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Here we examine the role of the amorphous insulating substrate in the thermal relaxation in thin NbN, InO$_x$, and Au/Ni films at temperatures above 5 K. The studied samples are made up of metal bridges on an amorphous insulating layer lying on or suspended above a crystalline substrate. Noise thermometry was used to measure the electron temperature $T_e$ of the films as a function of Joule power per unit of area $P_{2D}$. In all samples, we observe the dependence $P_{2D}\propto T_e^n$ with the exponent $n\simeq 2$, which is inconsistent with both electron-phonon coupling and Kapitza thermal resistance. In suspended samples, the functional dependence of $P_{2D}(T_e)$ on the length of the amorphous insulating layer is consistent with the linear $T$-dependence of the thermal conductivity, which is related to lattice excitations (diffusons) for the phonon mean free path smaller than the dominant phonon wavelength. Our findings are important for understanding the operation of devices embedded in amorphous dielectrics., 9 pages, 5 figures

We have measured the electron–phonon energy-relaxation time, ${\boldsymbol{\tau }_{{{\rm eph}}}}$ , in superconducting boron-doped diamond films grown on silicon substrate by chemical vapor deposition. The observed electron–phonon cooling times vary from 160 ns at 2.70 K to 410 ns at 1.8 K following a ${\boldsymbol{T}^{ - 2}}$ -dependence. The data are consistent with the values of ${\boldsymbol{\tau }_{{{\rm eph}}}}$ previously reported for single-crystal boron-doped diamond films epitaxially grown on diamond substrate. Such a noticeable slow electron–phonon relaxation in boron-doped diamond, in combination with a high normal-state resistivity, confirms a potential of superconducting diamond for ultrasensitive superconducting bolometers.

We report on the voltage response of carbon nanotube devices to sub-terahertz (THz) radiation. The devices contain carbon nanotubes (CNTs), which are over their length partially suspended and partially Van der Waals bonded to a SiO2 substrate, causing a difference in thermal contact. We observe a DC voltage upon exposure to 140?GHz radiation. Based on the observed gate voltage and power dependence, at different temperatures, we argue that the observed signal is both thermal and photovoltaic. The room temperature responsivity in the microwave to THz range exceeds that of CNT based devices reported before.