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 Photoelectron Spectroscopy

Abstract: The interaction of photon and the electron goes back to the early part of 19th century emanating from the photo-electric effect depicted by none other than Albert Einstein (Ref 1) described in 1905, and the redistribution of kinetic energy resulting from the interaction of x-ray and solids reported during early part of the century (Ref.2). The spectrum resolutions obtained at that time was not sufficient to observe distinct peaks in spectra for materials. Thus, these phenomena hardly attracted any attention for many years following these discoveries. The modern X-ray Photoelectron Spectroscopy (XPS) has been possible by the extensive and significant contribution from Kai Siegbahn and others (Ref.3, 4) of Uppsala University. Siegbahn developed and employed a high-resolution electron spectrometer that revealed electron peaks in a spectrum emerging from the interaction of x-rays and solids. Eventually, Kai Siegbahn received Nobel Prize in 1981 for his contributions to XPS. Around 1958, shifts in elemental peaks were realized in compounds when the same elements are bound to other but different elements. This discovery resulted in the chemical state identification in various chemicals as well as the oxidation states of atoms in compounds. Because of these useful physical effects, the Uppsala group named XPS with a synonymous name of ESCA (Electron Spectroscopy for Chemical Analysis) used widely today and will be used here alternatively. Therefore, XPS or ESCA not only identifies the element, but also the compound these elements form, from their chemical shifts. Compared to other micro-analytical techniques such as Energy Dispersive (EDS) or Wavelength Dispersive (WDS) techniques, XPS analyzes only few atomic layers present on the surface. This was discovered early in 1966 (Ref. 5). While this has awarded a merit to the analytical technique to analyze very thin layers such as films and coatings, it often analyzes the adsorbed superficial gases and contaminations on a sample introduced to its analytical chamber. This necessitates the surface is cleaned and the underlying material, material of interest, is exposed in a clean environment such that the material of interest is analyzed. The cleaning is accomplished by a scanning ion gun within the analytical chamber of the instrument. Ion gun uses an argon gas and is commonly attached in most modern machines. Reliable and efficient vacuum systems employed in modern machines does not allow adsorbed layers to rebuild after the surface is cleaned. Development of efficient and reliable vacuum pumps over these developmental years is yet another important step in the commercialization of XPS machines. Vacuum levels of better than 10-7 torr are essential to increase the mean free path of electrons released from the sample surface. Thus, modern machines are equipped with high capacity ion, turbo or cryogenic pumps in their analytical chambers. Today, XPS has advanced from an applied physics laboratory to industry for use in quality control as well as analysis of contaminants and has taken a dominant role in microanalysis. Its uniqueness arises from the fact that it is considered non-destructive compared to other common micro-analytical techniques using the electron and ion excitation sources. Polymers and plastics could be analyzed since the binding energies of saturated and unsaturated bonds in atoms could be separated. Extremely thin layers could be analyzed including materials with layered structures. The technique, though did not advance for many years, has now opened a new window for research as well as applications in industry due to its ability to separate and measure the chemical shifts in bound elements. Principles

Characterization of Ti/TiN Films and SiO2/Ti Interfaces by Use of X-Ray Photoelectron Spectroscopy

Abstract: The deposition and processing of thin films, such as barrier metals and anti-reflective coatings, can be enhanced using the information provided by various surface analysis techniques. We will show the application of x-ray photoelectron spectroscopy(XPS) to the production of Ti and TiN films suitable for use in ULSI CMOS integrated circuits. XPS can separate Ti and N photoelectron peaks and detect low (1.0-5.0 atomic%) contamination levels while providing surface and interface chemical state information. In this paper we will show that a) the effect of TiN deposition on subsequent Ti film quality from the same Ti target was determined to be minimal, b) the relation of anneal temperature to the extent of SiO 2 reduction by Ti metal was characterized on SiO 2 /Ti/TiN structures for temperatures from 600°C to 800°C, and c) the absorption of O into TiN films from ambient air was detected and confirmed.

Investigation of Ge profile on SiGe islands by scanning photoelectron microscopy

Abstract: The effect of annealing on SiGe films was investigated using scanning photoelectron spectroscopy (SPEM). Films annealed at a temperature above 950 °C in N2 ambient show a drastic morphological change. The difference in the chemical state between an islandlike surface and flat surface is dependent on the Si and Ge contents. In addition, the chemical state of the flat surface is closely related to differences in Si and Ge content, resulting in a donutlike shape. The oxidation of Ge is suppressed during the annealing process because of the lower heat of formation of GeO2 than for SiO2. Thus, differences in content and the extent of oxidation are major determinants of the chemical state in the islandlike shape. The characteristic donutlike shape reflects kinetic changes in the SiGe content during the annealing process.

SURFACE ANALYSIS | Auger Electron Spectroscopy*

Abstract: A survey on Auger electron spectroscopy is given Auger electron spectroscopy is a mature method in the field of surface chemical analysis The article addresses physical basics of the method, the principal design of recent instruments together with modes of measurements and options for the presentation of spectra, the different approaches for qualitative (including identification of chemical species) and quantitative surface analysis of elements, main fields of applications and quality assurance with a short view on standardization issues The Applications paragraph provides examples from highly resolved Auger spectroscopy aiming on chemical state identification of elements, depth profiling analysis of elements in layer stacks and imaging analysis by scanning Auger microscopy (SAM) at lateral resolution from the sub-micrometer down to the nanometer scale aiming on surface chemical analysis of inhomogeneous surfaces and individual nanoparticles

On the Nature of the Chemical Bond

Abstract: To this point, we have been considering ever smaller length scales in our efforts to understand the fundamental nature of matter. We shall now pivot and begin considering larger entities. Most of the world around us is not composed of individual atoms but is, instead, composed of molecules: specific combinations of atoms that are bound in specific arrangements. This is the world of chemistry.