Chemical state

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

A porous (La, Sm) co-doped Sialon-polytypoid ceramic with colour and structure differences in multilayers

Abstract: In this paper, a porous Sialon polytypoid material with multilayered structure was in situ synthesized at 1700 °C for 3 h in a nitrogen atmosphere via a nitriding process. The plate-like Sialon grains were observed using a scanning electron microscope (SEM), and the chemical composition, structure, chemical state and optical absorption of this material were characterized by energy dispersive X-ray spectroscopy (EDX), synchrotron X-ray diffraction (SXRD), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy (DRS). There are four layers with two ranges of grain sizes. The grains with sizes of 18–35 μm are in the inner layer (layer-4) and light-grey, while those grains with bigger sizes of 60–80 μm are present in the outer layers in green colour. These two types of grains have a slight difference in chemical composition, i.e. (La,Sm)0.1Si8Al14O5N21.1 and (La,Sm)0.33Si6Al12O1N21, respectively. They are polytypoids with different structures, which precipitated from the lanthanide-rich Sialon glass. The chemical states of the elements were different as indicated from XPS data. It is believed that the colour and size differences within layers resulted from the intrinsic differences of chemical composition, structure and chemical state of the two types of grains. This porous ceramic might be of potential applications in water treatment, building and automotive industries as a functionally gradient material (FGM) or ceramic filter.

Role of hexagonal boron nitride in protecting ferromagnetic nanostructures from oxidation

Abstract: Ferromagnetic contacts are widely used to inject spin polarized currents into non-magnetic materials such as semiconductors or 2-dimensional materials like graphene. In these systems, oxidation of the ferromagnetic materials poses an intrinsic limitation on device performance. Here we investigate the role of ex-situ transferred chemical vapour deposited hexagonal boron nitride (hBN) as an oxidation barrier for nanostructured cobalt and permalloy electrodes. The chemical state of the ferromagnets was investigated using X-ray photoemission electron microscopy owing to its high sensitivity and lateral resolution. We have compared the oxide thickness formed on ferromagnetic nanostructures covered by hBN to uncovered reference structures. Our results show that hBN reduces the oxidation rate of ferromagnetic nanostructures suggesting that it could be used as an ultra-thin protection layer in future spintronic devices.

Structure of mono- and bimetallic heterogeneous catalysts based on noble metals obtained by means of fluid technology and metal-vapor synthesis

Abstract: Monometallic nanocomposites are obtained with the use of supercritical carbon dioxide (fluid technique) and metal-vapor synthesis (MVS), while bimetallic nanocomposites of Pt and Au noble metals and γ-Al2O3 oxide matrix are synthesized by a combination of these two methods The structures, concentrations, and chemical states of metal atoms in composites are studied by means of small-angle X-ray scattering (SAXS), transparent electron microscopy (TEM), X-ray fluorescent analysis (XFA), and X-ray photoelectron spectroscopy (XPS) The neutral state of metal atoms in clusters is shown by XPS and their size distribution is found according to SAXS; as is shown, it is determined by the pore sizes of the oxide matrices and lies in the range of 1 to 50 nm The obtained composites manifest themselves as effective catalysts in the oxidation of CO to CO2

Characterization of air-exposed surface of β-FeSi2 fabricated by ion beam sputter deposition method

Abstract: The surface composition and chemical states of β-FeSi2 on a Si(1 0 0) substrate after exposure to the ambient atmosphere was investigated by using X-ray photoelectron spectroscopy with synchrotron radiation (SR-XPS). The analysis revealed that about 70% of the Si substrate was covered with β-FeSi2. In addition, it was found that a SiO2 overlayer with a thickness of about 1 nm covered the whole surface of the sample. These results suggest that Si was segregated during the IBSD process and that the readily formed SiO2 layer behaved as a protective layer against further oxidation of β-FeSi2 surface.