ELSEVIER Surface Science 377-379 (1997) 1051-1055 Hard and soft landing of mass selected Ag clusters on Pt ( 111) Karsten Bromann *, Harald Brune, Christian FClix, Wolfgang Harbich, Rentt Monot, Jean Buttet, Klaus Kern Institut de Physique Exp&imentale, EPFL, CH-101.5 Lausanne, Switzerland Received 1 August 1996; accepted for publication 15 October 1996 Abstract Mass selected Ag, 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 (= 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. Keywords: Clusters; Epitaxy; Low index single crystal surfaces; Platinum; Scanning tunneling microscopy; Silver; Surface structure, morphology, roughness, and topography 1. Intcoduction A central goal in nanostructuring of surfaces is the creation of well deiined island populations. In molecular beam epitaxy (MBE), the standard growth technique for nanosized features on crystal surfaces, the island nucleation- and growth process is basically determined by statistic events. This yields island populations with relatively large size distributions [ 11. A promising alternative is the deposition of size selected nanoclusters [2-lo]. One can hope that the aggregates which form upon deposition of such objects from the gas phase will maintain their sharp size distribution. In a normal cluster deposition experiment, however, the energy which is released during the impact is sufficient to disintegrate at least parts of the clus- * Corresponding author. ters or to create even substrate damage or implant- ation. One has thus to ensure a nondestructive soft landing in order to ensure that the nanoclus- ters maintain their individual characteristics. A promising way to do so has been proposed by Cheng and Landman [ 111 who studied in detail the deposition dynamics of Cu nanoclusters on Cu( 111) by molecular-dynamics simulations and predicted controlled soft landing via energy dissi- pation in a rare gas buffer layer. We performed the fkt in situ STM study to test this important prediction. 2. Experimental The experiments were performed with a variable temperature STM operating in UHV (Fig. 1). The accessible temperature range for in situ 0039-6028/97/$17.00 Copyright 0 1997 Elsevier Science B.V. All rights reserved PZ1 SOO39-6028(96)01544-O