An investigation was made of the low EEL region in this wide band-gap system. UHV electron energy loss spectrometry, combined with digital micrograph acquisition and processing, made possible the reliable detection of absorption losses below 10eV. When incorporated into a dedicated STEM, this permitted the acquisition of spectral information via spectrum maps (spectrum imaging) of sample areas which were hundreds of nm across, with nm pixel sizes, adequate spectrum statistics and 0.3eV energy resolution; directly correlated with microstructural features in the mapped area. Discerning defect-related losses at band-gap energies then involved extracting the zeroloss peak from each spectrum and constructing ratio maps from the intensities in 2 energy windows, one which was defect-related and one at a higher, crystal band-structure dominated, energy. This was applied to residual spectrum maps and their first derivatives. Guided by theoretical EEL spectra calculations, the low loss spectra were then fitted using a series of Gaussian distributions. Pixel maps were constructed from the amplitude ratios of the Gaussians situated in the defect, and in the unaffected energy regime. The results revealed the existence of sp2-bonded C in the vicinity of stacking faults and partial dislocations in chemical vapor deposited diamond as well as additional states below the conduction band, tailing deep into the band-gap, at a node in a perfect dislocation. Calculated EEL spectra of shuffle dislocations gave similar absorption features at 5 to 8eV, and it was suggested that this common feature was due to sp2-type bonding.

Extended Defect Related Energy Loss in CVD Diamond Revealed by Spectrum Imaging in a Dedicated STEM. U.Bangert, A.J.Harvey, M.Schreck, F.Hormann: Ultramicroscopy, 2005, 104[1], 46-56