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Biological, dynamic processes and whole cells in liquid can be imaged in real-time in In Situ liquid TEM and STEM analysis. However, the highly mobile liquid can rapidly propagate both physical and chemical damages induced by the electron beam heating, direct momentum transfer, specimen charging, carbon contamination, and sputtering and knock-on. These damages cause imaging artifacts:
i) The growth of crystals on the liquid state windows,
ii) The repulsion of particles from the irradiated area,
iii) The bubble information,
iv) The degradation of atomic information during prolonged imaging of individual nanoparticles.
As listed in Table 2570, these artifacts can arise from different sources:
i) The experimental apparatus, for instance, from the silicon nitride (SiNx) windows,
ii) The indirect interactions between the specimen and aqueous chemical species induced by the electron beam, for instance, forming the production of reactive radicals in the gaseous water by radiolysis, and the associated crystal growth,
iii) The direct interaction between the electron beam and specimen.
Table 2570. Summary of the effects of common problems and artifacts on liquid TEM and STEM experiments, their root causes, and solutions to mitigate their effects. [1]
| Artifact |
Root cause |
Ways to mitigate |
Liquid stage windows and tip |
| Large liquid path length, degraded the spatial resolutions of imaging and EELS |
Window bulging |
Adjust window geometry, add membrane supports |
| Evaporation of the liquid layer, vacuum degradation in microscope |
Incomplete vacuum sealing |
Avoid large particulate matter, low vapor pressure liquid, use designated liquid holders |
| Liquid void between windows |
Dewetting of liquid film |
Plasma and glow discharge treatment of windows, excess liquid in well surrounding chips |
| |
Specimen preparation |
Material deposition in beam-irradiated area causes contrast degradation
|
Carbon contamination on vacuum and/or
liquid side |
Plasma and glow discharge treatment of windows, avoid carbon species from specimen, careful specimen handling |
| |
Beam–specimen interactions |
Rapid growth of nanocrystals on SiNx windows inside and/or outside of irradiated area
|
Reduction of reactive ions by radicals in solution |
Image below electron dose threshold, avoid reactive species from solution |
| Repulsion of freely-diffusing nanoparticles from beam-irradiated area |
Charging of window and particles by electron beam
|
Low dose imaging, deposit a thin conductive film on the window, add electolyte to reduce the charging |
Loss of atomic information over time at high magnifications and electron doses
|
Contamination, atomic rearrangement |
Low dose imaging techniques, avoid carbon and
crystal contamination precursors from solution |
Fortunately, many of the artifacts become negligible below a critical electron dose, mainly due to the decreased inelastic scattering in the liquid layer.
[1] Taylor J. Woehl, Katherine L. Jungjohann, James E. Evans, Ilke Arslan, William D. Ristenpart, Nigel D. Browning, Experimental procedures to mitigate electron beam induced artifacts during in situ fluid imaging of nanomaterials, Ultramicroscopy 127(2013)53–63.
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