The activation and decomposition of silane on Cu( 1 1 1) have been studied using Fourier transform infrared (FTIR), Auger electron (AES), and temperature-programmed reaction (TPRS) spectroscopies, as well as low-energy electron diffraction (LEED). Silane dissociatively chemisorbs on C u ( l l 1 ) at 90 K. Cleavage of the Si-H bond yields two structurally distinct adsorbed silyl fragments. Infrared spectroscopy identifies the predominant intermediates formed under these conditions as being adsorbed SiH2 and SiH species. The relative and absolute concentrations of these intermediates depend sensitively on the surface coverage of both Si and H , which themselves depend upon the silane exposure. SiH2 is stable over a wide range of coverage up to 180 K, where it then undergoes Si-H bond cleavage to form surface bound SiH. At higher temperatures, bond scission in the Si-H moiety results in the formation of adsorbed silicon atoms and the desorption of dihydrogen in a peak centered at -330 K. Auger electron spectra show that the amount of silicon deposited on the Cu ( 1 1 1) surface in this way is approximately one-third of the amount deposited on a stable Cu3Si surface. This latter surface is readily formed by carrying out the silane exposure at temperatures above 300 K. The reactivity of a copper silicide surface toward silane was also studied. Silicon bearing copper surfaces are less reactive than is the parent clean surface. What reactions are seen lead to a variety of adsorbed silyl fragments including SiH3. It is believed that defects play a key role in these latter reaction pathways.processes involved in both the growth and chemical etching of this material. We restrict our focus in this paper to the reactions of silane, SiH4, on Cu, as this reagent is the simplest organosilicon reagent for the growth of the Cu& phase on Cu.Silane has been reported previously as undergoing Si-H bond cleavage on a variety of single crystalline metal surfaces to form adsorbed silyl fragments (SiH,, x < 4) and hydrogen, although

We report a study of the thermal decomposition and reactions of isobutyl iodide on Al(111). Using temperature-programmed reaction and Auger electron spectroscopies, it was found that more than one product-forming pathway involving the alkyl moiety exists on this surface. A first-order, β-hydride elimination reaction converts surface-bound isobutyl groups derived from the dissociation of the C−I bond to gas phase isobutene and dihydrogen at temperatures above ∼420 K. Competing with this unimolecular process is a collection of complex associative reactions which effect the etching of the aluminum surface via the formation of volatile organometallic species. This includes formation and subsequent desorption of diisobutylaluminum iodide (desorption peak maximum at ∼490 K), diisobutylaluminum hydride (∼515 K), methylaluminum dihydride (∼725 K), and AlI x , x = 1−3 (∼620 K). The kinetics of the processes yielding the various aluminum hydrides are coupled to that of the β-hydride elimination pathway (which serves as the hydrogen atom source) and are strongly coverage dependent. The formation of MeAlH2 reveals the occurrence of a kinetically competitive β-methyl elimination reaction of the surface alkyl groups.

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The collision-induced activation of the endothermic surface reaction of isobutyl iodide chemisorbed on an Al(111) surface is demonstrated using inert-gas, hyperthermal atomic beams. The collision-induced reaction (CIR) is highly selective towards promoting the β-hydride elimination pathway of the chemisorbed isobutyl fragments. The cross section for the collision-induced reaction was measured over a wide range of energies (14–92 kcal/mol) at normal incidence for Ar, Kr, and Xe atom beams. The CIR cross section exhibits scaling as a function of the normal kinetic energy of the incident atoms. The threshold energy for the β-hydride elimination reaction calculated from the experimental results using a classical energy transfer model is ∼1.1 eV (∼25 kcal/mol). This value is in excellent agreement with that obtained from an analysis of the thermally activated kinetics of the reaction. The measured cross section shows a complex dependence on both the incident energy of the colliding atom and the thermal energy provided by the surface where the two energy modes are interchangeable. The dynamics are explained on the basis of an impulsive, bimolecular collision event where the β-hydride elimination proceeds via a possible tunneling mechanism. The threshold energy calculated in this manner is an upper limit given that it is derived from an analysis which ignores excitations of the internal modes of the chemisorbed alkyl groups.