Geometric and electronic structures of monolayer potassium fullerides on Si(111)-√3×√3-Ag.

[Display omitted] • A range of potassium fullerides, K x C 60 (x = 1, 4/3 and 2) monolayers, are newly fabricated on Si(111)-√3×√3-Ag. • All the fulleride monolayers show an energy gap at the Fermi level due to electronic interactions and structural distortion. • The energy gap in K 2 C 60 is significantly softened by partial electron doping from the Si(111)-√3×√3-Ag surface. Metal-terminated silicon surfaces are a specific class of templates for growth of fulleride ultrathin films. Using scanning tunneling microscope and spectroscope, we investigate the geometric and electronic structures of K x C 60 monolayers on Si(111)-√3×√3-Ag with x gradually increased to 2. Besides long-range ordered KC 60 and K 2 C 60 monolayers, a fraction-stoichiometric fulleride, K 4/3 C 60 monolayer, is newly discovered. All these fulleride monolayers open an energy gap at the Fermi level owing to electronic correlations and Jahn-Teller distortion. The gap of the even-stoichiometric fulleride, K 2 C 60 , is prominently softened by partial electron doping from the Si(111)-√3×√3-Ag surface. [ABSTRACT FROM AUTHOR]