Role of Bilayer Graphene Microstructure on the Nucleation of WSe₂ Overlayers

Abstract

Over the past few years, graphene grown by chemical vapor deposition (CVD) has gained prominence as a template to grow transition metal dichalcogenide (TMD) overlayers. The resulting two-dimensional (2D) TMD/graphene vertical heterostructures are attractive for optoelectronic and energy applications. However, the effects of the microstructural heterogeneities of graphene grown by CVD on the growth of the TMD overlayers are relatively unknown. Here, we present a detailed investigation of how the stacking order and twist angle of CVD graphene influence the nucleation of WSe2 triangular crystals. Through the combination of experiments and theory, we correlate the presence of interlayer dislocations in bilayer graphene with how WSe2 nucleates, in agreement with the observation of a higher nucleation density of WSe2 on top of Bernal-stacked bilayer graphene versus twisted bilayer graphene. Scanning/transmission electron microscopy (S/TEM) data show that interlayer dislocations are present only in Bernal-stacked bilayer graphene but not in twisted bilayer graphene. Atomistic ReaxFF reactive force field molecular dynamics simulations reveal that strain relaxation promotes the formation of these interlayer dislocations with localized buckling in Bernal-stacked bilayer graphene, whereas the strain becomes distributed in twisted bilayer graphene. Furthermore, these localized buckles in graphene are predicted to serve as thermodynamically favorable sites for binding WSe x molecules, leading to the higher nucleation density of WSe2 on Bernal-stacked graphene. Overall, this study explores synthesis–structure correlations in the WSe2/graphene vertical heterostructure system toward the site-selective synthesis of TMDs by controlling the structural attributes of the graphene substrate.

Self-Rolled-Up WSe2 One-Dimensional/Two-Dimensional Homojunctions: Enabling High-Performance Self-Powered Polarization-Sensitive Photodetectors

“…The mixed-dimensional structure, combining two-dimensional (2D) materials with other low-dimensional counterparts, displays unique physical properties, such as quantum effects and enhanced interfaces. − This design demonstrates great promise in self-powered devices, high-efficiency electronics, and optoelectronics, attracting a considerable amount of interest because of its potential in advancing novel materials and devices. − In particular, extensive research and application exploration have been conducted on mixed-dimensional heterostructures based on 2D transition metal dichalcogenides (TMDs) in the field of self-powered photovoltaics and optoelectronic detectors. This is because of the excellent properties of TMD materials, including broad-spectrum absorption, strong light–matter interactions, , tunable bandgaps, , and the ease of hybrid assembly with other materials. − Recently, a mixed-dimensional structure based on TMDs has been trending in multiple research areas, for instance, a zero-dimensional (0D) CsPbBr 3 quantum dots/2D MoS 2 mixed-dimensional heterojunction as a photoelectric visual adaptation transistor, 0D perovskite quantum dot/2D Ta 2 NiSe 5 mixed-dimensional van der Waals (vdW) heterojunctions for near-infrared (NIR) photodetection, one-dimensional (1D) GaAsSb/2D MoS 2 mixed-dimensional heterojunctions as anti-ambipolar phototransistors, 1D carbon nanotube/2D MoS 2 heterostructures as reconfigurable tunneling transistors, and 1D Ta 2 Pd 3 Se 8 /2D MoS 2 mixed-dimensional heterojunctions as ultrafast polarization-sensitive photodetectors …”