Cryogenic Focused Ion Beam Enables Atomic-Resolution Imaging of Local Structures in Highly Sensitive Bulk Crystals and Devices

With the development
of ultralow-dose (scanning) transmission electron
microscopy ((S)­TEM) techniques, atomic-resolution imaging of highly
sensitive nanomaterials has recently become possible. However, applying
these techniques to the study of sensitive bulk materials remains
challenging due to the lack of suitable specimen preparation methods.
We report that cryogenic focused ion beam (cryo-FIB) can provide a
solution to this challenge. We successfully extracted thin specimens
from metal–organic framework (MOF) crystals and a hybrid halide
perovskite single-crystal film solar cell using cryo-FIB without
damaging the inherent structures. The high quality of the specimens
enabled the subsequent (S)­TEM and electron diffraction studies to
reveal complex unknown local structures at an atomic resolution. The
obtained structural information allowed us to resolve planar defects
in MOF HKUST-1, three-dimensionally reconstruct a concomitant phase
in MOF UiO-66, and discover a new CH3NH3PbI3 structure and locate its distribution in a single-crystal
film perovskite solar cell. This proof-of-concept study demonstrates
that cryo-FIB has a unique ability to handle highly sensitive materials,
which can substantially expand the range of applications for electron
microscopy.