SURFACE ENHANCED 2ND HARMONIC-GENERATION IN COLD DEPOSITED SILVER FILMS AND SCANNING TUNNELING MICROSCOPY

The nature of surface enhancement in cold deposited silver films (CDF) is studied by means of reflected second harmonic (RSH) generation and scanning tunneling microscopy. A strong dependence of RSH radiation intensity, polarization and angular distribution on film mass thickness and temperature is observed. The surface enhancement vanishes irreversibly in CDF heated up to >220 K. Intercrystallite fractures (pores) are detected in the structure of annealed films. This residual porosity is interpreted as a result of self-diffusion healing of deeper fractures. The experimental results confirm that in CDF the surface enhancement has a ″classical ″ electromagnetic origin and is due to intercrystallite pores with sufficiently small values of the width/depth ratio. A simple theoretical model is proposed to estimate analytically the enhancement in structures such as deep narrow crevices. © 1990.