Liberating Wafer-scale Topological Insulator Ultrathin Films

Heterostructural thin films have become a promising platform to explore and manipulate the emergent phenomena of quantum materials. One of the biggest challenges in fabricating these heterostructures lies in creating wafer-scale thin films and transferring them onto another thin film or targeted substrate. Although the traditional mechanical exfoliation method that involves tapes and Polydimethylsiloxane (PDMS) works well on many chemical vapor deposition (CVD) grown 2D materials such as MoS₂ and WS₂, it is extremely challenging to exfoliate wafer-sized few-layer thin films grown using molecular beam epitaxy (MBE) with this method. While MBE films are known for their pristine sample quality, single-crystalline structure, and precise doping control, the film quality is highly dependent on the substrate, which imposes an additional constraint. Here, we propose a technique that allows us to liberate and transfer wafer-sized topological insulator thin films grown on oxide substrates using MBE down to 3nm to any targeted materials. We have shown using atomic force microscopy (AFM) and angular-resolved photoemission spectroscopy (ARPES) that this transfer technique allows the film to maintain its surface morphology and electronic properties. This technique allows us to benefit from MBE’s intricate control of electronic and structural properties while lifting the substrate constraint. This opens up many revenue opportunities such as the construction of superlattices, devices, twistronics, and the study of suspended films.