Observation of contactless graphene transfer onto h-BN during encapsulation

The transfer of two-dimensional (2D) materials between substrates is a pivotal technique in contemporary research. Specifically, encapsulating graphene with hexagonal boron nitride (h-BN) flakes significantly enhances sample quality. Currently, the pick-up method has been reported, yet the underlying fundamental process remains obscure. To address this, we meticulously investigated the pick-up process using a polydimethylsiloxane (PDMS) cantilever coated with poly(methyl methacrylate) (PMMA) in direct contact with graphene. During the transfer of graphene onto h-BN, we observed contactless transfer occurring in a considerable portion of the graphene flake, preceding direct contact with h-BN. This phenomenon may be qualitatively explained by the interplay between the van der Waals forces acting between h-BN and graphene, graphene and the Si/SiO₂ substrate, and the intrinsic tension within the graphene. This observation may also shed light on the formation of bubbles during the transfer process.