Graphene nanoribbons (GNR) are quasi-one-dimensional graphene nanostructures, which can exhibit metalloid or semiconductor properties depending on the structure. This characteristic depends on the chirality of the GNR, including width, lattice orientation and edge structure. According to different edge structures, GNR can be divided into "sawtooth type" (ZZ) and "armchair type" (AC). GNR has high mobility and current carrying capacity, and due to quantum confinement and edge effects, it can open the band gap. This feature makes GNR a promising candidate for materials including nanoscale field effect transistors, spintronic devices, and on-chip interconnects. However, on the surface of an insulating substrate, it is still difficult to controllably prepare a sub-5 nanometer wide GNR with edge specificity.
Recently, the team of Wang Haomin, a researcher at the Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, prepared for the first time a chiral controllable GNR on the surface of hexagonal boron nitride (h-BN) and studied its transport properties. The related research results are titled Towards Chirality Control of Graphene Nanoribbons Embedded in Hexagonal Boron Nitride and published online in Nature Materials.
h-BN is a wide band gap two-dimensional material with excellent chemical and thermal stability. It has a hexagonal honeycomb network crystal structure and an atomic level flat surface. There are no surface dangling bonds and trapped charges, and it can maintain the intrinsic GNR Ideal substrate for electrical properties.
Previously, Wang Haomin`s team used silane for gas phase catalysis to achieve rapid growth of graphene domains on the surface of h-BN (Nat. Commun. 6, 6499 (2015)) and boundary control (Nanoscale, 9, 11475 (2017)) ; For the first time, through the use of h-BN trenches as a growth template, the controlled growth of oriented GNR was realized and the band gap was opened (Nat. Commun. 8, 14703 (2017)). The above research lays the experimental foundation for the preparation of sub-5nm wide chirality controllable GNR on h-BN substrate.
The researchers used different metal nanoparticles to etch trenches with straight edges and a specific orientation (ZZ and AC) with a thickness of a single atomic layer on the surface of h-BN. The trenches were prepared by chemical vapor deposition with a width less than 5nm high-quality orientation controllable GNR. The researchers collaborated with the research group of Professor Jannik Meyer of the University of Vienna and used scanning transmission electron microscopy to reveal the in-plane and epitaxial growth method at the boundary between graphene and h-BN, and the prepared GNR edge was atomically flat. Further electrical transport measurement results show that all ZGNRs with a width of sub-5 nanometers show band gaps greater than 0.4 eV, while the band gaps of narrow AGNRs vary greatly with width. Transistors made of GNR with a larger band gap have a switching ratio greater than 105 at room temperature, and a carrier mobility higher than 1500 cm2 V-1 s-1. In addition, a clear conductance peak is observed in the transfer curve of ZGNR with a width of 8-10 nm, but not in most AGNRs. The magnetic transport study of GNR shows that ZGNR has a smaller permeability, while AGNR has a higher permeability.