Adsorption chemistry of cyanogen iodide on silicon ( [formula omitted

Abstract

The adsorption of cyanogen iodide (ICN) on a silicon (1 0 0) surface is studied by X-ray photoelectron spectroscopy (XPS), ultra-violet photoelectron spectroscopy (UPS) and temperature programmed desorption (TPD) spectroscopy. After submonolayer exposures, XPS indicates that the CN triple bond of ICN remains intact upon adsorption at 100 K. The UPS spectrum for submonolayer exposures at 100 K contains two peaks assigned principally to the π electrons in the CN triple bond. The splitting is due to the interaction between the π electrons of the cyanogen and the p electrons of the iodine. These results show that a portion of ICN molecules adsorbed molecularly. Higher exposures result in multilayer molecular ICN film. TPD spectra from both the submonolayer and multilayer films formed at 100 K show a peak at 170 K due to the desorption of adsorbed molecular ICN. In contrast to the low-temperature results, the UPS spectrum of ICN adsorbed at room temperature (RT) on Si(1 0 0) contains only one peak which originates principally from the π electrons in the CN triple bond. The lack of splitting in the RT UPS spectrum is a result of IC bond dissociation upon adsorption on Si(1 0 0). At RT the IC bond breaks while the CN bond remains intact. Upon annealing the Si(1 0 0) surface to higher temperatures, the UPS and XPS spectra indicate that the CN triple bond starts to disappear at ≈470 K. Simultaneous changes in the C 1s and N 1s photoelectron peaks between 470 and 800 K are consistent with the idea that CN bond cleavage in ICN is correlated with silicon carbide and nitride formation. By 800 K, all adsorbed CN species decompose completely into silicon carbide and nitride.