Talk given by Prof. Wolfgang Jäger High-resolution imaging and spectroscopic techniques of advanced transmission electron microscopy (TEM) play a crucial role in characterizing the structure-property relationships of inorganic functional materials and interfaces. The microstructure, the elemental composition, and physical properties of nanomaterials can be characterized quantitatively and with resolutions in the nanometer regime or even on the atomic level. The presentation will summarize three application areas to microstructure research on nanomaterials and interfaces. At first, the potential of aberration-corrected high-resolution TEM for imaging incommensurate interfaces is illustrated for the misfit compound layered compound system (PbS)1.14NbS2. Direct images of the projected crystal structure, consisting of ‘light’ S atomic columns and ‘heavy’ mixed Pb/S atomic columns, are obtained by imaging with negative values of the spherical aberration coefficient Cs (‘NCSI contrast’ conditions), thus allowing to quantitatively investigate layer distortions, stacking disorder, and interface structures1,2. Oxide semiconductor nanomaterials, such as In2O3 and ZnO, are of interest for applications in nanoelectronics, spintronics, or solar cells. For vapour-solid growth of ZnO, investigations by TEM and by scanning (S)TEM in combination with energy-dispersive X-ray spectroscopy allow understanding growth and doping phenomena and give insight into the likely origin of spatially varying cathodoluminescence. For ZnO nanotubes with Sn core regions, in situ TEM experiments enable investigating the melting and solidification phenomena of Sn by applying variable electron beam flux locally to to local nanotube regions3,4. Multi-junction solar cells based on III-V compound semiconductor layers are of interest for power generation in terrestrial concentrator photovoltaics and in space applications. High-resolution imaging and spectroscopic TEM methods were applied successfully to supporting the development of novel solar cell concepts. Two application areas will be illustrated: analyses for the control of defect and layer strains in lattice-mismatched epitaxial layer growth on Ge5, 6 , and analyses of interfaces after thin layer transfer combined with semiconductor wafer bonding for solar cells on Si substrates7,8. Aberration-corrected TEM extends the analytical capabilities as is clearly shown by the spectroscopic electron-energy loss analyses of GaAs/Si interfaces in wafer-bonded solar cells [4]. Optimized solar cell concepts result in active cell regions with significantly reduced defect densities. The success of such concept developments led to a GaInP/GaAs/Ge cell with a record efficiency of 41.1 % and a GaInP/GaAs/Si solar cell with an AM1.5g efficiency of 26.1%. It is my pleasure to acknowledge the collaborations and the contributions of all my colleagues mentioned in the references. 1. M. Garbrecht, E. Spiecker, K. Tillmann, W. Jäger: Quantitative atom column position analysis at the incommensurate interfaces of a (PbS)1.14NbS2 misfit layered compound with aberration-corrected HRTEM. Ultramicroscopy 111, 245-250 (2011). 2. E. Spiecker, M. Garbrecht, W. Jäger, K. Tillmann: Advantages of aberration correction for HRTEM investigation of complex layer compounds. Journal of Microscopy 237(3), 341 (2010). 3. Y. Ortega, W. Jäger, J. Piqueras, D. Häussler, P. Fernández: In situ TEM and analytical STEM studies of ZnO nanotubes with Sn cores and Sn nanodrops. J. Phys. D: Appl. Phys., DOI: 10.1088/0022- 3727/46/39/395301, 46, 395301 - 395308 (2013). 4. Y. Ortega Villafuerte, Ch. Dieker, W. Jäger J. Piqueras, P. Fernández: Voids, nanochannels and formation of nanotubes with mobile Sn fillings in Sn-doped ZnO nanorods. Nanotechnology 21, 225604 (2010). 5. J. Schöne, E. Spiecker, F. Dimroth, A. W. Bett, W. Jäger: Misfit dislocation blocking by dilute nitride intermediate layers. Appl. Phys. Lett. 92, 081905 (2008). 6. J. Schöne, E. Spiecker, F. Dimroth, A. W. Bett, W. Jäger: Defect Formation and Strain Relaxation in graded GaPAs/GaAs, GaNAs/GaAs and GaInNAs/Ge Buffer Systems for high-efficiency Solar Cells. Journal of Physics: Conference Series 471, 012008 (2013). DOI:10.1088/1742- 6596/471/1/012008 7. F. Dimroth, T. Roesener, S. Essig, Ch. Weuffen, A. Wekkeli, E. Oliva, G. Siefer, K. Volz, Th. Hannappel, D. Häussler, W. Jäger, A. W. Bett: Comparison of Direct Growth and Wafer Bonding for the Fabrication of GaInP/GaAs Dual-Junction Solar Cells on Silicon. IEEE Journal of Photovoltaics, accepted for publication (2014). 8. D. Häussler, L. Houben, S. Essig, M. Kurttepeli, F. Dimroth, R. E. Duni-Borkowski, W. Jäger: Aberration-corrected transmission electron microscopy analyses of GaAs/Si interfaces in wafer-bonded multi- junction solar cells. Ultramicroscopy 134, 55–61 (2013).

This event is part of the eventgroup INT Talks

Homepage
https://www.int.kit.edu/events.php

Speaker
Prof. Wolfgang Jäger

Christian-Albrechts-University (CAU) Kiel
Institute for Materials Science

Organizer
Dr. Christian Kübel
Institute of Nanotechnology (INT)
Karlsruhe Institute of Technology (KIT)
Eggenstein-Leopoldshafen
Mail: christian kuebel ∂does-not-exist.kit edu

Targetgroup
Interested / Everyone