J. Buttet

Controlled Deposition of Size-Selected Silver Nanoclusters

Variable-temperature scanning tunneling microscopy was used to study the effect of kinetic cluster energy and rare-gas buffer layers on the deposition process of size-selected silver nanoclusters on a platinum(111) surface. Clusters with impact energies of ≤1 electron volt per atom could be landed nondestructively on the bare substrate, whereas at higher kinetic energies fragmentation and substrate damage were observed. Clusters with elevated impact energy could be soft-landed via an argon buffer layer on the platinum substrate, which efficiently dissipated the kinetic energy. Nondestructive cluster deposition represents a promising method to produce monodispersed nanostructures at surfaces.

Optical response of Ag2, Ag3, Au2, and Au3 in argon matrices

We report on the optical response of size selected Ag2, Ag3, Au2, and Au3 embedded in argon matrices. Cluster samples were investigated in situ by excitation, fluorescence, and absorption spectroscopy. The spectra for the dimers are in agreement with previous measurements made on conventionally prepared matrices. Our previously reported spectra of trimers in krypton are confirmed by the argon results. The influence of the matrix gas will briefly be discussed.

Electronic properties of alkali trimers

The electronic properties of the alkali trimers Li3, Na3, and K3 are studied using the pseudopotential and the local‐spin‐density approximations. More than 100 configurations were calculated for each trimer in order to obtain a complete picture of the adiabatic Born–Oppenheimer surfaces. The equilibrium geometry of the trimers are Jahn–Teller distortions of an equilateral triangle. Although the three surfaces are quite similar, Li3 is more affected than Na3 or K3 by the dynamical character of the Jahn–Teller distortion. The calculated ionization potentials agree very well with the experimental values and the qualitative features of the Born–Oppenheimer surface are confirmed by recent ESR experiments.

Variational spherical model of small metallic particles

Abstract We study the structural and electronic properties of simple metal clusters with a model based on the density functional formalism. Our model takes into account electron relaxation effects and the lattice structure through the introduction of pseudopotentials. Results for the ionization potential and electron affinity, binding and surface energies and lattice relaxation are presented for bcc and icosahedral Na clusters having up to 350 atoms.

Fluorescence and excitation spectra of Ag4 in an argon matrix

We report the fluorescence and excitation spectra of size selected Ag4 deposited in an argon matrix. The main fluorescence peak for Ag4 is observed at 458 nm. The excitation spectrum for this emission is in good agreement with recent theoretical calculations and photodepletion experiments.

The optical absorption spectra of small silver clusters (n=5–11) embedded in argon matrices

Abstract The optical absorption of small mass selected Agn clusters (n=5, 7, 8, 9, 11) embedded in solid Ar has been measured. Strong absorption has been found between 3 and 4.5 eV. The absorption spectra show 1–3 major peaks depending on the cluster size. The width of these peaks is considerably smaller than commonly found in gas phase photodepletion experiments. A simple model based on a Drude metal, and neglecting the dielectric constant of the surrounding medium, gives satisfactory agreement with experiment.

Auger and X-ray photoelectron spectroscopy of small Au particles

Abstract Measurements of both Auger electron spectroscopy and X-ray photoelectron spectroscopy have been done as a function of the size of gold clusters, with diameters ranging from 14 to 100 A, deposited on an amorphous carbon substrate. The kinetic energy of the Auger electrons (transition N6,7VV) decreases when the size of the clusters decreases. The shifts are analyzed by taking into account the change due to incomplete screening of the hole-hole Coulomb repulsion energy.

The optical absorption spectra of small silver clusters (n=8-39) embedded in rare gas matrices

The optical absorption of small mass selected Agn-clusters (n=8–39) embedded in solid Ar, Kr and Xe has been measured. Strong absorption has been found between 3 and 4.5 eV. The absorption spectra show 1 to 3 major peaks depending on the cluster size. The width of these peaks is smaller than in gas phase photodepletion experiments of silver ions, most likely due to the low and well defined temperature of the clusters in the matrix. The results are compared to a simple model based on a Drude metal, taking into account the spillout of the electrons and allowing for a deviation of the cluster from a spherical shape. Absorption cross sections scale with the number of valence electrons.

Hard and soft landing of mass selected Ag clusters on Pt(111)

Mass selected Ag/sub n/ clusters (n=1,7,19) from a secondary ion source have been deposited onto a Pt(111) substrate at low temperature. The surface and resulting cluster morphology have subsequently been characterized within the same UHV chamber by variable temperature STM as a function of cluster size, kinetic impact energy, and substrate temperature. The kinetic energy per cluster atom was found to be the decisive parameter for a controlled deposition. Noble gas buffer layers ( approximately=10 ML Ar), which were pre-adsorbed onto the surface at low temperatures, were found to efficiently dissipate the impact energy opening up the possibility of soft landing clusters with elevated kinetic energy.

Electronic properties and local densities of states in clean and hydrogen covered Pt particles

Abstract 195 Pt pulsed nuclear magnetic resonance has been applied to the study of electronic properties of small supported platinum particles, having a mean size between 16 and 27 A. Special attention has been given to the effect of hydrogen adsorption. The relevant quantities for the analysis are the Knight shift related NMR intensities and spin lattice relaxation times. This information together with information from the size distributions obtained by electron microscopy allow a determination of the local density of states (LDOS) at the Fermi energy inside and at the surface of the particles. The LDOS at E F the clean surface shows a decrease of 39% with respect to the bulk which is mostly due to d-like electrons. The LDOS at E F of the hydrogen covered surface is further diminished and we have to go three Pt layers deep to recover an almost bulk LDOS.