Quantitative Chemical Mapping of InGaN Quantum Wells from Calibrated High-Angle Annular Dark Field Micrographs

• Published in: Microscopy and microanalysis 2015-08, Vol.21 (4), p.994-1005
• Main Authors: Carvalho, Daniel, Morales, Francisco M., Ben, Teresa, García, Rafael, Redondo-Cubero, Andrés, Alves, Eduardo, Lorenz, Katharina, Edwards, Paul R., O’Donnell, Kevin P., Wetzel, Christian
• Format: Article
• Language: English
• Subjects: Electrons; Fluctuations; Materials Applications and Techniques; Scientific imaging; Sensors; Transmission electron microscopy
• ISSN: 1431-9276; 1435-8115
• DOI: 10.1017/S143192761501301X

We present a simple and robust method to acquire quantitative maps of compositional fluctuations in nanostructures from low magnification high-angle annular dark field (HAADF) micrographs calibrated by energy-dispersive X-ray (EDX) spectroscopy in scanning transmission electron microscopy (STEM) mode. We show that a nonuniform background in HAADF-STEM micrographs can be eliminated, to a first approximation, by use of a suitable analytic function. The uncertainty in probe position when collecting an EDX spectrum renders the calibration of HAADF-STEM micrographs indirect, and a statistical approach has been developed to determine the position with confidence. Our analysis procedure, presented in a flowchart to facilitate the successful implementation of the method by users, was applied to discontinuous InGaN/GaN quantum wells in order to obtain quantitative determinations of compositional fluctuations on the nanoscale.