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Stainless steel and copper technical substrates have been coated by free standing graphene using electrophoretic deposition technique, with the final goal to obtain chemically inert low secondary electron emission surfaces. This class of materials is of utmost interest in future accelerators in order to increase further the flux of accelerated charged particles in the beam. The measured maximum total electron yield of pristine graphene, which has been previously characterized by electron microscopies and X-ray photoelectron spectroscopy, appears to be about 1.0. The deposition parameters have been optimized in order to obtain surfaces with lowest total electron yield, but also composition and morphology close to that of pristine graphene. When applying these optimized deposition parameters graphene coatings on two substrates, i.e. stainless steel and copper, the maximum total electron yield of about 1.04 was obtained. The composition of coatings and the relative amounts of sp2 bonds are slightly worse than those of the pristine graphene, while the surface morphology appears to be the same. Annealing at 150 °C for 64 h in high vacuum, showed that vacuum baking did not affect considerably the electron emission properties of the coatings. © 2019 Elsevier B.V.

Recently introduced model for quantitative analysis of in-depth non-uniform surfaces is applied to reexamine the X-ray Photoelectron Spectroscopy (XPS) data of Cd0.99Fe0.01Te0.97Se0.03 and Zn0.98Fe0.02Te0.91Se0.09 crystalline samples. Special attention is paid to the precise identification of phases which form the bulk-like near-surface region and the surface overlayers (the oxide layer and the layer of organic impurities), as well as the influence of surface morphology on the measurements. The obtained results fully support earlier qualitative estimations, but also provide new quantitative insight into the composition of the three investigated regions. The near-surface region of Cd0.99Fe0.01Te0.97Se0.03 and Zn0.98Fe0.02Te0.91Se0.09 samples is slightly electropositive, with cation/anion ratio 52:48 and 53:47, respectively. Model surface structures, which are fully compatible with the experimental results, comprise 0.76 nm thick CdTeO3 layer at the surface of Cd0.99Fe0.01Te0.97Se0.03 and 0.33 nm thick mixed ZnO/TeO2 oxide layer on Zn0.98Fe0.02Te0.91Se0.09. In both samples the oxide layer is only a few atomic layers thick, implying that it suppresses further rapid migration of oxygen into the bulk.

Local structural and electronic properties around Fe in multi-component Cd0.99Fe0.01Te0.97S0.03 system were studied by means of X-ray absorption fine structure (XAFS). Composition of non-polar (110) surfaces of Cd0.97Fe0.03Te and Cd0.99Fe0.01Te0.97S0.03 systems and mechanism of their oxidation in ambient conditions were studied by Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). It has been found that Fe preferentially substitutes Cd, but due to much smaller covalent radius and preferences for paring with S, it causes local distortion of the host CdTe lattice. The distortion is confined to the Fe-immediate surrounding and the second and third coordination shell atoms are (inside experimental uncertainties) placed at distances expected in CdTe. Although local structure around Fe is well defined in the bulk of both samples, their near-surface region is completely depleted from Fe, and in case of Cd0.99Fe0.01Te0.97S0.03 somewhat enriched in S. Special attention is, therefore, paid to characterization of the near-surface region and evaluation of its composition and structure. To that end we have introduced a general standard-free algorithm for XPS data analysis of the two-layer surface structure (bulk, oxide layer, and the impurity layer). Results of the in-depth composition analysis revealed that despite different bulk composition and impurity layer thickness, underneath the topmost impurity layer lays approximately one monolayer of CdTeO3 which passivates the surface. © 2018 Elsevier B.V.

Using X-ray induced Photoelectron Spectroscopy, Time of Flight Secondary Ion Mass Spectrometry and Atomic Force Microscopy we have investigated elemental composition, structure and oxidation process taking place at the surfaces of polycrystalline Cd0.99Fe0.01Te0.97Se0.03 and Cd0.95Mn0.05Te0.97Se0.03 systems stored in ambient conditions. The surface oxidation destroys the native CdTe matrix and provokes substantial atomic rearrangement in the first few atomic layers. The near surface region of both systems is enriched in Cd and to some extent Te-deficient, but the surface structure, morphology and the native oxide composition are all found to be considerably different. In Cd0.99Fe0.01Te0.97Se0.03 system both Fe and Se dopants diffuse into the bulk and oxidation of its surface results in formation of a thin CdTeO3 layer which covers the CdTe matrix. In Cd0.95Mn0.05Te0.97Se0.03 system oxygen-rich atmosphere triggers Mn and Se out diffusion and the nonuniform oxide layer predominantly consists of MnO and a small amount of Te-oxide which both lay underneath a thin layer of metallic Cd segregated at the top of the surface. (C) 2016 Elsevier B.V. All rights reserved.

A range of industrial by-products are currently under the consideration as cost-effective alternatives to conventional sorbent materials for environmental clean-up and remediation applications. Bauxite residue (red mud) has demonstrated exceptionally high potential for the immobilization of cationic pollutants. Due to heterogeneity of such material, determination of the role of individual mineral phases in the overall sorption mechanism is a challenging task. To enlighten the mechanism of Co(II) sorption by mineral assemblage of the red mud, sequential extraction analysis of Co-loaded sample was combined with the microscopic and spectroscopic studies performed by Scanning Field Emission Electron Microscope (FE-SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS). Sorbed Co(II) ions were found associated with operationally defined Fe,Mn-oxide and carbonate/acid soluble fractions. Binding of Co(II) by the red mud was achieved primarily by means of chemisorption/surface precipitation on Fe- and Ti-oxides. In coexistence with these highly selective surfaces, gibbsite and silica appeared to be low affinity sites for Co(II). Incongruent dissolution of sodalite phase was detected, indicating that its function was not to ensure sorption centers, but to increase the solution pH creating favorable environment for Co(II) binding by Fe- and Ti-oxides. The results demonstrate high stability of sorbed Co(II) and synergistic action of mineral constituents as essentially important property for red mud implementation as a purifying and remediation agent.

Self-standing N-graphene sheets were produced in low-pressure microwave N-2-Ar plasma. The graphene sheets were exposed to the plasma for various durations and doped with nitrogen atoms, which were incorporated into the hexagonal carbon lattice in pyridinic, pyrrolic and quaternary functional groups, mainly. Atomic nitrogen emissions at the substrate position in the plasma were detected using optical emission spectroscopy. Raman spectroscopy, x-ray photoelectron spectroscopy and transmission electron microscopy techniques were also applied for material characterization. Doping levels as high as 5.6% were achieved and an increase in the sp(2)/sp(3) ratio was observed for a relatively short exposure time.

A range of industrial by-products are currently under the consideration as cost-effective alternatives to conventional sorbent materials for environmental clean-up and remediation applications. Bauxite residue (red mud) has demonstrated exceptionally high potential for the immobilization of cationic pollutants. Due to heterogeneity of such material, determination of the role of individual mineral phases in the overall sorption mechanism is a challenging task. To enlighten the mechanism of Co(II) sorption by mineral assemblage of the red mud, sequential extraction analysis of Co-loaded sample was combined with the microscopic and spectroscopic studies performed by Scanning Field Emission Electron Microscope (FE-SEM), Energy Dispersive Spectroscopy (EDS) and X-ray Photoelectron Spectroscopy (XPS). Sorbed Co(II) ions were found associated with operationally defined Fe,Mn-oxide and carbonate/acid soluble fractions. Binding of Co(II) by the red mud was achieved primarily by means of chemisorption/surface precipitation on Fe- and Ti-oxides. In coexistence with these highly selective surfaces, gibbsite and silica appeared to be low affinity sites for Co(II). Incongruent dissolution of sodalite phase was detected, indicating that its function was not to ensure sorption centers, but to increase the solution pH creating favorable environment for Co(II) binding by Fe- and Ti-oxides. The results demonstrate high stability of sorbed Co(II) and synergistic action of mineral constituents as essentially important property for red mud implementation as a purifying and remediation agent. (C) 2016 Elsevier B.V. All rights reserved.

X-ray absorption (XANES, EXAFS, XMCD) and photoelectron (XPS) spectroscopic techniques were employed to study local structural, electronic and magnetic properties of Zn0.95Co0.05O nanopowders. The substitutional Co2+ ions are incorporated in ZnO lattice at regular Zn sites and the sample is characterized by high structural order. There was no sign of ferromagnetic ordering of Co magnetic moments and the sample is in paramagnetic state at all temperatures down to 5 K. The possible connection of the structural defects with the absence of ferromagnetism is discussed on the basis of theoretical calculations of the O K-edge absorption spectra. (C) 2015 Elsevier Ltd. All rights reserved.

Secondary electron emission plays an important role in many applic. ations such as scanning electron microscopy, space applications and accelerator technologies. Secondary electron yield delta(E)at normal incidence of a primary electron beam is frequently modelled by the well-known semi-empirical law. However, this model is not used in a consistent way to predict the angular dependence. Additionally, neglecting the energy reflection has particular influence on the angular dependence of the secondary electron yield and therefore cannot be ignored. We propose here a simple approach to calculate delta(E) for any incident angle based on the experimental result achieved at normal incidence. The secondary electron yield is calculated according to the universal semi-empirical law, while a fraction of the electron energy deposited into the sample is calculated using a Monte Carlo simulation. A simple modification of the original model for calculating a total electron yield (i.e. the sum of the true secondaries and backscattered electrons) is also presented. Very good agreement is observed between measurements and the calculation as long as the roughness is not significant The model works very well for both, low Z and high Z materials. In the case of rough samples this approach cannot predict the angular dependence of the total electron yield. (C) 2015 Elsevier Ltd. All rights reserved.

Local structures and electronic properties of II-VI quaternary Zn0.98Fe0.02Te0.91Se0.09 mixed crystal are studied by X-ray absorption fine structure (XAFS) while the surface composition and its oxidation in air are studied by X-ray photoelectron spectroscopy (XPS). That way the surface stability and its modification with respect to the bulk are elucidated. The effects of surface oxidation on rearrangement and segregation of constituent atomic species at the surface are revealed and possible mechanisms of oxygen adsorption are discussed. (C) 2015 Elsevier B.V. All rights reserved.