Nanoscale mechanical contacts probed with ultrashort acoustic and thermal waves

Using an ultrafast optical technique we measure coherent phonon-pulse reflection from-and heat flow across-a mechanical contact of nanoscale thickness between a thin metal film and a spherical dielectric indenter. Picosecond phonon wave packets at similar to 50 GHz returning from this interface probe the pressure distribution, the contact area, and the indentation profile to subnanometer resolution, revealing the film deformation in situ. These measurements and simultaneous thermal-wave imaging at greater than or similar to 1 MHz are consistent with significant enhancement of phonon transport across the near-contact nanogap.