Graphitization of the 6H-SiC(0001) surface studied by HREELS

By using high-resolution electron energy loss spectroscopy (HREELS), we have studied the vibrational properties of the various 6H-SiC(0001) reconstructions, from the Si-rich to the graphitized surface. The 6H-SiC(0001)-(3 x 3) exhibits the Fuchs-Kliewer (FK) optical phonons commonly observed on strongly polar materials. The lowering of the energy width of the elastically reflected electrons with increasing primary energies reveals the coupling of FK with the plasmon that derives from the bulk doping level. No particular modification in the HREELS spectra is observed after preparation of the 6H-SiC(0001)-(root3 x root3)R30degrees surface. On the (6root3 x 6root3)R30degrees reconstructed surface, the FK phonon modes display both a blue shift and an increased damping factor. In the ultra-violet energy region we observed a loss structure at approximate to6 eV whose dispersion relation allows to readily conclude on the presence of a pure graphite layer: it almost perfectly match the dispersion relation measured on highly oriented pyrolitic graphite for the so-called 'n-plasmon' arising from the electronic excitation of pi-pi* interband transition. (C) 2002 Elsevier Science B.V. All rights reserved.