Abstract
We have investigated electron energy relaxation in copper wires with several film thicknesses (t=14-90 nm) evaporated on (a) 30 nm thick suspended silicon nitride membranes, and (b) bulk nitridized substrates. The experiment was performed at sub-Kelvin temperatures by heating the electron gas by current, and measuring the resulting temperature rise using sensitive normal metal-insulator-superconductor (NIS) tunnel junction thermometers. A clear effect of 2D phonon dimensionality was observed in all wires on top of the membranes, resulting in strengthened electron-phonon interaction below 0.5 K. Thinning the metal film on a bulk substrate also weakens the energy relaxation notably at the lowest temperatures.
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