Study on polystyrene thin film on glass substrate by scanning acoustic microscope

Acoustic micrograph and V(z) curves of polystyrene thin films on hydrophobic modified and unmodified alumino silicate glass substrates were studied in the frequency range from 170 to 450 MHz by a scanning acoustic microscope. The bright and dark parts in the acoustic micrograph of the unmodified glass samples appeared owing to permeation of water into the film. The blister was observed after about 20 s from dropping water. Sizes of the blister depended on the time and the thickness of thin films. On the other hand, the acoustic micrograph of the hydrophobic modified samples was a uniform image and the peeling of the thin film was not observed. V(z) curves of polystyrene thin film on the modified glass substrates had two oscillation periods in a certain frequency range that depended on the thickness of thin films. The short cycle and the long cycle components were assigned to a leaky surface acoustic wave (LSAW) and a leaky pseudo Sezawa wave, respectively. Velocities of the LSAW decreased linearly with an increase in film thickness.