DIRECT IMAGES OF ISOTROPIC AND ANISOTROPIC VIBRATIONS IN THE CL-SI AND H-O-SI CHEMISORPTION BONDS ON SI(100)

The electron-stimulated desorption ion angular distribution (ESDIAD) technique combined with a digital subtraction method have been employed to generate difference ESDIAD pattems between measurements made at 130 and 305 K for both adsorbed Cl and OH on Si(100). The difference ESDIAD pattems reveal, in real space, images qualitatively related to the thermally excited vibrational amplitudes of the adsorbates. This permits a qualitative visualization of the potential energy surface associated with an adsorbate on its adsorption site. For Cl/Si(100), isotropic thermal broadening of the Cl+ beams from 130 to 305 K is observed. In contrast, OH/Si(100) exhibits anisotropic thermal broadening of the H+ beams on heating from 130 to 305 K. These results are correlated with the vibrational frequencies of the surface oscillators.