Femtosecond thermoreflectance data for thin films and bulk quantities of Au, Cr, and Al are compared with the parabolic two-step thermal diffusion model for the purpose of determining the electron-phonon coupling factor. The thin films were evaporated and sputtered onto different substrates to produce films that vary structurally. The measurement of the electron-phonon coupling factor is shown to be sensitive to grain size and film thickness. The thin-film thermoreflectance data are compared with that of the corresponding bulk material and to a theoretical model relating the coupling rate to the grain-boundary scattering and size effects on the mean free path of the relevant energy carrier.
© 1999 Optical Society of America
(120.5700) Instrumentation, measurement, and metrology : Reflection
(240.0310) Optics at surfaces : Thin films
(260.3910) Physical optics : Metal optics
(350.5340) Other areas of optics : Photothermal effects
John L. Hostetler, Andrew N. Smith, Daniel M. Czajkowsky, and Pamela M. Norris, "Measurement of the Electron-Phonon Coupling Factor Dependence on Film Thickness and Grain Size in Au, Cr, and Al," Appl. Opt. 38, 3614-3620 (1999)