Orientation dependence of electron and phonon thermal conduction and its correlation with mechanical strength in aluminum interfaces

Abstract

This work presents an understanding of orientation dependence of electronic and phononic thermal conduction in Al interfaces. Focus is on quantifying the effect of interface orientation, the effect of tensile strain, and the effect of temperature on electronic and phononic thermal conduction across examined Al interfaces at temperatures ranging from 300 K to 900 K. Al being metal has free electrons as the primary source of heat carriers. Analyses indicate that the Al strength reduction with increase in temperature occurs in combination with phonon and electron thermal conductivity change. Single crystalline Al shows a direct correlation among the temperature increase, strength reduction, phonon thermal conductivity decrease, and electron thermal conductivity increase. The anisotropy and mismatch in thermal expansion at examined interfaces contributes to reduction in temperature increase associated material softening and to reductions in associated electron thermal conductance and phonon thermal conductance changes. Analyses further indicate that thermal conductivity reduction at a material interface due to tensile straining is attributed to phonon frequency range reduction caused by selective passage of long wavelength phonon through material interfaces. On the other hand, thermal conductivity reduction due to temperature increase can be attributed to anisotropy in thermal expansion and to phonon dispersion relation shape change. Based on physical observations a relation describing thermal conductivity of examined interfaces as a function of interface area and interface atom density as a function of interface orientation is proposed.