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Suspended Asymmetric Graphene Nanomesh Achieves High Heat Rectification Ratio up to 60 Per Cent

This graphene nanomesh device is expected to advance the practical applications of graphene in thermal management.

With the development of cutting edge, large-scale integration technology, cooling computer cores and achieving effective thermal management have become key challenges in the global energy crisis. To solve these problems, engineers have been exploring methods to precisely control heat transport at the same level that we have been able to control electrical current. In particular, they have been looking into stand-alone thermal information processing systems and thermal storage systems. However, to build such systems, a high-efficiency thermal rectifier or thermal diode is required.

Recently, scientists at the Japan Advanced Institute of Science and Technology have proposed a promising candidate – an asymmetric graphene nanomesh device that shows a high thermal rectification ratio at low temperatures. Their study also provides a practical guideline for developing a high-efficiency thermal rectifier based on graphene nanomesh structures.

First demonstrated by Starr C. in 1936, a thermal rectifier or diode is a device that allows heat to flow preferentially in one direction since its thermal resistance is different for heat flow in one direction than for heat flow in the other direction. In most bulk material devices, a thermal rectifier’s mode of action is based on the different temperature dependence of thermal conductivities in two different composition materials. However, most thermal rectifiers developed to date based on this mechanism have only achieved a low rectification ratio of around 10 to 20 per cent. Although researchers have now shifted their focus from bulk materials to nanomaterials, it is generally difficult to measure the thermal conductivities for each part of a thermal rectifier in nanoscale devices, hence the need for a new development strategy for a high-performance thermal rectifier.

In the current study, a phonon research team, led by Dr. Fayong Liu and Professor Hiroshi Mizuta, collaborated with researchers at the National Institute of Advanced Industrial Science and Technology to investigate graphene-based thermal rectification by measuring the thermal transport properties of asymmetric suspended graphene nanomesh devices. Leveraging the helium ion beam milling technology, the researchers introduced graphene nanomesh as an artificial phononic crystal structure on half the area of the heat flux channel, with the nanopore diameter measuring up to approximately 6 nm, and the pitch 20 nm.

Their experiment revealed that the thermal rectification phenomenon can be observed with a high ratio of up to 60 per cent on suspended asymmetric graphene nanomesh devices at low temperatures (150K and 250K). To characterise the thermal transport properties in two directions, the researchers also developed a “differential thermal leakage” method for high-accuracy thermal measurement. By using this method, they were able to perform heat flux measurements undisturbed by the leakage of electron current through the suspended channel.

As the first study to report the observation of thermal rectification on asymmetric suspended graphene nanomesh devices, their findings are expected to provide a systematic way to enhance the performance of the thermal rectifier and open up the possibility of extending it to room temperature applications. “This research outcome is a significant advancement towards the practical application of graphene to thermal management. It is also a notable milestone for our final aim to apply graphene to build a greener world”, said Professor Hiroshi Mizuta, the Head of Mizuta Lab. [APBN]

Source: Liu et al. (2021). Thermal rectification on asymmetric suspended graphene nanomesh devices. Nano Futures, 5(4), 045002.