Moduli determination in polyimide film bilayer systems: Prospects for depth profiling using impulsive stimulated thermal scattering

A laser-based ultrasonic technique, impulsive stimulated thermal scattering (ISTS), is used to characterize the acoustic waveguide behavior in a series of silicon-supported and free-standing polyimide bilayer structures. The experimental results demonstrate that multilayer structures are characterizable using ISTS measurements. In addition, simulations of acoustic waveguide behavior in coatings with very thin interfacial layers adjacent to the substrate and in films with continuously changing elastic properties are presented. The results indicate depth-profiling possibilities using ISTS.