A tale of two transfers: characterizing polydimethylsiloxane viscoelastic stamping and heated poly bis-A carbonate transfer of hexagonal boron nitride

Two-dimensional (2D) materials have many applications ranging from heterostructure electronics to nanofluidics and quantum technology. In order to effectively utilize 2D materials towards these ends, they must be transferred and integrated into complex device geometries. In this report, we investigate two conventional methods for the transfer of 2D materials: viscoelastic stamping with polydimethylsiloxane (PDMS) and a heated transfer with poly bis-A carbonate (PC). We use both methods to transfer mechanically-exfoliated flakes of hexagonal boron nitride onto silicon nitride (SiN_x) substrates and characterize the resulting transfers using atomic force microscopy (AFM), aberration-corrected scanning transmission electron microscopy (AC-STEM) and electron energy loss spectroscopy (EELS). We find that both transfer methods yield flakes with significant and comparable residue (within the limitations of our study on eight samples). Qualitative interpretation of EELS maps demonstrates that this residue is comprised of silicon, carbon and oxygen for both transfer methods. Quantitative analysis of AC-STEM images reveals that the area covered in residue is on average, slightly lower for PDMS transfers (31 % ± 1 %), compared to PC transfers (41 % ± 4 %). This work underscores the importance of improving existing transfer protocols towards applications where cleaner materials are critical, as well as the need for robust methods to clean 2D materials.