Infrared ellipsometry study of the oxidation mechanisms of hydrogenated amorphous silicon

A detailed study of the oxidation of plasma deposited amorphous silicon (a-Si : H) using infrared phase modulated ellipsometry (IRPME) is presented. a-Si : H is found to be resistant against air oxidation confirming previous measurements. A 5–6 Å thick oxide layer at the surface of a-Si : H is observed after a few months of exposure to air. The extreme sensitivity of IRPME is emphasized. In particular Si-O-Si and (O_n)Si-H stretching vibrations are identified at the film surface at the submonolayer level. The oxidation mechanisms are discussed. The weak reactivity of a-Si : H with atmosphere is correlated with the presence of a hydrogen rich thin layer at the top surface.     

Optimized Mueller polarimeter with liquid crystals

We demonstrate a Mueller polarimeter in which the polarization-state generator and analyzer are both composed of a linear polarizer and two liquid-crystal variable retarders. The polarimeter is designed to optimize the accuracy of the final results by minimization of the condition numbers of the modulation and analysis matrices. The polarimeter calibration, a difficult task by conventional procedures, is achieved easily by use of the eigenvalue method of Compain et al. [Appl. Opt. 38, 3490 (1999)]. The overall polarimeter performance is tested with a linear polarizer at various angles and a compensator at various retardations.     

The versatility of pentalene coordination to transition metals: a density functional theory investigation

DFT calculations with full geometry optimization have been carried out on a series of real and hypothetical compounds of the type [CpM(C8H6)], [(CO)3M(C8H6)], [M(C8H6)2], [(CpM)2(C8H6)], [[(CO)3M]2(C8H6)], and [M2(C8H6)2] (M = transition metal). The bonding in all the currently known compounds is rationalized, as well as in the (so far) hypothetical stable complexes. Depending on the electron count and the nature of the metal(s), eta2 (predicted), eta3, eta5, eta8, or intermediate coordination modes can be adopted. In the case of the mononuclear species, the most favored closed-shell electron counts are 18 and 16 metal valence electrons (MVE). In the case of the dinuclear species, an electron count of 34 MVEs is most favored. However, other electron counts can be stabilized, especially in the case of dinuclear complexes. Coordinated pentalene should most often be considered as formally being a dianion, but sometimes as a neutral ligand. In the former case it can behave as an aromatic species made of two equivalent fused rings, as a C5 aromatic ring connected to an allylic anion, or even as two allylic anions bridged by a C7=C8 double bond. In the latter case, it can behave as a bond-alternating cyclic polyene or as a C5 aromatic ring connected to an allylic cation.     

Ab initio study of La-doped BaSnO<Subscript>3</Subscript> proton conductor

The hydration properties of Lanthanum-doped barium stannate have been studied using density functional calculations. The interaction energy between elementary defects (proton-dopant and oxygen vacancy-dopant) have been calculated in charged states corresponding to p-type conditions. Surprisingly, the most attractive energies are not found for first-neighbor relative positions. The geometric distortions and the electronic densities of state in the different configurations involved are presented. With these data, two simple models are used to estimate the energy of the hydration reaction. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Coherent thermal emission in midinfrared from a bilayer structure

Recent years, there has been an increased interest to the conception of micro/nanostructures with unusual radiative properties, especially thermal sources with temporal and/or spatial coherent emission. Such structures are indeed extremely interesting for energy conversion systems, radiative cooling devices,…. The present study investigate numerically temporal coherent emission from a very simple structure composed with one stack of germanium and one of silicon carbide. Our investigation shows that, for well-defined thicknesses, this two-stack structure is able to emit in narrow spectral peak.     

K−π− elastic scattering cross section measured in 14.3 GeV/c K−p interactions

Results are presented on a measurement of the I = 3/2 Kπ elastic scattering cross section by applying the Chew-Low extrapolation method in the reaction K^?p → K^?π^?Δ⁺⁺at14.3GeV/c. The magnitude of σ(K^?π^? → K^?π^?) is found to be about 3 mb at threshold and slowly falling with energy to about 1.5 mb at 2.8 GeV. The off-mass-shell moments of the differential elastic cross section are given. The absolute value of δ₃⁰ is found to be increasing slowly from 0° to 20° between threshold and 1.2 GeV.     

The inclusive reaction K− p → pX at 14.3 GeV/c

We have measured the reaction K^?p → pX at 14.3 GeV/c, in the fragmentation region of the target proton. The differential cross section is studied as a function of momentum transfer and missing mass squared. In the triple-Regge limit, it is consistent with the dominance of a MMP coupling at large t but it is possible that couplings of the type PPP and ππP also contribute at small |t| values.