Adsorption of HCl and HBr on Si(111): AES, ELS, and EID studies

Abstract

The combined techniques in situ of Auger electron spectroscopy, electron energy loss spectroscopy, electron impact desorption, and work-function change measurement have been applied to the study of the adsorption of HCl and HBr on thermally cleaned Si(111) surfaces. Major results are summarized as follows: (1) HCl shows a fast adsorption to the saturation coverage of θ s ⋍ 0.3 (estimated using the continuum approximation) by the exposure of about 1 L at room temperature. (2) The average sticking probabilities for HCl and HBr are ∼0.7. (3) Two adsorbed states of HCl or HBr at room temperature are discriminated. For HCl, the first state is characterized by the emission of ∼1.2 eV ions and the electronic transition at 8.4 eV, which is subsequently converted to the second state characterized by the emission of ∼3.2 eV ions and the electronic transitions at 7.0 and 8.4 eV. Heating the sample at ∼800 K causes the desorption of hydrogen and the appearance of the Cl-related peaks at 6.0, 7.0, and 9.0 eV in the loss spectra. For HBr, the first and the second states are characterizied by the emission of ∼1.2 and ∼3.2 eV ions, respectively. The electronic transition is observed at 7.8 eV in both states. (4) It is proposed that HCl and HBr are adsorbed as molecules initially, which are subsequently dissociated into atoms spontaneously at room temperature.