The study of the thermal properties of materials and heat transport at the nanoscale is complicated by the speed needed to generate and probe thermal transport. At the nanoscale, the use of ultrafast lasers is needed to generate and probe heat transport. Two techniques based on ultrafast lasers are used to probe heat transport in metals and semiconductors. The first is based on femtosecond transient thermomodulation reflectance and transmittance. In this technique electron heating and transport is probed by the modulation in the optical properties of a thin film. Results on Au 25–400 nm films show that heat transport occurs due to ballistic electrons up to a thickness of 200–300 nm, while diffusive transport occurs for the 400 nm film. The second is based on time-resolved reflection high-energy electron diffraction used to probe the surface temperature through the Debye-Waller factor, which is a direct measure of lattice vibration. The results show that for heating with 100-ps laser pulses, the surface temperature follows that modeled by the Fourier law of heat diffusion.
展开▼
