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Inelastic mean free path measurement by STEM-EELS technique using needle-shaped specimen
Keiichiro Oh-Ishi1, Tetsu Ohsuna1
1Toyota Central R&D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192, Japan.
Ultramicroscopy
|February 23, 2020
Summary
Electron energy loss spectroscopy (EELS) determined the inelastic mean free path (IMFP) to accurately measure TEM thin foil thickness. This method, using needle-shaped specimens, provides reliable thickness estimations for materials like Al, Si, and Fe.
Area of Science:
- Materials Science
- Solid State Physics
- Analytical Chemistry
Background:
- Accurate thickness measurement of Transmission Electron Microscopy (TEM) thin foils is crucial for material characterization.
- Electron Energy Loss Spectroscopy (EELS) is a powerful technique for analyzing the electronic structure and composition of materials.
- Determining the Inelastic Mean Free Path (IMFP) is essential for quantitative EELS analysis and thickness determination.
Purpose of the Study:
- To establish a reliable method for estimating the accurate thickness of TEM thin foils using EELS.
- To determine the Inelastic Mean Free Path (IMFP) for Aluminum (Al), Silicon (Si), and Iron (Fe) using a novel approach.
- To investigate the influence of specimen geometry and collection semi-angle on IMFP measurements.
Main Methods:
- Utilized needle-shaped specimens of 99.99% Al, Si wafer, and 99.99% Fe for TEM analysis.
- Performed Electron Energy Loss Spectroscopy (EELS) measurements at an accelerated voltage of 200 kV.
- Analyzed the linear relationship between TEM thin foil thickness and the ratio of total EELS spectrum intensity to zero-loss spectrum intensity.
- Employed weighted least-square fitting to estimate IMFP values.
Main Results:
- Confirmed linear relationships between foil thickness and spectral intensity ratios for Al, Si, and Fe.
- Estimated IMFP values: 143-150 nm for Al, 159-165 nm for Si (with amorphous layer), and 92-94 nm for Fe.
- Demonstrated that the dependence of IMFP on the collection semi-angle (β = 11.9–35.7 mrad) is not dominant.
- Observed that the accuracy of the method is influenced by the roundness of the needle-shaped specimen's cross-section.
Conclusions:
- The EELS-based method using needle-shaped specimens provides an accurate means to determine TEM thin foil thickness.
- The derived IMFP values are consistent with existing literature, validating the methodology.
- The study highlights the importance of specimen geometry for achieving high accuracy in quantitative EELS analysis.
