Thermal and electron driven chemistry of CCl4 on oxidized Si(100)

Abstract

Dosed on oxidized Si(100) at 100 K, carbon tetrachloride adsorbs and desorbs without dissociation. The monolayer desorbs at 135 K, 10 K lower than the multilayer. This unusual behavior is attributed to stronger interactions between condensed CCl4 molecules than between CCl4 and SiO2. Irradiation with either low-energy (⩽50 eV) electrons or Mg Kα x rays causes C–Cl cleavage. For 50 eV incident electrons, the decay of the CCl4 temperature programmed desorption peak area occurs with an effective cross section of (2.0±0.1)×10−16 cm2. The same cross section characterizes the ejection of CCl (CCl+) during electron irradiation. After low electron fluences, C2 and C3 molecules desorb reflecting both electron-induced C–Cl bond dissociation and C–C bond formation. At 2.5 eV incident electron energy, the cross section is still high—10−17 cm2. Electron activation is attributed to a combination of impact ionization and electron attachment mechanisms.