Hamers The use of scanning tunneling microscopy (STM) to study chemical reactions has been hampered by the inability to a priori identify adsorbed molecules and molecular fragments. The goal of this work is to overcome this limitation by first studying a homologous series of unsaturated hydrocarbons, their decomposition products, and some functionalized derivatives of these molecules to develop an empirical basis set for molecular identification, and then applying this knowledge to study the reaction chemistry of these hydrocarbons on surfaces of Pd, platinum, and nickel both in the absence and in the presence of "modifiers" such as sulfur, chlorine, and silicon. Studies will be performed using a unique scanning tunneling microscope system which can image surfaces at 77 Kelvin in ultrahigh vacuum, in conjunction with other techniques including infrared spectroscopy, Auger, and low-energy electron diffraction. STM will be used to provide atomic-resolution analysis of the identity and spatial location of molecules and molecular fragments and to directly observe the influence of steps, defects, and chemical inhomogeneities on the reactions of small unsaturated hydrocarbons on metal surfaces, while FTIR will provide information on the chemical functionalities present on the surface. A statistical analysis of this spatial information will be used to quantitatively describe the surface lateral chemical composition and to identify spatial correlations between the positions of various surface species. By studying the adsorption and decomposition of small hydrocarbons on metals, the adsorption of chemical modifiers, and co-adsorption of molecules in the presence of modifiers, we will achieve new insight into the nature of heterogeneous catalysis at transition metal surfaces. %%% The explosive growth of scanning tunneling microscopy as an atomic-resolution tool for probing the geometry and electronic properties of surfaces brings with it exciting new opportunities to probe materials chemistry at the atomic level. However, the use of STM to study chemical reactions has been hampered by the inability to a priori identify adsorbed molecules and molecular fragments. The goal of this work is to overcome this limitation by first studying a homologous series of unsaturated hydrocarbons, their decomposition products, and some functionalized derivatives of these molecules to develop an empirical basis set for molecular identification, and then applying this knowledge to study the reaction chemistry of these hydrocarbons on surfaces of Pd, platinum, and nickel both in the absence and in the presence of "modifiers" such as sulfur, chlorine, and silicon. These studies will provide a fundamental basis of knowledge about the appearance of various molecular fragments in the STM which can then be applied to study the reaction chemistry of a wide range of molecular functionalities, and will provide insight into how promoters and poisons modify the reactivity of metals toward hydrocarbon species.
