The thermal chemistry of copper(I)-N,N 0 -di-secbutylacetamidinate on Ni(110) single-crystal and cobalt polycrystalline surfaces was characterized under ultrahigh vacuum (UHV) conditions by X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD). A complex network of reactions were identified, starting with the dissociative adsorption of the precursor, from its dimeric form in its free state to a monomer once bonded to the nickel surface. The dissociation of a CÀN bond in the acetamidinate ligand at ∼200 K leads to the formation of adsorbed 2-butene and N-secbutylacetamidinate. Some of the latter intermediates hydrogenate around 300 K to release N-sec-butylacetamidine into the gas phase, while the remaining adsorbed species dissociate further around 400 K, as the copper atoms become reduced to a metallic state, possibly to form acetonitrile and a sec-butylamido surface species that reacts further at 485 K to release 2-butene. By 800 K, only copper and a small amount of carbon can be seen on the surface by XPS. The implications of this chemistry to the growth of metal films by atomic layer deposition (ALD) are discussed.

Examples from recent studies in our laboratory are presented to illustrate the main tools available to surface scientists for the determination of the kinetics of surface reactions. Emphasis is given here to hydrocarbon conversions and studies that rely on the use of model systems, typically single crystals and controlled (ultrahigh vacuum) environments. A detailed discussion is provided on the use of temperature-programmed desorption for the determination of activation energies as well as for product identification and yield estimations. Isothermal kinetic measurements are addressed next by focusing on studies under vacuum using molecular beams and surface-sensitive spectroscopies. That is followed by a review of the usefulness of high-pressure cells and other reactor designs for the emulation of realistic catalytic conditions. Finally, an analysis of the power of isotope labeling and chemical substitutions in mechanistic research on surface reactions is presented.

The adsorption and thermal activation of copper(I)-N,N 0 -di-sec-butylacetamidinate on a Ni(110) single-crystal surface were characterized in connection with the use of that compound as a precursor for the growth of copper films via atomic layer deposition (ALD) processes. Studies were carried out under ultrahigh vacuum (UHV) conditions by using a combination of X-ray photoelectron spectroscopy (XPS), low-energy ion scattering (LEIS), and temperature-programmed desorption (TPD). A temperature window between approximately 350 and 450 K was identified for the clean deposition of the precursor on the surface: lower temperatures are insufficient for activation of the dissociative adsorption, and higher temperatures lead to continuous decomposition beyond Cu monolayer saturation. Approximately three ALD-like cycles are required to reach full Cu monolayer saturation, the equivalent of a film growth rate of approximately 0.75 A ˚/cycle. Preadsorption of hydrogen on the surface does not modify any of this behavior because of its rapid desorption at temperatures above 350 K once the gas-phase H 2 is removed. A discussion is provided on how hydrogen pressures above the mbar range are required to maintain significant steady-state coverages of hydrogen on the surface. Copper precursors leading to relatively stable organic surface intermediates are required in ALD because their clean removal can only happen in the second half-cycle of processes that rely on hydrogenation reactions.

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