QUANTUM-CHEMICAL STUDY ON SIO DESORPTION FROM A SI(111) SURFACE

SiO molecule formation during the oxidation of a Si(lll) surface has b een described for the first time by using the density functional metho d. The Si(lll) surface was represented by an Si4H9 cluster. Searching for a stable chemisorption state of an oxygen atom we obtained a weakl y stable on-top state and a stable bridging arrangement for the oxygen atom. Comparison of their structural and vibrational properties with experimental data supported their reliability as possible initial stru ctures for SiO desorption. Energy curves for SiO desorption from these chemisorbed states were calculated. The energy curves indicated smoot h desorption routes for both models. The theoretical activation energy values for the on-top and the bridging desorption processes, 79.6 kca l mol(-1) and 96.3 kcal mol(-1) respectively, are in qualitative agree ment with the experiment. Possible weak physisorbed states were found at the last part of the desorption in both cases. These results were u sed to interpret experimental spectroscopic observations. (C) 1997 Els evier Science B.V.