Van der Waals crystals are a class of materials composed of stacked layers. Individual layers are single- or few-atoms thick and exhibit unique mechanical, electrical, and optical properties, and are thus expected to see widespread adoption in devices across a range of fields such as optical, electronic, sensing, and biomedical devices. Graphene and transition metal dichalcogenides offer desirable properties as few-layer or monolayer film. Accessing the monolayer form in a repeatable fashion, as part of a predictable and high-yield manufacturing process is critical to realizing the many potential applications of two-dimensional materials at scale. In order to fabricate devices made from few- or monolayer materials, layer(s) of material of specified size and shape, arranged in a pre-determined pattern, must be deposited on a desired substrate and conventional transfer methods include pressure-sensitive adhesives and other viscoelastic polymers and require applied pressure to adhere to their target which can cause out-of-plane deformations and problems with isolating and transferring the patterned few- or monolayer material. Deep etching has similar drawbacks.
UC Berkeley researchers have discovered methods and compositions that enable the transfer medium to adhere strictly to patterned regions, allowing the transfer to remove only patterned material and leave behind unpatterned bulk. This method involves the creation of an intermediate layer between the source material and the transfer medium. Because this layer must strictly cover patterned material, it serves as an etch mask for isolating few-layer material in the desired pattern. Any material which is microns-thick, patternable at the desired lateral pattern scale (likely micron-scale), and subsequently removable would make a suitable intermediate layer.