Laser induced desorption of alkali atoms from one dimensional chains of structural defects on the surface of sapphire.

Alkali adsorption on the surface of the monocrystalline sapphire was studied by means of laser stimulated desorption. The photo-desorption yield was found to be proportional to the laser fluency up to the threshold of the thermo-desorption process. The feature of the experimental apparatus was the possibility to control the coverage by means of the surface temperature provided the adsorbate was in dynamic equilibrium with a vapor of constant pressure. 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 dependence of surface coverage is consistent with the conventional Langmuir model for adsorption on the isolated centers, the estimated adsorption energy of about 1 eV is too large to account for the quantum yield of photo-desorption process which is as high as 5 x 10(-5). To resolve this contradiction we assumed that adsorption centers make up chains along the steps on the surface. Lateral interaction between neighboring adatoms were accounted for by means of methods developed for Ising model. Theoretical results are in agreement with the experiment.