Picosecond acoustic measurements of longitudinal wave velocity of submicron polymer films

Abstract

We apply picosecond acoustic techniques to determine the longitudinal wave speed of submicron polymer films in the through-thickness dimension. The time-of-flight of an elastic wave propagating through the polymer film is measured using an optical pump/probe technique. The longitudinal wave speed in poly(methyl methacrylate) films of thickness ranging from 20 to 130 nm has been determined. A pronounced increase in longitudinal wave speed is observed for films of thickness less than 40 nm.