Irreparable Defects Produced by the Patching of <i>h</i>‑BN Frontiers on Strongly Interacting Re(0001) and Their Electronic Properties

Clarifying the origin and the electronic properties of defects in materials is crucial since the mechanical, electronic and magnetic properties can be tuned by defects. Herein, we find that, for the growth of <i>h</i>-BN monolayer on Re(0001), the patching frontiers of different domains can be classified into three types, i.e., the patching of B- and N-terminated (B|N-terminated) frontiers, B|B-terminated frontiers and N|N-terminated frontiers, which introduce three types of defects, i.e., the “heart” shaped moiré-level defect, the nonbonded and bonded line defects, respectively. These defects were found to bring significant modulations to the electronic properties of <i>h</i>-BN, by introducing band gap reductions and in-gap states, comparing with perfect <i>h</i>-BN on Re(0001) with a band gap of ∼3.7 eV. The intrinsic binary composition nature of <i>h</i>-BN and the strong <i>h</i>-BN-Re­(0001) interaction are proposed to be cooperatively responsible for the formation of these three types of defects. The former one provides different types of <i>h</i>-BN frontiers for domain patching. And the later one induces multinucleation but aligned growth of <i>h</i>-BN domains on Re(0001), thus precluding their subsequent coalescence to some extent. This work offers a deep insight into the categories of defects introduced from the patching growth of two-dimensional layered materials, as well as their electronic property modulation through the defect engineering

Grain Boundary Structures and Electronic Properties of Hexagonal Boron Nitride on Cu(111)

Grain boundaries (GBs) of hexagonal boron nitride (h-BN) grown on Cu(111) were investigated by scanning tunneling microscopy/spectroscopy (STM/STS). The first experimental evidence of the GBs composed of square-octagon pairs (4|8 GBs) was given, together with those containing pentagon-heptagon pairs (5|7 GBs). Two types of GBs were found to exhibit significantly different electronic properties, where the band gap of the 5|7 GB was dramatically decreased as compared with that of the 4|8 GB, consistent with our obtained result from density functional theory (DFT) calculations. Moreover, the present work may provide a possibility of tuning the inert electronic property of h-BN via grain boundary engineering

Strong Adlayer–Substrate Interactions “Break” the Patching Growth of <i>h</i>‑BN onto Graphene on Re(0001)

Hetero-epitaxial growth of hexagonal boron nitride (<i>h</i>-BN) from the edges of graphene domains or vice versa has been widely observed during synthesis of in-plane heterostructures of <i>h</i>-BN-G on Rh(111), Ir(111), and even Cu foil. We report that on a strongly coupled Re(0001) substrate <i>via</i> a similar two-step sequential growth strategy, <i>h</i>-BN preferably nucleated on the edges of Re(0001) steps rather than on the edges of existing graphene domains. Statistically, one-third of the domain boundaries of graphene and <i>h</i>-BN were patched seamlessly, and the others were characterized by obvious “defect lines” when the total coverage approached a full monolayer. This imperfect merging behavior can be explained by translational misalignment and lattice mismatch of the resulting separated component domains. According to density functional theory calculations, this coexisting patching and non-patching growth behavior was radically mediated by the strong adlayer–substrate (A–S) interactions, as well as the disparate formation energies of the attachment of B–N pairs or B–N lines along the edges of the Re(0001) steps <i>versus</i> the graphene domains. This work will be of fundamental significance for the controllable synthesis of in-plane heterostructures constructed from two-dimensional layered materials with consideration of A–S interactions

Quasi-Freestanding Monolayer Heterostructure of Graphene and Hexagonal Boron Nitride on Ir(111) with a Zigzag Boundary

In-plane heterostructure of hexagonal boron nitride and graphene (h-BN-G) has become a focus of graphene research owing to its tunable bandgap and intriguing properties. We report herein the synthesis of a quasi-freestanding h-BN-G monolayer heterostructure on a weakly coupled Ir(111) substrate, where graphene and h-BN possess distinctly different heights and surface corrugations. An atomically sharp zigzag type boundary has been found to dominate the patching interface between graphene and h-BN, as evidenced by high-resolution Scanning tunneling microscopy investigation as well as density functional theory calculation. Scanning tunneling spectroscopy studies indicate that the graphene and h-BN tend to exhibit their own intrinsic electronic features near the patching boundary. The present work offers a deep insight into the h-BN-graphene boundary structures both geometrically and electronically together with the effect of adlayer-substrate coupling

Modulating the Electronic Properties of Monolayer Graphene Using a Periodic Quasi-One-Dimensional Potential Generated by Hex-Reconstructed Au(001)

The structural and electronic properties of monolayer graphene synthesized on a periodically reconstructed substrate can be widely modulated by the generation of superstructure patterns, thereby producing interesting physical properties, such as magnetism and superconductivity. Herein, using a facile chemical vapor deposition method, we successfully synthesized high-quality monolayer graphene with a uniform thickness on Au foils. The hex-reconstruction of Au(001), which is characterized by striped patterns with a periodicity of 1.44 nm, promoted the formation of a quasi-one-dimensional (1D) graphene superlattice, which served as a periodic quasi-1D modulator for the graphene overlayer, as evidenced by scanning tunneling microscopy/spectroscopy. Intriguingly, two new Dirac points were generated for the quasi-1D graphene superlattice located at −1.73 ± 0.02 and 1.12 ± 0.12 eV. Briefly, this work demonstrates that the periodic modulation effect of reconstructed metal substrates can dramatically alter the electronic properties of graphene and provides insight into the modulation of these properties using 1D potentials