Ultraviolet photoelectron spectroscopy of supported mass selected silver clusters

Ultraviolet photoelectron spectroscopy (UPS) was used to investigate size selected Ag923� 9 and Ag55 clusters which were softlanded on a clean graphite substrate (HOPG) at 100 and 50 K, respectively. With increasing cluster coverage closer to the centre of the deposition spot a continuous change of the d-band signal is observed. Differences in the fine structure of the d-band and comparison to UPS spectra of clusters grown at nanopits on HOPG show that the clusters in the centre of the deposition spot coalesced. However, Ag55 spectra measured at the rim of the deposition spot indicate that the clusters stay separated in regions of lower coverage for a deposition temperature of 50 K. This is corroborated by scanning tunnelling microscopy (STM) images measured at 5 K using 1 monolayer (ML) Xe to fix the Ag55 clusters to the substrate, thus making them observable with STM. By comparison to UPS data taken on different sample positions in a 1 � 1m m 2 grid it was determined that at the rim of the deposition spot the coverage of 30 clusters per 100 � 100 nm 2 was low enough for an UPS measurement of single separated Ag55 clusters. Differences in the spectra for the largest coverage of Ag55 and Ag923 clusters in the deposition spot centre indicate that the resulting Ag film has a partial (111) orientation for the deposition of Ag55 at 50 K whereas it is mostly polycrystalline for Ag923 deposited at 100 K.