High-Temperature Kapitza Resistance at the Interface Between Solids.
Phonon transport in solids over very short distances and on very short time-scales has been investigated using ultrashort light pulses. This technique has made possible for the first time measurements of the temperature dependence of the Kapitza resistance at temperatures up to room temperature. In these experiments a thin metal film is deposited onto the clean surface of a dielectric material. The film is heated by an ultrashort light pulse and the temperature dependent reflectivity of the metal film is measured with a second, time delayed light pulse. Several samples of this type were measured; gold and aluminum films on lithium fluoride, calcium fluoride and barium fluoride. The measured Kapitza resistance is extracted from a fit of the cooling curve to the heat flow equations. The results are compared to a lattice dynamical calculation in which the Kapitza resistance is obtained from a detailed analysis of the spectral density of the phonon flux transmitted across the interface between two semi-infinite, harmonic fcc lattices in register. The calculated spectral density of the transmitted flux is found to be roughly proportional to the phonon density of states in either material. Calculated values of the Kapitza resistance for the interfaces with aluminum films are in good agreement with the measured values. For the interfaces with gold films, the calculated values of the Kapitza resistance are typically much larger than the measured values.
- Pub Date:
- Physics: Condensed Matter