Investigation of annealing effects on the adsorption of Ni on 4H–SiC (0001) surfaces using scanning tunneling microscopy and spectroscopy

Abstract

The adsorption of Ni on 4H-SiC surfaces as a function of temperature has been investigated using scanning tunneling microscopy (STM) and variable tip-sample separation scanning tunneling spectroscopy (VTSS-STS). A submonolayer of Ni was deposited on an atomically clean (√3×√3) 4H-SiC sample, which was then annealed sequentially from 400to1000°C. VTSS-STS showed a reduction in the apparent surface band gap after Ni deposition, attributed to metal induced gap states. The size of the Ni clusters changed after annealing, due to the formation of Ni-silicides and diffusion. The surface band bending on Ni clusters increased upon annealing to 500°C, in good agreement with Schottky contact formation models. After annealing at 1000°C for 3min, various surface reconstructions were observed with STM, which are typical of graphite. Ni-silicide clusters also diffused into the SiC and some could still be observed below the graphite surface. VTSS-STS measurements of the graphite surface above diffused clusters displayed Ohmic behavior.