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The reactivity of D2 16O and H2 18O with thin films of MgO(1 0 0) at room temperature was studied by electron stimulated desorption time of flight (ESDTOF) mass spectrometry. The MgO(1 0 0) thin films were grown on Si(1 0 0) at 1000 K by RF sputtering in an Ar (90%) and O (10%) atmosphere. The energy of the incident electrons ranged from 5 to 600 eV and the incident electron current on the sample was 100 nA. When the surface is exposed to D2O, the peaks of the ESDTOF surface ion spectra correspond to H+, D+, O+ and OD+ desorbed ions. After H2 18O exposure, H+, 16O+, and 18O+ desorbed ions are observed. Both 16O+ and 18O+ ions have a bimodal structure, which corresponds to oxygen ions with most probable kinetic energies of 5.3±0.5 and 9.0±0.9 eV. This bimodal structure is strongly affected by the energy of the incident electrons as well as by the adsorbed species. At electron energies lower than 250 eV the state with the lowest kinetic energy almost disappears. The two peaks at 5.3±0.5 and 9.0±0.9 eV of the bimodal structure are consistent with those observed in previous studies on bulk MgO(1 0 0) at 6.0±0.6 and 9.0±0.9 eV energies. The ion yields of desorbed ions for thin films and bulk samples are dramatically different. These results are discussed with respect to the surface reactive adsorption sites as well as to the secondary electron yield.

Processes of adsorption–desorption with glycine admitted to the TiO2(110)(1×2) reconstructed surface have been studied using synchrotron light, energy 55 eV, and with coverages both sub to monolayer, and multilayer at room temperature. The findings are discussed in terms of processes of dissociative adsorption at the sub-monolayer stage with only minor amounts of the amino radical of the glycine molecule remaining at the surface. The Ti 3d) peak is significantly affected in the evolution towards initial monolayer coverage. Aspects of photon induced desorption with photoelectron spectroscopy are compared with thermal treatments of the glycine-covered surface.

Photon damage of multilayers of glycine adsorbed on a TiO 2 (110) surface at room temperature has been studied with photoelectron spectroscopy of the valence band, the 2s band, and the Ti 3p level using synchrotron radiation at the Daresbury S.R.S. The UPS spectra of the multilayer (comprising about seven monolayers) show structures which can be assigned to the molecular structure of the zwitterionic form of glycine. Photon induced damage of multilayers up to θ =2 monolayers produces a first order desorption of the zwitterionic molecules with total cross section 5.4×10 −16 cm 2 which is similar to the ionisation cross section in the gas phase. The remaining layer is formed by C, NH x ( x =1,2) and OH hydroxyl species. A significant feature is the increase of the structure at 0.8 eV pointing to the growth of Ti 3+ surface species. This could be due to the formation of OH radicals on the surface or the adsorption of fragments on top of the O surface atoms involving some charge transfer to the surface.

An electron-stimulated desorption (ESD) study of electron damage of a D2O layer adsorbed on the MgO(100) surface at room temperature is presented. After exposing the surface to D2O, the surface spectrum shows the main ESD component to be D+ ions, with lower intensity signals corresponding to O+ and OD+ ions. When the surface is simultaneously exposed to heavy water and electron bombardment, there is a rapid initial increase of the D+ intensity accompanied by a decrease of the intensity of the O+ ions. Electron damage of the surface after exposing to D2O produces a significant decrease of the D+ intensity, while the O+ and OD+ intensities decrease more slowly. Heavy water adsorption does not change the form of the ion kinetic energy distribution of the O+ ions with electron dose, except for a decrease in intensity. Electron damage increases the intensity of the ion kinetic energy distribution of D+ again without changing its shape. These experiments show that heavy water adsorption under electron bombardment does not induce any chemistry of the adsorbed species, but enhances the fragmentation rate of the OD species which, in turn, increases the yield of D+ ions. Values of total desorption cross-sections for the three ions species are reported.

The adsorption of acetic acid on the TiO 2 (110) surface has been studied with PES, using synchrotron radiation ∼47 eV, both at the stoichiometric (1 × 1) surface and the (1 × 2)-reconstructed surface. The results indicate a similar bonding configuration for each surface, and that the saturation acetate coverage at room temperature on the (1 × 2)-reconstructed surface is approximately half that of the (1 × 1) surface. The results are interpreted in favour of the added Ti 2 O 3 -row model of the (1 × 2) reconstruction at the clean surface.

CO adsorption on a defective TiO2(110) surface at 150 K incorporating about 1.7 × 1014cm−2 vacancies produced by Ar+ sputtering has been studied by electron stimulated desorption, ESD, and with Auger electron spectroscopy, AES, as a complementary technique. When the surface was exposed to CO up to 5 × 105L the AES spectra revealed a small C signal. From the O(KLL)Ti(LMM) ratio increase a CO coverage of 0.06 ± 0.01 ML was determined. In spite of this small amount of CO the ESD technique showed dramatic changes in ion yield and energy. The characteristic dominant peak at 4.0 eV and the small structure at about 7.0 eV of the ion kinetic energy distribution curve of the clean defective surface changed to a triple peak structure with maxima at 3.4, 4.3 and 7.4 eV. The first is identified with the most probable kinetic energy of O+ ions ejected from non-dissociated CO molecules. The 4.3 and 7.4 eV maxima correspond to the most probable kinetic energy of O+ ions desorbed from O in-plane and from the bridging O-ligand of the TiO2(110) surface, respectively. The growth of the 7.4 eV peak upon adsorption is a consequence of the filling of the bridging O-ligand initial vacancies by dissociated O from the CO molecule. The ion yield curves show, in addition to the onset at 35 eV electron energy of the clean surface, a threshold at about 290 eV electron energy corresponding to excitation of the C 1s core level. The total ion yield also shows a decrease upon CO adsorption. The O+ ion yield curves are found to be related to the secondary electron yield. The chemisorption of CO is discussed in terms of a model where the CO is molecularly adsorbed on the Ti five-fold coordination sites with a part being dissociated and leading to O adsorbed on bridging O-ligand vacancies.

CO reactivity with a defective (O vacancies, Ar+-sputtered) TiO2(110) surface evaporated with Ta has been studied by electron stimulated desorption, ESD, and using Auger electron spectroscopy, AES, as a complementary technique. The clean surface shows thresholds of the O+-desorbed ions at incident electron energies that can be assigned to ionisation of the Ti 3p, Ta 4f, and 4p core levels. After CO exposure of the surface to saturation with 6 × 104 L, the ion yield shows a significant increase and a new threshold at 290 eV identified with the C 1s excitation is observed. The CO coverage was 0.09 ML, the number of O vacancies before the CO adsorption was 7% of the total number of O atoms of the nearly perfect surface (1.56 × 1015 atoms/cm2) and the AES Ta(NVV)Ti(LMM) ratio was 7%. The O+ ion yield follows quite well the secondary electron yield. Ion energy distribution curves of the O+-desorbed ions show structures that are identified with O+-desorbed ions from O species bonded to Ti and Ta atoms as well as from the CO. About 76% of the adsorbed CO is dissociated.

The energy and angular distribution of the electron-stimulated O+ ion yield have been measured from clean and SO2-dosed rutile TiO2(110). ESD spectra from the clean surface indicate ion emission at three energies: 2.5, 4.0 and 6.5 eV. By comparison with previous calculations, the 4.0 and 6.5 eV features can be assigned to emission of in-plane and bridging O atoms, respectively. The elongation of the ESDIAD image in the [110] azimuth is consistent with that predicted for the in-plane O atoms. While the O+ energy distribution changes significantly following SO2 adsorption at 130 K and again following sequential annealing, there is little change to the ESDIAD pattern. The latter result is consistent with emission from surface sulphate species, although it could also be due to a residual substrate effect.

The reaction of oxygen on the Nb (110) surface at 240 K after exposure to H2O and O2 under e-bombardment has been investigated by using AES and EELS techniques- The uptake of oxygen atoms is much more efficient when the surface is exposed to H2O than to O2. The chemistry of the oxygen adatoms is analysed on the basis of the AES Nb(M45N23V) and EELS structures. At the highest H2O exposure the oxygen atoms are in the form of Nb2O5 oxide, while for O2 the final state is an oxide of less valence. Initial sticking coefficients of ~ 1 and 0.41 for oxygen and water respectively, at 240 K adsorption temperature, have been determined. A model based on dissociative adsorption and electron stimulated desorption processes is presented to explain the differences between both molecules.

Measurements have been initiated of H+ ion energy distributions from a water dosed Si(100) substrate at room temperature and with multilayer formation at ~ 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.