Controlling Structural Anisotropy of Anisotropic 2D Layers in Pseudo-1D/2D Material Heterojunctions

Chemical vapor deposition and growth dynamics of highly anisotropic 2D lateral heterojunctions between pseudo-1D ReS₂ and isotropic WS₂ monolayers are reported for the first time. Constituent ReS₂ and WS₂ layers have vastly different atomic structure, crystallizing in anisotropic 1T' and isotropic 2H phases, respectively. Through high-resolution scanning transmission electron microscopy, electron energy loss spectroscopy, and angle-resolved Raman spectroscopy, this study is able to provide the very first atomic look at intimate interfaces between these dissimilar 2D materials. Surprisingly, the results reveal that ReS₂ lateral heterojunctions to WS₂ produce well-oriented (highly anisotropic) Re-chains perpendicular to WS₂ edges. When vertically stacked, Re-chains orient themselves along the WS₂ zigzag direction, and consequently, Re-chains exhibit six-fold rotation, resulting in loss of macroscopic scale anisotropy. The degree of anisotropy of ReS₂ on WS₂ largely depends on the domain size, and decreases for increasing domain size due to randomization of Re-chains and formation of ReS₂ subdomains. Present work establishes the growth dynamics of atomic junctions between novel anisotropic/isotropic 2D materials, and overall results mark the very first demonstration of control over anisotropy direction, which is a significant leap forward for large-scale nanomanufacturing of anisotropic systems.