Dimensionality Analysis of Thermal Transport in Multilayer Thin Film Systems

Pump-probe transient thermoreflectance (TTR) techniques are powerful tools for measuring thermophysical properties of thin films, such as thermal conductivity, Λ, or thermal boundary conductance, G. This paper examines the assumption of one-dimensional heating on Λ and G determination in nanostructures using a pump-probe transient thermoreflectance technique. The traditionally used one dimensional and radial (3D) models are reviewed. To test the assumptions of the thermal models, experimental data from Al films on bulk substrates (Si and glass) are taken with the TTR technique. This analysis is extended to thin film multilayer structures. Results show that at 11 MHz modulation frequency, thermal transport is indeed one dimensional. Error among the various models arises due to pulse accumulation and not accounting for residual heating.