Large area thin exfoliation of van der Waals magnetic and topological crystals and pickup using a Au-assisted method*

The exfoliation of large area, thin flakes from van der Waals (vdW) crystals remains a challenge for advancing their integration into functional devices. Conventional techniques, such as tape mechanical exfoliation, often yield small flakes with poor reproducibility, limiting their utility in systematic studies and heterostructure assembly. Exfoliation onto a gold wafer has resulted in a wider, thinner crystal. However, this type of exfoliation does not generally allow for subsequent pickups for vdW device fabrication due to the pseudo covalent bond between the crystals and the Au film which is stronger than the vdW forces within the crystal itself.  In my work, I demonstrate a gold assisted exfoliation method for producing large area, thin flakes of vdW crystals with magnetic or topological properties. Our motivation was twofold: first, to test whether Au assisted exfoliation could reproducibly generate large scale crystals; and second, to determine whether these flakes could be reliably picked up and integrated into devices. 

Leveraging the stronger vdW attraction to Au, we exfoliate crystals with an evaporated Au coating. Upon etching away the Au, we produced our large area, thick flakes. Using this method, we exfoliated PtTe₂, Fe3GeTe2, Cr₃Te₄, and graphene. Graphene proved most successful: we obtained monolayer flakes hundreds of microns long which were successfully picked up and integrated into samples. These graphene layers were caps for magnetic crystals measured with a Spin Polarized Low Energy Electron Microscope, demonstrating the viability of the Au assisted method for preparing 2D materials. For PtTe₂, Au assisted exfoliation yielded large area flakes with uniform surfaces and thicknesses of about 10 nm, confirmed by atomic force microscopy. Though not yet integrated into devices, the ability to readily produce thin, large area flakes represents a key step toward device fabrication. Overall, our use of Au assisted exfoliation demonstrates two major achievements: production and pickup of monolayer graphene flakes at large scales, and exfoliation of PtTe₂ of similar scale suitable for future integration. These results establish a method for fabricating high quality heterostructures and extending this to additional 2D crystals.