Atomic interactions in neon and helium

The first two quantum corrections to the second virial coefficients of the Smith-Thakkar potential are calculated. Parameters for neon and helium, gases in which quantum effects are important, are then determined by fitting to semiempirical dispersion coefficients and experimental second virial coefficients. Viscosity coefficients for both gases and vibrational energy level spacings for the neon dimer are calculated as independent tests of the potentials. Overall agreement with experiment is excellent for neon and moderate for helium. The previously determined parameters for argon are found to be only very slightly perturbed by the inclusion of quantum corrections in the calculated second virial coefficients.     

Quantifying desorption of saturated hydrocarbons from silicon with quantum calculations and scanning tunneling microscopy

Electron stimulated desorption of cyclopentene from the Si(100)-(2 x 1) surface is studied experimentally with cryogenic UHV STM and theoretically with transport, electronic structure, and dynamical calculations. Unexpectedly for a saturated hydrocarbon on silicon, desorption is observed at bias magnitudes as low as 2.5 V, albeit the desorption yields are a factor of 500 to 1000 lower than previously reported for unsaturated molecules on silicon. The low threshold voltage for desorption is attributed to hybridization of the molecule with the silicon surface, which results in low-lying ionic resonances within 2-3 eV of the Fermi level. These resonances are long-lived, spatially localized, and displaced in equilibrium with respect to the neutral state. This study highlights the importance of nuclear dynamics in silicon-based molecular electronics and suggests new guidelines for the control of such dynamics.     

SiP化合物结构和电子特性的第一性原理研究

应用第一性原理方法研究了SiP化合物的结构和电子特性,并且将研究推广到其他第四族元素磷化物(IV-P).在研究的各种结构中,SiP单斜晶体结构是能量最低、最稳定的结构.SiP的体弹性模量比CN和CP化合物以及相对应的第三族元素氮化物和磷化物要小.SiP不同的结构间能发生相变,其单斜晶体结构(monoclinic)在压强为6.2 GPa, 15.0 GPa, 19.3 GPa, 20.0 GPa 和 10.3 GPa时分别转变成GeP型结构、Rhom.型结构、β-InS型结构、 CsCl型结构和NaCl型结构.能带计算结果显示SiP单斜晶体结构(monoclinic)和GaSe型结构是间接带隙分别为1.123 eV 和 0.123 eV的半导体,SiP其他结构则显示出金属特性.其他化学比为1:1的第四族元素磷化物(IV-P)具有相同的性质.     

Electron impact studies of autoionizing states in neon and helium

A study has been made of autoionizing states in neon in the energy region 42–48 eV by low energy electron impact. Observations have been made of stru     

A study of the size-dependent elastic properties of silicon carbide nanotubes: First-principles calculations

The size dependence of elastic properties in single-walled silicon carbide nanotubes are investigated by first-principles calculations. We found the Young?s modulus of the nanotubes increases with increasing diameter and is inversely proportional to Si–C bond length, whereas the Poisson ratio shows an opposite trend. For small tubes the elastic properties change dramatically with the tube size. While for the tubes with the diameter larger than 8 Å, the difference of these properties is small and almost independent of the size and symmetry. The strength of bonding between Si and C atoms is elucidated by the amount of the charge transfer calculated by the Bader analysis.     

Elastic scattering of electrons by helium and neon atoms

Summary  Partial and total cross-sections of electrons scattering by helium and neon atoms are calculated at eleven values of incident energy ranging from 0.1 a.u. to 1.1 a.u. The calculations are carried out via model potential (describing the electron target interaction). The iterative Green’s function partial-wave expansion technique was used. The comparison between our results and those obtained by other authors show significant agreement and supports our simple model scattering process.     

Role of neon in a decaying high-purity helium plasma

The evolution of the electron and atomic and molecular metastable densities and the radiation of the decaying plasma of helium with a 10^–5-fraction of neon additive is experimentally studied. A model of elementary processes in He–Ne plasma is constructed, which describes the formation and destruction of HeNe⁺ and Ne₂ ⁺ molecular ions and their contribution to the formation of the afterglow spectrum by the electronion recombination. The various criteria influence of neon on the parameters of the decaying plasma are studied. The possibility of determining the amount of neon in helium by measuring the relative intensities of helium molecular bands and neon spectral lines in the afterglow is considered.     

铒、钪膜中离子注入氦的热解析行为

采用热解析法初步研究了铒、钪膜中离子注入氦的热解析行为。研究结果表明：同种元素铒中离子注入氦的热释放峰位相同,但膜的致密性将影响氦的释放量,结构疏松的膜中存在的孔洞是氦的快速释放通道;在相同注入剂量和能量条件下,铒、钪膜中注入氦的热释放峰位不同,这可能与氦在铒、钪膜中的深度分布及膜的致密性有关,利用质子增强背散射法测量出能量为60 keV的4He+在铒、钪膜中的注入深度分别为210,308 nm。     

Light emission from porous silicon single and multiple cavities

Experimental and theoretical techniques are used to examine the effects of microstructuring on the optical properties of multilayer, single and multiple microcavity structures fabricated from porous silicon. Measurements of the reflectivity and photoluminescence spectra of three multilayer samples are presented. The results are modelled using a transfer matrix technique including a negative absorption term to represent the effect of spontaneous emission which gives luminescence. The emitted light is strongly controlled by the optical modes of the structures and very good agreement is observed between theory and experiment.     

铒、钪膜中离子注入氦的热解析行为

采用热解析法初步研究了铒、钪膜中离子注入氦的热解析行为。研究结果表明:同种元素铒中离子注入氦的热释放峰位相同,但膜的致密性将影响氦的释放量,结构疏松的膜中存在的孔洞是氦的快速释放通道;在相同注入剂量和能量条件下,铒、钪膜中注入氦的热释放峰位不同,这可能与氦在铒、钪膜中的深度分布及膜的致密性有关,利用质子增强背散射法测量出能量为60 keV的4He+在铒、钪膜中的注入深度分别为210,308 nm。     

The capture of slow antiprotons in helium, neon and argon

We consider the capture of antiprotons with energies less than roughly 27 eV by helium, neon and argon atoms. We use the adiabatic ‘hidden-crossing’ theory to calculate both the capture cross-sections and the angular distribution of the antiprotons. We find that important differences between helium and the other noble gases can be attributed to the properties of the ‘hidden’ crossings appropriate to each system. This revised version was published online in August 2006 with corrections to the Cover Date.