Chemical state

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

Analytical and electrochemical study of passive films formed on nickel—chromium alloys: Influence of the chromium bulk concentration

Abstract: Depth composition and chemical states of elements constituting the overlayers of NixCr alloys (x = 0–30 at.%) passivated in borate buffer solutions (pH = 9.2) were determined as a function of the chromium bulk content of the alloy. Depth sputter profiling was performed using both Auger electron spectroscopy (AES) and low energy ion scattering spectroscopy (LEIS). Chemical bonding and (oxy-hydroxy) structures of alloying elements in the passive films were investigated by x-ray photoelectron spectroscopy (XPS). The electrochemical study mainly consists in establishing the cathodic reduction kinetics of the passive layers to characterize the resistance of the internal Cr2O3 barrier to reduction. Very thin films (less than 2.5 nm) were obtained in those conditions showing duplex structures where minor external nickel oxy-hydroxide layers are depicted covering an inner protective barrier mainly composed of chromium oxide Cr2O3. Only at high bulk chromium contents (> 15 at.%) are complete Cr2O3 layers built at the interface with the metallic alloy. Beneath the film, in the underlying matrix, a metallic nickel enrichment combined with a chromium depletion is observed, which seems to confirm, as for FeCr alloys, a mechanism by which Cr oxidizes preferentially in this medium during the first steps of the film growth.

Role of hetero-junctions in oxide semiconductor gas sensors

Abstract: A new design concept of semiconductor gas sensors, which introduces a foreign antenna material to a gas in problem, is described for the detection of dilute odorous gases such as HN 3 and H 2 S. The antenna material, dispersed on the surface of a semiconducting oxide, interacts with the gas sensitively and selectively, and the resulting change in its chemical state induces a change in semiconducting properties of the underlying oxide through hetero-junctions. Typical examples of such sensors include NH 3 sensors using Au and Pt WO 3 and an H 2 S sensor using CuO--SnO 2 .

Near-Field Optical Microscopy, Spectroscopy, and Chemical Sensors

Abstract: Introduction Optical microscopy and spectroscopy have long been key techniques in medicine, biology, chemistry, and materials science. Among their advantages are: 1. Universality. All materials and samples attenuate light and have spectroscopic states. 2. Noninvasiveness. Most often the sample is not altered in a microscopic and/or spectroscopic investigation. Moreover, biological samples usually can be studied in their native environment. Most chemical reactions are not perturbed by light of long enough wavelength. 3. Real-time observation. Biological phenomena, chemical reactions, crystallization, and so on can be observed under the microscope as they happen in situ (even with one's eyes); spectroscopic measurements can be performed on line in an industrial process or other setting. 4. Energy and chemical state resolution. The obvious advantages of spectroscopy and photochemistry, at ambient temperature, can be trivially added to the optical methods mentioned above. By contrast, this is not easily accom...

X‐Ray Spectroscopic Investigation of Chlorinated Graphene: Surface Structure and Electronic Effects

Abstract: Chemical doping of graphene represents a powerful means of tailoring its electronic properties. Synchrotron-based X-ray spectroscopy offers an effective route to investigate the surface electronic and chemical states of functionalizing dopants. In this work, a suite of X-ray techniques is used, including near edge X-ray absorption fi ne structure spectroscopy, X-ray photoemission spectroscopy, and photoemission threshold measurements, to systematically study plasma-based chlorinated graphene on different substrates, with special focus on its dopant concentration, surface binding energy, bonding confi guration, and work function shift. Detailed spectroscopic evidence of C‐Cl bond formation at the surface of single layer graphene and correlation of the magnitude of p-type doping with the surface coverage of adsorbed chlorine is demonstrated for the fi rst time. It is shown that the chlorination process is a highly nonintrusive doping technology, which can effectively produce strongly p-doped graphene with the 2D nature and long-range periodicity of the electronic structure of graphene intact. The measurements also reveal that the interaction between graphene and chlorine atoms shows strong substrate effects in terms of both surface coverage and work function shift.

A decomposition procedure for the determination of copper oxidation states in Cu‐zeolites by XPS

Abstract: A procedure to determine the chemical state of copper in differently prepared catalysts is proposed. It is based on a peak decomposition of the main Cu 2p 3/2 signal only, which involves both Cu(II) and Cu(I) contributions. The presence of the closest shake-up satellite is related to the Cu(II) contribution only, in fact a linear dependence of the satellite area versus the Cu(II) area has been found. This method has been applied to characterize variously prepared catalysts and to quantify the different copper states at the surface. A molecular picture is formulated to describe a possible mechanism for copper reduction occurring during the catalyst preparation route at the zeolite surface.