Inelastic mean free path measurement by STEM-EELS technique using needle-shaped specimen

Keiichiro Oh-Ishi; Tetsu Ohsuna

doi:10.1016/j.ultramic.2020.112955

Inelastic mean free path measurement by STEM-EELS technique using needle-shaped specimen

Ultramicroscopy. 2020 May:212:112955. doi: 10.1016/j.ultramic.2020.112955. Epub 2020 Feb 13.

Authors

Keiichiro Oh-Ishi¹, Tetsu Ohsuna²

Affiliations

¹ Toyota Central R&D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192, Japan. Electronic address: e1632@mosk.tytlabs.co.jp.
² Toyota Central R&D Labs., Inc., 41-1 Yokomichi, Nagakute, Aichi 480-1192, Japan.

PMID: 32086184
DOI: 10.1016/j.ultramic.2020.112955

Abstract

Inelastic mean free path (IMFP) was determined by electron energy loss spectroscopy (EELS) to estimate the accurate thickness of TEM thin foil using needle-shaped specimen. From EELS measurements performed for 99.99% Al, Si wafer and 99.99% Fe, linear relationships were confirmed between the thickness of the TEM thin foil and the ratio of the total intensity of EELS spectrum to the total intensity of zero-loss spectrum for all samples. By weighted least-square fitting, the IMFP was estimated to be 143-150 nm for Al, 159-165 nm for Si with amorphous layer, and 92-94 nm for Fe with the collection semi-angle β = 11.9 - 35.7 mrad, and accelerated voltage of 200 kV. Thus, the dependence of IMFP on β is not dominant. The accuracy depends on the roundness of the cross-section of the needle-shaped specimen, and is observed to be low in terms of percentage in this work.

Keywords: EELS; Inelastic mean free path; Number density; Plasmon; STEM; Thickness.