EFFECT OF NH3 ADSORPTION ON THE ATOMIC-STRUCTURE OF SI(111)ROOT-3 X ROOT-3-AL AND SI(111)ROOT-3 X ROOT-3-AG SURFACES

The room temperature (RT) adsorption of ammonia (NH3) on Si(111) squar e-root 3 x square-root 3-Al and Si(111) square-root 3 x square-root 3- Ag surfaces has been studied using LEED and AES. The transformation fr om Si(111) square-root 3 x square-root 3-Al surface structure to Si(11 1)1 x 1-(Al, H) upon NH3 exposure has been found to be similar to the previously observed structural transformation induced by exposure in t he atomic hydrogen. It has been demonstrated that the transformation i s caused by hydrogen atoms which are generated by NH3 dissociation on the Si(111) square-root 3 x square-root 3-Al surface. It has been esti mated that about 0.1 ML of ammonia molecules is needed to complete the structural transformation. No interaction of NH3 with the Si(111) squ are-root 3 x square-root 3-Ag surface has been found. The dissociation of NH3 molecules is believed to be impossible on this surface.