Thermal Relaxation in Titanium Nanowires: Signatures of Inelastic Electron-Boundary Scattering in Heat Transfer.

We have employed noise thermometry for investigations of thermal relaxation between the electrons and the substrate in nanowires patterned from 40-nm-thick titanium film on top of silicon wafers covered by a native oxide. By controlling the electronic temperature $$T_\mathrm{e}$$ by Joule heating at the base temperature of a dilution refrigerator, we probe the electron-phonon coupling and the thermal boundary resistance at temperatures $$T_\mathrm{e}= 0.5$$ -3 K. Using a regular $$T^5$$ -dependent electron-phonon coupling of clean metals and a $$T^4$$ -dependent interfacial heat flow, we deduce a small contribution for the direct energy transfer from the titanium electrons to the substrate phonons due to inelastic electron-boundary scattering. [ABSTRACT FROM AUTHOR]