Automated searching and assembly of atomic layers: a robotic building system of van der Waals superlattices

Ever since the advent of mechanical exfoliation of atomically thin two-dimensional (2D) crystals and van der Waals (vdW) heterostructures, random nature in the shape, thickness, and positions of exfoliated 2D crystals have insisted researchers for repetitive manual tasks of optical microscopy-based searching and subsequent mechanical transfer. In this work, we developed a robotic system that automatically searches exfoliated 2D crystals and assembles them into vdW superlattices. The system was built in an enclosure with inert gas, and fully remotely operated by a computer software. Its enduring capacity was shown to be the analyzing of 12,000 optical microscope images per hour, detecting of 400 monolayer graphene flakes per hour with a small error rate (< 7%), and stacking of four cycles of the designated 2D crystals per hour. The system enabled fabrication of the vdW superlattice structures consisting of 29 alternating layers of the graphene and the hexagonal boron nitride (hBN) flakes. The system's enduring capacity provides a scalable approach for prototyping a variety of vdW superlattices.