Ultrathin Ni layers grown epitaxially on SiC(0001) at room temperature

Ultrathin (1-20 ML) Ni layers deposited on 6H-SiC(0001)-root3xroot3 at room temperature (RT) were analyzed in situ by high-resolution medium energy ion scattering (MEIS), reflection high-energy electron diffraction (RHEED), and photoelectron spectroscopy using synchrotron-radiation light. For a Ni coverage of more than 3 ML [1 ML for SiC(0001):1.21x10(15) atoms/cm(2)] uniform Ni(111) layers grow epitaxially at RT in spite of a large lattice mismatch of 20%. There are two domains, (A) Ni-[110]//SiC-[1120] and (B) Ni-[112]//SiC-[1120], and the occupation ratio of (A) to (B) is 5:1. The ion shadowing effect reveals significant expansion of the interplanar distance of Ni(111), which relaxes with increasing the Ni thickness. The MEIS analysis shows that a small amount of Si segregate to the surface and the crystalline Ni(111) layer contains Si atoms (3-15 at. %). The segregation rate is derived to be 0.015 s(-1) by solving a simple rate equation. The uniform stack and epitaxial growth of Ni layers at RT may be responsible for the surface-segregating Si atoms as a surfactant. The two components from Si on top and in the Ni layer are clearly observed in the Si 2p spectra and a higher binding energy shift of the latter relative to the former indicates an electronic charge transfer from Si to Ni. The binding energy shift of the Si 2p level of the bulk SiC gives the Schottky barrier height, which reaches the Schottky limit for a thickness above 3 ML.