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Effects of Mg Doping on Photoconductivity of GaN Films

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Journal of Materials Science & Technology 2003年第6期19卷 575-577页

作者： Deheng ZHANG, Qingpu WANG and Yunyan LIUschool of physics and microelectronics, shandong university, jinan 250100, China Sch. of Phys. and microelectronics Shandong Univ. Ji'nan 250100 China

This paper presents the UV photoconductivity properties of GaN films doped with different Mg concentrations deposited by MOCVD. It was observed that for the undoped and weakly doped GaN films the UV photocurrent response was relatively large and the relax time was relatively short. With an increase in doped Mg content, the samples became p-type, the photocurrent response became weak and the relax time became longer.

关键词： GaN UV photodetector Doping MOCVD

Exchange-coupling interaction, effective anisotropy and magnetic property of nano-magnetic materials

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Progress in Natural Science:Materials International 2007年第2期17卷 131-137页

作者： SUN Yan, GAO Ruwei, HAN Baiping, LIU Min, HAN Guangbing and FENG Weicun (school of physics and microelectronics, shandong university, jinan 250100, China) school of physics and microelectronics Shandong University Jinan 250100 China

The theories and models of exchange-coupling interaction between grains in nanocrystalline magnetic materials are introduced here. Their insufficiencies and distinctions from the experimental results are pointed out, and some revisions are made. The effects of the phase component ratio, the grain size and microstructure on the effective anisotropy and magnetic properties in the nanocomposite permanent materials and the improved models are discussed in detail.

关键词： nano-magnetic materials exchange-coupling interaction microstructure effective anisotropy magnetic property.

Electronic Structure of New Superconducting Perovskite MgCNi3

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Journal of Materials Science & Technology 2004年第2期20卷 203-205页

作者： Li CHEN, Hua LI and Liangmo MEIphysics and Microelectronic school, shandong university,{3., China Department of physics, Linyi Teachers university, shandong 276005, China Phys. and Microelectron. Sch. Shandong Univ. Ji'nan 250100 China Dept. of Phys. Linyi Teachers Univ. Linyi 276005 China

The electronic structures of new superconducting perovskite MgCNi3.and related compounds MgCNi2T (T=Co, Fe, and Cu) have been studied using MS-Xa method. In MgCNi3. the main peak of density of states is located below the Fermi level and dominated by Ni d. From the results of total energy calculations, it was found that the number of Ni valence electron decreases faster for the Fe-doped case than that for the Co-doped case. The valence state of Ni changes from +1.43.in MgCNi2Co to +3.02 in MgCNi2Fe. It was confirmed that Co and Fe dopants in MgCNi3.behave as a source of d-band holes and the suppression of superconductivity occurs faster for the Fe-doped case than that for the Co-doped case. In order to explain the fact that Co and Fe dopants in MgCNi3.behave as a source of d-band holes rather than magnetic scattering centers that quench superconductivity, we have also investigated the effects of electron (Cu) doping on the superconductivity and found that both electron (Cu) doping and hole (Co, Fe) doping quench superconductivity exist. Comparing with the hole (Co) doping, there was no much difference between Cu and Co doping. This suggests that Co and Fe doping do not act as magnetic impurity.

关键词： Electronic structure Superconductivity Density of states

DFT study of the conductance of molecular wire:The effect of coupling geometry and intermolecular interaction on the transport properties

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Science China Chemistry 2006年第6期49卷 492-498页

作者： QI Yuanhua1,2, GUAN Daren1 & LIU Chengbu1 1. Institute of Theoretical Chemistry, shandong university, jinan 250100, China 2. school of physics and microelectronics, shandong university, jinan 250061, China Institute of Theoretical Chemistry Shandong University Jinan China school of physics and microelectronics Shandong University Jinan China

The density functional theory (DFT) combining with the non-equilibrium Green functions (NEGF) method is applied to the study of the electronic transport properties for a Di-thiol-benzene (DTB) molecule coupled to two Au(111) surfaces. The dependence of the transport properties on the bias, the coupling geometry of the molecule-electrode interface, and the intermolecular interaction are examined in detail. The results show that the existence of the hydrogen atom at the end of the DTB molecule would significantly decrease the transmission coefficients, and then the differential conductance (dI/dV). By changing the position of the DTB molecule located between two electrodes a maximum value of calculated current is observed. It is also found that the intermolecular interaction will strongly influence the transport properties of the system studied.

关键词： non-equilibrium Green functions method, transmission spectrum, the molecular projected selfconsistent Hamiltonian, projected density of state.

Influence of solidification rate on the microstructure of (Nd,Dy)_(12.8)(Fe,Co)_(80.7)B_(6.5) cast strips

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Rare Metals 2005年第2期24卷 200-204页

作者： LIUHanqiang WANGBiao HANGuangbing GAORuwei schoolofphysicsandmicroelectronics ShandongUniversityJinan250100China

The influence of solidification rate on the microstructure of (Nd,Dy)(12.8)(Fe,Co)(80.7)B-6.5 cast strips was reported in this paper. The strips prepared at different wheel speeds were analyzed by X-ray diffraction (XRD). The microstructure of the strips was investigated by backscattered scanning microscope (BSM). The XRD results show that the strips are mainly composed of the main phase (T-1) existing apparent alignment along [00L]. The thickness of T-1 columnar grains is larger when the solidification rate is lower and the over-small isotropic microcrystalline appear on the cooling surface of the strips when the solidification rate is too high. The adequate wheel speed for obtaining the optimum microstructure of the strips is about V = 2.0 m/s. The strip prepared at V = 2.0 m/s possesses suitable thickness and the highest alignment degree of T-1 columnar grains, uniformly distributed Nd-rich phase, and no existence of alpha-Fe phase. This kind of cast strip is an ideal starting material for preparing sintered magnets with high magnetic properties.

关键词： metal material microstructure solidification rate cast strip Nd-Fe-B

An investigation of hadronization mechanism at a Z^0 factory

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Science China(physics,Mechanics & Astronomy) 2010年第11期53卷 1998-2004页

作者： JIN Yi 1,SI ZongGuo 2,XIE QuBing 2 & YAO Tao 2 1 Department of physics,university of jinan,jinan 250022,China 2 school of physics,shandong university,jinan 250100,China Department of physics University of Jinan Jinan China school of physics Shandong University Jinan China

We briefly review the hadronization pictures adopted in the LUND String Fragmentation Model (LSFM),Webber Cluster Fragmentation Model (WCFM) and Quark Combination Model (QCM),*** of hadron multiplicity,baryon to meson ratios and baryon-antibaryon flavor correlations,especially those related to heavy hadrons at a Z 0 factory obtained by LSFM and QCM,are reported.

关键词： Z0 factory hadronization model baryon to meson ratio B correlation

A first-principles study of dihydroazulene as a possible optical molecular switch

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Science China(physics,Mechanics & Astronomy) 2011年第3期Mechanics & Astronomy) .卷 437-441页

作者： XIA CaiJuan1, LIU DeSheng2,3.& LIU HanChen1 1 school of Science, Xi’an Polytechnic university, Xi’an 710048, China 2 school of {3., State Key Laboratory of Crystal Materials, shandong university, jinan 250100, China 3.Department of {3., Jining university, Qufu 273.55, China school of Science Xi’an Polytechnic University Xi’an China school of physics State Key Laboratory of Crystal Materials Shandong University Jinan China Department of physics Jining University Qufu China

By applying nonequilibrium Green's function formalism combined with first-principles density functional theory, we investigate the electronic transport properties of the dihydroazulene optical molecular switch. Three kinds of adsorption sites including the hollow, bridge and top sites are studied. The two forms of this molecule, namely the open form and the closed form, can reversibly switch from each other upon photoexcitation. Their transmission spectra are remarkably distinctive. Theoretical results show that the current of the closed form is always significantly larger than that of the open form for all three adsorption sites, which promises this system as possibly one of the good candidates for optical switches due to its unique advantage, and which may have some potential applications in the future molecular circuit.

关键词： molecular switch nonequilibrium Green’s function electronic transport density functional theory

Geometric and Electronic Structure of Squaric Acid from DFT Calculation

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Journal of Materials Science & Technology 2004年第2期20卷 206-208页

作者： Xuyan XUE, Chunlei WANG and Weilie ZHONGschool of physics and microelectronics, State Key Laboratory of Crystal Materials, shandong university, jinan 250100, China shandong Univ Sch Phys & Microelect State Key Lab Crystal Mat Jinan 250100 Peoples R China

The crystal and electronic structure of antiferroelectric squaric acid is studied using density functional theory method, and the exchange correlation effects are treated by the generalized approximation. In order to understand the ferroelectricity of H2SQ in the molecular plane and the antiferroelectricity in whole crystal, the density of states, charge density distribution and band structure are calculated. The result showed that O2p and C2p play important roles in the interactions between layers. The hybridizations of 02s-Hls and 02p-Hls are responsible for the tendency to ferroelectricity within each layer.

关键词： Antiferroelectricity Electronic structure Squaric acid

Ground state and polaron and bipolaron excited states in polydiacetylene

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Science China(physics,Mechanics & Astronomy) 2006年第4期49卷 430-439页

作者： LI Yuan1, HU Guichao1, XIA Caijuan1, LIU Desheng1,2 & XIE Shijie1,2 1. school of physics and microelectronics, shandong university, jinan 250100, China 2. National Key Laboratory of Crystal Materials, shandong university, jinan 250100, China school of physics and microelectronics Shandong University Jinan China National Key Laboratory of Crystal Materials Shandong University Jinan China

The electronic properties of ground state and charged excited states of nondegenerate polydiacetylene were investigated by means of a tight-binding model. The parameters of the model were obtained by comparison of the experimental and other theoretical results. It was found that there is a stable dimerized structure of polydiacetylene in ground state and the doping induces the nonlinear excitations, such as polarons and bipolarons. In order to compare the stability of polaron and bipolaron, the creation energy and binding energy were separately defined. By neglecting the electron-electron Coulomb interaction, a bipolaron is more stable than two independent polarons.

关键词： dimerization, polaron, bipolaron, binding energy.