(164j) Solution Synthesis of Regular-Shaped Sns/SnS2 van Der Waals Heterostructures

2D structured metal chalcogenides have shown extraordinary electronic properties due to their layer structure which contributes to high charge carrier mobility, superconductivity and topologically insulating behavior. Also, recently Van der Waals heterostructures (vdWHs) have been vigorously investigated and shown drastic property changes compared to their parent bulks as single layer thickness drops down to a few nanometers or even below 1 nanometer. In vdWHs, covalently bonding in-plane and weak Van der Waals interaction out-of-plane result in anisotropic electron transport behavior, like long-lived interlayer excitons and ultrahigh in-plane mobility, for devices of this structure. Detectors, LEDs, etc. have been reported based on vdWHs. In addition to application of vdWHs in electronics, they also have potential application in photocatalysis. A number of photocatalysts have been developed to help converting water into hydrogen while some problems still remain unsolved, some of which are limited absorption of a small portion of solar energy, quick recombination of separated electrons and holes etc. vdWHs demonstrate efficient charge separation and a large surface area. Inspired of this, we come up with a new strategy which employs both concepts of vdWHs structure and photocatalyst for SnS/SnS₂ photocatalyst for water splitting. Due to the match of SnS band gap with the relatively low energy needed for hydrogen and oxygen evolution, effective portion of solar energy in water splitting will increase. The vdW heterostructure will keep electron-hole separation more stable, thus evolution efficiency higher. Despite all the very interesting properties and so many potential applications of vdWHs, it is indeed difficult to fabricate them. The traditional fabrication usually needs expensive equipment and delicate operations, like microscope, micromanipulator, to mechanically align each layer over another. The throughput is also extremely low.

In this work, SnS and SnS₂ are synthesized utilizing heat decomposition method with single-source precursors. Such method allows us to gain extraordinarily large regular-shaped 2D flakes of both SnS and SnS₂ dispersed in solution compared with the exfoliated 2D layers or otherwise synthesized flakes, which further allows us to assemble them into vdW heterostructures in solutions. TEM and SEM have been used to confirm the morphology of SnS, SnS₂ and the vdW heterostructure. SnS shows regular rectangular shape of a few micrometers while SnS₂ exhibits hexagonal shape of hundreds of nanometers, both of which have a thickness of tens of nanometers. Layer-by-layer structures are also observed.