New Study Reveals Best Graphite Films – ScienceDaily

High-quality graphite has excellent mechanical strength, thermal stability, high flexibility, and very high in-plane thermal and electrical conductivity, and is thus one of the most important modern materials for many applications, such as being used as a lightweight thermal conductor on cell phones. For example, a specific type of graphite, highly ordered pyrolytic graphite (HOPG), is one of the most commonly used in the laboratory. materials. These excellent properties derive from the layered structure of graphite, where the strong covalent bonding between carbon atoms in a graphene layer contributes to the excellent mechanical properties, thermal and electrical conductivity, and the very weak interaction between graphene layers leads to the high flexibility of graphite.

Although graphite has been found in nature for more than 1000 years and its artificial synthesis has been studied for more than 100 years, the quality of graphite samples, whether natural or synthesized, is far from ideal. For example, the size of the largest single crystal graphite domains in graphite materials is usually less than 1 mm, which is in sharp contrast to the size of many crystals, such as the size of quartz single crystal and silicon single crystals can reach the meter scale. The very small size of the single crystal graphite is due to the weak interaction between the graphite layers, where the flatness of the graphene layer is difficult to maintain during the growth process, and thus the graphite can easily break into several single crystals with disordered boundaries of the nipples.

To address the critical issue, Ulsan National Institute of Science and Technology (UNIST) Distinguished Professor and his collaborators Professor Kaihui Liu, Peking University Professor Enge Wang, and others proposed a strategy to synthesize single-crystal graphite films on orders of magnitude, up to inch scale. In their approach, single crystal Ni foils are used as a substrate and caron atoms are supplied from the back side of the Ni foil by an “isothermal dissolution-diffusion-precipitation process”. Instead of using a cardboard box source in the gas phase, they chose solid carbon materials to power the graphite growth. Such a new strategy enables ~1 inch single crystal graphite films with a thickness of 35 ┬Ám or more than 100,000 graphene layers within a few days. Single crystal graphite has a recorded thermal conductivity of ~2,880 Wm-1K-1, negligible impurity content, and the smallest interlayer spacings of all available graphite samples.

“This success really addresses several critical issues of experimental design:

(1) the successful synthesis of large single crystal Ni films serves as an ultra-flat substrate, and thus the disorders in the synthesized graphite can be avoided;

(2) the isothermal growth of 100,000 graphene layers in ~100 h allows each graphene layer to be synthesized under exactly the same chemical environment and temperature, thus ensuring uniformity of graphite quality;

(3) the continuous supply of carbon through the back side of the Ni foil enables the continuous growth of graphene layers at a very high growth rate, ~ one layer every five seconds,” Professor Ding explained.

The results of this research are published in the October 2022 issue of Nature Nanotechnology. Professor Kaihui Liu and Professor Enge Wang from Peking University jointly participated in this study.

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Materials provided by Ulsan National Institute of Science and Technology (UNIST). Original written by JooHyeon Heo. Note: Content may be edited for style and length.

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