THE ADSORPTION OF H-ATOMS ON POLYCRYSTALLINE BETA-SILICON CARBIDE

The adsorption of atomic hydrogen on a polycrystalline beta-silicon carbide (SiC) surface has been studied using temperature-programmed desorption (TPD). Atomic hydrogen adsorbs on this surface, whereas molecular hydrogen does not. Upon heating, the hydrogen recombines and desorbs as H-2, producing two peaks in the TPD spectrum at 975 and 1130 K. The unusually broad width of the desorption peaks is attributed to a distribution of surface binding energies for hydrogen atoms. The desorption spectra are fit using a model that assumes two adsorption sites and a Gaussian distribution of binding energies. The average activation energies derived for the two peaks are 63 and 72 kcal/mol.