  High quality thin films of topological insulators (TI) such as Bi2Se3 have
been successfully synthesized by molecular beam epitaxy (MBE). Although the
surface of MBE films can be protected by capping with inert materials such as
amorphous Se, restoring an atomically clean pristine surface after decapping
has never been demonstrated, which prevents in-depth investigations of the
intrinsic properties of TI thin films with ex-situ tools. Using high resolution
scanning tunneling microscopy/spectroscopy (STM/STS), we demonstrate a simple
and highly reproducible Se decapping method that allows recovery of the
pristine surface of extremely high quality Bi2Se3 thin films grown and capped
with Se in a separate MBE system then exposed to atmosphere during transfer
into the STM system. The crucial step of our decapping process is the removal
of the surface contaminants on top of amorphous Se before thermal desorption of
Se at a mild temperature (~210 {\deg}C). This effective Se decapping process
opens up the possibility of ex-situ characterizations of pristine surfaces of
interesting selenide materials and beyond using cutting-edge techniques.
