Deterministic exfoliation of the uppermost layers of van der Waals crystals

• PVA lamination enables controlled exfoliation of the uppermost layers of vdW crystals. • The process is a safe, simple, convenient and reproducible method using low-cost commercially available PVA foils. • The method produces many, large and low-defect monolayers with good electronic performance. Selective exfoliation of the uppermost surface of a van der Waals (vdW) crystal is valuable for scientific and technological applications, particularly after functionalization or lithography. Conventional micromechanical exfoliation using adhesive tapes cannot deterministically isolate specific layers, instead producing a range of flakes with varying thicknesses. Here, we present a mechanical cleavage technique using polyvinyl alcohol (PVA) foil lamination, enabling controlled exfoliation of the uppermost layers of vdW crystals in a simple, reproducible manner. The exfoliated layers can be readily transferred from the foil to target substrates for further use. We demonstrate this method by isolating the top layers of graphite and MoS 2 , WS 2 , and WSe 2 monolayers, confirmed via optical imaging, photoluminescence (PL) and Raman spectroscopy, and atomic force microscopy (AFM). Additionally, selective exfoliation of fluorographene from SPT bulk crystals confirms the method’s precision. Compared to conventional tape-based exfoliation, this technique yields larger monolayers with fewer defects, surpassing Au-assisted exfoliation, which requires wet etching. MoS 2 monolayers produced via this method exceed 30 µm inside length, exhibiting n-doping, a field-effect mobility of 12.2 cm 2 V −1 s −1 , and an on/off ratio of ≈10 5 in air. Our results demonstrate that PVA-based cleavage offers a promising approach for selective exfoliation of process-accessible upper layers of bulk vdW materials for technological applications.