Gold deposition onto ultrathin MgO films on Ag͑001͒ results in the formation of linear Au clusters, as revealed from a combined scanning tunneling microscopy and density-functional theory study. The equilibrium structure of small Au clusters containing three to seven atoms is therefore different on thin film and bulk MgO͑001͒ but also deviates from the shape of the respective gas-phase clusters. The peculiar one-dimensional growth regime of gold is stimulated by an electron transfer from the MgO/Ag interface to the deposited Au clusters, resulting in singly and doubly charged cluster anions. Only for larger atom numbers, the formation of compact two-dimensional clusters prevails on the MgO thin films.

Oxidation catalysts are modeled by oxide single crystals, thin oxide films, as well as supported oxide nanoparticles. We characterize the surface of those materials using a variety of surface sensitive techniques including scanning tunneling microscopy and spectroscopy, photoelectron spectroscopy, infrared spectroscopy, and thermal desorption spectroscopy. We find temperature dependent structural transformations from V 2 O 5 (001) to V 2 O 3 (0001) via V 6 O 13 (001). V 2 O 3 (0001) is found to be vanadyl terminated in an oxygen ambient and it loses the vanadyl termination after electron bombardment. It is shown that the concentration of vanadyl groups controls the selectivity of the methanol oxydehydrogenation towards formaldehyde. A proposal for the mechanism is made. The results on single crystalline thin films are compared with similar measurements on deposited vanadia nanoparticles. The experimental results are correlated with theoretical calculations and models.

A scanning tunneling microscope operating at 5 K is used to induce the isomerization of single chloronitrobenzene molecules on Cu(111) and verify the reaction. The threshold voltage of (227+/-7) mV for this reaction is explained based on electron-induced vibrational heating. We propose that the isomerization is initiated by simultaneous excitation of two vibrational molecular modes via inelastically tunneling electrons. This excitation results in a shift of the distribution probability of chlorine and hydrogen positions, which facilitates their mutual exchange.

A combination of low temperature scanning tunneling microscopy (STM) and theoretical calculations is used to investigate Au dimers, supported on thin MgO(001) films, whose thickness was chosen such that charge transfer from the Ag substrate to the deposited Au is possible. Au dimers exist not only in an upright geometry--as theoretically predicted to be the most stable configuration--but also as flat lying dimers which populate a manifold of different azimuthal orientations. Apart from the difference in adsorption configurations, these two isomers exhibit rather different electronic structures: while upright dimers are neutral, flat ones are charged.

No abstract