DEFECT PROCESSES INDUCED BY ELECTRONIC EXCITATION AT HALIDE CRYSTAL-SURFACES

Atomic force microscopy (AFM) provides a new topographic view of radia tion effects near surfaces, complementing earlier electron microscopy as well as desorption and spectroscopic studies. Potassium iodide crys tal surfaces have been imaged by AFM while undergoing exposure to ultr aviolet light in the exciton absorption spectrum. Pronounced erosion a nd modification of the surface by ultraviolet radiation has been obser ved with resolution down to approximately 50 nm. Prospects for extendi ng such measurements to atomic resolution are considered. In related s tudies of KI under illumination in the exciton region, photoelectron s pectra reveal photoinduced gap states which appear attributable to F c enters and alkali clusters. In both of these studies, fourth harmonic radiation from a Ti:sapphire mode-locked laser has proven especially u seful because of its tuneability through the strongly absorbing excito n region of alkali iodides, producing near-surface excitation densitie s comparable to electron beams.