Chemical state

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

Surface Science Letters Chemical states of nitrogen in ZnO studied by near-edge X-ray absorption fine structure and core-level photoemission spectroscopies

Abstract: Interaction of low-energy nitrogen ions with ZnO surface has been studied by photoemission spectroscopy (PES) around N 1s corelevel and near-edge X-ray absorption fine structure (NEXAFS) around N K-edge. Nitrogen can break Zn–O bonds at the surface and form N–O, Zn–N or Zn–N–O bonds, characterised by specific chemical shifts in PES or absorption peaks in NEXAFS. A distinctive signal from molecular nitrogen has also been observed in ion-bombarded samples in both NEXAFS and PES. � 2006 Elsevier B.V. All rights reserved.

In Situ Tracking of Organic Reactions at the Vapor/Liquid Interfaces of Ionic Liquids

Abstract: The molecular structures of ionic liquids at interfaces play a crucial role in determining their chemical activities in applications. In situ X-ray photoelectron spectroscopy (XPS) was used to track the evolution of X-ray irradiation-induced chemical reactions in a series of ionic liquids ([Cn mim][AuCl4 ]; n=4, 6, 8, 10) on the Si (111) single-crystal surface. Analyses of microstructure and chemical bonding based on the XPS results indicated that reactions occurred at the vapor/liquid interfaces of the ionic liquids. The time-resolved XPS spectra revealed that with increasing irradiation time, the intensity of the peak corresponding to trivalent Au anion decreased for the four ionic liquids as Au was continually reduced to a lower chemical state and finally converted to gold nanoparticles. The rate and conversion of the reaction were associated with the length of the alkyl chain of the ionic liquids cation. Molecular dynamics simulations further revealed that the alkyl chain of the cation in the ionic liquids was oriented towards the vacuum environment at the vapor/liquid interface. Our results provide a real-time atomic-scale experimental evidence of organic reactions at the vapor/liquid interfaces of ionic liquids. The findings are important for understanding the roles of ionic liquids in catalysis, separation, electrochemistry, functional materials, and so on.

Mechanism of sulfur-doping on TiO_2 photo-response under visible light

Abstract: S-TiO2 photocatalysts,with thiourea as source substance of S and titanium tetrabutoxide(Ti(OC4H9)4 as precursor of titanium dioxide,were prepared by sol-gel method.The effects of sulfur-doping on TiO2 crystal structure,the chemical states of S atom in TiO2 crystals and the chemical bonds formed in TiO2 were analyzed by XRD,XPS and FTIR.The results show that S atom as the state of S4+ in TiO2 crystal lattices substitutes part of Ti atoms and form Ti1?xSxO2 catalyst,and S4+ forms an electron-occupied level in valence band(VB),and the electron occupies level above the VB consists of S3p states,at the same time,the S3p states contribute to the formation of a conduction band with Ti3d and O2p states,the chiasma of S3p states and the VB make VB broaden and result in energy gap narrow down,and then improve the optical response of TiO2 and extend its absorption edge into the visible-light region.

Real-Time Observation of Surface Chemical Reactions Proceeding in the Depth Direction by Wavelength-Dispersive Soft X-ray Absorption Spectroscopy.

Abstract: It has long been a challenging task to observe surface chemical reactions proceeding in the depth direction without stopping the reaction (i.e., real-time observation), with subnanometer depth resolution. X-ray absorption spectroscopy (XAS) in the soft X-ray region is one of the most crucial methods to analyze the chemical states of light elements; however, simultaneous time- and depth-resolved XAS measurements during the reaction have not been realized before. Herein, we show the real-time observation of the time-evolving oxidation process of a Co thin film with a fluorescence-yield wavelength-dispersive XAS method, which also has subnanometer depth resolution. The series of Co L-edge XAS spectra show that the oxide component increases from the surface to deeper regions as the reaction proceeds. The progress of oxidation in the depth direction was interpreted by the reaction with O2 gas at the surface and the interlayer reaction by oxygen migration.

Structure of Al2O3 thin layers synthesized on the silicon surface by atomic layer deposition

Abstract: The distribution of the phase and chemical composition at an Al2O3/Si interface is studied by depth-resolved ultrasoft x-ray emission spectroscopy. The interface is formed by atomic layer deposition of Al2O3 films of various thicknesses (from several to several nanometers to several hundreds of nanometers) on the Si(100) surface (c-Si) or on a 50-nm-thick SiO2 buffer layer on Si. L 2,3 bands of Al and Si are used for analysis. It is found that the properties of coatings and Al2O3/Si interfaces substantially depend on the thickness of the Al2O3 layer, which is explained by the complicated character of the process kinetics. At a small thickness of coatings (up to 10–30 nm), the Al2O3 layer contains inclusions of oxidized Si atoms, whose concentration increases as the interface is approached. As the thickness increases, a layer containing inclusions of metallic Al clusters forms. A thin interlayer of Si atoms occurring in an unconventional chemical state is found. When the SiO2 buffer layer is used (Al2O3/SiO2/Si), the structure of the interface and the coating becomes more perfect. The Al2O3 layer does not contain inclusions of metallic aluminum, does not vary with the sample thickness, and has a distinguished boundary with silicon.