Micropatterned PDMS stamps for spatially selective dry transfer of exfoliated flakes

PDMS+polymer transfer slides are one of the primary tools for making van der Waals heterostructures from exfoliated flakes using a dry transfer process. However, such transfer slides are typically made from either flat stamps or round droplets of PDMS, whose macroscopic size makes it difficult to selectively pick up flakes in a crowded environment. A ready solution can be drawn from the field of microfluidics, where micropatterned SU-8 or silicon are used as molds to form fine details on the surface of PDMS stamps for techniques such as microcontact printing. We will discuss the efficacy of using such PDMS micropatterning to construct ten-micron scale features to improve the spatial selectivity of the dry transfer process.