Search results for " layer"

Photocurrent spectroscopy in passivity studies

2018

The aim of this article is to present photocurrent spectroscopy as useful in situ technique for the physicochemical characterization of passive films and corrosion layers. The response of (both amorphous and crystalline) semiconductor/electrolyte junction under irradiation is treated and discussed in order to get information about solid-state properties such as band gap and flat band potential. The possibility to use Photocurrent Spectroscopy (PCS), in a quantitative way, to get information on the composition of corrosion layers is discussed through a semiempirical correlation between the band gap of the oxides (or hydroxides) and the difference of electronegativity of their constituents. F…

Ab initio hybrid DFT calculations of BaTiO3, PbTiO3, SrZrO3 and PbZrO3 (111) surfaces

2015

Abstract The results of ab initio calculations for polar BaTiO 3 , PbTiO 3 , SrZrO 3 and PbZrO 3 (111) surfaces using the CRYSTAL code are presented. By means of the hybrid B3LYP approach, the surface relaxation has been calculated for two possible B (B = Ti or Zr) or AO 3 (A = Ba, Pb or Sr) BaTiO 3 , PbTiO 3 , SrZrO 3 and PbZrO 3 (111) surface terminations. According to performed B3LYP calculations, all atoms of the first surface layer, for both terminations, relax inwards. The only exception is a small outward relaxation of the PbO 3 -terminated PbTiO 3 (111) surface upper layer Pb atom. B3LYP calculated surface energies for BaO 3 , PbO 3 , SrO 3 and PbO 3 -terminated BaTiO 3 , PbTiO 3 , …

Growth Kinetics of Wetting Layers at Surfaces

1990

Monte Carlo simulation of lattice gas models for the wetting transitions in systems with short range forces are described. A nearest-neighbor simple cubic lattice with nonconserved “Glauber dynamics” is used, applying a slab geometry (LxL cross section). It is shown that the growth proceeds in two stages: for short times t, the thickness of the wetting layer at an initially nonwet wall increases proportional to the logarithm of the time; for t » L2(lnL)2 the thickness increases proportional to t1/2/L. Generalizations to other systems are briefly discussed. Also two-dimensional growth of a wetting film at surface steps is considered, considering “terraces” of an LxM geometry with M»L as subs…

Visible photothermal deflection spectroscopy using microcantilevers

2012

International audience; Photothermal deflection spectroscopy based on bi-material cantilevers combines the sensitivity of miniature sensors and the selectivity of optical spectroscopy. In this paper, we report on the photothermal response of the microcantilevers functionalized with nanometer thin organic films in the visible region. Unlike responses in the infrared regime, in the optical region, light absorption by all the cantilever constituents must be considered for extraction of the physical parameters of the organic layer. A model of photothermal deflection for the optical region has been developed for two absorbing layers consisting of a thick metal (>200 nm) and a thin organic film. …

Atomic layer deposition of Ti-Nb-O thin films onto electrospun fibers for fibrous and tubular catalyst support structures

2018

Here, the authors report on the preparation of core-shell carbon-ceramic fibrous as well as ceramic tubular catalyst supports utilizing electrospinning and atomic layer deposition (ALD). In this paper, ALD of Ti-Nb-O thin films using TiCl4, Nb(OEt)5, and H2O as precursors is demonstrated. According to the time-of-flight-elastic recoil detection analysis and Rutherford backscattering spectrometry, carbon and hydrogen impurities were relatively low, but depend on the pulsing ratio of the precursors. Optimized ALD process was used for coating of sacrificial electrospun polyvinyl alcohol (PVA) template fibers to yield tubular Ti-Nb-O structures after thermal or solution based PVA removal. Anoth…

Layer-by-Layer Grafting of Molecularly Imprinted Polymers via Iniferter Modified Supports

2002

Using the single-ring infiltrometer method to detect temporal changes in surface soil field-saturated hydraulic conductivity

2004

Abstract Determining temporal changes in field-saturated hydraulic conductivity ( K fs ) is important for understanding and modelling hydrological phenomena at the field scale. Little is known about the sensitivity of temporal change estimates to the method used for measuring K fs . The objective of this study was to compare temporal changes in K fs obtained in the surface layer of a clayey soil using two application procedures of the single-ring infiltrometer method. Rings installed permanently at the beginning of a 1.5-year study period (permanent sites, PSs, sample size N =16) and rings installed immediately before conducting the infiltrometer measurement (non-permanent sites, NPSs, N =1…

Mechanical behavior of polylactic acid/polycaprolactone porous layered functional composites

2016

Abstract Biopolymeric porous devices exhibiting graded properties can play a crucial role in several fields, such as tissue engineering or controlled drugs release. In this context, the gradient of a specific property can be achieved by developing porous laminates composed by different types of materials. This work presents for the first time a multi-phasic porous laminate based on polycaprolactone (PCL) and polylactic acid (PLA) prepared by combining melt mixing, compression molding and particle leaching. All the materials were characterized from a morphological and a mechanical point of view. The results put into evidence the possibility to tune and to predict the mechanical properties by…

Progress in Violet Light-Emitting Diodes Based on ZnO/GaN Heterojunction

2020

Progress in light-emitting diodes (LEDs) based on ZnO/GaN heterojunctions has run into several obstacles during the last twenty years. While both the energy bandgap and lattice parameter of the two semiconductors are favorable to the development of such devices, other features related to the electrical and structural properties of the GaN layer prevent an efficient radiative recombination. This work illustrates some advances made on ZnO/GaN-based LEDs, by using high-thickness GaN layers for the p-region of the device and an ad hoc device topology. Heterojunction LEDs consist of a quasicoalesced non-intentionally doped ZnO nanorod layer deposited by chemical bath deposition onto a metal&ndash

An Ising ferromagnet with an antiferromagnetic surface layer: A simple model for magnetic surface reconstruction

1985

Simple cubic Ising lattices are studied by Monte Carlo simulation, using a thin film geometry (usually 40 atomic layers thick), with nearest neighbour ferromagnetic exchange J in the bulk and nearest neighbour antiferromagnetic interaction Js between surface spins. Applying a technique of preferential sampling in the surface layers, we investigate the ordering for a variety of values of JsJ and for various temperatures. For JsAF < Js < − 0.25J (where JsAF ≈ − 2.01J) ferromagnetic ordering occurs at a higher temperature than the antiferromagnetic surface ordering, while for − 0.25J < Js no antiferromagnetic long range order is possible. For Js < JsAF the surface transition occurs at a higher…