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The size evolution of platinum nanoparticles formed on a SiO2/Si(111) substrate as a function of the level of surface coverage with deposited clusters has been investigated. The anisotropic shapes of sub-nanometer-size nanoparticles are changed to isotropic on the amorphous substrate as their sizes increased. Using anomalous grazing incidence small-angle x-ray scattering (AGISAXS), the scattering from nanoparticles on the surface of a substrate is well separated from that of surface roughness and fluorescence. We show that AGISAXS is a very effective method to subtract the background and can provide unbiased information about particle sizes of less than 1 nm. [ABSTRACT FROM AUTHOR]

The study reports thermal stability of deposited platinum nanoparticles by employing grazing incidence small-angle X-ray scattering technique (GISAXS). The analysis of the GISAXS data concluded that the supported particles preserve their original size in a very broad temperature range, before an abrupt onset of the agglomeration takes place.

The threshold photoionization efficiency (PIE) curves for nickel clusters in the size range Ni3 to Ni90 have been measured by laser photoionization with detection by time-of-flight mass spectrometry. Both warm (≤298 K) and cold (≤77 K) clusters have been studied. The PIE curves for 298 K clusters display thermal tails, while these tails are smaller for cold clusters. Cluster ionization potentials (I.P.s) have been determined by two methods: the Watanabe procedure and linear extrapolation of the PIE curves. Dramatic dependence of I.P. on cluster size is found for clusters smaller than 11 atoms, while the I.P.s of larger clusters decrease relatively smoothly and nearly monotonically from 5.84 eV for Ni11 to 5.56 eV for Ni90. The I.P.s for clusters larger than Ni40 show the linear dependence on reciprocal radius (R-1) predicted by the conducting spherical drop model of small particle I.P.s, but do not fit the model quantitatively unless the limiting (R-1→ 0) work function is reduced by 0.46 eV from the bulk polycrystalline value. The differences between the thermal tails of the room temperature and 77 K PIE curves diminish with increasing cluster size, suggesting a reduced difference between neutral and ionic structures for larger clusters. In general, there is poor agreement between our experimental results and theoretically calculated I.P.s for small nickel clusters, with the exception of the recently reported tight-binding theory results of Pastor et al. [Chem. Phys. Lett. 148, 459 (1988)]. [ABSTRACT FROM AUTHOR]