Laboratory of Electron NanoScopies, LENS-MIND-IN2UB, Dept. Electrónica, Universitat de Barcelona, Marti i Franqués 1, 08028 Barcelona, Spain.
Microsc Microanal. 2013 Jun;19(3):698-705. doi: 10.1017/S1431927613000512. Epub 2013 May 9.
III-V nitride (AlGa)N distributed Bragg reflector devices are characterized by combined high-angle annular dark-field (HAADF) and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope. Besides the complete structural characterization of the AlN and GaN layers, the formation of AlGaN transient layers is revealed using Vegard law on profiles of the position of the bulk plasmon peak maximum. This result is confirmed by comparison of experimental and simulated HAADF intensities. In addition, we present an advantageous method for the characterization of nano-feature structures using low-loss EELS spectrum image (EEL-SI) analysis. Information from the materials in the sample is extracted from these EEL-SI at high spatial resolution.The log-ratio formula is used to calculate the relative thickness, related to the electron inelastic mean free path. Fitting of the bulk plasmon is performed using a damped plasmon model (DPM) equation. The maximum of this peak is related to the chemical composition variation using the previous Vegard law analysis. In addition, within the context of the DPM, information regarding the structural properties of the material can be obtained from the lifetime of the oscillation. Three anomalous segregation regions are characterized, revealing formation of metallic Al islands.
III-V 族氮化物（AlGa）N 分布式布拉格反射器器件的特点是在扫描透射电子显微镜中结合使用高角度环形暗场（HAADF）和电子能量损失谱（EELS）。除了对 AlN 和 GaN 层进行完整的结构表征外，还通过体等离子体峰值位置的位置分布的维加律揭示了 AlGaN 瞬变层的形成。通过实验和模拟 HAADF 强度的比较来验证这一结果。此外，我们还提出了一种使用低损耗电子能量损失谱（EELS）谱图像（EEL-SI）分析对纳米特征结构进行表征的有利方法。通过这些 EEL-SI 可以从样品中的材料中提取信息，其具有高空间分辨率。使用对数比公式计算与电子非弹性平均自由程相关的相对厚度。使用阻尼等离子体模型（DPM）方程对体等离子体进行拟合。该峰的最大值与之前的维加律分析中使用的化学成分变化有关。此外，在 DPM 的背景下，可以从振荡的寿命中获得有关材料结构特性的信息。对三个异常偏析区域进行了表征，揭示了金属 Al 岛的形成。
