Until now, a variety of methods have been developed 13, 14, 15, 16 to fabricate a few layers or monolayer MoS 2, including mechanically exfoliation, liquid exfoliation, thermal decomposition and chemical vapour deposition (CVD). It has been expected as a candidate of flexible small quantum transistor materials 8, 9 in post-Moore era, due to its moderate direct band gap at few layers 10, 11, 12 comparing to semi-metallic graphene. Among many transition-metal dichalcogenides, one of the most promising representatives is molybdenum disulfide (MoS 2). In the past ten years, two dimensional (2D) transition-metal dichalcogenides (TMDs) materials have received considerable research interests in many fields for their wide range of potential applications, including optoelectronic devices 1, 2, 3, capacitors 4, hydrogen storage 5, catalysis 6, and solid lubricant 7, because of their unique electrical, chemical and mechanical properties.
This work provides one possibility of inducing the growth orientation of dendritic crystals through controlling the substrate surface symmetry artificially. In a word, the symmetry of SiC substrate determined the symmetry and the fractal dimension of the dendritic MoS 2. Its average fractal dimension 1.83 is slightly larger than the fractal dimension 1.76 of the previous MoS 2 dendrite with six-fold symmetry. And then we successfully synthesized cross-type dendritic crystal MoS 2 with two-fold symmetry.
To further demonstrating the substrate effect, we break the natural six-fold lattice symmetry of SiC (0001) into groove arrays through etching the substrate. The first principle calculation indicates that the six-fold symmetry of the dendritic MoS 2 is determined by the lattice symmetry of SiC. Interestingly, these MoS 2 dendritic crystals on SiC exhibit an average fractal dimension 1.76, which is slightly larger than the classical Diffusion-limited-Aggregation fractal dimension 1.66. The obtained MoS 2 dendritic crystals show six-fold symmetry, which are different from the conventional triangular shapes on SiO 2 substrate and from those with three-fold symmetry on SrTiO 3 substrate. Here, we synthesized MoS 2 by chemical vapour deposition on silicon carbide (SiC).
In van der Waals epitaxial growth, the substrate plays a particularly important role in the crystal morphology.
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