Vanadia-silica xerogels: optical and structural properties

Vanadium doped silica gels were prepared from tetraethyl orthosilicate and three different inorganic vanadium precursors with formal oxidation states of V³⁺, V⁴⁺ and V⁵⁺ respectively. Optical and EPR studies were carried out on the dried gels to understand the changes in the oxidation state and coordination of vanadium in the doped silica gel matrix. The observed optical and EPR results provide very strong evidence to establish that irrespective of the starting material, vanadium is stabilized as vanadyl ion in the gel monoliths. EPR studies on the powdered samples corroborate the optical data on the gel samples and confirmed that the stabilized vanadyl ion is situated in a distorted octahedral geometry in these silica gels.     

Sol-gel preparation and optical properties of SiO2-Ta2O5 glass

Tantalum-doped silica glass was fabricated by the sol-gel process in order to obtain a glass with a high refractive index for optical use. A crack-free, clear glass rod was successfully prepared from a low-density gel and used as the core material for fabricating optical fibers. Transmission loss in the fabricated fibers was high, in the range of 10³-10⁴ dB/km, which may be caused by coloration due to the multivalency of tantalum; however, the loss was reduced by nearly one order of magnitude by heat treatment at 800 °C, that is, to 75 dB/km at a wavelength of 0.8 μm.     

Adsorption of benzene, fluorobenzene and meta-di-fluorobenzene on Cu(110): a computational study

We modelled the adsorption of benzene, fluorobenzene and meta-di-fluorobenzene on Cu(110) by Density Functional Theory. We found that the adsorption configuration depends on the coverage. At high coverage, benzene assumes a tilted position, while at low coverage a horizontal slightly distorted geometry is favoured. Functionalizing the benzene ring with one or two fluorine atoms weakens the bonding to the surface. A rotation is induced, which decreases the distance of the fluorine atom from the surface. STM simulations reveal that details about both, benzene adsorption geometry and fluorine position, can be only detected at short tip-surface distances.     

Oxidative cyclization of 2-pyrrolidinyl-acetamide and 2-pyrrolidinyl-propionamide local anaesthetics

2 - Pyrrolidinyl - acetamide and -propionamide local anaesthetics (1a–d) on oxidation with mercuric acetate, potassium hexacyanoferrate(III) and potassium permanganate underwent oxidative cyclization to give new bicyclic compounds, hexahydro - 1H - pyrrolo[1,2 - a]imidazolin - 2 - ones (2a–d). The propionamides (1c–d) yielded mixtures of the two possible diastereoisomers of 2c and 2d. These were separated; in solution and above their melting points they epimerized via ring opening and reclosure between the 7a-carbon and 1-nitrogen atoms.     

吸附O的Cu(110)c(2×1)表面原子结构和电子态

采用第一性原理的密度泛函理论方法计算了清洁Cu(110)表面和吸附O原子的Cu(110) c(2×1)表面的原子结构, 结构弛豫和电子结构, 得到了各种表面结构参数. 分别计算了O原子在Cu(110)表面三个可能吸附位置吸附后的能量, 并给出了能量最低的吸附位置上各层原子的弛豫特性和态密度. 结果表明O吸附后的Cu(110)表面有附加列(added-row)再构的特性, O原子吸附在最表层铜原子上方, 与衬底Cu原子的垂直距离为0.016 nm, 以氧分子为能量基准的吸附能为－1.94 eV; 同时由于Cu 3d- O 2p态的杂化作用使得低于费米能级5.5~6.0 eV的范围内出现了局域的表面态. 计算得到清洁的和氧吸附的Cu(110)表面的功函数分别为4.51 eV和4.68 eV. 电子态密度的结果表明：在Cu(110) c(2×1) 表面O吸附的结构下, 吸附O原子和金属衬底之间的结合主要是由于最表层Cu原子3d态和O原子2p态的相互作用.     

Lead underpotential deposition on Au(110)

The electrochemical underpotential deposition (UPD) of lead on Au(110) was investigated by XPS using a custom‐built ultrahigh vacuum apparatus containing a chamber for electrochemical studies. A two‐step deposition process for lead UPD was confirmed. A large increase in the surface concentration of oxygen was found in solutions containing lead. The presence of lead was detected on the gold surface at all potentials within the range investigated (?500 mV to 1500 mV vs. Ag/AgCl). Degradation of chlorine by x‐rays was observed. The change in surface components with potential was investigated and linked to models of UPD and oxidation. The initial random deposition of lead from solution led to surface disordering. Copyright © 2003 John Wiley & Sons, Ltd.     

Zinc underpotential deposition at Pt(111) and Pt(110) under the influence of boric acid and chloride anions

Zinc underpotential deposition (Zn UPD) was studied by cyclic voltammetry in solutions of various pH and composition, where the effects of the presence of boric acid or chloride in the solution were observed. We have found that the cyclic voltammograms of Zn UPD at Pt(111) were dependent on boric acid concentrations, zinc ion concentrations, and pH in acidic solutions. These suggest that the induced adsorption of borate by releasing of H⁺ is accompanied with Zn UPD. The preadsorbed chloride species on Pt(110) accelerate the UPD process by their removal just before the UPD, making the surface sites available for the process, and the UPD remains at identical electrode potentials, while the chloride ions do not take part in the induced adsorption on UPD Zn at Pt, as clearly found by the radiotracer method. These show that the anions play versatile roles in the process of adlayer formation by their different but essential chemical characteristics. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 6, pp. 745–751 The text was submitted by the authors in English.     

Structure and properties of Ge2.5PSx glasses

Ge_2.5PS_x glasses were studied with a combination of Raman spectroscopy, nuclear magnetic resonance, and neutron diffraction. From these experiments the distribution of bonding configurations was determined, and used to explain the compositional dependence of the index of refraction and the glass transition temperature. On reducing the sulfur content of these glasses below the stoichiometric amount, the sulfur deficit is accommodated by the progressive loss of the non-bridging sulfur of SPS_3/2 groups, followed by the conversion of the resultant PS_3/2 groups into species such as P₄S₃ characterized by P-P bonding. The presence of metal-metal bonds involving germanium, found in samples with the lowest sulfur content, was found to be the most important structural feature in determining the optical response.     

Er-doped hydrogenated amorphous silicon: structural and optical properties

The effect of erbium-doping on the structural and optical properties of hydrogenated amorphous silicon (a-Si:H) is investigated. Optical absorption and Raman spectra indicate that erbium doping introduces defect states, and that above a concentration of 0.27 at.%, induces strong structural disorder. The photoluminescence measurements show that erbium doping introduces non-radiative decay paths for carriers in a-Si:H, leading to decrease in both the Er³⁺ and intrinsic a-Si:H luminescence intensity when the Er concentration is increased to more than 0.04 at.%. The results are compared to that of Er-doped crystalline Si, and the possible excitation mechanisms of Er in a-Si:H are discussed.     

Novel carbon materials obtained by reactions of C60 fullerene with phosphorus at high temperature

C₆₀ fullerene reacted with phosphorus at high temperatures to graphitic materials with strongly differing properties. Several spectroscopic investigations as Raman, ESR, XPS and ³¹P-NMR as well as TEM and ESEM have shown that the structural order of the mostly micro-crystalline materials increased with increasing reaction temperatures and decreasing phosphorus content. At suitable preparation conditions carbon nanotubes are formed, which are disordered in most cases, but partly exhibit high structural order (single-wall nanotubes), too. The prepared materials are very hard, e.g. harder than silica, intensely coloured and electrically conductive. Their hardness decreased with rising phosphorus content, and their conductivity increased with decreasing phosphorus content.