Structural transitions on Si(1 1 1) surface during Sn adsorption, electromigration, and desorption studied by in situ UHV REM

Using in situ ultrahigh vacuum reflection electron microscopy, we have studied structural transitions on the Si(1 1 1) surface induced by Sn deposition up to 2 ML coverage (1 ML = 7.8∙1014 cm−2) and by Sn desorption at substrate temperatures T = 200–860 °C. We have shown that Si–Sn intermixing in the adsorption layer during Sn deposition onto the Si(1 1 1)-(7 × 7) surface at T > 650 °C leads to the shift of the monatomic steps in the step-up direction, and there is formed a mosaic (√3×√3)-Sn phase. The electromigration of Sn adatoms induced by DC resistive heating has been shown to redistribute adsorbed Sn layer and to cause local (√3×√3)-Sn ⇔ “1 × 1”-Sn structural transitions on the surface. We have estimated the lower bound of the Sn adatom positive effective charge on the Si(1 1 1) surface qeffSn ≥ 0.001∙e. During AC annealing, the rate of desorption-induced “1 × 1”-Sn domain area shrinkage has been measured as a function of substrate temperature, and the activation energy of Sn adatom desorption has been estimated to be 2.5 ± 0.1 eV.