Nanoscale Cathodoluminescence and Conductive Mode Scanning Electron Microscopy of van der Waals Heterostructures

Hugh Ramsden; Soumya Sarkar; Yan Wang; Yiru Zhu; James Kerfoot; Evgeny M. Alexeev; Takashi Taniguchi; Kenji Watanabe; Sefaattin Tongay; Andrea C. Ferrari; Manish Chhowalla

doi:10.1021/acsnano.3c03261

Article Nanoscale Cathodoluminescence and Conductive Mode Scanning Electron Microscopy of van der Waals Heterostructures

Hugh Ramsden ; Soumya Sarkar ; Yan Wang ; Yiru Zhu ; James Kerfoot ; Evgeny M. Alexeev ; Takashi Taniguchi (National Institute for Materials Science) ; Kenji Watanabe (National Institute for Materials Science) ; Sefaattin Tongay ; Andrea C. Ferrari ; Manish Chhowalla

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Hugh Ramsden, Soumya Sarkar, Yan Wang, Yiru Zhu, James Kerfoot, Evgeny M. Alexeev, Takashi Taniguchi, Kenji Watanabe, Sefaattin Tongay, Andrea C. Ferrari, Manish Chhowalla. Nanoscale Cathodoluminescence and Conductive Mode Scanning Electron Microscopy of van der Waals Heterostructures. ACS Nano. 2023, 17 (12), 11882-11891. https://doi.org/10.1021/acsnano.3c03261

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Van der Waals heterostructures (vdW-HS) allow the integration of dissimilar materials to form complex devices. These devices commonly rely on the careful manipulation of charges in and across multiple materials and interfaces. However, at present, submicron variations in strain, doping or electrical breakages may exist undetected within a device, adversely affecting macroscale performance. Here we propose the use of conductive mode and cathodoluminescence scanning electron microscopy (CM-SEM and SEM-CL respectively) to investigate these phenomena. As a model system, we study a sample of monolayer WSe2 encapsulated in hexagonal boron nitride (hBN). CM-SEM allows for quantification of the flow of electrons out of a sample during SEM measurements. Through this, we reveal during electron irradiation that, at 5 keV, up to 70% of beam electrons are deposited into the vdW-HS and can subsequently transfer into the WSe2. We then demonstrate this accumulation of charge leads to dynamic doping of WSe2, reducing its CL efficiency by up to 30% over 30 s. Finally, we show by providing a path for excess electrons to leave the sample, near full restoration of the initial CL signal can be achieved. These results indicate trapping of charges in vdW-HS during electron irradiation must be considered to obtain and maintain optimal performance of vdW-HS devices during processes such as e-beam lithography or SEM. We also demonstrate CM-SEM and SEM-CL form a toolkit through which nanoscale characterisation of vdW-HS devices can be performed, allowing electrical and optical properties to be correlated.

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