Chemical state

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

Near Edge X-Ray Absorption Fine Structure Spectroscopy: A Powerful Tool for Investigating the Surface Structure and Chemistry of Solid Lubricants

Abstract: Synchrotron-based spectroscopic techniques have been critical tools for developing a better understanding of the structure and properties of materials and material surfaces as well as their evolution in response to energetics inputs, such as mechanical strains present in tribological contacts. Among these techniques, near edge X-ray absorption fine structure (NEXAFS) spectroscopy is one of the most powerful tools thanks to its elemental specificity, surface sensitivity, and ability to provide important information about local bonding configurations, such as hybridization, chemical states, and bond orientations. In addition, when coupled with imaging methods like photoemission electron microscopy and magnetically-guided imaging, NEXAFS spectroscopy enables chemical imaging of materials with high spatial resolution. This capability can be critical when investigating materials after tribological experiments, where chemical changes and structural transformations occur in the first few atomic layers and spatial inhomogeneities can be present across small length scales. The present contribution first describes the principles of NEXAFS spectroscopy, followed by experimental methods for the acquisition and processing of NEXAFS data. Finally, the potential of this analytical method for fundamental and applied research in tribology is demonstrated by discussing case studies in the area of solid lubricating carbon-based thin films.

XPS Study on Chemical State and Phase Structure of PBII Nitriding M50 Steel

Abstract: X-ray diffraction (XRD) and X-ray photoelectron spectroscopy were used to study the structure and the element chemical states of plasma-based ion implantation (PBII) nitriding M50 steel. An ~70-nm-thick oxygen-rich layer was formed in the surface after PBII treatment, where C and V elements were absent, Cr and Mo elements were in the manner of oxide, and Fe element was in the manner of Fe3O4 and iron nitride. XRD patterns revealed that the Fe16N2 phase was formed in the subsurface of the nitrided layer. Four different chemical states of nitrogen with binding energies of 404.1, 399.2, 396.7, and 394.3 eV were found in sequence with sputtering time increasing, which were confirmed to belong to NO bonding, Fe3(N, O) [or Fe4(NO)], Fe3N (or Fe4N), and Fe16N2.

In-depth study of the chemical/electronic structures of two-dimensional molybdenum disulfide materials with sub-micrometer-resolution scanning photoelectron microscopy

Abstract: The limitation of X-ray photoelectron spectroscopy (XPS) carried out with an in-lab source can be overcome by synchrotron-based scanning photoelectron microscopy (SPEM) that integrates the XPS technique with scanning microscopy, enabling the analysis of the chemical/electronic structure of a material with sub-micrometer spatial resolution. Using this analytical method, the changes in the structural properties of two-dimensional (2D) molybdenum disulfide (MoS2) materials according to the synthetic method used were studied. In addition to the monolayer form of a 2D MoS2 material (MoS2 monolayer), multilayered 2D MoS2 materials and MoS2 monolayers doped with the widely used p-type dopants, gold chloride (AuCl3) and bis(trifluoromethane)sulfonamide (TFSI), were prepared by a controlled synthetic process. Through comparative analysis of the SPEM data with those obtained by other techniques such as Raman spectroscopy, auger electron spectroscopy, and atomic force microscopy, the variation in the chemical/electronic structures of MoS2 2D materials depending on the synthetic process was clarified. From SPEM data acquired from locations where AuCl3 or TFSI dopant molecules were present, all the MoS2 chemical states were confirmed to have relatively lower binding energies than those of an as-grown MoS2 monolayer. These differences are related to the effects of p-type doping on the MoS2 2D material. Separately, the increase in the MoS2 layer number is manifested in the form of brightness difference in the SPEM data. Meanwhile, all the binding energies of the MoS2 chemical states including the onset of the valence band maximum are slightly lower in the bright regions than in the dark regions, and these binding energy differences are presumably due to the change in the bandgap change based on the MoS2 layer number.

Evaluation of the Antimicrobial Protection of Pharmaceutical Kaolin and Talc Modified with Copper and Zinc.

Abstract: Six pharmaceutical pastes were prepared using chemically modified kaolin and talc powders. Tests were conducted to determine their structural and chemical characteristics as well as their antimicrobial protection, thus rendering them suitable for cosmetic and pharmaceutical uses. Kaolin and talc were treated chemically via the cation exchange method to load the clay particles with copper and zinc ions, two cations well known for their antimicrobial properties. Mineralogical analyses were conducted by using X-ray diffraction (XRD) before and after the modification, confirming the mineralogical purity of the samples. Scanning electron microscopy was also used in conjunction with energy dispersed spectroscopy (SEM-EDS) to obtain chemical mapping images, revealing the dispersion of the added metals upon the clay minerals surfaces. Moreover, chemical analysis has been performed (XRF) to validate the enrichment of the clays with each metal utilizing the cation exchange capacity. All modified samples showed the expected elevated concentration in copper or zinc in comparison to their unmodified versions. From the X-ray photoelectron spectroscopy (XPS), the chemical state of the samples’ surfaces was investigated, revealing the presence of salt compounds and indicating the oxidation state of adsorbed metals. Finally, the resistance of pastes in microbial growth when challenged with bacteria, molds, and yeasts was assessed. The evaluation is based on the European Pharmacopeia (EP) criteria.

Modification Mechanism of the Surface-treated PAN-based Carbon Fiber by Electrochemical Oxidation

Abstract: Surface treatment is one of the most important procedures for the preparation of the high performance carbon fiber. The morphology of the surface-treated PAN carbon fiber was characterized in terms of AFM,SEM,XPS and XRD. And the modification mechanism of the electrochemical oxidation method was also discussed. Results show that the weaker layer of carbon fiber surface is removed by the electrochemistrical etching. As compared with the untreated carbon fiber,the grooves after treatment become widened and deepened,and the surface roughness is also increased one-fold. The functional groups on the carbon fiber surface are increased after the chemical oxidation of electrochemistry,as confirmed by that the (O1s+N1s)/C1s atomic ratio is increased by 9.7%. The physical and chemical double effectiveness mechanism is put forward that the physical and chemical state of the carbon fiber surface can be improved simultaneously by the electrochemical oxidation.