Nanometer-scale passivation of Si(111) surfaces by using the √3 × √3-Ga reconstruction

Si(111) surfaces with a nanometer-scale Si(111)-√3 × √3-Ga area have been observed by scanning tunneling microscopy after exposure of molecular oxygen at room temperature, in order to compare the chemical activities on Si(111)-7 × 7 and √3 × √3-Ga surfaces. After exposure to 10 L of oxygen, the 7 × 7 reconstruction around the √3 × √3-Ga area disappears, while the √3 × √3-Ga reconstruction remains due to the effect of surface passivation. The √3 × √3-Ga reconstruction is preserved after exposure to more than 20 L, though Ga atoms are oxidized from boundaries between the 7 × 7 surface and the √3 × √3-Ga area and surface defects in the √3 × √3-Ga.