  Mechanical exfoliation of bulk crystals has been widely used to obtain thin
topological insulator (TI) flakes for device fabrication. However, such a
process produces only micro-sized flakes that are highly irregular in shape and
thickness. In this work, we developed a process to transfer the entire area of
TI Bi2Se3 thin films grown epitaxially on Al2O3 and SiO2 to arbitrary
substrates, maintaining their pristine morphology and crystallinity. Transport
measurements show that these transferred films have lower carrier
concentrations and comparable or higher mobilities than before the transfer.
Furthermore, using this process we demonstrated a clear metal-insulator
transition in an ultrathin Bi2Se3 film by gate-tuning its Fermi level into the
hybridization gap formed at the Dirac point. The ability to transfer large area
TI films to any substrate will facilitate fabrication of TI heterostructure
devices, which will help explore exotic phenomena such as Majorana fermions and
topological magnetoelectricity.
