CHEMICAL-REACTIVITY OF SIZE-SELECTED SUPPORTED CLUSTERS - AN EXPERIMENTAL SETUP

We describe an experimental setup for the investigation of the chemica l reactivity of size-selected, supported clusters. The clusters are ge nerated by a high frequency laser vaporization source. After mass sele ction and energy control the clusters are deposited under ultrahigh-va cuum conditions and with low kinetic energy onto thin oxide films grow n on metal single crystals. Such films are ideal in their function as supports for size-selected deposited metal clusters. Measured currents of mass-selected niobium cluster ions were of the order of 1 nA and a re high enough for fast deposition rates. Adsorbed molecules used on t he one hand as probes to characterize the supported clusters and on th e other hand for studying chemical reactions on these clusters are inv estigated in situ by Fourier transform infrared spectroscopy, temperat ure desorption spectroscopy, and Anger electron spectroscopy. The perf ormance of these analytical tools is illustrated with CO adsorbed on N i atoms supported on thin MgO(100) films grown on a Mo(100) single cry stal. (C) 1997 American Institute of Physics.