John T. Wolan

Surface characterization study of AgF and AgF2 powders using XPS and ISS

Abstract XPS and ISS data have been collected from pressed AgF and AgF2 powder samples obtained from AESAR. The samples were sputter-cleaned in vacuum for 10 min with 1 keV He+ to reduce the amounts of surface contaminants present. Negative shifts in XPS BEs and increased peak widths are observed with increasing silver oxidation state for the Ag 3d peaks according to the XPS data. This negative BE shift with increasing oxidation state is opposite to that expected based on simple charge-transfer arguments. Significant negative KE shifts between the Auger features are obtained from Ag metal, AgF, and AgF2 similar to those observed for Ag metal, Ag2O and AgO. The XPS F 1s and F 2s peaks indicate the presence of multiple chemical states of fluorine including fluoro-hydrocarbon and/or-alcohol-like species in addition to fluorides. As prepared AgF and AgF2 samples were found to have F Ag ratios of 0.60 and 1.75, respectively. Since the stoichiometries of AgF and AgF2 predict F Ag ratios of 1.00 and 2.00, respectively, the excess Ag is present in chemical forms other than the silver-halide. Both samples contain mixed chemical states of Ag0, Ag+ and Ag2+. The primary contaminants consist of O and C. Multiple chemical states of O are present on the outermost and near-surface regions of the as-prepared samples including atomically adsorbed oxygen, carbonates, absorbed water, hydroxyl groups and various oxygen-containing carbon compounds. The XPS C 1s peak shapes are quite complex with features due to the presence of several different carbon species including carbide, hydrocarbons, alcohols, carbonate, CHF and CFO(OH)-like species.

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 growth of ZrO2 thin films using a novel hyperthermal oxygen-atom source

Thin ZrO2 films have been grown on Si(100) and on glassy carbon substrates using a novel atomic oxygen source in a standard molecular beam epitaxy system. The oxygen source produces a flux of hyperthermal oxygen atoms with an ion/atom-ratio ≪0.001 through electron stimulated desorption from a Ag alloy surface at an operating pressure <10−8 Torr. The films were grown at room temperature and analyzed using Rutherford backscattering spectroscopy, x-ray diffraction (XRD), x-ray photoelectron spectroscopy and transmission electron microscopy (TEM). The results show the successful growth of fully stoichiometric ZrO2 films on nonheated Si(100) and on amorphous glassy carbon substrates at a rate of 0.58 μm/hr. The XRD and TEM investigations indicate the formation of a mixed amorphous/orthorhombic film structure. Based on the film growth rate, the O flux produced by the electron stimulated desorption atom source is estimated to be 8×1014 atoms/cm2 s. This flux value is consistent with other determinations using io...

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 alteration of the native oxide layer on LiGaO2(001) by exposure to hyperthermal atomic hydrogen

X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS) have been used to examine the near-surface region and outermost atomic layer of air-exposed, solvent-cleaned, LiGaO2(001) substrates, respectively, before and after room-temperature exposures to the flux produced by a novel electron stimulated desorption hyperthermal H-atom source. The native oxide layer on the solvent-cleaned LiGaO2(001) substrate is nonhomogeneous and contains primarily LiO, Ga, and small amounts of C. Li is initially present in the near-surface region as Li2O, LiGaO2, and a small amount of LiOH. Several forms of O are present including adsorbed water, LiGaO2, Li, and Ga-oxides, and hydroxyl groups with Ga2O3 as the predominant species. Upon exposure to the hyperthermal H-atom flux, low-temperature removal of oxygen and carbon contaminants occurs, and the near-surface region approaches the stoichiometry of a clean LiGaO2(001) surface except for an increased O concentration. The usually difficult to observe Li 1...

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...

Characterization study of GaAs(001) surfaces using ion scattering spectroscopy and x-ray photoelectron spectroscopy

A surface characterization study using ion scattering spectroscopy (ISS) and x-ray photoelectron spectroscopy (XPS) has been performed on solvent cleaned, n-type GaAs(001) substrates before and after cleaning by ion sputtering and annealing. The native oxide layer on this surface contains large amounts of As2O5,As2O3, and Ga2O3 according to XPS with Ga2O3 being the predominant species. Before cleaning C is present as hydrocarbons, carbonates, and carbide with hydrocarbons as the predominant chemical state. Ion sputtering converts the hydrocarbons into carbide, which is difficult to remove by further sputtering/annealing cleaning cycles, but O is removed by these cycles. According to ISS data, the outermost atomic layer is enriched in Ga before cleaning, but after cleaning the ISS Ga-to-As atom ratio is about 1:2. The results obtained in this study are consistent with the presence of a layered oxide structure with Ga2O3 just above the interface. A sputter-cleaned surface initially exhibits an increase in t...

Application of novel O- and H-atom sources in molecular beam epitaxy

A novel source based on electron stimulated desorption (ESD) has been developed for the production of O-atom and H-atom fluxes. The fluxes produced by these sources are greater than 1015 atoms/cm2 s with an ion-to-atom ratio of about 10−8, and no other contaminants are present. During operation in a typical molecular beam epitaxial (MBE) system, the pressure remains below 10−9 Torr. The energies of the atoms range from about 1 to 4 eV, and no high energy species, which would damage a surface, are present in the flux. Therefore, these ESD atom sources are superior to plasma sources in all respects. The application of these sources for the in situ, room-temperature cleaning of GaAs and InP surfaces, the room-temperature growth of an insulating oxide layer on GaAs(001), and the room-temperature MBE growth of ZrO2 are described.

In Situ Xps Studies of Kapton Exposed to 5 EV Atomic Oxygen

In this study, a novel hyperthermal oxygen atom source has been used to perform in situ O-atom erosion of Kapton surfaces at room temperature; this surface has been examined using X-ray photoelectron spectroscopy before and after exposure to different fluences of O atoms, and then after exposure to air. The XPS data indicate that the 0:C ratio decreases from 0.23 to 0.11 during a 24-hour exposure to a 5 eV O-atom flux of about 1.4×1014 O atoms/cm2-s. This decrease in surface oxygen content is consistent with loss of the carbonyl groups. The nitrogen concentration increases with O-atom exposure, and a new N chemical state forms. Following the 24-hour, O-atom exposure, the sample was exposed to air for 3 hours and re-examined using XPS. The O, N and C concentrations return to the same values obtained before O-atom exposure due to reaction with O2 in the air. Small amounts of atmospheric moisture may adsorb as well. Previous data from space and ground simulations indicate an increase in the O Is signal with exposure to atomic oxygen. The results obtained in this study demonstrate that it is necessary to examine the chemical effects of O-atom degradation of Kapton without air exposure before surface characterization.