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Lookup NU author(s): Professor Adam Harvey,
Professor Patrick Briddon
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The advent of cold field emission scanning transmission electron microscopes with high mechanical and energy stability and a monochromacity of 0.3 eV has made spectroscopy of sub-nm size features possible. High spectrometer dispersions (0.01 eV/channel) furthermore allow electron energy loss spectroscopy (EELS) to be carried out at low energy losses, i.e., in the bandgap regime of semiconductors with bandgaps down to 2 eV. In this paper the technical procedures and the evaluation of low loss spectra, as well as limits imposed by energy resolution, point spread function and delocalisation are highlighted. The 'spectrum imaging' technique employing the UHV ENFINA EELS detector and software package has proven invaluable for the detection of the subtle changes involved with dislocations: these may go unnoticed in the balance between local stability and spectrum statistics, which this kind of highly spatially resolved spectroscopy entails. However, in contrast to results from singular spectra, a spectrum map captures systematic changes ever an extended area in direct correlation with the microstructural feature. EELS results of dislocation obtained of GaN are presented. Supported by ab initio calculations, changes to the density of states can be observed in low loss spectra maps at individual dislocations at bandedge. Preliminary results on pre-bandedge absorption of basal stacking faults in SiC are also reported.
Author(s): Bangert U, Gutierrez-Sosa A, Harvey A, Jones R, Fall CJ, Blumenau A, Briddon R
Editor(s): McVitie, S., McComb, D.
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Published
Conference Name: Institute of Physics Conference Series: Proceedings of the Institute of Physics Electron Microscopy and Analysis Group Conference
Year of Conference: 2004
Publisher: Institute of Physics Publishing Ltd.