Improving the measurement of dielectric function by TEM-EELS: avoiding the retardation effect

Area of Science:

• Materials Science
• Condensed Matter Physics
• Spectroscopy

Background:

• Electron energy-loss spectroscopy (EELS) is a powerful technique for characterizing material properties.
• Retardation effects can introduce inaccuracies in EELS measurements, particularly in the dielectric function.
• Existing methods struggle to fully mitigate these retardation effects.

Purpose of the Study:

• To develop and validate an improved Kramers-Kronig analysis (KKA) routine for EELS.
• To accurately measure the dielectric function of α-Al2O3 by eliminating retardation effects.
• To provide a reliable method for EELS dielectric function measurements with small collection angles.

Main Methods:

• Implementation of an enhanced Kramers-Kronig analysis (KKA) routine.
• Acquisition of electron energy-loss spectroscopy (EELS) data for α-Al2O3.
• Analysis of differential cross-section to identify retardation effect influences.
• Comparison of EELS-derived dielectric function with optical data.

Main Results:

• The improved KKA routine successfully eliminated retardation effects in EELS data.
• EELS data discrepancies with optical data in the 10-20 eV range were resolved.
• Retardation effects were found to be significant at scattering angles below 0.2 mrad for 10-15 eV loss energy.
• The dielectric function obtained using the improved KKA routine showed excellent agreement with optical measurements.

Conclusions:

• The developed KKA routine provides accurate dielectric function measurements via EELS.
• This technique is particularly effective for measurements using small collection semi-angles.
• The findings enhance the reliability of EELS for nanoscale material characterization.