Chemical state

About: Chemical state is a research topic. Over the lifetime, 2378 publications have been published within this topic receiving 78183 citations.

Coincidence, Resonant, and High-Energy Electron Spectroscopies – Resonant Auger, Electron Coincidence for Surface Analysis

Abstract: Electron spectroscopic methods are powerful and efficient tools for characterization of chemical and electronic structures of surface and interface layers of solids. The electron spectroscopic methods most widely applied for surface chemical analysis, the X-ray photoelectron spectroscopy (XPS), and Auger electron spectroscopy (AES) are providing information on the elemental composition of the surface and interface layers, as well as on the chemical state of the components. In addition, these techniques can offer possibilities for depth-resolved and/or laterally resolved analysis in a nondestructive (up to several nanometers depth) or destructive (in combination with ion sputtering, up to several hundred nanometers depth) way. Quantitative surface chemical analytical applications of these methods are greatly helped by physical quantities characterizing electron transport, which can be derived from reflection electron energy loss spectroscopic (REELS) studies of given materials. There are, however, a plenty of opportunities available how to improve the sensitivity, selectivity, and information depth of these techniques. Among these, the coincidence techniques help to identify the physical processes leading to specific structures in the experimental electron spectra, clean up the spectra from unwanted contributions of interfering processes, and limit the depth of analytical information. The resonant excitation can yield unprecedented chemical state selectivity and can greatly improve the detection limit for particular species while providing unique information on the electronic structure in the proximity of the excited atom. High-energy-resolution spectroscopy of high-energy electrons induced by hard X-rays from solids allows to get an insight into deeper subsurface regions owing to the much increased information depth for energetic electrons, and in addition to the possibility for collecting information on the bulk chemical and electronic structures without interfering effects because of the presence of the surface, this spectroscopy provides a nondestructive access to the chemical state-resolved composition at deeply buried interfaces. This article intends to give a brief review on selected electron–electron coincidence techniques, resonant Auger electron spectroscopic methods, and high-energy electron spectroscopic methods, namely, the hard X-ray photoelectron spectroscopy (HAXPES), focusing on the principle and specific instrumentation of the techniques, the underlying physics of the fundamental processes utilized, the analytical information provided, and important fields of applications. These highly sensitive, selective, and uniquely informative electron spectroscopic methods are expected to be used increasingly in studies of sophisticated novel materials of great practical importance, especially in fields of nanotechnology, micro- and nanoelectronics, nano-biotechnology, nanomedicine, and development of novel solar cells.

Synchrotron XPS and EXAFS identification of chemical state and crystal phase changes of HfO 2 films doped with Si, N, Al, and La

Abstract: The recent industry wide investigation of incorporating various elemental dopant species into HfO 2 to achieve higher-k gate dielectric alloy materials in order to maintain the rapid pace of scaling according to Moore's Law has been expanded to include enhancement of the SiO/HfO interface dipole to tune the effective work function (EWF) of n and p-type gate electrodes. This work illustrates the value of high resolution synchrotron X-ray photoemission spectroscopy (XPS), X-ray photoabsorption spectroscopy (XAS), and extended X-ray absorption fine structure (EXAFS) techniques to identify changes in chemical state bonding and associated crystalline polymorph transitions as a function of dopant species and anneal parameters. Direct correlation of these spectra with representative device data greatly elucidates critical process optimization pathways.

Polymer-assisted deposition of Co-doped zinc oxide thin film for the detection of aromatic organic compounds

Abstract: Cobalt-doped Zinc oxide thin film was deposited onto SiO 2 /Si substrate using polymer-assisted deposition method. The surface morphology, phase structure and chemical state of the thin film were characterized by SEM, XRD, and XPS. The gas-sensing characteristics of the thin film upon exposure to aromatic organic compound vapors were investigated with a home-made sensor measurement system. The current results show that the film morphology is influenced by the doping of Co, and the sensor behavior was quite different between undoped and Co-doped ZnO thin films.

Free-Standing Porous Cu-Based Nanowires as Robust Electrocatalyst for Alkaline Oxygen Evolution Reaction

Abstract: Cu-based catalysts have emerged as important candidates for oxygen evolution reaction (OER) electrocatalysts. Based on Mg72Cu28 alloy ribbon, a free-standing porous Cu hydroxide/oxide nanowires (p-CuNWs) was fabricated by a combined method of chemical dealloying and electrochemical treatment. The structure and chemical state of p-CuNWs were characterized by X-ray diffraction pattern analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy. The p-CuNWs were identified as mixed Cu(OH)2 and CuO with a high active surface area, which exhibit robust activity for OER in alkaline solution with an overpotential of only 377 mV to offer current density of 50 mA cm−2, small Tafel slope of 85 mV dec−1. The catalytic durability of p-CuNWs was also evaluated by cyclic voltammetry cycles and a small decay of activity was observed.

Revealing the Chemical State of Palladium in Operating In2O3 Gas Sensors: Metallic Pd Enhances Sensing Response and Intermetallic InxPdy Compound Blocks it.

Abstract: The sensing response of metal oxides activated with noble metal nanoparticles is significantly influenced by changes to the chemical state of corresponding elements under operating conditions. Here, a PdO/rh-In2O3 consisting of PdO nanoparticles loaded onto rhombohedral In2O3 was studied as a gas sensor for H2 gas (100 - 40000 ppm in an oxygen-free atmosphere) in the temperature range of 25 - 450 °C. The phase composition and chemical state of elements were examined by resistance measurements combined with synchrotron-based in-situ X-ray diffraction and ex-situ X-ray photoelectron spectroscopy. As found, PdO/rh-In2O3 undergoes a series of structural and chemical transformations during operation: from PdO to Pd/PdHx and finally to the intermetallic InxPdy phase. The maximal sensing response (RN2/RH2 ) of ~5∙107 towards 40000 ppm (4 vol.%) H2 at 70 °C is correlated with the formation of PdH0.706 /Pd. The InxPdy intermetallic compounds formed around 250 °C significantly decreases the sensing response.