Bangert U, Harvey A J, Schreck M, Hörmann F
Department of Physics, UMIST, Sackville Street, Manchester M60 1QD, UK.
Ultramicroscopy. 2005 Aug;104(1):46-56. doi: 10.1016/j.ultramic.2005.02.007. Epub 2005 Apr 7.
This article aims at investigations of the low EEL region in the wide band gap system diamond. The advent of the UHV Enfina electron energy loss spectrometer combined with Digital Micrograph acquisition and processing software has made reliable detection of absorption losses below 10 eV possible. Incorporated into a dedicated STEM this instrumentation allows the acquisition of spectral information via spectrum maps (spectrum imaging) of sample areas hundreds of nanometers across, with nanometers pixel sizes, adequate spectrum statistics and 0.3 eV energy resolution, in direct correlation with microstructural features in the mapping area. We aim at discerning defect related losses at band gap energies, and discuss different routes to simultaneously process and analyse the spectra in a map. This involves extracting the zero loss peak from each spectrum and constructing ratio maps from the intensities in two energy windows, one defect related and one at a higher, crystal bandstructure dominated energy. This was applied to the residual spectrum maps and their first derivatives. Secondly, guided by theoretical EEL spectra calculations, the low loss spectra were fitted by a series of gaussian distributions. Pixel maps were constructed from amplitude ratios of gaussians, situated in the defect and the unaffected energy regime. The results demonstrate the existence of sp2-bonded carbon in the vicinity of stacking faults and partial dislocations in CVD diamond as well as additional states below conduction band, tailing deep into the band gap, at a node in a perfect dislocation. Calculated EEL spectra of shuffle dislocations give similar absorption features at 5-8 eV, and it is thought that this common feature is due to sp2-type bonding.
本文旨在研究宽带隙系统金刚石中的低能量损失（EEL）区域。超高真空Enfina电子能量损失谱仪与数字显微图像采集和处理软件的出现，使得可靠检测低于10 eV的吸收损失成为可能。将该仪器集成到专用扫描透射电子显微镜（STEM）中，能够通过对数百纳米大小的样品区域进行谱图（光谱成像）采集光谱信息，像素尺寸为纳米级，具有足够的光谱统计数据和0.3 eV的能量分辨率，且与映射区域的微观结构特征直接相关。我们旨在识别带隙能量处与缺陷相关的损失，并讨论在图谱中同时处理和分析光谱的不同方法。这包括从每个光谱中提取零损失峰，并根据两个能量窗口中的强度构建比率图谱，一个窗口与缺陷相关，另一个窗口处于较高的、由晶体能带结构主导的能量处。这应用于残余谱图及其一阶导数。其次，在理论EEL光谱计算的指导下，低损失光谱由一系列高斯分布拟合。根据位于缺陷和未受影响能量区域的高斯振幅比构建像素图谱。结果表明，在CVD金刚石的堆垛层错和部分位错附近存在sp2键合碳，以及在完美位错的节点处，导带以下存在延伸至带隙深处的附加态。计算得到的错排位错的EEL光谱在5 - 8 eV处具有相似的吸收特征，据认为这种共同特征是由于sp2型键合。
