DOE OSTI · 2865162
Synthesis‐Related Nanoscale Defects in Mo‐Based Janus Monolayers Revealed by Cross‐Correlated AFM and TERS Imaging
Abstract
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 2 and MoS 2 . 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 2 - ${\mathrm{Mo}}_{{\mathrm{Se}}}^{\mathrm{S}}$ (MoS 2 -${\mathrm{Mo}}_{\mathrm{S}}^{{\mathrm{Se}}}$) 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.
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Zhang, Tianyi [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)] (ORCID:0000000289983837), Krayev, Andrey [HORIBA Scientific, Novato, CA (United States)], Yang, Tilo H. [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)], Mao, Nannan [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)], Hoang, Lauren [Stanford Univ., CA (United States)], Wang, Zhien [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)], Liu, Hongwei [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)], Peng, Yu‐Ren [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States); National Tsing Hua Univ., Hsinchu (Taiwan)], Zhu, Yunyue [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)], Zheng, Xudong [Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)], Isotta, Eleonora [Department of Materials Science and Engineering Northwestern University 2220 Campus Drive Evanston IL 60208 USA], Kira, Maria E. [Departamento de Física Universidade Federal de Minas Gerais Av. Antônio Carlos, 6627, Pampulha Belo Horizonte Minas Gerais 31270‐901 Brazil], Righi, Ariete [Departamento de Física Universidade Federal de Minas Gerais Av. Antônio Carlos, 6627, Pampulha Belo Horizonte Minas Gerais 31270‐901 Brazil], Pimenta, Marcos A. [Departamento de Física Universidade Federal de Minas Gerais Av. Antônio Carlos, 6627, Pampulha Belo Horizonte Minas Gerais 31270‐901 Brazil], Chueh, Yu‐Lun [Department of Materials Science and Engineering National Tsing Hua University Hsinchu 30013 Taiwan], Pop, Eric [Department of Electrical Engineering Stanford University Stanford CA 94305 USA; Department of Materials Science & Engineering Stanford University Stanford CA 94305 USA], Mannix, Andrew J. [Department of Materials Science & Engineering Stanford University Stanford CA 94305 USA], Kong, Jing [Department of Electrical Engineering and Computer Science Massachusetts Institute of Technology Cambridge MA 02139 USA] (ORCID:0000000305511208). 2025-08-08. Synthesis‐Related Nanoscale Defects in Mo‐Based Janus Monolayers Revealed by Cross‐Correlated AFM and TERS Imaging. https://doi.org/10.1002/smll.202504742
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