Dechanneling Effects in EELS and EDXS Analysis of Ybacu-Oxides

Abstract

Quantitative analysis in the TEM by EELS or EDXS depends on the K-factor method in which uniform ionization, independent of specimen orientation and thickness, is assumed. This assumption is of limited validity for crystals, where channeling of the electron wave ψ affects the ionization rate as observed in both energy loss and X-ray signals. Both EELS and EDXS are sensitive to changes in ψψ*near the atomic sites, and this variation as a function of crystal orientation forms the basis for ALCHEMI. Simultaneously recorded EELS and EDXS spectra were used to monitor changes in Cu/Ba ratio from YBaCu-oxides using L2,3/M4,5 ionization edges or K/L X-rays respectively. Although the acceptance aperture for EELS (11 mrad at 300 keV) may not be sufficiently large to mask double-channeling effects, it is small enough that momentum transfer is sufficiently limited to enhance derealization. Thus it is expected that the EELS signal should be less sensitive to crystal orientation than EDXS (an estimate of impact parameters yields 0.73 and 0.61 Å for the Ba and Cu energy loss signals, reducing to 0.06 and 0.04 Å respectively for X-ray emissions).