ONE-DIMENSIONAL CHAINS OF STRUCTURAL DEFECTS ON THE SURFACE OF SAPPHIRE AND THEIR ROLE IN ADSORPTION OF ALKALI ATOMS

Alkali adsorption on the (0001) surface of the monocrystalline alpha-A l2O3 was studied by means of laser-simulated desorption. It was found that alkali atoms are adsorbed mostly on the centers with the surface concentration of about 10(13) cm(-2). Although the temperature depende nce of surface coverage is consistent with the conventional Langmuir m odel for adsorption on the isolated centers, the estimated adsorption energy of about 1 eV is too large to account for the quantum yield of the photodesorption process, which is as high as 5 x 10(-5). To resolv e this contradiction we assumed that adsorption centers make up chains along the steps on the surface. Lateral interactions between neighbor ing adatoms were accounted for by means of methods developed for the I sing model. Theoretical results are in agreement with the experiment.