Electromagnetic mechanism of surface enhanced second harmonic generation by 'smooth' silver electrodes and scanning tunneling microscopy

The surface of originally smooth silver electrodes is studied by means of reflected second harmonic (SH) generation and scanning tunneling microscopy after electrochemical etching of N monoatomic surface layers ( N ∼ 0minus;10). At N ∼ 1 a generation of surface enhanced, diffuse, and depolarized SH is observed, and a distinct superatomic (of the scale ∼ 10 A) granular roughness is detected on the electrode surface. The fluctuation electromagnetic mechanism is proposed to explain the surface enhancement of diffuse and depolarized SH component: the effect is interpreted as resulting from exciton of local plasmons in irregular surface structures formed in the process of etching.