Nanometer-scale passivation of Si/(111) surfaces by using the root 3x root 3-Ga reconstruction

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