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ULTRA STEM

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Nanometric resolved luminescence in h-BN Flakes: excitons and stacking order

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Hexagonal boron nitride (h-BN) is one of the most promising candidates for light emitting devices in the far UV region, presenting a single strong excitonic emission at 5.8 eV. However, a single line appears only in extremely pure monocrystals that can hardly be obtained only though complex synthesis processes. Common h-BN samples present more complex emission spectra that have been generally attributed to the presence of structural defects. Despite a large number of experimental studies up to now it was not possible to attribute specific emission features to well identify defective structures. In this work we address this fundamental questions by adopting a theoretical and experimental approach combining few nanometer resolved cathodoluminescence techniques with high resolution transmission electron microscopy images and state of the art quantum mechanical simulations. Read more »

Direct Evidence of Fe2+/Fe3+ Charge Ordering in the Ferrimagnetic Hematite-Ilmenite Fe1.35Ti0.65O3-d Thin Films

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Here we report on the direct experimental evidence of Fe2+/Fe3+ charge ordering at room temperature in hematite-ilmenite Fe1.35Ti0.65O3-d epitaxial thin films grown by pulsed laser deposition, using aberration-corrected scanning transmission electron microscopy (STEM) coupled to high-resolution energy electron-loss spectroscopy (EELS). Read more »

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