Electron-phonon interaction at the Si(111)-7 x 7 surface

It is shown that electron-phonon interaction provides a natural explanation for the unusual band dispersion of the metallic surface states at the Si(111)-(7 x 7) surface. Angle-resolved photoemission reveals a discontinuity of the adatom band at a binding energy close to the dominant surface phonon mode at h(omega0) = 70 meV. This mode has been assigned to adatom vibrations by molecular dynamics calculations. A calculation of the spectral function for electron-phonon interaction with this well-defined Einstein mode matches the data. Two independent determinations of the electron-phonon coupling parameter from the band dispersion and from the temperature-dependent phonon broadening yield similar values of lambda = 1.09 and lambda = 1.06.     

Vibrational characterization of the oxidation products on Si(111)-(7 x 7)

The oxidation products on Si(111)-(7x7) are investigated at 82 K by means of high-resolution electron energy loss spectroscopy. The isotope-labeled vibrational spectra with 16O2, 18O2, and 16O 18O show that, in the initial stage of the oxidation, an O2 molecule dissociates to form a metastable product with an O atom bonding on top of the Si adatom and the other inserted into the backbond. The metastable product is observed as a dark site in the topographic scanning tunneling microscopy (STM) image and can be transformed to a stable product by the STM manipulation. Our results are in good agreement with recent theoretical calculations.     

Direct observation of long-range assisted formation of Ag clusters on Si(111)7 x 7

Formation of Ag clusters on reconstructed surface Si(111)7 x 7 was for the first time observed in real time during deposition by means of scanning tunneling microscopy. The sequences of images taken at room temperature show mechanisms controlling the growth and behavior of individual Ag adatoms. Obtained data reveal new details of attractive interaction between adsorbates occupying adjacent half-unit cells of the 7 x 7 reconstruction. Time evolution of growth characteristics was simulated by means of a simple model. The growth scenario observed in vivo is discussed with respect to previously reported models based on data obtained after finishing the deposition--post-mortem.     

Low temperature scanning force microscopy of the Si(111)-(7x7) surface

A low temperature scanning force microscope (SFM) operating in a dynamic mode in ultrahigh vacuum was used to study the Si(111)- (7x7) surface at 7.2 K. Not only the twelve adatoms but also the six rest atoms of the unit cell are clearly resolved for the first time with SFM. In addition, the first measurements of the short range chemical bonding forces above specific atomic sites are presented. The data are in good agreement with first principles computations and indicate that the nearest atoms in the tip and sample relax significantly when the tip is within a few A of the surface.