High resolution electron energy loss spectroscopy study of the Si(001)3x1 hydrogenated surface

Hydrogenation of the Si(001) 2 X 1 surface held at 400 K has been performed in a new experimental set-up for a characterization by high resolution electron energy loss spectroscopy (HREELS), Angular scan along the [110] direction recorded at 55 eV primary energy confirms the 3 X 1 surface reconstruction. HREELS performed at 6 eV demonstrates the existence of a dihydride phase, in particular through the observation of the scissor mode around 904 cm(-1). The good quality of this surface, as shown by a high count rate on the elastic peak, allowed to obtain a resolution as good as 45 cm(-1) at room temperature. Lineshape studies of the vibrational peaks related to hydrogen reveal an abnormal width of the 639 cm(-1) mode, In fact, the resolution was improved by cooling down to similar to 110 K, and a double peak was clearly resolved, separated by 35 cm(-1). In view of previous HREELS studies of the Si(001) 1 X 1 and 2 X 1 hydrogenated surfaces, as well as of theoretical calculations of the vibrational modes of SiH2 species, the assignment of these modes is given. For the first time, a clear monohydride signature within a dihydride phase is reported by HREELS.