Chemical state

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

X-ray Absorption Spectroscopy on Copper Trace Impurities on Silicon Wafers

Abstract: Trace metal contamination during wet cleaning processes on silicon wafer surfaces is a detrimental effect that impairs device performance and yield. Determining the chemical state of deposited impurities helps in understanding how silicon surfaces interact with chemical species in cleaning solutions. However, since impurity concentrations of interest to the semiconductor industry are so low, conventional techniques such as x-ray photoelectron spectroscopy cannot be applied. Nonetheless, chemical information on trace levels of contaminants can be determined with x-ray absorption near edge spectroscopy (XANES) in a grazing incidence geometry. In this study, silicon samples were dipped in ultra pure water (UPW) and 2% hydrofluoric (HF) solutions with copper concentrations of 5 and 1000 ppb, respectively. These samples were then analyzed using XANES in fluorescence yield mode to determine the oxidation state of deposited copper contaminants. It was found that copper impurities on the silicon surface from HF solution were metal in character while copper impurities deposited from the spiked UPW solution were deposited as an oxide. These results show that XANES can provide information on the chemical state of trace impurities even at surface concentrations below a few thousandths of a monolayer.

A Review of X-ray Photoelectron Spectroscopy Technique to Analyze the Stability and Degradation Mechanism of Solid Oxide Fuel Cell Cathode Materials

Abstract: Nondestructive characterization of solid oxide fuel cell (SOFC) materials has drawn attention owing to the advances in instrumentation that enable in situ characterization during high-temperature cell operation. X-ray photoelectron spectroscopy (XPS) is widely used to investigate the surface of SOFC cathode materials because of its excellent chemical specificity and surface sensitivity. The XPS can be used to analyze the elemental composition and oxidation state of cathode layers from the surface to a depth of approximately 5–10 nm. Any change in the chemical state of the SOFC cathode at the surface affects the migration of oxygen ions to the cathode/electrolyte interface via the cathode layer and causes performance degradation. The objective of this article is to provide a comprehensive review of the adoption of XPS for the characterization of SOFC cathode materials to understand its degradation mechanism in absolute terms. The use of XPS to confirm the chemical stability at the interface and the enrichment of cations on the surface is reviewed. Finally, the strategies adopted to improve the structural stability and electrochemical performance of the LSCF cathode are also discussed.

Structure, microstructure and surface of Nd 3+ -doped mesoporous anatase-phase TiO 2

Abstract: We prepared nanocrystalline mesoporous anatase-phase TiO2 doped in the range from 0.0 to 1.0 at.% of Nd3+ by the reverse microemulsion method (RMM). The analysis of electron microscopy of the nanocrystal revealed a truncated-tetragonal bipyramidal shape and agglomerates of spheroidal nanoparticles with inter-particle porosity. The inductively coupled plasma (ICP) technique corroborated the doping concentrations. The analysis of structural parameters by the Rietveld refinement technique indicated the variation of Ti–O(1) and Ti–O(2) bond lengths, suggesting the Nd3+ insertion in the lattice. The microstructural analysis by the Williamson–Hall plot (WH) and whole powder pattern fitting (WPPF) revealed that the doping addition has a slight inhibition effect on the crystal size (6–8 nm) with a minor strain increment. The surface analysis from N2 adsorption/desorption isotherms showed that the incorporation of the dopant in low amounts improved the mesoporous structure stability, increased the diameter of opening pores, and changed the pore structure network. The XPS analysis of the chemical states on the surface suggests that the Nd3+ presence changed the Ti 2p region and the presence of the two chemical states of oxygen (OI and OII).

Dielectric characteristics and chemical structures of Nb2O5 thin films grown by sol-gel techniques

Abstract: Nb2O5 thin films were produced on silicon substrates by sol-gel spin-coating technique. The films were heat-treated at temperatures ranging from 600°C to 1000°C in oxygen atmosphere, and their crystalline phases, chemical states, and dielectric characteristics were investigated by X-ray diffractometry (XRD), Auger electron spectroscopy(AES), and C-V measurements, respectively. The Nb2O5 thin films annealed at temperatures ranging from 600°C to 1000°C as well as the powders annealed in the temperature region from 600°C to 800°C are of the T-type structure, while the powders annealed at 1000°C are of the H-type structure. The films heat-treated at temperatures ranging from 600°C to 800°C exhibit dielectric constants of less than 20, while the films annealed at 1000°C show a dielectric constant of 28.