For the first time, we report the thermal conductivity of vertically aligned boron nitride nanotube (BNNT) films produced by catalytic chemical vapor deposition. High-quality BNNTs were synthesized at 1200 °C on fused silica substrates precoated with Pt thin-film thermometers. The thermal conductivity of the BNNTs was measured at room temperature by using a pulsed photothermal technique. The apparent thermal conductivity of the BNNT coatings increased from 55 to 170 W m⁻¹ K⁻¹ when the thickness increased from 10 to 28 µm, while the thermal conductivity attained a value as high as 2400 W m⁻¹ K⁻¹. These results suggested that BNNTs, which are highly thermally conductive, but electrically insulating, are promising materials with unique properties.

In this paper, we report on investigation concerning the substrate-dependent thermal conductivity (k) of Aluminum Nitride (AlN) thin-films processed at low temperature by reactive magnetron sputtering. The thermal conductivity of AlN films grown at low temperature (<200 °C) on single-crystal silicon (Si) and amorphous silicon nitride (SiN) with thicknesses ranging from 100 nm to 4000 nm was measured with the transient hot-strip technique. The k values for AlN films on SiN were found significantly lower than those on Silicon consistently with their microstructures revealed by X-ray diffraction, high resolution scanning electron microscopy, and transmission electron microscopy. The change in k was due to the thermal boundary resistance found to be equal to 10 × 10⁻⁹ Km²W⁻¹ on SiN against 3.5 × 10⁻⁹ Km²W⁻¹ on Si. However, the intrinsic thermal conductivity was determined with a value as high as 200 Wm⁻¹K⁻¹ whatever the substrate.

In the frame of this work, we report a profound insight into the thermal conductivity (k) of aluminum nitride (AlN) thin films deposited on AlN-molecular beam epitaxy (MBE)/Si(111) and AlN-Kyma/Si(111) substrates at low temperatures (<200 °C) using reactive direct current magnetron sputtering (DCMS). Our concern is not on the thermal properties at the nanoscale, but rather on relating thermal macroscopic properties to the microstructure for submicronic to micronic AlN films. As the mean free path for AlN material is about 100 nm, the thickness of our films lies between 400 nm and 2 μm. The k measurements were conducted using the ultra-fast transient hot strip technique. It was found that the k values of the deposited films change depending on both the substrate type and the film thickness. For the 500 nm AlN thick film, k value was about 250 W m−1 K−1 for AlN-DCMS films grown on 10 nm AlN-MBE/Si against 90 W m−1 K−1 for those deposited on 200 nm AlN-Kyma/Si. The thermal boundary resistance has been computed equal to (0.25 ± 0.08) × 10−9 K m2 W−1 on 10 nm AlN-MBE/Si against (3.56 ± 1.50) × 10−9 K m2 W−1 on 200 nm AlN-Kyma/Si. Additionally, both pole figures and high resolution transmission electron microscopy confirm k results. In fact, pole figures confirm the good crystal quality of the film on both substrates, but HR-TEM analyses show that the AlN films grown on 10 nm AlN-MBE/Si template exhibit good crystalline quality with an epitaxial regrowth and abrupt interface compared to those obtained for 200 nm AlN-Kyma/Si. It also appears that the thermal boundary resistance plays a major role in the thermal properties of AlN films.

This paper introduces an ultrafast transient hot-bridge technique for the microscale measurement of thermal properties. The system comprises microfabricated heaters and resistance thermometers, arranged in a Wheatstone bridge configuration, deposited on sample surface. These components are used in order to generate and detect electrical pulses, leading to temperature increases on micro- and nanosecond scales. The design and performance of various probes are discussed, with an evaluation of their capabilities in terms of time response, precision and resolution. Electrical pulses are applied via metalized probes, and the resultant temperature increases are analyzed within selected time periods ranging from 10 ns to 100 μs. By ensuring a self-balanced condition for all Wheatstone bridges, the technique facilitates the detection of rapid, time-dependent changes in thermal properties due to temperature evolution or structural transformations. This innovative method enables the measurement of thermal conductivity in very thin films and demonstrates the potential for measuring thermal properties at micrometric or even nanometric scales.