Electron beam damage is a significant limitation for transmission electron
microscopy (TEM) studies of beam-sensitive samples. An approach for studying
surface reactions on alkali halide crystals using 200 kV TEM is presented.
Experiments were designed to monitor the reaction of NaCl crystals with
HNO3 gas followed by water vapor to form solid NaNO3.
During beam damage experiments, TEM micrographs record structural changes to
both NaCl and NaNO3, including dislocation loops, void formation,
and decomposition. Sample decomposition can be successfully minimized by a
combination of commonly used techniques: (1) focusing the beam
adjacent to the area of interest, (2) lowering the electron density,
(3) choosing to image larger (micrometer- versus submicrometer-sized)
alkali halide crystals, and (4) lowering temperature by the use of a
liquid nitrogen cooling stage. From these results, additional studies were
designed that monitored sequential experiments. Sensitive micrometer-sized
sodium chloride single crystals before and after exposure to nitric acid vapor
and water vapor and the subsequent growth of submicrometer-sized sodium
nitrate single crystals could then be successfully imaged using TEM.