Electron Energy Loss Spectroscopy - Thickness Measurements

Thickness Measurements

EELS allows quick and reliable measurement of local thickness in transmission electron microscopy. The most efficient procedure is the following:

• Measure the energy loss spectrum in the energy range about -5..200 eV (wider better). Such measurement is quick (milliseconds) and thus can be applied to materials normally unstable under electron beam.
• Analyse the spectrum: (i) extract zero-loss peak (ZLP) using standard routines; (ii) calculate integrals under the ZLP (I₀) and under the whole spectrum (I).
• The thickness t is calculated as mfp*ln(I/I₀). Here mfp is the mean free path of electron inelastic scattering, which has recently been tabulated for most elemental solids and oxides.

The spatial resolution of this procedure is limited by the plasmon localization and is about 1 nm, meaning that spatial thickness maps can be measured in scanning transmission electron microscopy with ~1 nm resolution.