OPTICAL 2ND-HARMONIC INVESTIGATIONS OF THE ISOTHERMAL DESORPTION OF SIO FROM THE SI(100) AND SI(111) SURFACES

The isothermal desorption of SiO from the Si(100) and Si(lll) surfaces was investigated by means of optical second-harmonic generation (SHG) . Due to the high adsorbate sensitivity of this method, desorption rat es could be measured over a wide range from 10(-1) to 10(-6) ML s(-1). From their temperature dependence between 780 and 1000 K, activation energies of E-A=3.4+/-0.2 eV and E-A=4.0+/-0.3 eV and pre-exponential factors of nu(0)= 10(16+/-1) s(-1) and nu(0)= 10(20+/-1) s(-1) for SiO desorption were obtained for Si(100) and Si(lll), respectively. In th e case of the Si(100) surface, a pronounced decrease of the first-orde r rate constants was observed upon increasing the initial coverage fro m 0.02 to 0.6 ML. The results are interpreted in terms of coverage-dep endent oxygen-binding configurations, which influence the stability of the oxide layer. (C) 1998 Elsevier Science B.V. All rights reserved.