By pressing small stamps of polydimethylsiloxane (PDMS) into a bulk van der Waals (vdW) material powders (such as graphite, transition metal dichalcogenides (TMDC) etc), they ensure the full adhesion of micron-sized powder particles to the PDMS surface before using it as a writing pad. The PDMS pad is then oscillated back and forth against a number of substrates to deposit the materials through basal cleavage of micro-crystallites within the bulk material powder as it is rubbed against the layers already adhered to the substrate.
This results in the deposition of a thin abraded nanocrystalline film controlled by the rubbing time and the force applied to the writing pad. The researchers applied a tape mask to the substrate before writing, removing it after writing to leave only the unmasked region coated in the vdW material. Repeating this process, the scientists were able to build up bespoke heterostructures, without any material intermixing, under straight-forward ambient conditions.
In a separate fabrication route, the researchers first abraded graphite onto a polydimethylglutarimide (PMGI) polymer layer before spin coating it with polymethyl methacrylate (PMMA).
The sacrificial PMGI layer was then dissolved in a developer to leave the graphitic film attached to the underside of the PMMA layer, which could then be transferred directly onto the target heterostructure, without damaging the underlying substrate. They found that the resistance of thin abraded graphitic channels could be controlled via a gate voltage. Unlike previous inkjet printing techniques, no prior treatment of the substrate is required for strong adhesion of the vdW material.