Two-Dimensional Covalent Crystals by Chemical Conversion of Thin van der Waals Materials

Sreepal, Vishnu; Yagmurcukardes, Mehmet; Vasu, Kalangi S.; Kelly, Daniel J.; Taylor, Sarah F. R.; Kravets, Vasyl G.; Kudrynskyi, Zakhar; Kovalyuk, Zakhar D.; Patanè, Amalia; Grigorenko, Alexander N.; Haigh, Sarah J.; Hardacre, Christopher; Eaves, Laurence; Sahin, Hasan; Geim, Andre K.; Peeters, Francois M.; Nair, Rahul R.

Abstract

Most of the studied two-dimensional (2D) materials have been obtained by exfoliation of van der Waals crystals. Recently, there has been growing interest in fabricating synthetic 2D crystals which have no layered bulk analogues. These efforts have been focused mainly on the surface growth of molecules in high vacuum. Here, we report an approach to making 2D crystals of covalent solids by chemical conversion of van der Waals layers. As an example, we used 2D indium selenide (InSe) obtained by exfoliation and converted it by direct fluorination into indium fluoride (InF3), which has a nonlayered, rhombohedral structure and therefore cannot possibly be obtained by exfoliation. The conversion of InSe into InF3 is found to be feasible for thicknesses down to three layers of InSe, and the obtained stable InF3 layers are doped with selenium. We study this new 2D material by optical, electron transport, and Raman measurements and show that it is a semiconductor with a direct bandgap of 2.2 eV, exhibiting high optical transparency across the visible and infrared spectral ranges. We also demonstrate the scalability of our approach by chemical conversion of large-area, thin InSe laminates obtained by liquid exfoliation, into InF3 films. The concept of chemical conversion of cleavable thin van der Waals crystals into covalently bonded noncleavable ones opens exciting prospects for synthesizing a wide variety of novel atomically thin covalent crystals.

Citation

Sreepal, V., Yagmurcukardes, M., Vasu, K. S., Kelly, D. J., Taylor, S. F. R., Kravets, V. G., …Nair, R. R. (2019). Two-Dimensional Covalent Crystals by Chemical Conversion of Thin van der Waals Materials. Nano Letters, 19(9), 6475-6481. https://doi.org/10.1021/acs.nanolett.9b02700

• Journal Article Type: Article
• Acceptance Date: Aug 20, 2019
• Online Publication Date: Aug 26, 2019
• Publication Date: Aug 20, 2019
• Deposit Date: Aug 27, 2019
• Publicly Available Date: Aug 21, 2020
• Journal: Nano Letters
• Print ISSN: 1530-6984
• Electronic ISSN: 1530-6992
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 19
• Issue: 9
• Pages: 6475-6481
• DOI: https://doi.org/10.1021/acs.nanolett.9b02700
• Keywords: Indium selenide; fluorination; indium fluoride; 2D covalent crystal; van der Waals materials
• Public URL: https://nottingham-repository.worktribe.com/output/2506733
• Publisher URL: https://pubs.acs.org/doi/10.1021/acs.nanolett.9b02700
• Additional Information: This document is the Accepted Manuscript of a Published Work that appeared in final form in ACS Nano Letters, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acs.nanolett.9b02700