INDUCING AND IMAGING SINGLE-MOLECULE DISSOCIATION ON A SEMICONDUCTOR SURFACE - H2S AND D2S ON SI(111)-7X7

Using a variable-temperature, ultrahigh vacuum scanning tunneling micr oscope (STM), we have induced and imaged the dissociation of H2S and D 2S on Si(111)-7x7. H2S and D2S adsorb dissociatively at low coverage, from 50 to 300 K. Individual HS (or Ds) fragments can be further disso ciated with the STM at low temperatures without affecting neighboring adsorbates. The hydrogen (deuterium) atom either desorbs or re-attache s to a nearby silicon atom. Near room temperature (297 K) and above, D S dissociates thermally, with an activation barrier of 0.73+/-0.15 eV. The activation barrier was calculated from atomistic studies of the d issociation rates at temperatures between 297 and 312 K. (C) 1998 Amer ican Institute of Physics. [S0021-9606(98)70538-0].