Transient thermoreflectance from thin metal films

Abstract

This report describes the first demonstration of thermal diffusivity measurements using picosecond transient thermoreflectance (TTR). Although previously reported methods of measuring thermal transport properties of thin films require precise knowledge of the thermal properties of the substrate, this technique allows measurements on films as thin as 100 nm without any evidence of substrate interaction. The TTR measurement is modeled with a one-dimensional heat flow equation using a two-parameter fitting routine to determine the thermal diffusivity. The validity of our approach is confirmed by the TTR measured thermal diffusivity of single crystal nickel. We have also measured the thermal diffusivity of sputtered and evaporated single element metal films. Preliminary results from TTR measurements on compositionally modulated structures are also presented.

Operational Approach and Solutions of Hyperbolic Heat Conduction Equations

“…Recently the conditions for the transition region between the ballistic heat transport and the diffusion were described in [92]. Whether the heat transfer is ballistic or diffusive is also important for experimentalists, because the account for the ballistic phonon transport requires the knowledge of the boundary quality, while the wave and diffusive transport constants are intrinsic material properties [94][95][96]. The three dimensional Guyer-Krumhansl (GK) heat law was derived from the solution of the linearized Boltzmann equation for a phonon field in dielectric crystals at low temperature.…”

Influence of sample processing parameters on thermal boundary conductance value in an Al/AlN system

“…While for theoretical calculations of the TBC the phonon density of states in the two phases forming the interface are considered, recent experimental evidence has highlighted that the chemical nature of the bonds at the interface may be very important for the TBC as well. [1][2][3][4] The present communication uses the transient thermoreflectance ͑TTR͒ technique [5][6][7][8][9][10][11][12] to determine the thermal conductance at Al/AlN interfaces while varying the condition of the AlN surface prior to deposition of the Al thin layer and the layer deposition method itself.…”

Picosecond Transient Thermoreflectance: Time-Resolved Studies of Thin Film Thermal Transport

“…The second pulse has a variable delay with respect to the heating pulse, and it is us~g to measure the thermally-induced change in surf ace reflectivitY(N10 jK). For small temperature deviations the reflectivity change is linear in temperature, and a temperature profile over several hundred picoseconds can be measured [11,20]. The penetration depth of visible light in a metal is approximately 20 nm, and thermal diffusion out of this region occurs in a few hundred picoseconds.…”