Segregation of Pt at clean surfaces of (Pt, Ni)3Al

Experimental evidence for surface segregation of Pt at (1 1 1) surfaces of ternary (Pt, Ni)₃Al alloys is presented, based upon Auger electron spectroscopy, low energy ion scattering, and angle-resolved X-ray photoelectron spectroscopy. Density functional calculations in the dilute limit confirm that Pt segregation is energetically favored.     

Effect of an aliphatic spacer group on the adsorption mechanism on the colloidal silver surface of L‐proline phosphonodipeptides

A comparative study of molecular structures of five L ‐proline (L ‐Pro) phosphonodipeptides: L ‐Pro‐NH‐C(Me,Me)‐PO₃H₂ (P1), L ‐Pro‐NH‐C(Me,iPr)‐PO₃H₂ (P2), L ‐Pro‐L ‐NH‐CH(iBu)‐PO₃H₂ (P3), L ‐Pro‐L ‐NH‐CH(PA)‐PO₃H₂ (P4) and L ‐Pro‐L ‐NH‐CH(BA)‐PO₃H₂ (P5) has been carried out using Raman and absorption infrared techniques of molecular spectroscopy. The interpretation of the obtained spectra has been supported by density functional theory calculations (DFT) at the B3LYP; 6–31 + + G** level using Gaussian 2003 software. The surface‐enhanced Raman scattering (SERS) on Ag‐sol in aqueous solutions of these phosphonopeptides has also been investigated. The surface geometry of these molecules on a silver colloidal surface has been determined by observing the position and relative intensity changes of the Pro ring, amide, phosphonate and so‐called spacer (−R) groups vibrations of the enhanced bands in their SERS spectra. Results show that P4 and P5 adsorb onto the silver as anionic molecules mainly via the amide bond (∼1630, ∼1533, ∼1248, ∼800 and ∼565 cm⁻¹), Pro ring (∼956, ∼907 and ∼876 cm⁻¹) and carboxylate group (∼1395 and ∼909 cm⁻¹). Coadsorption of the imine nitrogen atom and PO group with the silver surface, possibly by formation of a weaker interaction with the metal, is also suggested by the enhancement of the bands at 1158 and 1248 cm⁻¹. P1, P2 and P3 show two orientations of their main chain on the silver surface resulting from different interactions of the  C CH₃,  NH and  CONH fragments with this surface. Bonding to the Ag surface occurs mainly through the imino atom (1166 cm⁻¹) for P2, while for P1 and P3 it occurs via the methyl group(s) (1194–1208 cm⁻¹). The amide group functionality (CONH) is practically not involved in the adsorption process for P1 and P2, whereas the C_s P bonds do assist in the adsorption. Copyright © 2008 John Wiley & Sons, Ltd.     

Anisotropic Hubbard model on a triangular lattice — spin dynamics in HoMnO3

The recent neutron scattering data for spin-wave dispersion in HoMnO₃ are well-described by an anisotropic Hubbard model on a triangular lattice with a planar (XY) spin anisotropy. Best fit indicates that magnetic excitations in HoMnO₃ correspond to the strong-coupling limit U/t >∼ 15, with planar exchange energy J = 4t ² /U ≃ 2.5 meV and planar anisotropy ΔU ≃ 0.35 meV.      

含咔唑与偶氮分散红共聚物的表面增强共振拉曼光谱研究

借助于表面增强共振拉曼光谱散射(SERRS)技术,研究了一种新型的偶氮聚合物材料侧链含咔唑与偶氮分散红共聚物(CAP)在化学沉积法制备的银膜表面的拉曼峰增强和吸附行为。实验结果显示,CAP在银表面的状态为: 聚合物通过咔唑单体中咔唑基团和偶氮单体中硝基与银膜衬底发生物理吸附,而聚合物的主链与衬底相距较远没有相互作用。可以推测,聚合物在衬底表面的这种状态将对偶氮光存储器件的稳定性和工作效率产生不良影响。     

Nonstationary Maxwell equations

ABSTRACT

The paper deals with a mixed problem for nonstationary generalised Maxwell equations. The boundary conditions are of Riemann-Hilbert type. The problem is reduced to a mixed problem for a wave equation where the boundary conditions are of Dirichlet type as they were introduced by D. Spencer in the middle 1950?s. We use the Fourier method to construct an approximate solution to the problem in certain function spaces of Sobolev type.     

Size-dependent oxidation of Pdn (n 13) on alumina/NiAl(110): Correlation with Pd core level binding energies

Small Pd clusters Pd_n (n = 1, 4, 7, 10, 13) deposited on alumina/NiAl(110) at room temperature were examined by X-ray photoelectron spectroscopy (XPS), as-deposited and after exposure to O₂ at temperatures ranging from 100 to 500 K. After O₂ exposure at 100 K, the Pd clusters showed XPS shifts indicative of oxidation. The exception was Pd₄, which did not oxidize under any conditions. The inertness of Pd₄/alumina/NiAl(110) appears to be correlated with a significantly higher-than-expected Pd 3d binding energy, which we attribute to a particularly stable valence shell. None of the clusters examined oxidized during O₂ exposures at 300 K or above, but He⁺ scattering showed that oxygen was bound on the cluster surfaces. Upon heating, all the oxygen associated with these small clusters appeared to spill over and react with the alumina/NiAl(110) support.     

Limited volume thin film deposition on geometrically complicated substrates

In this paper we report a study on the elastic scattering of electrons by lithium and sodium atoms in the presence of circularly polarized resonant laser field within the framework of the two-state rotating wave approximation. The effect of laser on projectile electrons is described by Volkov states. The frequency of the laser field is chosen to match with the 2s–3p (3s–3p) transition frequency in lithium (sodium) atoms. The total and differential elastic cross sections with single photon exchange are calculated for intermediate energies (50–150 eV) and laser intensity (10⁷–10¹¹ W cm^-2). An erratum to this article can be found online at http://dx.doi.org/. An erratum to this article can be found at     

针对散射激光的全向激光告警系统激光威胁源定位技术研究

针对目前散射激光告警中只能定位到散射激光光斑,而不能追溯到敌方来袭激光源的现状,构建了战场环境下包括敌方威胁激光源、照射于某平台上的散射激光光斑以及全向激光告警系统在内的空间三维几何模型,推导了平台上散射激光光斑轮廓解析表达式,以及轮廓上任意一点相对鱼眼镜头的物方半视场角表达式。将成像于探测器上的光斑进行鱼眼成像畸变校正并取光斑边缘点,计算得到三维几何模型诸参数。再将模型参数与传感器阵列信息相结合,可最终获取敌方威胁激光源相对系统的方位和距离信息。最后对以上方法进行了实验验证并对产生误差的原因进行了分析。     

Crystal field in RPdIn (R=Ce, Pr, Nd) compounds

The RPdIn compounds (R = rare earth) crystallise in the hexagonal ZrNiAl-type crystal structure. The compounds from this family exhibit a great variety of interesting magnetic properties including heavy fermion behaviour. In order to get a deeper insight into nature of magnetism of RPdIn with light rare earths elements (La–Nd) an inelastic neutron scattering experiment was performed. For compounds with Pr and Nd excitations due to crystal field were clearly distinguished. On the other hand, interesting behaviour for the CePdIn sample was observed. The sample exhibits no signs of crystal field excitations, likely due to highly delocalised Ce 4f states leading to its heavy fermion behaviour.