Effect of a metallic thin film on the propagation of Rayleigh waves

An oscillator built with a thermostated Rayleigh-wave delay line can be shifted in frequency by a metallic (Au, Cu, Al) thin film evaporated in a vacuum on the ultrasonic wave path. For very thin films (<100 Å) there is a rapid decrease in frequency of the oscillator and electrical resistance of the metal. This phenomenon is due to the short circuiting of the electric field to the interface and gives a good method for measuring the value of electromechanical coupling constant. For thicker film (from 200 to 3000 Å) the variations are much slower. The slope of the frequency-vs thickness curve is propotional to the mass of deposited metal.