Batch-fabricated PDMS templates for the robotic transfer of 2D materials

Robotic stacking of van der Waals heterostructures has been at the verge, thanks to the convergence between artificial intelligence (AI) and two-dimensional (2D) materials research. Key ingredients to fulfill this pursuit often include algorithms to identify layer compounds on chips, hardwares to realize sophisticated operations of motion and/or rotation in a microscale, and, as importantly, highly standardized and uniform transfer stamps that are often used in picking up layered materials under a microscope. Here, we report a hot-cast-droplet batch fabrication method for polydimethylsiloxane (PDMS) templates tailored for dry transfer of 2D materials. Controlled precursor formulation, degassing, and motorized-syringe dispensing produce dome-shaped PDMS templates with ultra-smooth surfaces (root mean square roughness ∼0.3 nm at relatively low curing temperatures). By tuning the curing temperature, the reproducible and controllable apex curvature allows precisely defined contact area between the organic adhesive film and the substrate, via thermal expansion. Our results further reveal thermomechanical behaviors with different casting parameters of such PDMS domes. The capability of achieving defect-free van der Waals interfaces is further demonstrated by the fabrication of a high-quality BN/graphene/BN stack via dry transfer using the as-prepared PDMS templates. This scalable and parameterized fabrication protocol gives rise to uniform transfer stamps with ultra-smooth surface, which may be beneficial for future AI-driven robotic assembly of 2D material heterostructures.