Identification of Exciton Complexes in Charge-Tunable Janus W Se S Monolayers

• Published in: ACS nano Vol. 17; no. 8; pp. 7326 - 7334
• Main Authors: Feuer, Matthew S G, Montblanch, Alejandro R-P, Sayyad, Mohammed Y, Purser, Carola M, Qin, Ying, Alexeev, Evgeny M, Cadore, Alisson R, Rosa, Barbara L T, Kerfoot, James, Mostaani, Elaheh, Kalȩba, Radosław, Kolari, Pranvera, Kopaczek, Jan, Watanabe, Kenji, Taniguchi, Takashi, Ferrari, Andrea C, Kara, Dhiren M, Tongay, Sefaattin, Atatüre, Mete
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society (ACS) 25.04.2023
• Subjects: Chemistry; Materials Science; Science & Technology - Other Topics; WSeS monolayers; Janus transition-metal dichalcogenides; excitons; layered materials; charge tunable; 2D materials
• ISSN: 1936-0851; 1936-086X
• DOI: 10.1021/acsnano.2c10697

Janus transition-metal dichalcogenide monolayers are artificial materials, where one plane of chalcogen atoms is replaced by chalcogen atoms of a different type. Theory predicts an in-built out-of-plane electric field, giving rise to long-lived, dipolar excitons, while preserving direct-bandgap optical transitions in a uniform potential landscape. Previous Janus studies had broad photoluminescence (>18 meV) spectra obfuscating their specific excitonic origin. Here, we identify the neutral and the negatively charged inter- and intravalley exciton transitions in Janus W monolayers with ∼6 meV optical line widths. We integrate Janus monolayers into vertical heterostructures, allowing doping control. Magneto-optic measurements indicate that monolayer W has a direct bandgap at the K points. Our results pave the way for applications such as nanoscale sensing, which relies on resolving excitonic energy shifts, and the development of Janus-based optoelectronic devices, which requires charge-state control and integration into vertical heterostructures.