A new study led by the Ulsan National Institute of Science and Technology in South Korea reveals a technology capable of fabricating highly ordered arrays of graphene quantum dots.
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.
Until now, GQDs have been prepared through a simple chemical exfoliation method, which exfoliates graphene sheets from bulk graphite; however, these methods are often 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.
The 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.