Dielectric multilayer waveguides for TE and TM mode matching

We analyse theoretically for the first time to our knowledge the perfect phase matching of guided TE and TM modes with a multilayer waveguide composed of linear isotropic dielectric materials. Alongside strict investigation into dispersion relations for multilayer systems, we give an explicit qualitative explanation for the phenomenon of mode matching on the basis of the standard one-dimensional homogenization technique, and discuss the minimum number of layers and the refractive index profile for the proposed device scheme. Direct applications of the scheme include polarization-insensitive, intermodal dispersion-free planar propagation, efficient fibre-to-planar waveguide coupling and, potentially, mode filtering. As a self-sufficient result, we present compact analytical expressions for the mode dispersion in a finite, N-period, three-layer dielectric superlattice.Comment: 13 pages with figure

Optimization of a high work function solution processed vanadium oxide hole-extracting layer for small molecule and polymer organic photovoltaic cells

We report a method of fabricating a high work function, solution processable vanadium oxide (V2Ox(sol)) hole-extracting layer. The atmospheric processing conditions of film preparation have a critical influence on the electronic structure and stoichiometry of the V2Ox(sol), with a direct impact on organic photovoltaic (OPV) cell performance. Combined Kelvin probe (KP) and ultraviolet photoemission spectroscopy (UPS) measurements reveal a high work function, n-type character for the thin films, analogous to previously reported thermally evaporated transition metal oxides. Additional states within the band gap of V2Ox(sol) are observed in the UPS spectra and are demonstrated using X-ray photoelectron spectroscopy (XPS) to be due to the substoichiometric nature of V2Ox(sol). The optimized V2Ox(sol) layer performance is compared directly to bare indium–tin oxide (ITO), poly(ethyleneoxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and thermally evaporated molybdenum oxide (MoOx) interfaces in both small molecule/fullerene and polymer/fullerene structures. OPV cells incorporating V2Ox(sol) are reported to achieve favorable initial cell performance and cell stability attributes

Interface response theory of composite elastic media

A general theory for the study of any composite elastic media is proposed. It is then applied to layered composites. These general results are illustrated by examples of new localized vibrations within fluid and solid slabs sandwiched between two other semi-infinite solids.Une théorie générale permettant d'étudier n'importe quel matériau élastique et composite est proposée. Son application aux composites lamellaires est ensuite développée. Ces résultats généraux sont illustrés par des exemples de nouveaux modes de vibration localisés dans des couches fluide et solide comprises entre deux autres solides semi-infinis

X Ray Photoelectron Spectroscopy studies of laterite standard reference material

X-ray photoelectron spectroscopy is used to characterize two natural samples of laterite standard reference materials (certified geologically), a mechanical mixture of Fe2O3, SiO2 and Al2O3 in a 4/2/1 proportion. Fe2O3, SiO2, and Al2O3 samples were analyzed for, comparison purposes. Special attention was paid to peak shape, FWHM, comparison of the same XPS peaks of different samples, and peak shifts. The XPS results reveal the presence of some kind of iron aluminate prevailing on the surface of the laterite standard reference materials. It is also observed that the mechanical mixture exhibits a differential charging effect. Our report provides important information for the researchers doing XPS on these materials when they are used in catalytic reactions

Caracterizacion por XPS de lateritas estandar

Photoelectron spectroscopy (XPS) is used to characterize mainly two standard laterite samples. Samples of Fe2O3, SiO2, and Al2O3 were also analysed for comparison purposes. A detailed study of the O1s band of oxygen present in these samples allowed us to obtain information which was used to distinguish clearly the samples

X-ray induced surface modification of aluminovanadate oxide

Aluminovanadate oxide, ‘‘V–Al–O’’, has been studied by X-ray photoelectron spectroscopy (XPS) with the emphasis to reveal chemical modifications as a function of the X-irradiation time. Considerable damage was found for V–Al–O and less so for vanadium pentoxide, V2O5, and sapphire, a-Al2O3, both serving as reference samples. Modifications in V–Al–O were seen even at low radiation doses. Absolute and relative shifts in binding energies along with changes of peak intensities and widths demonstrate that an appreciable amount of V5+ is reduced to lower oxidation states. X-ray induced chemical modifications extend at least to the depth sampled by the V3p electrons. It is suggested that the damage is caused by electron-hole pair generation and Auger decay. Al–O–H in V–Al–O is also affected by X-rays. This causes O2 and water desorption as followed by mass spectrometry of the residual gas.info:eu-repo/semantics/publishe