Surface and electronic structure of 6H-SiC(0001)-(3 × 3) surfaces and ultrathin Ag films on Si(111) and Si(001)

Abstract

Surface topographic (LEED, STM) and spectroscopic (ARUPS, XPS, STS) studies have been performed on Si-terminated 6H-SiC(0001)-(3 × 3) surfaces and Ag superstructures and ultrathin films on Si(001) and Si(111) surfaces, using a scanning tunneling microscope (STM) in ultrahigh vacuum. Our results confirm that 2D epitaxial metal growth is favored on Si(001) at low temperatures and a solid, two-domain Ag(111) film has been achieved at coverages as low as 10 ML. The films reveal a morphology with 3-dimensional features and with a well defined honeycomb structure in between. An atomically flat Si(111)/Ag-(3×3)R30∘ surface has been modified by use of a scanning tunneling microscope (STM) in ultrahigh vacuum (UHV). High quality 6H-SiC(0001)-(3 × 3) and Si(111)/-Ag(3×3)R30∘ upper structures have been prepared and studied by means of ARUPS, XPS and LEED. The local density of states proportional to the spectrum of normalized differential conductivity (dI/dV)/(I/V) vs V reveals distinct bands of empty (−0.6 eV) and filled (0.65 eV) sites separated by 1.2 eV, for both areas. The results support the use of a Mott-Hubbard-type model for calculating the density of states of 6H-SiC(0001)-(3 × 3) surfaces with a Hubbard gap of 1 eV.