In-Place Exfoliation of 2D Materials*

Conventionally, adhesive tape is used to exfoliate layers from 2D materials like graphene or hexagonal boron nitride (hBN). Selected ideal flakes—ultra flat, with the desired thickness, and typically measuring tens of micrometers—are then transferred via a polymer film for stacking and device fabrication. The ratio of the desired ultrathin large flakes to thicker flakes is extremely low, so this conventional approach yields few usable flakes. Moreover, the polymer-assisted transfer often damages ultrathin flakes and leaves an undesirable residue, potentially compromising the reliability of measurements.

Here, we introduce a method for exfoliating a relatively thicker flake in-place. Instead of melting the polymer on the final substrate, a final exfoliation is performed at the precise location of interest. The result is an ultrathin flake positioned without polymer that requires removal. By applying this technique, we have successfully placed a suspended monolayer of hBN over a specifically designed hole (10 μm x 10 μm) in an SiO₂/Si substrate.