Single adatom adsorption and diffusion on Si(111)-(7×7) surfaces: Scanning tunneling microscopy and first-principles calculations

The adsorption and diffusion of single Pb atoms on Si(111)-(7×7) surfaces have been studied by scanning tunneling microscopy (STM) and first-principles density functional calculations. STM experiments at temperatures from 100 to 130 K have revealed three regions of preferential adsorption, inside each half-unit cell, as well as real time diffusion events between them. The stable adsorption sites have been determined by first-principles calculations and by comparing simulated and measured STM images. The activation barriers for the motion inside the half-unit cells have been calculated and measured experimentally. A very good agreement between calculations and experiments has been found.