Crystallographic site-occupancy refinements in thin-film oxides by channelling-enhanced microanalysis

Abstract

Specific site-occupation determinations of rare-earth (RE) additions in thin-film garnets of nominal composition Yi.7Sm0.6Luo.7Fe5012 based on the orientation dependence of electron-induced characteristic X-ray emissions are described. The application of this technique called 'channelling-enhanced microaaalysis' to a general non-layered crystal structure requires a theoretical prediction of the characteristic X-ray production as a function of incident-beam orientation because the specific-site-sensitive orientations cannot be determined by inspection of the crystal structure. Hence, a real-space formulation considering flux loss from the incident beam and under the assumption of highly localized inner-shell excitations has been described for the characteristic X-ray production in thin crystals. Applying this theory, a g = 121 systematic orientation was predicted to be the orientation that is specific-site sensitive for these thin-film garnets. Experimentally observed data were then refined, using a constrained least-squares analysis to give probabilities for the occupation of RE additions in the different crystallographic sites. Thus, it has been shown that in these compounds, Lu 3+ and Sm 3+ additions prefer octahedral occupation with a probability ->95%. Assumptions, limitations and future potentials of this novel crystallographic technique are also discussed.

Biomedical Nanomagnetics: A Spin Through Possibilities in Imaging, Diagnostics, and Therapy

“…It is difficult to unequivocally distinguish between the crystal structures of magnetite and maghemite from standard X-ray θ – 2 θ scans. However, in addition to channeling methods in electron microscopy [98], [99] the oxidation state of Fe in the nanoparticles can be determined by measuring the electron energy-loss spectrum of the Fe L 3,2 edge in a TEM (Fig. 6(d)).…”

Polarity determination for GaN thin films by electron energy-loss spectroscopy

“…The delocalization effect is also discussed, as it is a sensitive factor in the experiment to determine the polarity, especially for the low-loss electrons. [9][10][11][12] The GaN thin film was deposited on a ͑111͒ silicon substrate with a ͑0001͒ AlN buffer layer, using metalorganic chemical vapor deposition. The direction of the cation ͑Ga͒ to the anion ͑N͒ is defined as ͓0001͔ in the real space.…”