Effects of electron-boundary scattering on changes in thermoreflectance in thin metal films undergoing intraband excitations

摘要

As characteristic sizes and lengths scales continue to decrease in nanostructures, carrier scattering processes at the geometric boundaries and interfaces in nanosystems become more prevalent. These scattering events can lead to additional resistances. This paper investigates electron-boundary scattering processes by examining changes in thermoreflectance signals in thin films after short pulsed laser heating. To take electron-boundary scattering into account, an additional scattering term is introduced into the Drude model for the complex dielectric function. Using an intraband thickness-dependent reflectance model, transient thermoreflectance data of Au films subject to intraband excitations are analyzed with the electron-boundary scattering Drude model introduced in this work. The electron-boundary scattering rate is determined from Au thermoreflectance data, showing that after short pulsed laser heating, electron-boundary scattering rates can be almost three orders of magnitude greater than the electron-electron and electron-phonon scattering rates. The scattering rates determined from the thermoreflectance data agree well with the theoretical predictions for electron-boundary scattering calculated from an electron-boundary scattering model for disordered conductors in the event of an electron-phonon nonequilibrium.