三明治结构Tan(B3N3H6)n+1 团簇的磁性和量子输运性质

利用密度泛函理论和非平衡格林函数方法, 本文对小尺寸团簇Ta_n(B₃N₃H₆)_n+1 (n ≤ 4)的磁性和量子输运性质进行了系统的研究. 计算结果表明, 此类体系采用三明治结构作为其基态并且具有较高的稳定性. 体系的磁矩随团簇尺寸的增大而线性增大. 当把Ta_n(B₃N₃H₆)_n+1团簇耦合到Au电极上时, 形成的Au-Ta_n(B₃N₃H₆)_n+1-Au体系在有限偏压下展示出了较强的自旋过滤能力, 因而可以被看做是一类新型的低维自旋过滤器.     

B12N12纳米笼：潜在的二氧化氮检测传感器

利用密度泛函理论通过计算吸附能量、HOMO/LUMO能隙变化、电荷转移、结构扭曲等研究二氧化氮分子在B12N12纳米笼的吸附．此外,通过计算B₁₂N₁₂的电子结合能、Gibbs自由能、态密度和分子表面的静电势研究其稳定性和其它特性．B₁₂N₁₂纳米笼吸附二氧化氮显示三种构型．B₁₂N₁₂团簇的HOMO/LUMO能隙变化对二氧化氮分子的存在非常敏感,从自由团簇的6.84 eV降为NO₂/团簇稳定团簇的3.23 eV．团簇的导电性被极大地提高,表明B₁₂N₁₂纳米簇可能是潜在的二氧化氮气体分子检测传感器.     

Using the e ± μ? + E Tmiss signature in the search for supersymmetry and lepton-flavor violation in neutralino decays

The LHC (CMS) discovery potential in the search for supersymmetry and lepton-flavor violation in neutralino decays using the e ^± μ^∓ + E _T ^miss signature is studied. A detailed study is done for the CMS test points LM1-LM9. It is shown that, for the point LM1, it is possible to detect lepton-flavor violation in neutralino decays with lepton-flavor-violating branching Br( → μ^± e ^∓ ) ≥ 0.04 Br( → e ⁺ e ⁻ , μ⁺ μ⁻ ) for an integral luminosity of 10 fb⁻¹. The discovery potential in the mSUGRA-SUSY scenario with tan β = 10, sgn(μ) = + in the (m ₀, m _1/2) plane using the e ^± μ^∓ + E _T ^miss signature is determined. The text was submitted by the authors in English.     

虚晶近似法研究AlN-Al2O3固溶体系的力学性能和电子结构

基于密度泛函理论的第一性原理平面波赝势方法, 运用虚晶近似方法计算了AlN-Al₂O₃固溶区内尖晶石相氮氧化铝(Al₂₄O₂₄N₈, Al₂₃O₂₇N₅和Al₂₂O₃₀N₂)和α-Al₂O₃, AlN的力学性能和电子结构. 结果证明虚晶近似法应用到氮氧化铝结构计算中是可行的. 力学常数计算结果和弹性模量B, 剪切模量G, 杨氏模量E反映的材料硬度变化趋势与实验基本一致;Al₂O₃-AlN固 溶区内五种结构均为脆性性质且Al₂₃O₂₇N₅脆性最低, 硬度高、脆性低的特性反映了Al₂₃O₂₇N₅优异的抗弯强度性能. 五种结构满足力学结构上的稳定性, 立方尖晶石相氮氧化铝表现为弹性各向异性. 能带和态密度的计算分析表明这五种结构均为直接宽带隙结构. 在费米能级附近, 氮氧化铝结构中阴离子的2p态和阳离子的3s, 3p态发生了轨道杂化. 理论结果与实验数据基本符合, 为进一步研究提供了一定的理论方法和依据.     

Exotic states X ±(1600, I G (J PC)=2+ (2++)) in photoproduction reactions

It is shown that the list of unusual mesons that are planned to be studied in photoproduction reactions can be supplemented with I ^G (J ^PC)=2⁺ (2⁺⁺) exotic states X ^±(1600), which are natural to seek as manifestations of the ρ^±ρ⁰ decay channels in the reactions γN → ρ^±ρ⁰ N and γN → ρ^±ρ⁰Δ. A classification of the ρ^±ρ⁰ states according to their quantum numbers is presented. A model for the spin structure of the amplitudes for the reactions γp → f ₂(1270)p, γp → a ₂ ⁰ (1320)p, and γN → X ^±(N, Δ) is proposed, and estimates are obtained for the corresponding cross sections. At E _γ≈6 GeV, it is found that σ(γP → f ₂(1270)p)≈0.12 μb, σ(γp → a ₂ ⁰ (1320)p)≈0.25 μb, σ(γN → X ^± N → ρ^±ρ⁰ N) ≈ 0.018 μb, and σ(γp → X ⁻Δ⁺⁺ → ρ⁻ρ⁰Δ⁺⁺≈0.031 μb. The problem of isolating signals from X ^± states against the natural background that is associated with other channels of π^±π⁰π⁺π⁻ production is discussed. It is deduced that searches for exotic states X ^±(2⁺ (2⁺⁺)) in experiments at JLAB will be quite efficient—for example, the yield of about 2.8×10⁶ events per month is expected to correspond to the estimated cross sections for the reactions γN → X ^± N → ρ^±ρ⁰ N. __________ Translated from Yadernaya Fizika, Vol. 63, No. 10, 2000, pp. 1904–1912. Original Russian Text Copyright ? 2000 by Achasov, Shestakov.     

Magnetotransport of the low-carrier density one-dimensional S=1/2 antiferromagnet Yb4As3

The transport properties of the semimetallic quasi-one-dimensional S=1/2 antiferromagnet Yb₄As₃ have been studied by performing low-temperature (T≥0.02 K) and high magneticfield (B≤60 T) measurements of the electrical resistivity ρ(T, B). For T ≿ 2 K a ‘heavy-fermion’-like behavior Δρ(T)=AT ² with huge and nearly field-independent coefficient A ≈ 3 μΩ cm/K² is observed, whereas at lower temperatures ρ(T) deviates from this behavior and slightly increases to the lowest T. In B>0 and T ≾ 6 K the resistivity shows an anomalous magnetic-history dependence together with an unusual relaxation behavior. In the isothermal resistivity Shubnikov-de Haas (SdH) oscillations, arising from a low-density system of mobile As-4p holes, with a frequency of 25 T have been recorded. From the T- and B-dependence of the SdH oscillations an effective carrier mass of (0.275±0.005)m ₀ and a charge-carrier mean-free path of 215 ? are determined. Furthermore, in B≥15 T, the system is near the quantum limit and spin-splitting effects are observed.     

Investigations of spectroscopic parameters and molecular constants for X1Σg+, w3Δu, and W1Δu electronic states of P2 molecule

The potential energy curves (PECs) of three low-lying electronic states (X¹Σ_g⁺, w³Δ_u, and W¹Δ_u)of P₂ molecule are investigated using the full valence complete active space self-consistent field (CASSCF) method followed by the highly accurate valence internally contracted multireference configuration interaction (MRCI) approach in conjunction with the correlation-consistent basis set in the valence range. The PECs of the electronic states involved are modified by the Davidson correction and extrapolated to the complete basis set (CBS) limit. With these PECs, the spectroscopic parameters of the three electronic states are determined and compared in detail with the experimental data. The comparison shows that excellent agreement exists between the present results and the available experimental data. The complete vibrational states are computed for the w³Δ_u, and W¹Δ_u electronic states when the rotational quantum number J equals zero and the vibrational level G(v), the inertial rotation constant B_v, and the centrifugal distortion constant D_v of the first 30 vibrational states are reported, which accord well with the experimental data. The present results show that the two-point extrapolation scheme can obviously improve the quality of spectroscopic parameters and molecular constants.     

Interactions of charmed mesons with nucleons in the ¯<Emphasis Type="Italic">p</Emphasis><Emphasis Type="Italic">d</Emphasis> reaction

We study the possibility to measure the elastic ΦN (Φ≡J/ψ,ψ(2S), ψ(3770), χ_2c) scattering cross section in the reaction ˉp+d→Φ+n _sp and the elastic D(ˉD)N scattering cross section in the reaction ˉp+d→D ⁻ D ⁰ p _sp. Our studies indicate that the elastic scattering cross sections can be determined for Φ momenta about 4–6 GeV/c and D/ˉD momenta 2–5 GeV/c by selecting events with p _t≥ 0.4 GeV/c for Φ's and p _t(p _sp) ≥ 0.5 GeV/c for D/ˉD-meson production. Received: 8 November 1999     

Observation of diamagnetic domains in beryllium

We have observed diamagnetic domains (Condon domains) in a beryllium single crystal in magnetic fields H⩽3 T (H∥[0001]) at liquid-helium temperatures. The formation of the domain structure was determined according to magnetic-breakdown quantum oscillations of the resistance thermoelectric power as well as according to the splitting of the resonance peak of the free spin precession frequency of muons (μSR). The alternation of a uniform state (with one μSR peak) and a state with domain structure (with two peaks) is consistent as regards the periodicity with the de Haas-van Alphen effect, the period is ΔH≅78 Oe, and the range of existence of domains and the difference in their magnetizations are ΔB=4πΔM=B ₂−B ₁≅30 Oe. Fiz. Tverd. Tela (St. Petersburg) 40, 524–526 (March 1998)     

多模奇相干态光场中的N-Y最小测不准态与N-H最小测不准态

本文根据新近建立的多模辐射场的广义非线性等阶高阶压缩理论,对多模奇相干态光场|Ψ,o〉_q中的N次方Y压缩、N次方H压缩、N-Y最小测不准态以及N-H最小测不准态等进行了详细研究.结果表明:1)当压缩阶数N为偶数时,多模奇相干态|Ψ,o〉_q总是恒处于N-Y最小测不准态;当N为奇数时,态|Ψ,o〉_q既不处于N-Y最小测不准态,也不呈现N次方Y压缩效应.2)当q & #183;N为偶数时,多模奇相干态|Ψ,o〉_q总是恒处于N-H最小测不准态;当q & #183;N为奇数时,态|Ψ,o〉_q既不处于N-H最小测不准态,也不呈现N次方H压缩效应.3)多模奇相干态|Ψ,o〉_q恒处于N-Y最小测不准态与恒处于N-H最小测不准态的条件明显不同,两者存在着严格的区别.     

Electronic structure and the infrared absorption and Raman spectra of the semiconductor clusters C24, B12N12, Si12C12, Zn12O12, and Ga12N12

The optimized configurations, electronic structures, charge transfers, band gaps, total energies, cohesive energies, electron density maps, infrared absorption spectra, Raman spectra, and relevant modes of natural acoustic vibrations for the semiconductor clusters C₂₄, B₁₂N₁₂, Si₁₂C₁₂, Zn₁₂O₁₂, and Ga₁₂N₁₂ are calculated using the ab initio Hartree-Fock method in the 6–31G basis set. Original Russian Text ? V.V. Pokropivny, L.I. Ovsyannikova, 2007, published in Fizika Tverdogo Tela, 2007, Vol. 49, No. 3, pp. 535–542.     

Ab initio investigation of hydrogenation of (BN)12

Ab initio molecular orbital theory was used to examine the hydrogenation of a B₁₂N₁₂ molecule. The 1,2 addition of the 4,6 bond is an energetically favorable adsorption site in one-hydrogen-molecule adsorption. We found that the averaged bind energy of hydrogen molecule is maximized in B₁₂N₁₂H₁₂. The largest energy gaps of B₁₂N₁₂H₁₂ and B₁₂N₁₂H₂₄ suggest they have special stability. Moreover, calculation of the Gibbs free energy of the B₁₂N₁₂ + 12H₂ → B₁₂N₁₂H₂₄ reaction showed that this reaction becomes endothermic above 320 K.     

金属/多孔硅/单晶硅(M/PS/Si)微结构的电学特性

采用双槽电化学腐蚀法制备多孔硅层,然后在多孔硅表面沉积形成金属电极,制备出M/PS/Si微结构.利用SEM分析多孔硅的表面形貌,通过测试其I-V特性分析M/PS/Si微结构的电学特性.结果表明:由Pt做电极形成的M/PS/Si结构,表现出非整流特性.M/PS/Si结构的I-V曲线由线性区和非线性区组成,多孔硅孔隙率越高的M/PS/Si结构的I-V特性曲线线性区越宽.由Cu做电极形成的M/PS/Si结构,表现出整流特性.其整流比随多孔硅孔隙率增加而减小. 关键词： M/PS/Si微结构 孔隙率 I-V特性')" href="#">I-V特性 欧姆接触     

Calculation of the spectroscopic constants for the electronic states A1Σ u+ , B1Πu, C1Πu, D1Σ u+ , and E1Σ u+ of the cesium dimer

The vibrational, rotational, and centrifugal distortion constants have been calculated for the electronic states A ¹Σ _u ⁺ , B ¹Π_u, C ¹Π_u, D ¹Σ _u ⁺ , and E ¹Σ _u ⁺ of the Cs₂ molecule. The calculation was performed on the basis of the semiempirical potential energy curves constructed in this paper. The calculated spectroscopic constants are compared with the experimental data. Original Russian Text ? A.D. Smirnov, 2007, published in Optika i Spektroskopiya, 2007, Vol. 102, No. 1, pp. 23–27.     

Effects of endohedral element in B24N24 clusters on hydrogenation studied by molecular orbital calculations

Possibility of hydrogen gas storage in boron nitride (BN) clusters was investigated by molecular orbital calculations. Chemisorption calculation was carried out for B₂₄N₂₄ with changing endohedral elements in BN cluster to compare the bonding energy at nitrogen and boron, which showed that Li is a suitable element for hydrogenation to B₂₄N₂₄.     

Nd0.7Sr0.3MnO3陶瓷EPIR效应的起源

用两线法和四线法对球磨合成后热处理的Nd_0.7Sr_0.3MnO₃陶瓷样品的电脉冲诱导电阻转变(EPIR)效应进行了测试.结果表明:在Nd_0.7Sr_0.3MnO₃块体中用四线法测得的I-V曲线为非线性,说明Nd_0.7Sr_0.3MnO₃样品在晶(相)界处存在空间电荷层和界面电阻.但用四线法测量EPIR效应时,没有EPIR效应发生,表明晶(相)界处的空间电荷层和肖特基势垒不能产生EPIR效应;对同一样品采用直流两线法测量,其I-V曲线也为非线性,但却发生明显的EPIR效应.说明在Nd_0.7Sr_0.3MnO₃陶瓷中发现的EPIR效应起源于样品与电极之间的接触界面,块体内的晶(相)界处虽能产生相似I-V特性,但却不能发生EPIR效应. 关键词： 电脉冲诱导电阻转变(EPIR) 亚锰酸盐 空间电荷层 I-V非线性')" href="#">I-V非线性     

A single molecule switch based on two Pd nanocrystals linked by a conjugated dithiol

Tunneling spectroscopy measurements have been carried out on a single molecule device formed by two Pd nanocrystals (dia. ∼5 nm) electronically coupled by a conducting molecule, dimercaptodiphenylacetylene. TheI-V data, obtained by positioning the tip over a nanocrystal electrode, exhibit negative differential resistance (NDR) on a background M-I-M characteristics. The NDR feature occurs at ∼0.67 V at 300 K and shifts to a higher bias of 1.93 V at 90 K. When the tip is held in the middle region of the device, a Coulomb blockade region is observed (±∼0.3 V)     

Smallest fullerene-like clusters in two-probe device junctions: first principle study

First principle calculations based on density functional theory are realised to investigate the electron transport of the smallest fullerene-like clusters as two-probe junction devices. The junction devices are constructed by mechanically controlled break junction techniques to ensure the maximum stability of the Be₂₀, B₂₀ and N₂₀ cluster molecular junctions. We investigate the density of states, transmission spectrum, molecular orbitals, current and differential conductance characteristics at discrete bias voltages to gain insight about the various transport phenomena occurring in these nano-junctions. The results show that B₂₀ molecule when stringed to gold electrodes works as an ideal nano-device similar to the pure C₂₀ device and is more symmetric in its characteristic nature. However, in N₂₀ molecular device, the conduction is negligible due to the higher atomic interactions within N₂₀ molecule, despite the fact that it is constructed with penta-valent atoms.     

Absolute cross sections of electron attachment to molecular clusters. Part II: Formation of (H2O) N? , (N2O) N? , and (N2) N?

Absolute cross sections σ⁻(E, N) of electron attachment to clusters (H₂O) _N , (N₂O) _N , and (N₂) _N for varying electron energy E and cluster size N are measured by using crossed electron and cluster beams in a vacuum. Continua of σ⁻(E) are found that correlate well with the functions of electron impact excitation of molecules’ internal degrees of freedom. The electron is attached through its solvation in a cluster. In the formation of (H₂O) _N ⁻ , (N₂O) _N ⁻ , and (N₂) _N ⁻ , the curves σ⁻(N) have a well-defined threshold because of a rise in the electron thermalization and solvation probability with N. For (H₂O)₉₀₀, (N₂O)₃₅₀, and (N₂)₂₆₀ clusters at E = 0.2 eV, the energy losses by the slow electron in the cluster are estimated as 3.0 × 10⁷, 2.7 × 10⁷, and 6.0 × 10⁵ eV/m, respectively. It is found that the growth of σ⁻ with N is the fastest for (H₂O) _N and (N₂) _N clusters at E → 0 as a result of polarization capture of the s-electron. Specifically, at E = 0.1 eV and N = 260, σ⁻ = 3.0 × 10⁻¹³ cm² for H₂O clusters, 8.0 × 10⁻¹⁴ cm² for N₂O clusters, and 1.4 × 10⁻¹⁵ cm² for N₂ clusters; at E = 11 eV, σ⁻ = 9.0 × 10⁻¹⁶ cm² for (H₂O)₂₀₀ clusters, 2.4 × 10⁻¹⁴ cm² for (N₂O)₃₅₀ clusters, and 5.0 × 10⁻¹⁷ cm² for (N₂)₂₆₀ clusters; finally, at E = 30 eV, σ⁻ = 3.6 × 10⁻¹⁷ cm² for (N₂O)₁₀ clusters and 3.0 × 10⁻¹⁷ cm² for (N₂)₁₂₅ clusters. Original Russian Text ? A.A. Vostrikov, D.Yu. Dubov, 2006, published in Zhurnal Tekhnicheskoĭ Fiziki, 2006, Vol. 76, No. 12, pp. 1–15.     

组合材料方法研究膜厚对Ni/SiC电极接触性质的影响

采用组合材料方法研究了金属Ni膜厚对Ni/SiC接触性质的影响.16个膜厚均为18 nm的Ni/SiC电极具有较为一致的肖特基接触性质;膜厚从10 nm增加到160 nm,肖特基接触的电流-电压（I-V）曲线随膜厚发生显著变化.分析表明这种变化源于膜厚对理想因子n和有效势垒高度Ф_B的影响.1000℃快速退火后,这些肖特基接触都转变为欧姆接触,Ni₂Si是主要的生成物.I-V曲线测 关键词： 碳化硅 肖特基接触 欧姆接触 组合材料方法