Fundamental surface science investigations of systems designed to address technological issues

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Yan, Xiaoming

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Organometallic chemical vapor deposition of (MeCp)Ir(COD) onto Rh is simulated experimentally with and without co-reactant oxygen via isothermal reaction mass spectrometry. Auger electron spectroscopy (AES) is used to analyze the resulting film purity. Without oxygen, continuous film deposition occurs above 750 K. A large amount of carbon incorporates, and a final composition of C4Ir is inferred. At the steady state of film growth, acetylene is the only volatile product. Before reaching steady state, various hydrocarbon species are observed. With enough oxygen, the precursor combusts and pure Ir is deposited above 600 K. At steady state, the main by-products are CO and H2O. The thermal decomposition of tert-butoxy (TBO) with co-adsorbed O and NO is studied using temperature programmed desorption and AES on Rh foil and Cu(111). On Cu(111) with NO(a), some TBO decomposes below 240 K to form H2O, CO, CO2, C2H2, proposed imide and acetate, and others disproportionate to tert-butyl alcohol, isobutene and adsorbed oxygen at 610 K. On Rh with NO(a), two oxygen-containing fragments—TBO and a stabilized oxametallacycle—coexist. The proposed oxametallacycle decomposes at 350 K to acetone, while TBO, relatively stable in the presence of N and NO, decomposes to isobutene at 500 K. On Rh with O(a), TBO is stable only up to 380 K where, assisted by O, it decomposes to acetone and butene via a transient form of the oxametallacycle. Thermally evaporated Ag is deposited onto a thin solid water layer on clean hafnia, titania and functionized titiania surfaces. After thermal desorption of water, scanning tunneling microscopy (STM) and atomic force microscopy (AFM) reveals Ag particles on these surfaces. On HfO2, particles have lateral dimensions between 5 and 20 nm and, in many cases, with heights exceeding the thickness of the original water layer. More interesting, particles form 1D bead-like strings spontaneously on 18 L ice. However, on trimethyl acetic acid (TMAAH) pre-saturated TiO2(110), only a few huge particles form. The difference is attributed to the different surface hydrophilicities, which affect both the initial ice layer growth and the competition between dewetting and desorption of adsorbed water.