Chemical state

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

W-doped nanoporous TiO2 for high performances sensing material toward acetone gas

Abstract: W-doped TiO2 with nanoporous structure was synthesized by a one-step low temperature hydrothermal method using TiOSO4 and (NH4)6H2W12O40•xH2O as titanium and tungsten sources. Structure, morphology, specific surface area and chemical state of samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). W-doped nanoporous TiO2 samples were used as sensing materials of indirect-heating sensors and their gas-sensing performances were studied to detect acetone. The experimental results show that 7.5% W-doped nanoporous TiO2 can adsorb more oxygen molecules on the surface and provide large amount of active reaction sites on interface to profit reaction between material and gas molecules. The gas sensor based on 7.5% W-doped nanoporous TiO2 exhibits good gas-sensing performances, including high gas response value, shortened response/recovery time and good reproducibility, which make it a promising candidate in acetone detection. Apart from these, the mechanism related to the advanced properties was also investigated and presented.

Trace Element Analysis under 100 ppm and Chemical State Analysis in Small Area using Wavelength Dispersive Soft X-ray Emission Spectrometer in FE-SEM

Abstract: A novel wavelength dispersive soft X-ray emission spectrometer (WD-SXES) has been developed. It covers nominally the X-ray energy range between 50 and 210 eV [1, 2] using two kinds of gratings. One of the characteristic features of the WD-SXES is its parallel detection of the signal. This allows it to be used like a conventional energy dispersive spectrometer. A second feature is its high energy resolution, which is about 0.2 eV for Al-L emission. This resolution is comparable to that of X-ray photoelectron spectroscopy or electron energy-loss spectroscopy. This enables us the ability to obtain important information about chemical bonding in bulk samples from observed spectra as a result of the very highenergy resolution. We have already reported a few examples obtained with the WD-SXES [3]. One important feature of the WD-SXES is that it can detect the Li-K emission spectrum. In the case of an anode electrode from a lithium ion battery (LIB), two types of lithium peaks are observed; one lower energy peak at 50eV, from the valence band, and the other higher energy peak at 54 eV, from the core loss. In addition, we have documented the ability to measure various kinds of X-ray spectra of K, L, M and N emission from Lithium to Uranium [4]. In the modern FE-SEM, a wide variety of attachments are used, including multi-SDD, EBSD, WDS, many kinds of electron signal detectors, sputtering tools, low vacuum devices, cathodeluminescence detectors, etc. These are very important for characterizing a wide range of materials. Now, due to its good peak to background ratio and high sensitive CCD camera, the WD-SXES would be an ideal attachment for trace element analysis. Combining the WD-SXES with a FE-SEM, the higher spatial resolution and high sensitivity can provide new insights in material science. For example, the SEM is very useful for observing the distribution of microstructures for metals and ceramics. We have also demonstrated that trace carbon contents can be detected in concentrations from 67 ppm to 8700 ppm using low alloy steel NBS (NIST) series from 1261a to 1265a respectively. Backscattered electron images of these materials, along with their trace carbon peaks are shown in Figure 1 (a) and (b). In addition, from the peak shape of the C-Kspectra, it is possible to distinguish a carbide grain from graphite, as shown in Figure 2. Using a FE-SEM, we can observe tiny grains or grain boundaries, and by combining it with the WD-SXES, we can analyze these features for trace carbon abundances. It is also possible to analyze for trace boron and nitrogen. In this presentation, we will discuss the possibilities for using the WD-SXES for trace elemental analyses and chemical state analyses.

In situ TREXS Observation of Surface Reduction Reaction of NiO Film with ∼2 nm Surface Sensitivity.

Abstract: X-ray absorption fine structure (XAFS) spectroscopy is one of the most widely used methods at synchrotron radiation facilities. XAFS gives us information on chemical states and local structures. Fundamentally, XAFS is bulk sensitive, not surface sensitive. If a surface sensitive XAFS method was available, surface chemical reactions can be observed under realistic conditions. Here, we report the development and present status of a type of surface sensitive x-ray spectroscopy, which is named total reflection x-ray spectroscopy, TREXS.

Quantitative chemical state analysis of Ti and Mo in a high strength steel using X-ray absorption fine structure (XAFS)

Abstract: An X-ray absorption fine structure (XAFS) technique with the X-ray fluorescence yield mode was applied to a non-destructive chemical state analysis of Ti and Mo in a Ti-Mo added high-strength steel. The Ti-K and Mo-K edge XAFS spectra clearly showed a transition of Ti and Mo from in solution form in the α-Fe matrix to a carbide form with heat treatments. The authors propose this XAFS analysis for the quantification of the fraction of the precipitation of micro-alloy elements. The analysis revealed a significant difference between the precipitation kinetics of Ti and Mo in the steel.