THE ADSORPTION AND THERMAL-DECOMPOSITION OF CH2CO (CD2CO) ON SI(111)-7X7

The adsorption and thermal decomposition of ketene on Si(111)-7 x 7 we re investigated using various surface analysis techniques. When the su rface was exposed to ketene at 120 K, two CO stretching modes at 220 a nd 273 meV appeared in HREELS, corresponding to two adsorbed ketene st ates. After the sample was annealed at similar to 250 K, the 273 and t he 80 meV peaks vanished, indicating the disappearance of one of the a dsorption states by partial desorption of the adsorbate. In a correspo nding TPD measurement, a desorption peak for ketene species was noted at 220 K. Annealing the sample at 450 K caused the decomposition of th e adsorbate, producing CHx and O adspecies. Further annealing of the s urface at higher temperatures resulted in the breaking of the CH bond, the desorption of H and O species and the formation of Si carbide. Th e desorption of H at 800 K was confirmed by the appearance of the D-2 (m/e = 4) TPD peak at that temperature when CD2CO was used instead of CH2CO.