Philip N. Ross

The effect of chloride on the underpotential deposition of copper on Pt(111): AES, LEED, RRDE, and X-ray scattering studies

The details of the underpotential deposition (UPD) of Cu on Pt(111) in the presence of Cl− were re-examined using a combination of familiar ex-situ techniques (AES/LEED and new in-situ techniques, anomalous surface X-ray scattering (SXS) and Cu2+ flux measurements using a rotating ring disk configuration with the Pt(111) single crystal as the disk electrode. In combination these techniques show definitively that Cu UPD occurs in a two step process, the first being the formation of a CuCl adlattice having a bi-layer structure similar to the (111) plane of CuCl, the second being the formation of a pseudomorphic Cu monolayer covered with a Cl adlayer. The latter appears to have a structure similar to the structure of Cl adsorbed on Cu(111) to saturation in UHV.

Real-time observation of the dry oxidation of the Si (100) surface with ambient pressure x-ray photoelectron spectroscopy

We have applied ambient-pressure x-ray photoelectron spectroscopy with Si 2p chemical shifts to study the real-time dry oxidation of Si(100), using pressures in the range of 0.01-1 Torr and temperatures of 300-530 oC, and examining the oxide thickness range from 0 to ~;;25 Angstrom. The oxidation rate is initially very high (with rates of up to ~;;225 Angstrom/h) and then, after a certain initial thickness of the oxide in the range of 6-22 Angstrom is formed, decreases to a slow state (with rates of ~;;1.5-4.0 Angstrom/h). Neither the rapid nor the slow regime is explained by the standard Deal-Grove model for Si oxidation.

Contrasting film formation reactions of ethereal and carbonate solvents on metallic lithium

Abstract A summary of studies by photoelectron spectroscopy of the reactions of prototypical ethereal and alkyl carbonate solvents with lithium metal in ultra-high vacuum (UHV) is presented. The Li/solvent interface is formed by condensing solvent vapor onto the surface of freshly vacuum evaporated Li at 130 K. The reaction is observed by obtaining core-level photoelectron spectra as a function of temperature. The interfacial reactions are distinctly different for the ethereal vs. the carbonate solvents. The ethers, both cyclic (THF and 1,3-dioxolane) and linear (glymes), react initially to form an LiOR or radical anion (1,3-dioxolane) precursor, followed by the formation of a polyether layer. In the carbonates, there is a significant difference between linear and cyclical forms. The linear carbonates (DMC and DEC) are more reactive, reacting even below the melting point, and produce both LiOCO2R and LiR (alkyl lithium). There are no unreacted solvent molecules left on the surface at room temperature. Since alkyl lithium is soluble in the bulk solvent, the lithium surface will not passivate in this solvent until considerable dissolution of lithium has occurred. The cyclic carbonate PC forms only insoluble LiOCO2R, but no unreacted PC (or PC-like molecule) remains at room temperature. Thus, the corrosion of lithium in DMC/DEC is predicted to be significantly greater than in PC. Since the ethers incorporate a significant amount of solvent molecule in the passive layer, e.g. by polymerization, the SEI layer formed in the ethers is predicted to be more highly conducting than in the carbonates. This prediction is based on the chemistry of the pure solvent molecules, absent real life impurities, e.g. water, or an anion, which may react preferentially with lithium.

The study of surface segregation of Re3Pt polycrystalline alloy with photoelectron spectroscopy

The surface segregation and electronic structure of Re(3)Pt polycrystalline alloy were investigated via x-ray photoelectron spectroscopy (XPS). The results from angle-resolved core-level XPS show the enrichment of Pt at the top surface layer upon annealing at T=1200 K. The experimental results show excellent agreement with a theoretical model calculation, providing the element-specific depth profiles upon the high temperature annealing process. The presence of strong electron hybridization between Re and Pt is evident in the valence-band density-of-states ultraviolet photoemission spectra.