SIMS, TDS AND AES OF SMALL MOLECULES ON RUTHENIUM(001) (SPECTROSCOPY)
Abstract
Interactions of CO, D(,2), O(,2) and C(,2)H(,4) with a well defined Ru(001) single crystal surface have been studied using secondary ion mass spectroscopy (SIMS), thermal desorption spectroscopy (TDS) and auger electron spectroscopy (AES). Changes in the distribution of secondary ion yields in SIMS with coverage of oxygen and carbon monoxide are shown to correlate with coverage dependent changes of the adlayer structure observed by LEED. A lack of isotope mixing in RuCO('+) secondary ions in SIMS of a surface covered with equal amounts of ('13)CO and C('18)O shows that these ions are formed from CO molecules that are emitted from the surface intact. The interaction of ethylene with Ru(001) at 323K is accompanied by substantial dissociation and desorption of hydrogen, producing an adlayer consisting largely of elemental carbon and very small amonts of adsorbed hydrogen and hydrocarbon species. Correlations between the thermal desorption spectrum and the temperature dependence of secondary in yields shows strong evidence for intact emission of hydrocarbon species. Analysis of the carbon adlayer formed by the ethylene/Ru(001) interaction shows that a low density(--->)high density carbon phase transition occurs upon heating above (TURN)650 K and diffusion of carbon into the bulk occurs for temperatures above (TURN)1000 K. Changes in the distribution of secondary ions in SIMS appear to reflect both structural and electronic effects associated with these thermally induced changes in the carbon adlayer. Dissociation of CO is observed following high CO exposures at temperatures above 435 K. A positive interaction is observed between carbon formed by dissociation of CO and deuterium as evidenced by the appearance of a new high temperature deuterium thermal desorption state and the appearance of a RuCD('+) ion in the SIMS spectrum. No attractive interactions are observed between adsorbed deuterium and molecularly adsorbed CO.
Degree
Ph.D.
Subject Area
Chemical engineering
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