Change of optical second harmonic generation intensity during Ag deposition on Si(1 1 1)7×7 and Si(1 1 1)3×3-Ag surfaces

We investigated the change of optical second harmonic generation (SHG) intensity during Ag deposition on Si(1 1 1)7 × 7 and Si(1 1 1)3×3-Ag surfaces at room temperature. The SHG intensity oscillated on the Si(1 1 1)7 × 7 surface, while the SHG intensity decreased monotonically on the Si(1 1 1)3×3-Ag surface. The difference in the Ag coverage-dependent change of SHG intensity reflects the difference in the growth modes of the Ag films. The Ag atoms nucleated into islands on the Si(1 1 1)7 × 7 surface to cause the first peaks in SHG intensity oscillation by enhancing the local electric field with local plasmon resonance. The subsequent coalescence of the islands into a flat continuous layer caused peaks in the SHG intensity oscillation due to resonant transitions between the quantized states of the electrons confined in the flat Ag overlayer on the Si(1 1 1)7 × 7 surface. Island nucleation was more difficult on Si(1 1 1)3×3-Ag surfaces than on the Si(1 1 1)7 × 7 surface. The islands nucleated inhomogeneously and did not coalesce into continuous films on the Si(1 1 1)3×3-Ag surface.