Studies of alkali halide films deposited at low temperatures. Electron microscopy, electronic spectra from colour centres and infra-red spectra from the chemisorption of nitric oxide
The structure and sintering of the surface of alkali halide films, prepared by deposition onto low temperature substrates, have been studied with electron microscopy. At low temperatures the films are composed of crystallites less than 50 Å in size. U.-v. spectra of colour centres in the very small crystallites have shown the existence of trapped electron (i.e., F- and M-) centres and trapped “hole”(i.e., probably V1-, V2- and H-) centres. Evidence is also presented for the observation of transitions of surface F-centres. Annealing of the films and loss of colour centres with increasing temperature and with gas adsorption are demonstrated. Infra-red spectra have shown that adsorbed nitric oxide exists as NO+ and, on some surfaces, NO– ions. Correlation of the adsorption with colour centres in the films is also discussed.