Tunable strain and bandgap in subcritical-sized MoS2 nanobubbles

• Published in: NPJ 2D materials and applications 2023-10, Vol.7 (1), p.71-9, Article 71
• Main Authors: Gastaldo, Michele, Varillas, Javier, Rodríguez, Álvaro, Velický, Matěj, Frank, Otakar, Kalbáč, Martin
• Format: Article
• Language: English
• Subjects: 639/301/357/1018; 639/301/357/995; Aspect ratio; Bubbles; Chemistry and Materials Science; Electrons; Emitters; Energy gap; Excitons; Graphene; Materials Science; Microscopy; Molecular dynamics; Molybdenum disulfide; Nanotechnology; Scanning tunneling microscopy; Substrates; Surfaces and Interfaces; Thin Films; Topography; Two dimensional materials
• ISSN: 2397-7132; 2397-7132
• DOI: 10.1038/s41699-023-00432-x

Nanobubbles naturally formed at the interface between 2D materials and their substrate are known to act as exciton recombination centers because of the reduced bandgap due to local strain, which in turn scales with the aspect ratio of the bubbles. The common understanding suggests that the aspect ratio is a universal constant independent of the bubble size. Here, by combining scanning tunneling microscopy and molecular dynamics, we show that the universal aspect ratio breaks down in MoS 2 nanobubbles below a critical radius (≈10 nm), where the aspect ratio increases with increasing size. Accordingly, additional atomic-level analyses indicate that the strain increases from 3% to 6% in the sub-critical size range. Using scanning tunneling spectroscopy, we demonstrate that the bandgap decreases as a function of the size. Thus, tunable quantum emitters can be obtained in 2D semiconductors by controlling the radius of the nanobubbles.