PHOTOSTIMULATED DESORPTION OF METAL ADATOMS - POTASSIUM ON GRAPHITE

Photodesorption is observed of single K atoms from a graphite surface covered with less than 1 monolayer of potassium. The desorption cross section has a threshold at homegaBAR almost-equal-to 3 eV and a maximu m at homega(max)BAR almost-equal-to 4.9 eV. Polarization measurements indicate a substrate-mediated mechanism. The coverage dependence sugge sts that only the ionic 2D, K-phase is photoactive. The proposed mecha nism includes attachment of hot electrons, photoexcited in the bulk, t o the K4s adsorbate resonance of energy E(res). The band structure of graphite causes a narrow energy distribution of hot electrons, which y ields homega(max)BAR almost-equal-to 2E(res).