EVIDENCE OF MULTIPLE H+ ION DESORPTION PATHWAYS WITH ESD OF CHEMISORBED AND MULTILAYER WATER

Measurements have been initiated of H+ ion energy distributions from a water dosed Si(100) substrate at room temperature and with multilayer formation at approximately 100 K. The apparently wide energy distributions usually observed with electron stimulated desorption are attributed to desorption along multiple pathways. Increasing the beam energy from 170 to 200 eV causes a shift in the peak position from around 8.5 to 5.7 eV, and is assigned to the role of secondary electrons which increasingly dominate as the energy is increased (seemingly associated with the ionisation of the silicon 2p (L2,3) level). A further peak in the ion energy distribution is emphasised towards low electron energy (< 50 eV) with peak energy at around 3.6 eV. Overall the production of H+ is enhanced with multilayer growth, but similar features of the ion energy distribution are present also at room temperature.