Absolute thickness measurement of pyrolytic graphite spheroids by STEM-EELS

Area of Science:

• Materials Science
• Nanotechnology
• Electron Microscopy

Background:

• Accurate thickness measurement is crucial for understanding nanomaterials.
• Scanning Transmission Electron Energy Loss Spectroscopy (STEM-EELS) is a powerful tool for nanoscale analysis.
• Pyrolytic graphite spheroids (GSs) are relevant in various advanced applications.

Purpose of the Study:

• To determine the absolute thickness of pyrolytic graphite spheroids (GSs).
• To compare the accuracy of different STEM-EELS analysis methods for thickness measurement.
• To investigate the influence of collection semi-angle on measurement accuracy.

Main Methods:

• Utilized STEM-EELS in log-ratio and Kramers-Kronig (K-K) analysis modes.
• Employed Transmission Electron Microscopy (TEM) for reference thickness measurements.
• Investigated varying collection semi-angles (β) from 12.4 to 21.1 mrad.

Main Results:

• Kramers-Kronig (K-K) analysis with surface effect correction yielded the highest accuracy.
• Log-ratio method and K-K sum rule showed lower accuracy compared to corrected K-K analysis.
• An optimal collection semi-angle of 17.3 mrad was identified for K-K analysis, balancing over- and underestimation.

Conclusions:

• The Kramers-Kronig (K-K) method, particularly with surface correction, is the most reliable for absolute thickness measurement of GSs via STEM-EELS.
• Collection semi-angle significantly impacts measurement accuracy, with an optimal range identified.
• The study also characterized optical properties and microstructure of GSs using K-K analysis.