Treating Knock-On Displacements in Fluctuation Electron Microscopy Experiments.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Electron Microscopy

Background:

• Fluctuation electron microscopy (FEM) is sensitive to sample structure.
• Beam-induced atomic displacements can alter experimental results.
• Amorphous silicon is a model system for studying radiation effects.

Purpose of the Study:

• Investigate the influence of knock-on displacements on FEM experiments.
• Determine optimal experimental parameters to mitigate these effects.
• Evaluate the impact of different cameras and energy filtering.

Main Methods:

• Conducted FEM experiments on amorphous silicon using a transmission electron microscope.
• Varied acceleration voltage (300 kV vs. 60 kV), electron dose, binning, and camera type (CCD vs. CMOS).
• Utilized energy filtering to assess its effect on data quality.

Main Results:

• Energy filtering significantly improved speckle contrast by removing inelastic background.
• CMOS cameras showed slightly higher normalized variance but were more susceptible to noise at low counts.
• Beam-induced displacements suppressed normalized variance at 300 kV with increasing dose.
• Displacements were reduced at 60 kV due to energy transfer below the displacement threshold.

Conclusions:

• Knock-on displacements negatively impact FEM data quality at higher voltages.
• Minimizing electron dose and using lower acceleration voltages (60 kV) are effective strategies to control variance suppression.
• Experimental parameters must be carefully chosen to avoid beam-induced artifacts in FEM studies.