STM STS studies of tungsten clusters on Si(111) surfaces using a newly developed deposition apparatus

Metallic tungsten (W) was deposited in a 2 x 10(-10) Ton vacuum onto clean Si(lll) surfaces with a 7 X 7 structure to produce size-controlled W cluste rs (quantum dots) on Si surfaces and to study the silicide-formation with c oncomitant change of electronic structure. The atomic structures, particula rly the first adsorption sites of W atoms, were studied by scanning tunneli ng microscopy (STM) and reflection high energy electron diffraction (RHEED) . The electronic structure, as represented by the density of states (DOS), was measured by scanning tunneling spectroscopy (STS). W atoms initially ad sorb onto the hollow sites of adatoms and dimer-atoms on the 7 X 7 structur e, and the W-clusters of 1.0-1.5 nm diameter are already metallic, as deduc ed from a comparison between the STS data and the DOS calculations using th e DV-X alpha method for W clusters composed of 23 atoms with a bcc structur e. (C) 1999 Elsevier Science Ltd. All rights reserved.