Charles K. Mount

In Situ Erosion Study of Kapton ® Using Novel Hyperthermal Oxygen Atom Source

A novel hyperthermal oxygen atom source has been used to perform in situ erosion of Kapton ® surfaces at room temperature, and these surfaces have been examined using x-ray photoelectron spectroscopy before and afterexposureto different e uencesofoxygen atoms and then afterexposureto air. Thedata indicatethat theinitial attack site is the carbonyl portion of the Kapton by reaction with atomic oxygen to form carbon dioxide, which desorbs. The oxygen-to-carbon-atom ratio decreases from 0.23 to 0.11 during a 24-h exposure to a hyperthermal oxygen-atom e ux of about 1 :4 £ 10 14 atoms/cm 2 -s. Following the 24-h oxygen-atom exposure, the sample was exposed to air for 3 h. The oxygen, nitrogen, and carbon concentrations return to values similar to those obtained before the oxygen-atom exposure due to reaction with molecular oxygen in the air. Previous data from space and ground simulations indicate an increase in the surface oxygen content with exposure to atomic oxygen and then air before analysis. The results obtained demonstrate that it is necessary to examine the chemical effects of oxygen-atom degradation of Kapton without air exposure before surface characterization.

Room-temperature oxidation of a GaAs(001) surface induced by the interaction of hyperthermal atomic oxygen and studied by x-ray photoelectron spectroscopy and ion scattering spectroscopy

In this study a hyperthermal oxygen atom source has been used to form an oxide layer on an Ar+-sputtered GaAs(001) surface at room temperature, and this layer has been examined using x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). XPS data indicate that the Ga in the near-surface region is oxidized predominantly to Ga2O3 with a significant contribution from GaAsO4 while the As is oxidized predominantly to an AsOx species with significant contributions from As2O3 and GaAsO4 and/or As2O5. The oxide layer thickness is estimated to be about 25 A, and the XPS Ga:As atom ratio increases from 1.1 to 1.6 during the oxidation. The ISS data indicate that the resulting oxide layer formed is more electrically insulating than a native oxide layer on this surface.

Chemical reactions induced by the room temperature interaction of hyperthermal atomic hydrogen with the native oxide layer on GaAs(001) surfaces studied by ion scattering spectroscopy and x-ray photoelectron spectroscopy

A surface characterization study using x-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy has been performed on solvent-cleaned, n-type GaAs(001) substrates before and after room temperature exposure to the flux produced by a novel atomic hydrogen source based on electron-stimulated desorption of hyperthermal (∼1 eV) hydrogen atoms. The native oxide layer on the solvent-cleaned GaAs(001) substrate contains C, As2O5 , As2O3 , and Ga2O3 according to the XPS data with Ga2O3 being the predominant species. Before H atom exposure, the C is present as hydrocarbons, carbonates, alcohols, and carbides with hydrocarbons as the predominant chemical state. Upon room temperature exposure to a 1 eV hyperthermal H atom flux, the O in As and Ga oxides is removed, and the amount of C present is reduced through methane formation and desorption. In this process hydrocarbons are not converted to carbides, which are difficult to remove, as in the case of ion sputtering. After reduction the predominant form...

Study of a polycrystalline Ni/Cr alloy V. Hydrogen-atom exposure

Abstract An air-exposed polycrystalline nichrome (Ni/Cr) alloy was exposed to a hydrogen-atom flux at room temperature and then sputtered with Ar+ for 15 min. X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) were used to examine the changes, which occur at the surface of the sample during these treatments. The near-surface region of the alloy initially consists primarily of nickel hydroxide and carbon contamination. Small amounts of Na and Cl contaminants are also present on the surface, according to the ISS data. The amount of carbon contamination and oxygen in the near-surface region is decreased by the H-atom exposure, and the Ni and Cr concentrations are increased. The hydroxyl groups are rapidly removed during the exposure to H atoms presumably through formation of water molecules, which desorb. Ni(OH)2, NiO, Ni0, CrO2 and Cr0 are present in the near-surface region after the H-atom exposure. A subsequent 15-min, 1-keV Ar+ sputter removes the remaining carbon, nearly all of the oxygen, as well as the Na and Cl contaminants. The Ni is mostly metallic, and Cr is present as Cr0 and CrO2. In previous studies, multiple ion-beam sputtering and annealing cycles were necessary to obtain this level of cleanliness. The process using a H-atom beam flux provides an alternative and less time-consuming method for cleaning Ni/Cr alloy surfaces.

Surface characterization study of the chemical alteration of an air-exposed polycrystalline tin foil during H-atom exposures

Abstract An air-exposed polycrystalline Sn foil surface has been examined before and after exposure to H atoms using X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). The foil initially contains large amounts of oxygen and carbon at the surface. C is present mostly as hydrocarbon contamination, and O is present as Sn hydroxide and surface water in addition to SnO, SnO 2 and transitional oxide (possibly Sn 3 O 4 ), which has an O content between SnO and SnO 2 . The C and O contents of the near-surface region are significantly reduced by exposure to the H-atom flux. The large hydroxyl group concentration is reduced through formation and desorption of water. A short 1-min exposure results in reduction of some of the SnO 2 or transitional oxide to SnO. Longer reduction periods result in the formation of a large amount of transitional oxide and some metallic Sn. ISS data indicate that the O and C contents of the outermost atomic layer initially increase upon exposure to H atoms due to a chemically induced driving force and then decrease. Migration of subsurface C and O becomes the rate-limiting step with regard to further removal of these species at room temperature.

Chemical alteration of thin alumina films on aluminum during hydrogen-atom exposures

Abstract Hot-rolled and partially oxidized Al foil surfaces were examined before and after H-atom exposures using X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) to monitor the changes which occur at the sample surfaces. The near-surface region of the native oxide of the hot-rolled Al foil contains primarily C and O. Cl and Ca contamination also are present at the outermost atomic layer according to ISS. H-atom exposures reduce the amount of carbonates and hydrocarbons but causes an enrichment of sulfur in the outermost layer of the foil. The O-to-Al ratio is reduced, and the AlOx species initially present is converted to Al2O3. After sputtering the Al foil to remove the Cl, C, and Ca contaminants, the Al was exposed to oxygen at 10−7 Torr for 10 min. The near-surface region of this re-oxidized surface contains both Al metal and Al2O3. Exposing this partially oxidized surface to H-atoms produces a chemically-induced driving force which causes subsurface O to migrate toward the surface of the foil. This results in an increase of the Al2O3 concentration at the sample surface. These results suggest that the thickness of Al oxide layers may be controlled using H-atom exposures. Furthermore, the amounts of carbon contamination can be decreased and possibly eliminated without reducing the alumina.

Characterization study of nitrogen-ion-implanted amorphous bright chromium deposited films

Abstract Amorphous, bright, chromium deposited (ABCD) films have been developed in order to utilize chromium in high-temperature wear applications. The hardness of these films is increased at elevated temperatures (200–600 °C) whereas conventional chromium films become softer at elevated temperatures. Furthermore, the hardness of ABCD dfilms can be increased by nitrogen-ion-implantation and various types of annealing pretreatments. In this study a non-annealed film and a 600 °C annealed film were implanted with nitrogen ions and characterized using Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA or XPS) and X-ray diffraction (XRD). The resulting data yield information which relates the hardness of the films to their chemical and structural properties. Specifically, the annealed film is more highly crystalline than the non-annealed film. Diffraction lines due to Cr 7 C 3 and Cr 2 N are readily apparent. AES and ESCA show that the film compositions are similar but that the chemical states of the surface species differ in that most of the organic carbon contained in the film is converted to carbide during annealing. These differences are responsible for the increase in Knoop hardness (1660 to 2980) derived from annealing the sample prior to implantation.

Investigation of CO and H2 adsorption on polycrystalline Pt

The adsorption and coadsorption of CO and H2 on polycrystalline Pt have been examined using temperature programmed desorption (TPD) and ion scattering spectroscopy (ISS). The data show that CO adsorbs molecularly through the C with the O pointing away from the surface and that the surface is about 80% covered. TPD data obtained after coadsorption indicate that a CO-H complex forms at this surface.

Modification of amorphous bright chromium deposited (ABCD) films by nitrogen ion implantation

The hardness of amorphous bright chromium deposited (ABCD) layers can be increased by annealing or N ion implantation. In this study the N ion implantation parameters which influence hardness have been systematically examined. These parameters include sample pretreatment, ion beam energy and total dose. The properties of the resulting films have been characterized using Auger electron spectroscopy coupled with ion sputtering depth profiling. X-ray photoelectron spectroscopy and Knoop microhardness measurements. Auger depth profiles suggest the formation of a stoichiometric CrN subsurface layer after implantation of high N doses ( > 8 × 1017N/cm2). With higher doses this layer broadens toward the surface and N retention values decrease rapidly. Implanting at elevated temperatures increases the retained N, causes N to migrate more deeply into the bulk, and yields high hardness values.

Characterization study of nitrogen-ion-implanted conventional chromium platings: Part 6

Abstract A previous study (H. Ferber, G.B. Hoflund, C.K. Mount and S. Hoshino, Surf. Interface Anal. , 16 (1990) 488) has shown that the hardness of conventional chromium layers can be significantly enhanced by nitrogen ion implantation. The present study examines the complex chemical nature of nitrogen-ion-implanted conventional chromium films using electron spectroscopy for chemical analysis, Auger electron spectroscopy, depth profiling and ion scattering spectroscopy. Both the composition and chemical states of the species vary substantially with depth, and numerous forms of chromium, carbon, nitrogen and oxygen are present.