ultrasound in Semi-transparent Solid
BAI Yuhai, PEI Liwei, FANG Qiping, YAN Yuping, YING Chongfu
Chin. Phys. Lett. 1994, 11 (11): 673-676 .  
Abstract   PDF(pc) (215KB) ( 494 )
The study of the radiation patterns of laser-generated longitudinal ultrasound in semitransparent solid is presented. The experimental results are in good agreement with the theory based on the effect of optical penetration within the sample.
Model on L- to H-Mode Transition Driven with Lower-Hybrid Wave
QIU Xiaoming (X. M. Qiu), BAI Lin (L. Bai)
Chin. Phys. Lett. 1994, 11 (11): 677-680 .  
Abstract   PDF(pc) (225KB) ( 486 )
In this letter, a model for active suppressing tokamak edge turbulence and hence inducing the L-mode to H-mode transition with lower-hybrid wave (LHW) is proposed. The model includes the two contents: (a) The poloidal sheared flow of plasma is generated by the ponderomotive potential and induced magnetization acting on a tokamak plasma resulting from the oscillating electric field of the injected LHW. (b) During the time the LHW is injected into tokamak edge, the edge turbulence and the LHW-generated plasma poloidal flow compete with each other; if the shear of plasma poloidal flow is large enough to suppress the edge turbulence, the confinement will be remarkably improved and hence the system will enter the H operating mode. This model leads us to find that the threshold LHW power required for edge-turbulence suppression is proportional to A(ω) ≡ (ω / ωLH )2 |(ω / ωLH )2-1|, which enables us to explain the experiment in the JT-60 tokamak with lower-hybrid current drive.


Investigation of Amorphization of Nb-Si Alloys by Mechanical Alloying
LI Bing, MA Xueming, LIU Lin, QI Zhenzhong, DONG Yuanda*
Chin. Phys. Lett. 1994, 11 (11): 681-684 .  
Abstract   PDF(pc) (186KB) ( 547 )
Amorphous Nb62.5Si37.5 and Nb75Si25 alloys were produced from mixtures of elemental Nb and Si powders by mechanical alloying (MA). The structural changes of mechanically alloyed powders were monitored by x-ray diffraction. It was found that NbSi2, intermetallic compound was formed in the initial stage of MA of or Nb62.5Si37.5 or Nb75Si25 powders. With continued milling, the mixtures of intermetallic NbSi2 and elemental Nb transformed into amorphous Nb-Si alloys (Nb62.5Si37.5 or Nb75Si25). The slow interdiffusion of Nb and Si and the slower diffusion of silicon atoms to niobium matrix than that of niobium atoms to silicon matrix were suggested to be responsible for the formation of intermetallic NbSi2. The amorphization of 3NbSi2 + 7Nb mixtures (or NbSi2 + 5Nb mixtures) is believed to be controlled by material transfer, which moves composition of line intermetallic NbSi2 off stoichiometry, and causes the matrix of elemental Nb deformed.
Temperature Characteristics of Raman Spectra in Nanometer Material Titanium Dioxide
WU Xijun, ZHANG Ming-sheng, YIN Zhen, JI Xiaoli, CHEN Qiang
Chin. Phys. Lett. 1994, 11 (11): 685-688 .  
Abstract   PDF(pc) (210KB) ( 1059 )
Raman spectra of the nanophase titanium dioxide were examined at various annealing temperatures. The temperature dependences of the Raman modes at 702, 612, 422, 230 -250, and 152cm-1 are discussed. The 702 cm-1 A2g mode belongs to first-order phonon connected to a critical nature of the selection rules with respect to the grain size. Lower anatase-rutile transition temperature 700°C is closely related to smaller grain size. The Eg mode at 422 cm-1 at room temperature shifts upward 24 cm-1 after successive annealing in air for one hour at 700°C, indicating the dependence of the lower mode frequency upon the larger oxygen deficiency.
Electronic Structure of Si-C Alloys
LI Yongping, ZHANG Haifeng, HUANG Xintang
Chin. Phys. Lett. 1994, 11 (11): 689-692 .  
Abstract   PDF(pc) (193KB) ( 354 )
We have systematically studied the electronic structure of the ordered Si-C alloys, fourteen models were created according to the different carbon contents. The linear muffin-tin orbitals method was used to calculate their energy band informations. The functional relation of band gap upon carbon contents conflicts with the point of view of Soref [J. Appl. Phys. Lett. 56 (1990) 734], but agrees well with that of Alexander's [Phys. Rev. B 48 (1993) 2207].
Observation of Barrier-Induced Strain Relaxation in InGaAs/GaAs Single Quantum Wells
SHEN Wenzhong, SHEN Xuechu, TANG Wenguo, T. Andersson*
Chin. Phys. Lett. 1994, 11 (11): 693-696 .  
Abstract   PDF(pc) (211KB) ( 483 )
Resonably good agreement among the photoluminescence, absorption, in-plane photocurrent and theoretical calculation demonstrates the effect of GaAs barrier width on the strain in In0.20Ga0.80As/GaAs single quantum wells. The strain of each sample has been deduced.
Photoemission Studies of K-Promoted Nitridation of InP (100) Surface Using Synchrotron Radiation
ZHAO Texiu, JI Hong, LIANG Qi, WANG Xiaoping, XU Pengshou, LU Erdong, WU Jianxin, XU Zhenjia
Chin. Phys. Lett. 1994, 11 (11): 697-700 .  
Abstract   PDF(pc) (207KB) ( 451 )
The effect of molecular nitrogen exposure on the surfaces of InP(100) modified by potassium overlayers is investigated by core-level and valence-band photoemission spectroscopy using Synchrotron radiation. In comparison with InP(110) surface, we found the promotion is much stronger for InP(100) surface due to the central role of surface defects in the promotion; furthermore, in contrast with K-promoted oxidation of InP(100) where the bonding is observed between indium and oxygen, indium atoms did not react directly with nitrogen atoms during the K-promoted nitridation of InP(100).

High Temperature Limit of Weak Localization in Thin Silver Films
LI Guohong, WANG Min, CHEN Mingling, LIU Guoliang, LIU Sangtian, WANG Shiguang, YAN Shousheng
Chin. Phys. Lett. 1994, 11 (11): 701-704 .  
Abstract   PDF(pc) (196KB) ( 526 )
The behavior of magnetoresistance in thin silver films was investigated from 1.8 up to 104 K. Weak localization effect, manifested by negative magnetoresistance, remains until 88 K in magnetic fields below 2T. Experimental results indicate that weak localization theory for two-dimensional disordercd systems is applicable even when the phase relaxation length L is a few times longer than the elastic mean free path l, provided L is larger than the thickness of films. The obtained phase relaxation time τ obeys 1/T2.6 law.

Spontaneous Magnetization of Small Heisenberg System
SUN Jirong, WEI Yunian, YI Sunsheng, PU Fuke (Fu-cho pu),
Chin. Phys. Lett. 1994, 11 (11): 705-708 .  
Abstract   PDF(pc) (187KB) ( 402 )
Based upon the spin-wave theory, the influence of the size of a cubic Heisenberg system on the spontaneous magnetization was studied. It was found that the overall influence of finite size has a tendency to promote the excitation of spin-wave if the free boundary condition is applied. A comparison between the calculation and the experimental results was also given.
Cubic Silicon Carbite Film Growth and Characterization by Hot Filament Chemical Vapor Deposition
SHI Hongtao, ZHANG Rong, ZHENG Youdou, HE Yuliang, LIU Xiangna
Chin. Phys. Lett. 1994, 11 (11): 709-712 .  
Abstract   PDF(pc) (195KB) ( 556 )
Cubic silicon carbide films (β-Sic) have been successfully grown on monocrystalline silicon wafers by hot filament chemical vapor deposition (HFCVD) at temperatures ranging from 500 to 650°C, fulfilled by a two step process. Raman spectrum of the HFCVD-grown β-SiC films shows a characteristic peak at 975 cm-1 with a full width at half maximum (FWHM) of 76cm-1. At room temperature, the films emit visible photoluminescence at 580nm with an FWHM of 0.4eV. X-ray diffraction and x-ray photoelectron spectroscopy investigations reveal that the epitaxial films are of good quality.
Photoluminescence Study on InGaAs/InP MQW Structure with F+, Ne+-Implant Induced Compositional Disordering.
ZHAO Jie, WANG Yongchen
Chin. Phys. Lett. 1994, 11 (11): 713-716 .  
Abstract   PDF(pc) (190KB) ( 564 )
A photoluminescence (PL) study on InGaAs/InP multiple-quantum wells (MQW) structure with F+, Ne+ implant induced compositional disordering (I ICD) is presented. The effects of energy shift of PL peak depend on ion dose, annealing conditions, target temperature and implanted ion species. The results indicate that the optimum annealing condition is approximately 750°C for 30s, the ion dose which caused biggest blue shift is around 1 x 1014 cm-2 for room temperature implantation and 5 x 1014 cm-2 for elevated temperature of 200°C implantation. With the same condition of implantation and annealing, F+ and Ne+ implantation induced approximately the same blue shift of PL peak. This result suggests that the radiation enhanced diffusion by neutral ion implantation dominates the IICD processing. The secondary ion mass spectroscopy analysis indicates that the ion implantation caused slightly layer interdiffusion which makes the square potential well smear and results in the band gap blue shift.
Computer Simulation of Sputtering and Atomic Redistribution in Hg0.8Cd0.2Te Targets Under Ar+ Ions Bombardment
XING Yuelin, XIA Yueyuan, HU Xierong
Chin. Phys. Lett. 1994, 11 (11): 717-720 .  
Abstract   PDF(pc) (198KB) ( 354 )
The sputtering of Hg0.8Cd0.2Te target by low energy Ar+ ions has been simulated using Monte Carlo method. The simulation results show that the concentration of Hg in the surface region of the target after ion bombardment is lower than the one before ion bombardment, but in a deeper region an excess concentration of Hg is produced due to recoil implantation. The excess concentration of Hg there may act as a donor dopant diffusion source for over doping the acceptor levels in the adjacent region and turn the p-type Hg0.8Cd0.2Te into an n-type material.
16 articles