Monolayer Hexagonal Boron Nitride Will be the Next Hot Cooling Material
Posted by Cathie Montanez on August 15, 2019 11:15 PM EDT
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Take flexible wearable devices as an example, thermal management becomes more and more important with the lightweight and miniaturization of modern devices, and the development of insulating materials with high thermal conductivity becomes more and more important.
The results of the study conducted by Deakin University, funded by the Australian Research Council (ARC) through the science and technology achievement transformation award, showed that the thermal conductivity of the single-layer hexagonal boron nitride (BN) reached 751W/mK at room temperature. In terms of weight, it is the second-highest (diamond is the first) of all semiconductors and insulation materials and the thermal conductivity gradually decreases as the number of layers of hexagonal boron nitride increases. This means that monolayer boron hexagon nitride will be the preferred heat dissipation material for the next generation of flexible electronic devices.
Diamond and cubic boron nitride (CBN) is the highest thermal conductivity of these materials, but it is difficult to use them in flexible equipment due to production cost and brittleness. There is also the recently discovered high-quality cubic boron arsenide (BAs) with a bandgap of 1.5eV, which has a thermal conductivity of about 1000 W/mK, but also with question marks over flexibility. In contrast, the performance of highly oriented pyrolytic hexagonal BN (HOPBN) is close to that of single-crystal boron nitride. Despite many grain boundaries, defects and dislocation, its thermal conductivity coefficient is as high as 400 W/mK at room temperature.
In many previous studies, it was found that the thermal conductivity of BN with few layers was not even as good as that of ordinary hBN blocks. Some experimental data even showed that the thermal conductivity of BN with 5 layers was worse than that of BN with 11 layers. According to this study, there were defects in hBN samples before, and the use of polymers (such as PMMA) was involved in the sample transfer process, and there was residual contamination. Therefore, it inevitably destroys the experimental results.
In this experiment, the transparent tape method was used to prepare single-layer BN, and Raman spectrum method was used to measure the results. The researchers used the stripped monolayer BN to cover the nano silica-covered silicon substrate and the gold-plated silicon substrate, respectively. Both substrates were treated with prefabricated microholes and grooves to avoid gas expansion during heating.
Finally, by preparing and testing a high-quality monolayer BN, the researchers revealed the intrinsic thermal conductivity of the material. The results show that monolayer BN is the material with the highest thermal conductivity except for diamond and cubic boron arsenide in semiconductors and insulators. Besides that, it also has multiple advantages such as low density, high strength, high toughness, high ductility, high stability, and impermeability, which makes its application prospects particularly broad.