A Generalized Strategy for Synthesizing 2-D Core–Crown Heterostructures

The Science

Heterostructures, which combine multiple materials in one larger system, present opportunities for increased tunability. Synthesizing these complex materials involves challenges related to differences in the growth conditions and crystal structure of the individual materials. Researchers used a solution-based synthesis method to produce 2-D heterostructures of tin sulfide (SnS₂) and tin selenide (SnSe₂). The two-step synthesis pathway enables atomically precise matching of components at the interface and control over the size of both the core and crown in the final structure. The growth pathway is thermodynamically deterministic, indicating that the synthesis is highly reproducible and scalable and likely generalizable to other 2-D heterostructures.

The Impact

2-D heterostructures are promising materials for high-performance nanodevices due to their tunability and potential for precise electronic control. Developing scalable synthesis of heterostructures with the proper interfacial connections has proven challenging. The newly developed method leverages a structure-directing agent to modify the crystal structure of the seed edges. It also redirects growth of the second phase from the formation of isolated particles to epitaxial growth at the seed edges. The modified synthesis is expected to be extendable to other layered materials, enabling the fabrication of a range of 2-D heterostructures for optoelectronic and electronic devices.

Summary

Heterostructures based on atomically thin 2-D layers show promise for use in nanodevices that rely on controllable electronic properties. Current synthesis paradigms face challenges in reproducibility and scalability. Researchers developed a solution-based synthetic approach for creating core–crown heterostructures, using SnS₂ and SnSe₂ as an initial proof-of-concept system. With polyvinylpyrrolidone used as a structure-directing agent to reduce lattice mismatch between the two materials, the heterostructures exhibited well-connected epitaxial growth. The structure-controlling agent operated by lowering the interfacial energy of SnSe₂ on SnS₂, encouraging that specific growth route while inhibiting the formation of SnS₂ on SnSe₂. The overall growth path, examined through in situ electron microscopy and simulations, is the thermodynamically favored approach. The synthesis thus gives a single product with high reproducibility from experiment to experiment. Future work will take the general procedure and generalize it beyond tin-based chalcogenides, moving toward the synthesis of heterostructures of other layered materials.

Contact

Maria Sushko 
Pacific Northwest National Laboratory
maria.sushko@pnnl.gov

Funding

This research was performed at Pacific Northwest National Laboratory (PNNL) with support from the Department of Energy (DOE), Office of Science (SC), Basic Energy Sciences program, Division of Materials Sciences and Engineering, Synthesis and Processing Science Program, FWP12152. The authors thank Anthony Romero at the University of Washington for capturing EDS images after the cycling experiments and thank Xiaoxu Li from the Geochemistry Group at PNNL for valuable discussions. X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy characterizations were performed under user proposal 61041 at the Environmental Molecular Sciences Laboratory, a DOE, SC, Biological and Environmental Research program user facility located at PNNL. Simulations were performed using the resources of the National Energy Research Scientific Computing Center, a DOE Office of Science user facility supported by DOE SC under contract no. DE-AC02-05CH11231 through National Energy Research Scientific Computing Center award BES-ERCAP0028725. PNNL is operated by Battelle for the DOE under contract no. DE-AC05-76RLO1830.