As length scales continue to shrink, new tools are needed to measure mechanical properties. We are developing two such tools using different nondestructive acoustical techniques. Surface acoustic wave spectroscopy (SAWS) uses laser-ultrasonic methods to measure the phase velocity dispersion relation over several hundred megahertz. SAWS can accurately assess sub-micrometer-thick films, although it interrogates a centimeter-sized area. In contrast, atomic force acoustic microscopy (AFAM) has lateral spatial resolution of tens of nanometers. AFAM involves acoustical excitation of flexural resonances in the cantilever of an atomic force microscope. Here, we present AFAM and SAWS results for nickel films with thicknesses from 50 to 800 nm. For the thickest film, acoustical data are compared to results from microtensile testing and nanoindentation. Results are in only fair agreement if elastic isotropy is assumed. However, very good agreement is achieved using a transversely isotropic film model. This is consistent with a preferential <111 > film texture, confirn'led by x-ray analysis. We also discuss how SAWS results can be analyzed to obtain other information such as film thickness. Our results demonstrate how comparing results from several techniques yields more information about the film properties than that provided by anyone measurement.
Citation: Journal of Materials Research
Pub Type: Journals
acoustic AFM, surface acoustic waves, thin films