David F. Cox

Computer‐interfaced digital pulse counting circuit

An electronic circuit is presented which can be used in digital pulse counting applications such as ESCA, Auger spectroscopy, UPS, etc. It consists of a quartz crystal clock and integrated circuits, and can be interfaced easily to a laboratory computer through a parallel board. A modification allows this circuit to be used as a counter with a time delay, thus making it useful in applications involving time‐of‐flight mass spectrometry.

An electronic and structural interpretation of tin oxide ELS spectra

Abstract In this study electron energy-loss spectroscopy (ELS) is used to examine polycrystalline tin oxide films which have been annealed, ion sputtered and oxygen treated. The major features in the N ( E ) loss spectrum are interpreted as due to collections of optically allowed interband transitions. It is demonstrated that depth profile information may be obtained by varying the primary electron beam energy. Combined ELS and valence-band XPS results indicate that a significant amount of structural information may be inferred from the size, shape and/or position of the N ( E ) ELS features. Core-level features are found to be quite sensitive to the presence of defects in an SnO 2 lattice with some specificity as to the type of defect.

An investigation of the interaction of polycrystalline zirconium with O2, N2, CO, and N2O. Part I

The adsorption of O2, N2, CO, and N2O on polycrystalline zirconium has been studied using ESCA and AES over a wide temperature range from room temperature to nearly the melting point of zirconium. The gases adsorb dissociatively at all temperatures studied, and the room temperature sticking coefficients are low (<0.01). Heating causes migration of the adsorbate species into the bulk zirconium. Two distinct surface phases (states) of zirconium are identified. State 1 exists when the sample has not been heated above the hcp↔bcc transition temperature of 1135 K for prolonged periods while state 2 occurs after prolonged heating (the time is a function of temperature) above the transition temperature. The AES spectra and chemisorption properties of the two states are very different. State 1 AES spectra show a prominent 175 eV peak which is nearly gone in state 2 AES spectra. State 1 readily adsorbs CO and N2 at room temperature while state 2 adsorbs relatively small amounts of CO and is almost inert to N2. The...

Surface characteristics of antimony-doped tin oxide films

Abstract The surface composition of antimony-doped tin oxide films and its variation after electron bombardment and resistive heating were investigated. It was found that impurities such as carbon, potassium, sodium, calcium and chlorine segregate at the surface and that the carbon and chlorine are removed easily by electron bombardment. It is proposed that resistive heating caused the antimony to migrate rapidly to the surface at about 780°C, resulting in an antimony-rich phase which quickly reached a temperature high enough for sublimation. All substances except tin and oxygen and a trace amount of chlorine were removed. This process was accompanied by a resistivity change of the sample from 50 to 15000ω. Both electron bombardment and resistive heating above 780°C caused an increase in the tin-to- oxygen ratio as determined by Auger spectroscopy and electron spectroscopy for chemical analysis.

Preparation and surface characteristics of platinized antimony-doped tin oxide films

Abstract Thin antimony-doped tin oxide films were platinized electrochemically from an H 2 PtCl 6 ·6H 2 O solution. Auger spectroscopy and electron spectroscopy for chemical analysis (ESCA) were used to analyze the surface composition and electronic structure, and it was found that the platinum appears predominantly as Pt 0 with a small amount of Pt(OH) 2 . Valence band ESCA showed that the tin appears predominantly as SnO 2 with some SnO present.

A SIMS depth profiling study of the hydration layer formed at polycrystalline tin oxide surfaces by atmospheric exposure

Abstract Dynamic SIMS has been used to examine the hydrated surface layer formed on polycrystalline tin oxide films by exposure to atmospheric humidity. A strongly hydrated layer is found to occur within approximately the top 6 A of the surface with a hydrogen-rich region extending to a depth of about 20 A into the bulk. The Sn+ sputtering yield for the hydrated layer is greater than that of the bulk-oxide material. It is shown that the profile of the positive-ion 121 amu peak, which is attributed primarily to 120SnH+, appears to yield the least ambiguous measure of the extent of hydration. High-temperature annealing of the films is found to affect the bulk-sputtering properties possibly by altering the structure of the film and/or the form of the hydrogen incorporated in the bulk of the film.

An ESD and SIMS study of the composition of platinized, antimony-doped tin oxide films. I

Abstract Secondary-ion mass spectrometry (SIMS) and electron-stimulated desorption (ESD) have been used to characterize the composition of antimony-doped tin oxide films before and after a caustic treatment and before and after deposition of platinum. The impurities were identified qualitatively using dynamic SIMS and found to be Li, C, N, Na, Mg, Al, Si, S, K, Ca, Cr, V, Fe, Mn, Ni, Ti, and Zn. Both SIMS and ESD demonstrated that hydrogen is a major constituent of these films. Evidence is presented that the caustic treatment hydroxylates the surface and that Sb is segregated at the surface. It appears that platinum desorbs by electron stimulation probably in the form of an oxide species. This may prove useful in probing the composition of supported-metal crystallites.

A study of the dehydration of tin oxide surface layers

Abstract The hygroscopic nature of polycrystalline tin oxide surfaces has been investigated by studying the hydrated layers formed by exposure of tin oxide films to atmospheric humidity. The subsurface hydrated layers have been characterized using electron energy-loss spectroscopy (ELS) and valence band XPS. These subsurface layers apparently dehydrate in a stepwise fashion proceeding through a hydrogen containing intermediate (possibly Sn 8 O 16 H 2 ) at 500°C and yielding SnO 2 near 600°C. During the dehydration process the near surface region is reduced to SnO.

An investigation of the interaction of polycrystalline zirconium with O2, N2, CO and N2O. II: Pretreatment effects on O2 chemisorption properties

Abstract The chemisorption of oxygen at room temperature on polycrystalline zirconium has been studied using AES and ESCA as a function of sample pretreatment. It is shown that annealing at high temperature greatly reduces the ability of zirconium to chemisorb oxygen but that its activity can be restored by argon-ion bombardment. This suggests that chemisorption may be site specific and that the concentration of these sites can be manipulated by varying sample pretreatment.