Surface electron standing waves and adatom heights on Si(111)-root 3 X root 3-(Ga,In,Sn) surfaces

GaK and SnL x-ray emissions from Si(111)-root 3x root 3-Ga and -Sn surfaces induced by irradiation of an electron beam were measured as functions of t he incident glancing angle. By analyzing anomalous x-ray intensities under Bragg conditions, which are due to the formation of electron standing waves , the heights of Ga and Sn were determined. Compared with the previous resu lt for Si(111)-root 3x root 3-In structures, the height of Sn was found to be higher than that of In, although their atomic numbers and covalent radii are very close. The effects of atomic size and electronic structures on ad atom height will be discussed.