Gregory R. Corallo

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 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.

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.

Electron-stimulated desorption of atomic oxygen from polycrystalline Ag

Abstract Emission of neutral oxygen atoms from an oxygen-charged polycrystalline Ag wire has been examined by using electron-stimulated desorption (ESD) in conjunction with threshold ionization detection (appearance potential). A quadrupole mass spectrometer (QMS) was used to detect the neutral oxygen atoms, but the ionizer was operated in the appearance potential (AP) mode to make it possible to distinguish the oxygen atoms from products formed by collision of the oxygen atoms with the walls. Loss of the reactive oxygen atoms was also minimized by enclosing the ESD chamber in fused silica. With a primary beam energy of 100 eV, the ESD cross section for oxygen atom desorption was found to be 7 × 10 -19 cm 2 at 100 °C, and an ESD threshold was found to exist below 34 eV. Flash desorption of oxygen allowed estimation of the bulk diffusivity of oxygen through polycrystalline Ag. A value of 2.64 × 10 -6 cm 2 s -1 at 500 °C was obtained.