Synthesis‐Related Nanoscale Defects in Mo‐Based Janus Monolayers Revealed by Cross‐Correlated AFM and TERS Imaging
2D Janus transition metal dichalcogenides (TMDs) are promising candidates for various applications including non-linear optics, energy harvesting, and catalysis. These materials are usually synthesized via chemical conversion of pristine TMDs. Nanometer-scale characterization of the obtained Janus materials' morphology and local composition is crucial for both the synthesis optimization and the future device applications. In this work, we present the results of cross-correlated atomic force microscopy (AFM) and tip-enhanced Raman spectroscopy (TERS) study of Janus monolayers synthesized by the hydrogen plasma-assisted chemical conversion of MoSe<sub>2</sub> and MoS<sub>2</sub>. We demonstrate that the choice of both the growth substrate and the starting TMD influences the residual strain, thereby shaping the nanoscale morphology of the resulting Janus material. Furthermore, by employing TERS imaging, we show the presence of nanoscale islands (≈20 nm across) of MoSe<sub>2</sub>- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>Mo</mml:mi> <mml:mi>Se</mml:mi> <mml:mi>S</mml:mi></mml:msubsup> <mml:annotation>${\mathrm{Mo}}_{{\mathrm{Se}}}^{\mathrm{S}}$</mml:annotation></mml:semantics> </mml:math> (MoS<sub>2</sub>- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics><mml:msubsup><mml:mi>Mo</mml:mi> <mml:mi>S</mml:mi> <mml:mi>Se</mml:mi></mml:msubsup> <mml:annotation>${\mathrm{Mo}}_{\mathrm{S}}^{{\mathrm{Se}}}$</mml:annotation></mml:semantics> </mml:math> ) vertical heterostructures originating from the bilayer nanoislands in the precursor monolayer crystals. The understanding of the origins of nanoscale defects in Janus TMDs revealed in this study can help with further optimization of the Janus conversion process towards uniform and wrinkle-/crack-free Janus materials. Moreover, this work shows that cross-correlated AFM and TERS imaging is a powerful and accessible method for studying nanoscale composition and defects in Janus TMD monolayers.
Authors
- Tilo H. Yang (ORCID: https://orcid.org/0000-0002-7048-9513)
- Andrey Krayev (ORCID: https://orcid.org/0000-0001-7590-4002)
- M. A. Pimenta (ORCID: https://orcid.org/0000-0002-3389-0682)
- Yu‐Lun Chueh (ORCID: https://orcid.org/0000-0002-0155-9987)
- Lauren Hoang (ORCID: https://orcid.org/0009-0001-7556-8560)
- Ariete Righi (ORCID: https://orcid.org/0000-0001-8752-9609)
- Yu‐Ren Peng
- Zhien Wang (ORCID: https://orcid.org/0000-0002-6120-1952)
- Mitsuo Kira (ORCID: https://orcid.org/0000-0002-5146-2024)
- Eleonora Isotta (ORCID: https://orcid.org/0000-0002-5864-463X)
- Eric Pop (ORCID: https://orcid.org/0000-0003-0436-8534)
- Andrew J. Mannix (ORCID: https://orcid.org/0000-0003-4788-1506)
- Nannan Mao (ORCID: https://orcid.org/0000-0003-3522-5341)
- Jing Kong (ORCID: https://orcid.org/0000-0003-0551-1208)
- Yaguang Zhu (ORCID: https://orcid.org/0000-0002-1522-4491)
- Hongwei Liu (ORCID: https://orcid.org/0000-0001-7566-5224)
- Tianyi Zhang (ORCID: https://orcid.org/0000-0002-8998-3837)
- Xudong Zheng (ORCID: https://orcid.org/0009-0009-3783-7617)
Institutions
- Universidade Federal de Minas Gerais (BR)
- Northwestern University (US)
- National Tsing Hua University (TW)
- NOVA Scientific (United States) (US)
- Université Bourgogne Franche-Comté (FR)
- Massachusetts Institute of Technology (US)
- Stanford University (US)
Publication Details
- Journal
- Small
- Published
- 2025-08-08
- DOI
- https://doi.org/10.1002/smll.202504742
- Citations
- 3
- Primary Topic
- Machine Learning in Materials Science
- Type
- article
- Field-Weighted Citation Impact
- 1.55
Funders
- U.S. Department of Energy
- University of Pennsylvania
- Conselho Nacional de Desenvolvimento Científico e Tecnológico
- Office of Science
- Basic Energy Sciences
- Air Force Office of Scientific Research