Fourier transform infrared spectroscopy and temperature-programmed desorption mass spectrometry study of surface chemistry of porous 6H-SiC

Porous SiC (PSC) freestanding layers were prepared via UV light-assisted electrochemical etching of an n-type 6H-SiC wafer. Fourier transform infrared (FTIR) spectroscopy and temperature-programmed desorption mass spectrometry (TPD-MS) were applied to characterize functional groups on the PSC surface and their chemical reactivity. It was shown that as-prepared PSC contains silanol groups, carboxylic acid groups, minor amounts of SiH and CHx groups, and also a carbon-rich surface phase. Annealing of PSC in air at 673 K resulted in the oxidation of the carbon-containing surface species and the formation of a hydrated silicon oxide surface layer. Using -Si(CH3)(3) groups as a model, it was demonstrated that organic functional groups can easily be grafted on oxidized PSC via common silanization chemistry. Treatment of oxidized PSC with HF resulted in the formation of a surface terminated with methyl groups. It confirms that the walls of the PSC pores are constituted of the (0001) "silicon" crystal face of SiC and faces with similar atomic structure.