Calculation, consequences and measurement of the point spread function for low-loss inelastic scattering

Area of Science:

• Electron Microscopy
• Materials Science
• Physics

Background:

• Low-loss inelastic scattering in electron microscopy causes electron delocalization.
• Previous analytical formulas for the point spread function (PSF) exist.
• Accurate modeling of electron delocalization is crucial for imaging beam-sensitive materials.

Purpose of the Study:

• To modify the analytical PSF formula to account for variations in scattered-electron phase.
• To improve agreement between the PSF model and experimental delocalization measurements.
• To enable high-resolution imaging of beam-sensitive specimens with reduced electron beam damage.

Main Methods:

• Modification of the analytical formula for the point spread function (PSF).
• Incorporation of scattered-electron phase variations into the PSF model.
• Utilizing an exponentially attenuated Lorentzian form for the PSF.
• Direct measurement of the PSF using aberration-corrected transmission electron microscopy (TEM) and energy-filtered imaging.

Main Results:

• The modified PSF formula shows better agreement with median delocalization distances.
• The PSF's 1/r2 tails extend beyond the energy deposition region for low energy losses.
• This allows energy-loss data acquisition from undamaged specimen regions using small electron probes.
• Reduced damage imaging is possible via sparse scanning techniques for core-loss or elastic imaging.

Conclusions:

• The refined PSF model enhances the accuracy of electron delocalization analysis.
• The findings facilitate high-resolution imaging of beam-sensitive materials with minimal damage.
• A practical method for direct PSF measurement in TEM is proposed.