Korean researchers fabricate ordered graphene quantum dot arrays

The new method removes impurities at the edge of GQDs and adjusts the size of GQDs, as desired.

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IMAGE:SEM images show graphene quantum dots of various sizes in a stable, ordered array. (Image credit: UNIST)

A new study led by professor Hyeon Suk Shin in the School of Natural Science at the Ulsan National Institute of Science and Technology (UNIST; Ulsan, South Korea) reveals a technology capable of fabricating highly ordered arrays of graphene quantum dots. The new technology is expected to pave the way for many other types of devices and physical phenomena to be studied.

In their study, the research team demonstrated a novel way of synthesizing GQDs, embedded inside a hexagonal boron nitride (hBN) matrix. Thus, they demonstrated simultaneous use of in-plane and van der Waals heterostructures to build vertical single-electron tunneling transistors. Their findings have been published in Nature Communications.

Graphene quantum dots (GQDs) have received much research attention due to their unique fluorescence emission properties. Thus, they have emerged as an attractive tool for many applications, from cutting-edge displays to medical imaging. Besides that, they are applicable to materials for the next-generation quantum information communication technology, capable of processing information with low electricity use.

Until now, GQDs are prepared through a simple chemical exfoliation method, in which it exfoliates graphene sheets from bulk graphite; however, these methods are not successful at producing the desired size of GQDs. This not only invites impurities at the edge of GQDs, but also significantly impedes the flow of electrons, hindering the ability of GQDs to exhibit their unique optical and electrical properties.

Professor Shin and his research team succeeded in demonstrating a new way of removing the impurities at the edge of GQDs and adjusting the size of GQDs, as desired. The growth of in-plane GQD-hBN heterostructure was achieved on a silicon-dioxide substrate covered by an array of platinum (Pt) nanoparticles (NPs). Then, this was treated with heat in methane gas. As a result, the size of GQDs was decided according to the size of Pt particles, thereby generating highly-ordered GQDs inside the matrix of hexagonal boron nitride.

"Since graphene and h-BN are similar in structure, it was possible to grow GQDs inside the matrix of h-BN," says Gwangwoo Kim in the School of Energy and Chemical Engineering at UNIST, the first author of the study. "The growth of GQDs embedded in the hBN sheet are chemically bonded to BN, thus minimizing impurities." Using the technology, the team fabricated arrays of highly-ordered uniform GQDs and were able to adjust their sizes from 7 to 13 nm. They also succeeded in implementing vertical single-electron tunneling transistors that minimize impurities to stably move electrons.

This study was jointly conducted by professor Byeong-Hyeok Sohn from Seoul National University and professor Konstantin Novoselov from the University of Manchester in the UK. It was supported by IBS Center for Multidimensional Carbon Materials (CMCM) and the research grant from the Center for Advanced Soft Electronics under the Global Frontier Research Program through the National Research Foundation by the Korean Ministry of Science.

SOURCE: Ulsan National Institute of Science and Technology (UNIST); http://news.unist.ac.kr/novel-technology-for-highly-ordered-arrays-of-graphene-quantum-dot/

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