Synthesis of Lateral Heterostructures of Semiconducting Atomic Layers

Abstract

Atomically thin heterostructures of transition-metal dichalcogenides (TMDs) with various geometrical and energy band alignments are the key materials for next generation flexible nano-electronics. The individual TMD monolayers can be adjoined laterally to construct in-plane heterostructures which are difficult to reach with the laborious pick up-and-transfer method of the exfoliated flakes. The ability to produce copious amounts of high quality layered heterostructures on diverse surfaces is highly desirable but it has remained a challenging issue. Here, we have achieved a direct synthesis of lateral heterostructures of monolayer TMDs: MoS 2 -WS 2 and MoSe 2 -WSe 2 . The synthesis was performed using ambient-pressure CVD with aromatic molecules as seeding promoters. We discuss possible growth behaviors, and we examine the symmetry and the interface of these heterostructures using second-harmonic generation and atomic-resolution scanning TEM. We found that the 1D interface of the lateral heterostructures picks the zigzag direction of the lattice instead of the armchair direction. Our method offers a controllable synthesis to obtain high-quality in-plane heterostructures of TMD atomic layers with one-dimensional interface geometry. MAIN TEXT:The heterostructure of materials with various geometrical and energy band alignments can exhibit electronic properties macroscopically different from their constituent materials 1-13 . They offer novel phenomena in semiconducting multiple quantum wells, such as interlayer Coulomb drag between charge carriers and phonons, exciton Bose condensation, emergent massive Dirac fermions and fractal quantum Hall, and diverse applications including the quantum cascade laser and the high-mobility 2D electron gas 1,7-10 . More recently, the ability to construct atomically thin heterostructures has allowed for the first realization of the Hofstadter butterfly in vertically-stacked graphene/h-BN heterostructures 7-9 and interlayer excitons in TMD heterojunctions [15][16][17][18] . These monolayer materials are the building blocks for constructing various heterostructures with atomically sharp interfaces in the absence of dangling bonds 3,19-28 . Moreover, the heterostructures can be functionalized by energy band alignments, and also by electrostatic gating to control the charge doping concentration 26,[29][30] . In particular, the diverse properties of individual TMDs monolayer (such as MoS 2 , MoSe 2 , WS 2 and WSe 2 ) provide promising candidates to further construction of various heterostructures for nano-science, and next generation optoelectronic and valleytronic devices 4,22, 31-37 .The band structures and diverse performances of these heterostructures are significantly determined by their crystalline phases and symmetry, and interface quality 38,39 . Second harmonic generation (SHG) was considered as a robust characterization tool on interfaces, symmetry, and twisting angles of the atomic layers in the heterostructures 39-47 . The analytic spherical aberration corrected scanning trans...

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