Douglas A. Asbury

TPD and ESD studies of the interaction of hydrogen and oxygen on polycrystalline zirconium

Temperature programmed desorption (TPD) and electron stimulated desorption (ESD) have been used to study the interaction of hydrogen and oxygen on a polycrystalline zirconium surface. ESD and TPD features due to hydrogen bonding directly both to oxygen and to Zr are identified. Deuterium adsorption studies reveal that the presence of an oxide layer retards hydrogen adsorption but that the oxygen attracts bulk hydrogen forming a hydroxylated surface oxide layer.

A surface study of the oxidation of polycrystalline tin

The oxidation of a polycrystalline tin foil was examined using Auger electron spectroscopy (AES), x‐ray photoelectron spectroscopy (XPS), scanning Auger microscopy (SAM), ion scattering spectroscopy (ISS), and electron‐stimulated desorption (ESD). An oxidation state which does not correspond to SnO or SnO2 has been identified using XPS and retarding mode AES at low oxygen exposures (≤3000 L). It has been suggested in previous studies that oxygen penetrates beneath the outermost layers during the early stages of oxidation of certain metals such as tin. This suggestion has been verified in this study using ISS and ESD. Very small amounts of oxygen are detected with ISS on a sputter‐cleaned Sn surface, and this O signal does not increase with oxygen exposure even though XPS and AES show a significant oxygen uptake. Additionally, no O+signal is detected with ESD whereas large ESD O+ signals are obtained from surfaces of bulk tin oxides. The oxygen concentration is uniform across the sample surface at these ex...

The interaction of O2 and CO with polycrystalline Zr

This study examines (1) the production of a clean polycrystalline surface, (2) oxygen adsorption as a function of room‐temperature exposure using ion scattering spectroscopy (ISS), Auger electron spectroscopy (AES), and electron spectroscopy for chemical analysis (ESCA), and (3) CO adsorption. S and Cl are typical contaminants which modify the chemisorption properties of a Zr surface. However, they are difficult to detect using AES or ESCA but are readily observed using ISS. Sputtering a hot Zr surface provides an excellent method for producing a contaminant‐free surface. The adsorption of oxygen proceeds in a stepwise fashion by rapidly populating sites in the outermost surface layer, filling subsurface sites and then forming a multilayer oxide film even at room temperature and low O2 pressure (10−6 Torr). CO adsorbs dissociatively on Zr at room temperature. An oxide overlayer is formed which contains no C. The C lies beneath the oxide layer in a chemisorbed or interstitial form. Heating converts this C ...

A surface study of amorphous chromium films electrodeposited from chromic acid solutions. Part I

A previous study demonstrates that the addition of organic compounds containing a –CHO or –COOH group to a Cr plating bath results in a chromium deposit which has greatly improved properties. Such deposits have fewer defects than chromium layers produced by conventional methods, the hardness of these deposits increases with increasing annealing temperature in the range of 100 to 600 °C and they are more resistive to corrosion by hydrochloric acid than conventional deposits. In this study the composition and chemical interactions of a chromium layer prepared using this new method were examined with Auger electron spectroscopy (AES) and electron spectroscopy for chemical analysis (ESCA) before and after vacuum annealing at 700 °C and after argon‐ion bombardment. S, C, O, Cl, N, and Ca are incorporated into the deposits from the electrolytic bath. Cr is present as oxides, sulfide, and metal. Annealing causes segregation of S to the surface and diffusion of oxygen into the bulk. This results in conversion of the surface chromium oxides into Cr2S3 and metallic Cr. C also segregates to the surface during annealing forming chromium carbide.A previous study demonstrates that the addition of organic compounds containing a –CHO or –COOH group to a Cr plating bath results in a chromium deposit which has greatly improved properties. Such deposits have fewer defects than chromium layers produced by conventional methods, the hardness of these deposits increases with increasing annealing temperature in the range of 100 to 600 °C and they are more resistive to corrosion by hydrochloric acid than conventional deposits. In this study the composition and chemical interactions of a chromium layer prepared using this new method were examined with Auger electron spectroscopy (AES) and electron spectroscopy for chemical analysis (ESCA) before and after vacuum annealing at 700 °C and after argon‐ion bombardment. S, C, O, Cl, N, and Ca are incorporated into the deposits from the electrolytic bath. Cr is present as oxides, sulfide, and metal. Annealing causes segregation of S to the surface and diffusion of oxygen into the bulk. This results in conversion of ...

A characterization study of platinum-tin oxide films supported on Al2O3

Abstract Films which are about 20 A thick containing platinum and tin oxide were produced by impregnating γ-Al 2 O 3 in an acetone solution containing stannic chloride and chloroplatinic acid. Electron spectroscopy for chemical analysis, Auger electron spectroscopy, temperature-programmed decomposition and depth profiling were used to characterize these films after oxidation in air at 725 K and after reduction in hydrogen at 1 atm and 775 K. Both CO and H 2 O are incorporated in these films but in different relative amounts in the oxidized and reduced samples. The desorption characteristics also differ between the oxidized and reduced samples, but H 2 O and CO desorb simultaneously from each type of sample. Electron spectroscopy for chemical analysis shows that the interaction between the platinum and tin is through a Pt-O-Sn bond which is present in both oxidized and reduced samples. Reduction converts PtO and PtO 2 to metallic platinum and causes sintering of platinum crystallites to bulk-like platinum.

A characterization of thin titania layers deposited on polycrystalline Pt using ISS and ESCA

ISS and ESCA have been used to characterize titania overlayers on a polycrystalline Pt substrate as a function of pretreatment. Multilayers of TiO 2 were formed initially by vapor depositing Ti onto the Pt and then heating to 550 K in 1×10 −7 Torr of O 2 . Reduction in 10 −7 Torr H 2 and 550 K followed by flashing above 1100 K produced a very thin (one or two atoms thick) overlayer of reduced titania which covered more then 90% of the Pt surface as measured by ISS. This overlayer corresponds to the coverage required to completely suppress H 2 and CO chemisorption on these surfaces as determined previously by Ko and Gorte [Surface Sci. 161 (1985) 597]. These results directly contradict Levin et al. [Surface Sci. 169 (1986) 123] who stated that the coverage necessary for complete adsorption suppression in the study by Ko and Gorte corresponded to only one-third monolayer. ISS also shows that the titania species migrate into the bulk Pt at elevated temperatures and return to the surface during cooling.

Changes induced at Ni/Cr alloy surfaces by annealing and oxygen exposure

The changes induced at room-temperature oxidized Ni/Cr alloy surfaces by vacuum annealing and oxygen exposure have been studied using AES and ISS. Both NiO and Cr2O3 are present on an oxidized surface before annealing. The ISS and AES data show that annealing at 500°C causes Cr to migrate rapidly to the surface to form Cr oxides as NiO is reduced. This is consistent with thermodynamic predictions based on the strength of the CrO versus NiO bonds. Further annealing at 500°C for 10 min produces a complex surface consisting of metallic Ni and Cr and Cr oxide. Annealing the sample at 500 ° C for 4 h causes the Cr oxide at the surface to relocate to the subsurface region. The crucial role of sub-surface oxygen in determining the surface composition of a Ni/Cr alloy during annealing is discussed. Re-oxidation occurs very rapidly on a pre-oxidized, annealed surface. Compared to the oxide formed on a clean surface, the re-oxidized surface consists of a smaller amount of NiO and a thicker Cr oxide layer. This segregation behavior of Cr during the oxidation and annealing processes appears to be responsible for an increase in passivity of Ni/Cr alloys toward oxidation.

A method for performing angle‐resolved Auger electron spectroscopy using a cylindrical mirror analyzer

An experimental method is presented for performing angle‐resolved Auger electron spectroscopy (ARAES) using a cylindrical mirror analyzer. The significant increase in surface sensitivity attainable with this technique is illustrated by spectra taken from sputtered and annealed Pt3Sn surfaces and the native oxide layer on a Si(111) surface. Comparison of compositions obtained from Pt3Sn surfaces using surface‐sensitive Auger electron spectroscopy (AES) and ion scattering spectroscopy (ISS) show that the surface sensitivity of AES can approach that of ISS. Comparison of results taken from the native oxide layer on Si(111) suggests that ARAES may be more highly surface sensitive than angle‐resolved x‐ray photoelectron spectroscopy.

A characterization study of amorphous chromium films electrodeposited from chromic acid solutions. II

Abstract This study is part of a continuing effort to characterize Cr films prepared by the amorphous, bright chromium deposition (ABCD) method. These films have many desirable properties compared to deposits produced by conventional methods. Most importantly, the hardness increases with increasing annealing temperature whereas the hardness of conventional films decreases. It has been found that the hardness behavior is similar for films annealed in vacuum or air. This study presents a comparison of AES, ESCA and depth profiling data obtained from an as-prepared sample, a vacuum-annealed sample and an air-annealed sample. The air-annealed sample consists of Cr 2 O 3 and some CrO 3 in the near-surface region. Also, the air-annealed sample contains more oxygen than the as-deposited sample and much more oxygen than the vacuum-annealed sample. The AES O profile taken from the vacuum-annealed sample indicates that O diffuses to the surface and desorbs possibly as a carbon-containing species. Both the air-annealed and as-deposited samples contain more C than the vacuum-annealed sample, but C does segregate to the surface region during air annealing. S is almost completely removed from the film by air annealing. The fact that the composition and chemical states of the species in the vacuum-annealed and air-annealed films are quite different suggests that microstructural characteristics of the Cr films deposited by the ABCD method are responsible for the hardness behavior as a function of annealing temperature.

A characterization study of a hydroxylated polycrystalline tin oxide surface

In this study Auger electron spectroscopy, electron spectroscopy for chemical analysis (ESCA) and electron-stimulated desorption (ESD) have been used to examine a polycrystalline tin oxide surface before and after annealing in vacuum at 500 °C. Features due to surface hydroxyl groups are present in both the ESCA and ESD spectra, and ESD shows that several chemical states of hydrogen are present. Annealing at 500 °C causes a large reduction in the surface hydrogen concentration but not complete removal.