Chemical state

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

Monochromatized Ag Lα X‐rays as a source for higher energy XPS

Abstract: Monochromatization of Ag Lα X-rays is achieved by fitting an Ag anode to a conventional Al Kα monochromator. Many new XPS lines are generated by this high energy source including the 1s and KLL Auger series from Al to Cl. Chemical state determination by means of the Auger parameter for these elements is greatly assisted by the reduced X–ray linewidth after monochromatization. Three glass fibre samples with different surface pre-treatments were studied to show that chemical state information could be extracted from even these complex, rough and insulating surfaces by using this novel X-ray source.

Surface precipitation process of epitaxially grown graphite (0001) layers on carbon‐doped nickel(111) surface

Abstract: The surface precipitation process of epitaxially grown graphite (0001) layers on the C‐doped Ni(111) surface has been investigated by in situ x‐ray photoemission spectroscopy measurements. Peak intensity measurements at various temperatures clarified the change of the carbon chemical state from the segregated carbon through the monolayer graphite to the multilayer graphite. The simple thickness estimation in the transition region from the monolayer graphite to the multilayer graphite indicates that once the estimated thickness is calibrated, controlling the thickness of the graphite thin film in the monolayer range by a precise adjustment of the temperature may be possible. Changes of the chemical states of carbon on the Ni(111) surface with temperature were clarified by high‐resolution measurements with a monochromated Al Kα source. From the observed chemical shift of the C 1s peaks, a negative charge transfer from the monolayer graphite to the substrate can be postulated. This C–Ni interaction is consid...

Correlation between dielectric constant and chemical structure of sodium silicate glasses

Abstract: The chemical structure of sodium aluminosilicate glasses is determined by high resolution x‐ray photoelectron spectroscopy (XPS) as silicon is gradually replaced by aluminum. A well‐defined chemical state is found for silicon, aluminum, and sodium atoms, while three different environments are identified for oxygen atoms corresponding to Si–O–Si, Si–O–Al, and Si–O–Na bonds. The binding energy of Na 1s photoelectrons increases significantly with increasing aluminum substitution while that of Al 2p and components of O 1s photoelectrons remains approximately constant. Thus, the ionicity of sodium increases with aluminum amount, but the over all electron density around silicon, aluminum, and different types of oxygen atoms remains unchanged. The dielectric constant of the glasses increases with increasing aluminum substitution. It is analyzed in terms of the polarizabilities of constituent structural units, viz., silicon tetrahedra, nonbridging oxygen–sodium ion pairs, and aluminum tetrahedron–sodium ion pairs...

The state of zinc in methanol synthesis over a Zn/ZnO/Cu(211) model catalyst

Abstract: The active chemical state of zinc (Zn) in a zinc-copper (Zn-Cu) catalyst during carbon dioxide/carbon monoxide (CO2/CO) hydrogenation has been debated to be Zn oxide (ZnO) nanoparticles, metallic Zn, or a Zn-Cu surface alloy. We used x-ray photoelectron spectroscopy at 180 to 500 millibar to probe the nature of Zn and reaction intermediates during CO2/CO hydrogenation over Zn/ZnO/Cu(211), where the temperature is sufficiently high for the reaction to rapidly turn over, thus creating an almost adsorbate-free surface. Tuning of the grazing incidence angle makes it possible to achieve either surface or bulk sensitivity. Hydrogenation of CO2 gives preference to ZnO in the form of clusters or nanoparticles, whereas in pure CO a surface Zn-Cu alloy becomes more prominent. The results reveal a specific role of CO in the formation of the Zn-Cu surface alloy as an active phase that facilitates efficient CO2 methanol synthesis. Description Zinc’s state in methanol synthesis Methanol can be synthesized from carbon monoxide (CO), carbon dioxide (CO2), and molecular hydrogen (H2) over copper–zinc (Cu–Zn) catalysts, but studies have disagreed about the chemical state of Zn. Although x-ray photoelectron spectroscopy (XPS) can determine its oxidation state, many studies have been limited to reaction pressures of a few millibars, where the rates are low. Amann et al. performed XPS at 180 to 500 millibars for CO2 and CO hydrogenation over a Zn/ZnO/Cu(211) surface at high turnover rates. Stoichiometric mixtures of CO2 and H2 formed ZnO, but for CO and H2, Zn became more metallic and formed Cu alloys. In industrial synthesis, CO2 and H2 are mixed with CO, and the presence of CO would generate Cu–Zn alloy sites active for CO2 reduction to methanol. —PDS CO induces Zn–Cu surface alloy sites that are active for CO2 hydrogenation in catalytic methanol synthesis.

XPS Applications in Thin Films Research

Abstract: XPS (X-ray Photoelectron Spectroscopy) or ESCA (Electron Spectroscopy for Chemical Analysis) as a surface analytical technique has been developed over years and has been used successfully in characterization of a variety of thin films. Information such as composition, chemical states, depth profile, imaging and thickness of thin films is especially useful in thin film research. This paper aims at reviewing these applications of XPS in thin film area.