RHEED INTENSITY ANALYSIS OF LI/SI(111) STRUCTURES

In order to study surface reconstruction processes by Li adsorption on a Si(111) surface, RHEED intensity rocking curves for several coverages of Li atoms are analyzed by dynamical calculations. The rocking curves are measured for a one-beam condition and [112] incidence. On adsorption at room temperature the RHEED pattern gradually changes into a δ7×7 pattern. The best-fit model for this adsorption process is as follows: The backbonds of more than 0.2 ML (1 ML= 7.9×1014 atoms/cm2) of Si adatoms in DAS (dimer-adatom-stacking fault) structure are cut off by adsorption of 0.2 ML of Li atoms. Then Si adatoms bonded with Li atoms are formed at on-top sites of a stacking-fault layer. For further deposition Li atoms adsorb at both the adatoms and the stacking-fault layer atoms. The surface normal position of the Li atoms adsorbed at the adatom site changes with the coverage. After annealing 1 ML adsorbed surface at 300°C, a √3×√3 Li structure is observed. A structure model in which Li atoms adsorbed above 1.60 Å from a bulk-like Si(111) surface is proposed for this structure from analysis of the rocking curves. © 1989.