Molecular-Dynamics Study of the Morphological Evolution of a Metallic Cluster Deposited on a Surface
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0924-Z08-05
Molecular-Dynamics Study of the Morphological Evolution of a Metallic Cluster Deposited on a Surface K. Shintani, K. Terajima, and Y. Kometani Department of Mechanical Engineering and Intelligent Systems, University of ElectroCommunications, 1-5-1 Chofugaoka, Chofu, Tokyo, 182-8585, Japan
ABSTRACT The morphological evolution of a Co cluster deposited on a Cu substrate is investigated by means of molecular-dynamics simulation. The many-body potential based on the second moment approximation of a tight-binding Hamiltonian (TB-SMA) is employed to calculate the interactions between Co and Cu atoms. The results show that the effect of the substrate anisotropy appears in the morphology of a deposited cluster. It is also revealed that the structural and morphological change of such a cluster can be divided into the three stages, viz., (I)change to an epitaxial structure, (II)diffusion of Cu atoms over the deposited cluster, and (III)solid dissolution of Co atoms into the Cu substrate. INTRODUCTION Cluster deposition was developed as an efficient method of growing thin films at low temperatures. However, it is also suitable for use in fabricating nanostructures on surfaces. Deposited clusters are considered as controllable building blocks of nanostructures which are widely applicable to catalysts, magnetic devices, sensors, etc. Magnetic clusters supported by substrates attract researchers’ attention because the magnetic recording system consisting of self-ordered magnetic arrays (SOMA) where a bit of datum is recorded in a magnetic cluster is a promising method of rapidly increasing density of records [1]. On the other hand, deposition of Co clusters on Cu or Ag substrates has been addressed in the context of surface smoothing which occurs in the systems where the surface energy of clusters is much larger than that of the substrate. Zimmermann et al. [2] created Co clusters of about 10nm in diameter by dc magnetron sputtering, made them softly land on a Cu(100) surface, and annealed them at 600K, 750K, and 900K. At temperatures as low as 600K, their clusters did not remain on the surface, but reoriented and “burrowed” into the substrate. They concluded that burrowing is driven by capillary forces, and requires only diffusion along the cluster-substrate interface and not bulk diffusion so that it occurs at relatively lower temperatures. Frantz and Nordlund [3] studied the burrowing mechanism by means of the classical molecular-dynamics (MD) method with the embedded atom method (EAM) potential. They found two different mechanisms for the burrowing; deposited clusters in epitaxy burrow through vacancy migration along the Co-Cu interface, whereas ones not in epitaxy burrow through disordered motion of atoms. Silly and Castell [4] investigated the structure and morphology of self-assembled Co nanocrystals supported on a SrTiO3(001) substrate using scanning tunneling microscopy. They found the images of nanocrystals are of truncated pyramidal shape. In the present study, the morphological evolution of a Co cluster
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