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Molecular dynamics simulation of thermal stability of nanocrystalline vanadium

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Science china(Technological Sciences) 2006年第4期49卷 400-407页

作者： WEI Mingzhi1, XIAO Shifang1, YUAN Xiaojian2.& HU Wangyu1,2.1. Material Science and Engineering College, Hunan university, Changsha 410082. china 2. {2. of Applied physics, Hunan university, Changsha 410082. china Material Science Engineering College Hunan University Changsha 410082 China department of Applied physics Hunan University Changsha 410082 China

The microstructure and thermal stability of nanocrystalline vanadium with an average grain size ranging from 2.86 to 7.50 nm are calculated by means of the analytic embedded-atom method and molecular dynamics. The grain boundary and nanocrystal- line grain atoms are differentiated by the common neighbor analysis method. The results indicate that the fraction of grain boundary increases with the grain size decreasing, and the mean energy of atoms is higher than that of coarse crystals. The thermal-stable tem- peratures of nanocrystalline vanadium are determined from the evolution of atomic energy, fraction of grain boundary and radial distribution function. It is shown that the stable tem- perature decreases obviously with the grain size decreasing. In addition the reasons which cause the grain growth of nanocrystalline vanadium are discussed.

关键词： nanocrystalline, embedded-atom method, molecular dynamics, thermal stability.

I-V and C-V properties of TiO_2.thin film by pulsed-laser reactive deposition

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Chinese Science Bulletin 1998年第16期43卷 1344-1349页

作者： FU Zhengwen 1, ZHOU Mingfei 1, ZHANG Shengkun 2.CHEN Lianyao 2.and QIN Qizong 1 1. Laser Chemistry Institute, Fudan university, Shanghai 2.0433, china {2., Fudan university, Shanghai 2.0433, china Laser Chemistry Institute Fudan University Shanghai China department of Pnysics Fudan University Shanghai China

TiO-2.thin films have bee deposited on p-Si(111) substrates by pulsed-laser ablation of metallic Ti target in the O-3 ambient. The current-voltage and capacitance-voltage of the Al/TiO-2.Si capacitors are measured. The results show that the dielectric constant of thin film after being annealed at 700℃ is found to be 46, and the border trap density and the interface state density at the TiO-2.p-Si interface are 1.8×10 12.cm -2.and 2.10 12.eV -1·cm -2. respectively. The conduction mechanisms of as-deposited films are also discussed.

关键词： TiO-2 dielectric properties electrical properties pulsed-laser deposition.

Finite size effects on helical edge states in HgTe quantum wells with the spin orbit coupling due to bulk- and structure-inversion asymmetries

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Chinese physics B 2014年第3期23卷 498-503页

作者：成志周斌 department of physics Hubei University

There is a quantum spin Hall state in the inverted HgTe quantum well, characterized by the topologically protected gapless helical edge states lying within the bulk gap. It has been found that for a strip of finite width, the edge states on the two sides can couple together to produce a gap in the spectrum. The phenomenon is called the finite size effect in quantum spin Hall systems. In this paper, we investigate the effects of the spin-orbit coupling due to bulk- and structure-inversion asymmetries on the finite size effect in the HgTe quantum well by means of the numerical diagonalization method. When the bulk-inversion asymmetry is taken into account, it is shown that the energy gap Eg of the edge states due to the finite size effect features an oscillating exponential decay as a function of the strip width of the HgTe quantum well. The origin of this oscillatory pattern on the exponential decay is explained. Furthermore, if the bulk- and structure-inversion asymmetries are considered simultaneously, the structure-inversion asymmetry will induce a shift of the energy gap Eg closing point. Finally, based on the roles of the bulk- and structure-inversion asymmetries on the finite size effects, a way to realize the quantum spin Hall field effect transistor is proposed.

关键词： quantum spin Hall state finite size effect spin-orbit coupling

The size effect on transport properties of colossal magnetoresistance materials La_(0.67)Ca_(0.33)MnO_3

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Science china(physics,Mechanics & Astronomy) 2008年第3期51卷 251-257页

作者： LI PeiGang1,2.LEI Ming1,2.GUO YanFeng2.GUO Xi2.CHEN LeiMing2. TANG WeiHua1,2.SONG PengYun3 & CHEN JinPing3 1 department of physics,Center for Optoelectronics Materials and Devices,Zhejiang Sci-Tech {2.,Hangzhou 310018,china 2.National Laboratory for Condensed Matter physics,Institute of physics,Chinese Academy of Sciences,Beijing 100080,china 3 department of physics,Peking {2.,Beijing 100875,china 1. department of physics Center for Optoelectronics Materials and Devices Zhejiang Sci-Tech University Hangzhou 310018 China 2. National Laboratory for Condensed Matter physics Institute of Physics Chinese Academy of Sciences Beijing 100080 China 3. department of physics Peking University Beijing 100875 China

High quality La0.67Ca0.33MnO3 (LCMO) film was deposited via a novel pulsed electron deposition technique on SrTiO3(100) single crystal substrate. The micro-bridge with different widths was fabricated by using electron beam lithography (EBL) technique and their transport properties were studied. For the micro-bridges with width of 2.and 1.5 μm,the insulator-to-metal transition temperature (TP) keeps un-changed compared with the film. For the micro-bridges with width of 1 μm,the TP shifts towards the lower temperature by 50 K. When the width decreases down to 500 nm,the insulator-to-metal transition disappears. The magnetoresistance be-havior of these micro-bridges was studied,and the results show that the low field magnetoresistance (LFMR) decreases and the high field magnetoresistances (HFMR) keep almost unchanged as the width of micro-bridge is reduced.

关键词： colossal magnetoresistance pulsed electron deposition electron beam lithography electrical transport properties

Solvothermal synthesis of nanocrystalline FeS_2

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Science china(physics,Mechanics & Astronomy) 2005年第2期48卷 188-200页

作者： CHEN Yanhua1, ZHENG Yufeng1, ZHANG xiaogang2. SUN Yanfei1 & DONG Youzhong11. physics {2. of Xinjiang university, Urumqi 830046, china 2. Institute of Applied Chemistry of Xinjiang university, Urumqi 830046, china physics department of Xinjiang {2. Urumqi 830046 China Institute of Applied Chemistry of Xinjiang university Urumqi 830046 China

This paper reports on the synthesis of the nanocrystalline FeS2.via a solvent-thermal process. Using FeSO4 and NH2.SNH2.as precursors and polyvinyl- pyrrolidone (PVP) as a protective agent (dispersant), we have successfully synthesized nanocrystalline FeS2.both under acidic conditions (pH = 5) and under alkali conditions (pH = 10) at various temperatures and for different time in alcohol-water solution. X-ray diffraction (XRD), Transmission electron microscopy (TEM) and Ultraviolet Visible (UV-VIS) spectroscopy were used to characterize the morphology, structure, particle size and optical characterization of sample synthesized under acidic condition, and the XRD pattern was refined by Rietveld method. The experimental result shows that nanocrystalline FeS2.with uniform size, highly crystallized quality and excellent dispersivity has been synthesized at 2.0℃for 36 h.

关键词： FeS2 (Pyrite), solvothermal, PVP, the Rietveld method.

X-ray spectra induced by ^(12.)Xe^(q+) impacting the metal surface

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Science china(physics,Mechanics & Astronomy) 2008年第1期51卷 82-89页

作者： ZHANG XiaoAn 1,2.,XIAO GuoQing 1 ,YANG ZhiHu 1 ,CHEN XiMeng 3 ,ZHAO YongTao 1 , LI FuLi 4 ,WANG Li 1,2.,CUI Ying 3 ,ZHANG HongQiang 3 &ZHAN WenLong 1 1Institute of Modern physics,Chinese Academy of Sciences,Lanzhou 730000,china 2.2. of physics,Xianyang Normal university,Xianyang 712.00,china 3{2. of Modern physics,Lanzhou university,Lanzhou 730000,china 4{2. of Applied physics,Xi’an Jiaotong university,Xi’an 710049,china 1. Institute of Modern physics Chinese Academy of Sciences Lanzhou 730000 China 2. department of physics Xianyang Normal University Xianyang 712000 China 3. department of Modern physics Lanzhou University Lanzhou 730000 China 4. department of Applied physics Xi’an Jiaotong University Xi’an 710049 China

Using the slow highly charged ions 12. Xe q+ (q=2.,2.,2.;initial kinetic T0≤4.65 keV/a.u.)to impact Au surface,the Au atomic Mαcharacteristic X-ray spectrum is *** result shows that as long as the charge state of projectile is high enough,the heavy atomic characteristic X-ray can be effectively excited even though the incident beam is very weak(nA magnitude),and the X-ray yield per ion is in the order of 10-8and increases with the kinetic energy and potential energy of *** measuring the Au Mα-X-ray spectra,Au atomic N-level lifetime is estimated at about 1.33×10-18s based on Heisenberg uncertainty relation.

关键词： slow highly charged ions characteristic X-ray level lifetime

Imaging theory of nonlinear second harmonic and third harmonic generations in confocal microscopy

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Science china(physics,Mechanics & Astronomy) 2004年第1期47卷 8-16页

作者： TANG Zhilie1, XING Da2.& LIU Songhao2.1. department of physics, South{2. Normal university, Guangzhou 510631,{2. 2. School for Information and Optoelectronic Science and Engineering, South{2. Normal university, Guangzhou 510631,{2. Correspondence should be addressed to Tang Zhilie (email: tangzhl@***) Received April 2., 2.03 1. department of physics South China Normal University 510631 Guangzhou China 2. School for Information and Optoelectronic Science and Engineering South China Normal University 510631 Guangzhou China

The imaging theory of nonlinear second harmonic generation (SHG) and third harmonic generation (THG) in confocal microscopy is presented in this paper. The nonlinear effect of SHG and THG on the imaging properties of confocal microscopy has been analyzed in detail by the imaging theory. It is proved that the imaging process of SHG and THG in confocal microscopy, which is different from conventional coherent imaging or incoherent imaging, can be divided into two different processes of coherent imaging. The three-dimensional point spread functions (3D-PSF) of SHG and THG confocal microscopy are derived based on the nonlinear principles of SHG and THG. The imaging properties of SHG and THG confocal microscopy are discussed in detail according to its 3D-PSF. It is shown that the resolution of SHG and THG confocal microscopy is higher than that of single- and two-photon confocal microscopy.

关键词： second harmonic generation, third harmonic generation, confocal microscopy, three-dimensional point spread function.

Recurrence spectra of He atoms in strong external fields

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Science china(physics,Mechanics & Astronomy) 2004年第4期47卷 477-484页

作者： LIN Shenglu1, LI Hongyun1, WANG Dehua2. ZHAO Wenli1 & GAO Feng1 1. department of physics, Shandong Normal {2., Jinan 2.0014, china 2. department of Mathematics and physics, Shandong Institute of Architecture and Engineering, Jinan 2.0014, china 1. department of physics Shandong Normal University 250014 Jinan China 2. department of Mathematics and physics Shandong Institute of Architecture and Engineering 250014 Jinan China

By employing a model potential including the electron exchange energy, we extend the semiclassical closed orbit theory to study the multielectron atoms. Using special region-splitting consistent and iterative method, we figure out the closed orbits in the corresponding classical system and calculate the recurrence spectra of triplet helium atoms in parallel electric and magnetic fields at scaled energy ε=?0.03,n≈40,n=0. The core-scattering effects have been taken into account, which lead to more peaks in the spectra. It has also been confirmed by means of the direct comparison between the spectral portrait in such a plot and those of hydrogen case. In order to compare the theoretic results with experiment, we investigate the closed orbits and recurrence spectra of helium atoms for the similar exchange potential but applied only by single electric field at scaled energy ε=?2.7 case. The spectra are in good agreement with the experimental observation. We conclude that our model is correct and it is necessary to consider the exchange effect for determining the photoabsorption spectra of multielectron atoms in strong external fields.

关键词： exchange potential, recurrence spectra, semiclassical closed orbit theory, core-scattering.

A Classical Toda Family with a Common Virasoro Symmetry Algebra

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Communications in Theoretical physics 2004年第6期41卷 813-815页

作者： QIAN Xian-Min LOU Sen-Yue ~1department of physics,Shanghai Jiao Tong {2.,Shanghai 2.0030,china ~2.0} of physics,Shaoxing College of Arts and Sciences,Shaoxing 312.00,china department of physics,Ningbo {2.,Ningbo 3152.1,china department of physics Ningbo University Ningbo 315211 China

By means of a simple ideal,which is firstly proposed for the continuous system,we present an arbitraryorder classical Toda family invariant under common Virasoro-type symmetry algebra.

关键词： classical Toda family Virasoro symmetry algebra