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

Abstract

Metallic tungsten (W) was deposited in a 2×10 −10 Torr vacuum onto clean Si(111) surfaces with a 7×7 structure to produce size-controlled W clusters (quantum dots) on Si surfaces and to study the silicide-formation with concomitant change of electronic structure. The atomic structures, particularly the first adsorption sites of W atoms, were studied by scanning tunneling 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 adsorb onto the hollow sites of adatoms and dimer-atoms on the 7×7 structure, and the W-clusters of 1.0–1.5 nm diameter are already metallic, as deduced from a comparison between the STS data and the DOS calculations using the DV-Xα method for W clusters composed of 23 atoms with a bcc structure.