Dynamic secondary electron contrast effects in liquid systems studied by environmental scanning electron microscopy

Area of Science:

• Materials Science
• Surface Science
• Electron Microscopy

Background:

• Environmental scanning electron microscopy (ESEM) is crucial for imaging hydrated or volatile samples.
• Understanding charging artifacts is essential for accurate ESEM interpretation of emulsions.

Purpose of the Study:

• To investigate dynamic contrast phenomena in water-oil emulsions using ESEM.
• To elucidate the relationship between scan rate, charge accumulation, and secondary electron emission.

Main Methods:

• Imaging water-oil emulsions in an environmental scanning electron microscope (ESEM).
• Varying the electron beam scan rate to observe changes in secondary electron contrast.
• Correlating contrast variations with the electrical properties (conductivity) of emulsion phases.

Main Results:

• Secondary electron contrast between oil and water phases in emulsions is dependent on the scan rate.
• Contrast inversion occurs at high electron flux densities (slow scan rates) due to temporary charge accumulation.
• Oils, with lower conductivity than water, exhibit greater susceptibility to this charging effect.
• Charging is mitigated in oil regions where the electron interaction volume contacts the more conductive water phase.

Conclusions:

• Dynamic contrast in ESEM imaging of emulsions is influenced by charge carrier mobilities and scan speed.
• The observed phenomenon is a transient charging effect, not permanent specimen charging.
• Accurate interpretation of ESEM images of emulsions requires consideration of these dynamic contrast mechanisms.