In situ engineering hexagonal boron nitride in van der Waals heterostructures with selective SF<sub>6</sub> etching

Hitesh Agarwal; Antoine Reserbat-Plantey; David Barcons Ruiz; Karuppasamy Pandian Soundarapandian; Geng Li; Vahagn Mkhitaryan; Johann Osmond; Helena Lozano; Kenji Watanabe; Takashi Taniguchi; Petr Stepanov; Frank H L Koppens; Roshan Krishna Kumar

doi:10.1088/2515-7639/adfd15

Article In situ engineering hexagonal boron nitride in van der Waals heterostructures with selective SF₆ etching

Hitesh Agarwal ; Antoine Reserbat-Plantey ; David Barcons Ruiz ; Karuppasamy Pandian Soundarapandian ; Geng Li ; Vahagn Mkhitaryan ; Johann Osmond ; Helena Lozano ; Kenji Watanabe (National Institute for Materials Science) ; Takashi Taniguchi (National Institute for Materials Science) ; Petr Stepanov ; Frank H L Koppens ; Roshan Krishna Kumar

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Hitesh Agarwal, Antoine Reserbat-Plantey, David Barcons Ruiz, Karuppasamy Pandian Soundarapandian, Geng Li, Vahagn Mkhitaryan, Johann Osmond, Helena Lozano, Kenji Watanabe, Takashi Taniguchi, Petr Stepanov, Frank H L Koppens, Roshan Krishna Kumar. In situ engineering hexagonal boron nitride in van der Waals heterostructures with selective SF₆ etching. Journal of Physics: Materials. 2025, 8 (4), 045006. https://doi.org/10.1088/2515-7639/adfd15

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Van der Waals heterostructures are at the forefront in materials heterostructure engineering, offering the ultimate control in layer selectivity and capability to combine virtually any material. Hexagonal-boron nitride, the most commonly used dielectric material, has proven indispensable in this field, allowing on to encapsulate active 2D materials preserving their exceptional electronic quality. However, not all device applications require full encapsulation but rather require open surfaces, or even selective patterning of hBN layers. Here, we report on a procedure to engineer top hBN layers within Van der Waals heterostructures while preserving the underlying active 2D layers. Using a soft selective SF3 etching combined with a series of pre and post-etching treatments, we demonstrate that pristine surfaces can be opened with atomic flatness while preserving the active layers electronic quality. We benchmark our technique using graphene encapsulated with hBN Hall bar devices. Using Raman spectroscopy combined with quantum transport, we show high quality can be preserved in etched regions by demonstrating low temperature carrier mobilities > 200,000 cm2/Vs, ballistic transport probed through magnetic focusing, and intrinsic room temperature phonon-limited mobilities. Atomic force microscopy brooming and O2 plasma cleaning are identified as key pre-etching steps to obtaining pristine open surfaces that preserve electronic quality, while high temperature annealing may be employed to reduce slight fluorination that may occur by accidental over-etching. The technique provides a clean method for opening windows into mesoscopic Van der Waals devices that can be used for local probe experiments, patterning top hBN in-situ, and exposing 2D layers to their environment for sensing applications.

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