Reaction of palladium thin films with an Si-rich 6H-SiC(0001) (3 x 3) surface

The reaction of Pd thin films evaporated in ultrahigh vacuum on a clean and Si-rich 6H-SiC(0001)(3 x 3) surface has been investigated in situ by low-e nergy electron diffraction (LEED) and photoelectron spectroscopy (UPS and X PS), and ex situ by atomic force microscopy (AFM) and glancing-incidence X- ray diffraction (GIXRD). For studying the interface formation, submonolayer amounts of Pd were sequentially deposited up to similar to 20 Angstrom on the substrate maintained at room temperature. This deposit was subsequently annealed to 600-800 degrees C. At room temperature, Pd starts to react wit h SiC when the thickness attains similar to 2.5 Angstrom, giving an interfa ce Pd2Si silicide. Under annealing the film is transformed into Pd2Si islan ds standing on the SiC (1 x 1) surface. No extra-structure of C 1s is obser ved in the two cases; only an energy shift of about 0.25 eV is detected dur ing the metal deposition, which is attributed to a change in the band bendi ng. Further deposition of similar to 100 Angstrom of Pd on this annealed su rface gives an epitaxial Pd(111) film, despite a lattice mismatch of more t han 10% between the metal and the semiconductor. The film is disrupted afte r annealing at 600-800 degrees C. The combination of XPS, AFM and GIXRD ana lyses indicates that the film annealed at 800 degrees C is discontinuous an d formed of sharp epitaxial Pd2Si islands and graphite which probably surro unds the islands. (C) 1999 Elsevier Science S.A. All rights reserved.