Self-organized twist-heterostructures via aligned van der Waals epitaxy and solid-state transformations

Abstract

Vertical van der Waals (vdW) heterostructures of 2D crystals with defined interlayer twist are of interest for band-structure engineering via twist moiré superlattice potentials. To date, twist-heterostructures have been realized by micromechanical stacking. Direct synthesis is hindered by the tendency toward equilibrium stacking without interlayer twist. Here, we demonstrate that growing a 2D crystal with fixed azimuthal alignment to the substrate followed by transformation of this intermediate enables a potentially scalable synthesis of twisted heterostructures. Microscopy during growth of ultrathin orthorhombic SnS on trigonal SnS2 shows that vdW epitaxy yields azimuthal order even for non-isotypic 2D crystals. Excess sulfur drives a spontaneous transformation of the few-layer SnS to SnS2, whose orientation – rotated 30° against the underlying SnS2 crystal – is defined by the SnS intermediate rather than the substrate. Preferential nucleation of additional SnS on such twisted domains repeats the process, promising the realization of complex twisted stacks by bottom-up synthesis.

Hetero-site nucleation for growing twisted bilayer graphene with a wide range of twist angles

“…However, study and applications of the SiC-epitaxial tBLG are currently limited by the tedious transfer process and the relatively high price of SiC single crystal. In addition, the intermediate layer could also enable the formation of twist angle when growing the other two-dimensional (2D) materials 12 .…”

Van der Waals Nanowires with Continuously Variable Interlayer Twist and Twist Homojunctions

“…Micro‐mechanical stacking [ 9 ] has been the primary approach to preparing twisted van der Waals interfaces, [ 9b,10 ] although recent work has begun to explore avenues for bottom‐up synthesis of twisted bilayer graphene [ 11 ] and semiconducting chalcogenides, [ 12 ] albeit so far for larger twist angles. In sharp contrast with such conventional planar twisted van der Waals stacks, recent work showed that interlayer twist can be spontaneously generated in nanowires of layered crystals prepared by a scalable vapor–liquid–solid (VLS) growth process.…”

In Situ Characterization of Transformations in Nanoscale Layered Metal Chalcogenide Materials: A Review

“…Without the requirement of lattice matching during conventional epitaxial film growth, vdW heterostructures can feature unique and tunable properties. The interlayer crystallographic twist across the vdW interface also allows for tuning of interlayer coupling, electronic band structure, and conductivity [66] . Growth of ultra‐thin metal contacts epitaxially on MoS 2 crystals [67] can allow for improved and atomically sharp interfaces required to form transistors, while epitaxial growth of single‐crystalline MCs on 2D layered substrates can enhance lateral/surface diffusion and lower the required growth temperature, making them more amenable to conventional Si fabrication techniques [68–70] …”

“…Multiple in situ studies have explored the growth of vdW heterostructures. Sutter et al [66] . analyzed the epitaxial growth of amorphous SnS layers on bulk SnS 2 crystals using in situ low energy electron microscopy (LEEM).…”

“…[68][69][70] Multiple in situ studies have explored the growth of vdW heterostructures. Sutter et al [66] analyzed the epitaxial growth of amorphous SnS layers on bulk SnS 2 crystals using in situ low energy electron microscopy (LEEM). At 800°C, a spontaneous transformation of the overlayer SnS to twisted SnS 2 (twisted 30°w ith respect to the underlying SnS 2 ) was observed, which was driven by the presence of excess sulfur.…”