Development of an "In-Place" Exfoliation Technique

Standard techniques for exfoliating 2D materials from bulk precursors using adhesive tape provides low yield of ultrathin flakes, while the polymer-film-based flake transfer methods introduce risks of damage from solvents or leaves an undesirable residue. Here, we describe the development of an "in-place" exfoliation technique. Starting from a thick precursor flake (which is more readily available than ultrathin flakes) picked up by the standard transfer method, a final exfoliation is performed directly at the location of interest. The result is an ultrathin flake positioned without polymer residue on it. We have, for instance, successfully placed a monolayer of hBN over a specifically designed hole in an SiO₂/Si substrate to yield a clean suspended membrane. To refine the technique toward a more systematic and repeatable method, we define a standard process and observe the conditions (surface properties, temperature, etc) that will affect the result via controlled trials and device characterizations.