EELS log-ratio technique for specimen-thickness measurement in the TEM

Area of Science:

• Materials Science
• Analytical Chemistry
• Physics

Background:

• Transmission electron microscopy (TEM) is vital for nanoscale analysis.
• Accurate thickness measurement is essential for quantitative analysis in TEM.
• Electron energy loss spectroscopy (EELS) offers a powerful method for thickness determination.

Purpose of the Study:

• To present a refined method for measuring local specimen thickness in TEM.
• To develop a parameterization for the inelastic mean free path (IMFP) for diverse materials.
• To establish a reliable formula for absolute thickness determination using EELS.

Main Methods:

• Utilized the log-ratio formula: t = lambda ln (It/I0).
• Measured total inelastic mean free path (lambda) across 11 materials with varying atomic numbers (Z).
• Developed a parameterized model for lambda based on incident energy (E0), collection semiangle (beta), and material properties.

Main Results:

• Established the formula lambda = 106F (E0/Em)/ln (2 beta E0/Em), where F = (1 + E0/1,022)/(1 + E0/511)^2 and Em = 7.6Z^0.36.
• Demonstrated that this formulation enables absolute thickness measurement.
• Achieved an accuracy of +/- 20% for most inorganic specimens.

Conclusions:

• The proposed formulation offers a robust method for quantitative thickness analysis in TEM.
• This approach enhances the reliability of EELS-based measurements for materials characterization.
• The findings are applicable to a wide range of inorganic materials, advancing nanoscale research.