NEARLY COMPLETE TUNING OF THE FERMI-LEVEL POSITION AT A PROTOTYPICAL METAL-SILICON INTERFACE - LEAD ON UNPINNED SI(111)1X1-H

Upon studying with very high resolution synchrotron radiation photoemi ssion spectroscopy the ideally H-terminated Si(111)1 X 1 surfaces prep ared by wet chemical procedure we prove for the first time that both n -type and p-type surfaces do not posses any surface states in the gap and thus give flat band conditions at the surface. Starting from such unpinned n-type surfaces, totally unusuallly, a downward band bending is obtained for a prototypical system formed by condensing in situ a l ead overlayer under UHV. Moreover, by using differently prepared initi al Si(111) surfaces, with just this one metal, it is possible to move the Fermi level position from 130 meV above the valence band maximum t o 100 meV below the conduction band minimum, which is totally at varia nce with all results known for metal-silicon interfaces.