Periodic variations in the local surface potential of Si(111)-(5x2)-Au

ROM 2013-02
Author: S. Polei et al.
Institut für Physik, Universität Rostock, Germany Corresponding author: 
Ingo Barke,
Publication: Phys. Rev. B 85, 165414 (2012) /
Instrument: LT STM

The local surface potential has been mapped by scanning tunneling spectroscopy on a quasi one-dimensional system. The method is based on the analysis of energy positions of so-called field emission resonances (FER). Simple models reproduce the FER perfectly and allow extraction of the potential landscape. This landscape is confirmed by density functional theory calculations, revealing attractive wells along the chains.

On patches of Si(111)-(7x7) and Si(111)-(5x2)-Au, the local work function has been compared using scanning tunneling spectroscopy of field-emission resonances. On both areas, the spectra differ mainly by a constant shift, directly reflecting the work-function difference. In addition, the local surface potential of Si(111)-(5x2)-Au has been mapped, yielding one-dimensional variations of 0.46 eV between the AuSi rows and the Si honeycomb chains at a distance of about 3 Å. All peak positions could be perfectly reproduced by a simple one-dimensional model taking into account the equilibration of the potential variations away from the surface. Local density calculations reproduce these modulations, albeit with smaller amplitude. Finally, the observed double-peak feature of the first FER on theAuSi chain is explained by a mechanism based on the lateral extension of FER states into neighboring chains in conjunction with the experimental boundary condition of a constant tunneling current during spectroscopy.