We have investigated the deposition at zero impact kinetic energy of the Ag atom and clusters (Ag 7 ,Ag 19 ) on the ͑100͒ and ͑111͒ surfaces of Pd by molecular-dynamics simulations performed within the embeddedatom-method scheme. Our results elucidate the role played by the adsorption energy in determining the final morphology of the cluster/substrate system when ideal nondestructive deposition conditions are implemented. While implantation of the atom is not observed, we find a finite probability of site Ag-Pd exchanges in the case of clusters. Deposition-assisted mixing occurring at the topmost surface layer appears to be correlated to the size of the cluster and the orientation of the substrate, being higher for Ag 7 /Pd͑100͒ and lower for Ag 19 /Pd͑111͒. Total-energy calculations, combined with an analysis of the atomic motion, indicate that the structural transformation accompanying the deposition of the cluster provides the needed activation energy to induce the observed Ag-Pd atomic exchanges. ͓S0163-1829͑97͒00640-1͔

By means of molecular dynamics simulations based on realistic n-body potentials we investigate structural and dynamical features inherent to the energetic collision of a silver cluster (Ag 19 ) on the Pd(100) substrate. Both the system and the impact energy (E i = 95 eV) adopted have been chosen to parallel an experimental study of size selected Ag cluster deposition on Pd(100). Our results indicate that the experimental cross section obtained via thermal energy atom scattering at the same collision energy is well reproduced by the simulations.The modeling allows to rationalize the collision outcome in terms of defect production and cluster atoms implantation. The adsorbed structures have an heterogenous nature and are mostly two-dimensional. PACS: 36.40.Sx; 68.55.-a; 68.55.Ln I IntroductionCluster deposition and growth on solid surfaces are intimately related. The first approach allows, when combined with moderately low impact energies, to control the fabrication of adlayers made of peculiar structural units. These can give rise to adsorbed films displaying unique properties, which can be tailored by changing the nature of the systems involved and the accessible experimental parameters such as temperature and coverage. In this respect, size selection and "soft landing" of clusters are a viable alternative to traditional techniques of surface growth, provided the adsorption process and the thermodynamic conditions preserve to a large extent the structural nature of the adsorbed nanostructures. Recently, a series of experiments of size selection and cluster deposition have been performed on the system Ag + n /Pd(100) [1, 2] by using thermal energy atom scattering (TEAS). Three colliding systems have been investigated (Ag + 1 , Ag + 7 , Ag + 19 ) for impact energies equal to E i1 = 20 eV and E i2 = 95 eV and in the range of temperature 80 K< T < 400 K. In [1,2], an indirect analysis of surface morphology and dynamical formation of adsorbed islands has been performed in terms of the cluster cross section for diffuse scattering. This quantity is obtained from the attenuation of the helium specular intensity. The information extracted from the data of [1, 2] on the degree of defect production, implantation and cluster fragmentation are consistent with the existence of different regimes, related to the amount of colliding energy per atom, varying from ∼ 1 eV/atom (Ag + 19 , E i1 = 20 eV) to 95 eV (Ag + 1 ,E i2 = 95 eV). Molecular dynamics simulations and collision-adapted embedded atom method potentials have proved useful to describe microscopic details of the deposition process [3][4][5][6][7][8][9][10][11][12]. At low temperatures this approach is ideally suited to quantify the amount of structural modification induced on both the cluster and the substrate by the impact. Indeed, since relevant mobility is suppressed by kinetic constraints, the time interval spanned by the simulations (a few ps) becomes adequate to describe the relaxation process which follows the collision. The results recently obtained in the case o...

No abstract

No abstract

No abstract