Structural investigation of nanostructures by Extend X-ray Absorption Fine Structure (EXAFS) and Diffraction Anomalous Fine structure (DAFS)
Final Report Abstract
Processes of self-organization during epitaxial growth of semiconductor heterostructures represent methods for the fabrication of nanostructures (quantum wires and dots) with electronic and optical properties very promising for their technological applications, like optical sensors, lasers or storage media. Due to stochastic nature of the self-organization process a certain dispersion of their sizes, shapes and chemical composifions is observed. Such properties might be a limiting factor for nanostructure applications. Therefore, it is important to characterize their structure at the atomic-level. This type of information can be obtained by x-ray absorption spectroscopy (XAS) methods, namely X-ray Absorption Near Edge Structure XANES, Extended X-ray Absorption Fine Structure (EXAFS) and Diffraction Anomalous Fine Structure (DAFS). The former method is sensitive to the electron density of states, so that it is suitable for the study of chemical bonds of a chosen element, while the latter probes the positions of neighboring atoms of a given atom. In DAFS method the diffracted intensity is measured as a function of x-ray energy close to the absorption edge. XAFS techniques give the information form the whole volume of the sample. Therefore, it is hardly possible to separate the information from the substrate, the quantum structure and the cap layer. Unlike to this methods, in DAFS the measured signal is collected from a volume with a specific lattice-plane distance, i.e. with a given strain (iso-strain volume), from the volumes of quantum dots, for instance. Within the project, the spectroscopic synchrotron radiation techniques such XASF and DAFS were applied in order to investigate the structure parameters of quantum dots grown by MBE and MOVPE methods. Using spectroscopic methods, the atomic ordering, local chemical composition and strain distribution in CdZnSe and InGaN quantum dots were determined.
Publications
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Advanced Light Source Annual Report (2008), Lawrence Berkeley National Laboratory, ALS
I.N. Demchenko, W.C. Stolte, E. Piskorska-Hommel, D. Hommel, K. Lawniczak-Jablonska and O. Hemmers
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Atomic ordering in CdSe/ZnSe/MgS quantum dots studied by EXAFS, 29th Int. Conf. on the Physics of Semiconductors, 07- 01.08.2008, Rio de Janeiro, Brazylia, AIP Conf. Ser. 1199 (2009) 531
E. Piskorska-Hommel, A. Wolska, J. I. Flege, A. Gust, C. Kruse, D. Hommel, F. d'Acapito
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Local structure of uncapped and capped InGaN/GaN quantum dots, Journal of Synchrotron Radiation 16 (2009) 494
E. Piskorska-Hommel, Th. Schmidt, M. Siebert, T. Yamaguchi, D. Hommel, J. Falta, and J.O. Cross
