Chemical state

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

An investigation on surface conditions for Si molecular beam epitaxial (MBE) growth

Abstract: Contamination‐free Si substrate surfaces are vitally important to the subsequent molecular beam epitaxy (MBE) growth. A number of studies on the major contaminants, i.e., C and O, on Si surfaces have been done, and new cleaning procedures for reducing these contaminants have been proposed. However, to date the detailed behavior of C and O on Si surfaces and their effects on the subsequent Si MBE growths are not well established. In the present work, the behavior of the contaminants on heated Si surfaces were investigated using Auger electron spectroscopy (AES) and secondary ion mass spectrometry (SIMS). Also, the chemical bonding of C on Si surfaces was studied by analyzing the AES line shapes of carbon and comparing them with those known carbon chemical states. For the chemical cleaning procedures used in this study, a silicon oxide protection layer is grown onto the cleaned Si surface prior to sample loading. The property of this silicon oxide layer is studied using ellipsometry measurements. To verify ...

Chemical States of Bacterial Spores: Dry-Heat Resistance

Abstract: Mature bacterial spores can be manipulated by chemical pretreatments between states sensitive and resistant to dry heat. The two chemical forms of the spore differ in dry-heat resistance by about an order of magnitude. Log survivor curves for each chemical state were approximately straight lines. The temperature dependence of dry-heat resistance for each chemical state was similar to that usually found for dry-heat resistance. A method of testing spore resistance to dry heat has been designed to minimize artifacts resulting from (i) change of chemical state during the test, (ii) effects of water vapor activity, (iii) incomplete recovery of spores from the test container and clumping of spores. Implications of the existence of different chemical resistance states for experimental strategy and testing of dry-heat resistance are discussed.

An XPS Study of the Promotion of Ru-Cs/Sibunit Catalysts for Ammonia Synthesis

Abstract: The nature of surface cesium compounds in cesium-modified ruthenium-Sibunit catalysts for ammonia synthesis was studied by X-ray photoelectron spectroscopy (XPS). It was found that, on the reduction of promoted catalysts, cesium was incorporated into the micropores of Sibunit to form quasi-intercalation cesium-carbon bonds. In this case, the chemical state of cesium was close to its state in cesium suboxides. The subsequent interaction with atmospheric oxygen resulted in the oxidation of cesium, which occurred as cesium peroxide and cesium superoxide in the oxidized samples. Ruthenium occurred in a metallic state in the reduced samples. The activity of a Ru-Cs+/C(1) sample was higher than that of inactive Ru-Cs+/C(2). This is a consequence of the higher surface concentration of ruthenium, which is most likely due to an increase in the dispersity of metal particles, as well as of the higher probability of the interaction between the promoter and the active component due to a symbatic increase in the surface concentrations of both ruthenium and cesium.

The initial atomic layer deposition of HfO2∕Si(001) as followed in situ by synchrotron radiation photoelectron spectroscopy

Abstract: We have grown HfO2 on Si(001) by atomic layer deposition (ALD) using HfCl4 and H2O as precursors. The early stages of the ALD were investigated with high-resolution photoelectron spectroscopy and x-ray absorption spectroscopy. We observed the changes occurring in the Si2p, O1s, Hf4f, Hf4d, and Cl2p core level lines after each ALD cycle up to the complete formation of two layers of HfO2. From the analysis of those variations, we deduced the growth properties of HfO2. The first layer consists of a sparse and Cl-contaminated oxide because of the incomplete oxidation, and the second layer is denser than the first one and with an almost stoichiometric O∕Hf ratio. At the completion of the second layer, the x-ray absorption spectra revealed the change of the Hf-oxide chemical state due to the transition from the thin Hf-oxide to the bulklike HfO2.

XPS study of hydrogen permeation effect on SiC–C films

Abstract: 70%SiC–C films were deposited with r.f. magnetron sputtering on stainless steel substrates followed by ion beam mixing. These films were permeated by hydrogen gas under the pressure of 3.23 × 107 Pa for 3 h at 500 K. X-ray photoelectron spectroscopy was used to analyze the chemical bonding states of C and Si in these 70%SiC–C films before and after hydrogen gas permeation. In addition, chemical states of contaminated oxygen were also checked. The effect of hydrogen permeation on those states in the 70%SiC–C films is discussed in this paper.