Comment:
7.5 ML Y/GaAs(100). The yttrium coverage was estimated by XPS. 1E16 cm-3. The substrate was cleaned by Ar+ ion bombardment (Ep = 1 keV, j = 10 microamperes/cm2, time = 30 min) and subsequently annealed (T = 723 K, time = 15 min) by indirect electron bombardment. This was repeated several times