Defect processes induced by electronic excitation at halide crystal surfaces

Abstract Atomic force microscopy (AFM) provides a new topographic view of radiation effects near surfaces, complementing earlier electron microscopy as well as desorption and spectroscopic studies. Potassium iodide crystal surfaces have been imaged by AFM while undergoing exposure to ultraviolet light in the exciton absorption spectrum. Pronounced erosion and modification of the surface by ultraviolet radiation has been observed with resolution down to ∼ 50 nm. Prospects for extending such measurements to atomic resolution are considered. In related studies of KI under illumination in the exciton region, photoelectron spectra reveal photoinduced gap states which appear attributable to F centers and alkali clusters. In both of these studies, fourth harmonic radiation from a Ti:sapphire mode-locked laser has proven especially useful because of its tuneability through the strongly absorbing exciton region of alkali iodides, producing near-surface excitation densities comparable to electron beams.

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