Quantitative structure analysis of nanosized materials by transmission electron microscopy
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1184-GG03-02
Quantitative structure analysis of nanosized materials by transmission electron microscopy Wolfgang Neumann, Holm Kirmse, Ines Häusler, Changlin Zheng, Anna Mogilatenko Humboldt University of Berlin, Institute of Physics, Chair of Crystallography, Newtonstrasse 15, 12489 Berlin, Germany ABSTRACT The quantitative analysis of nanostructured materials increasingly requires the combined use of a variety of complementary electron microscopical techniques as well as new interpretation techniques as feature sizes decrease. The following studies of quantitative TEM analysis will illustrate this statement. The three-dimensional shape of (Si,Ge) semiconductor islands grown by liquid phase epitaxy (LPE) on Si substrates was determined by electron holography. The chemical composition of the islands was determined by quantitative high resolution electron microscopy (qHRTEM) and energy dispersive X-ray spectroscopy (EDXS). ZnTe nanowires and the Au-based catalyst droplet grown on GaAs via a vapour-liquid-solid (VLS) process were characterized by HRTEM, EDXS and electron energy loss spectroscopy (EELS). The possibilities of composition analysis of ternary semiconductors by combined application of conventional TEM (dark-field imaging) and HRTEM were demonstrated for the determination of the antimony content in Ga(Sb,As) quantum dots (QDs) grown by metal organic vapour deposition on GaAs substrates. Additionally, studies of chemically sensitive imaging of this QD-system by means of scanning transmission electron microscopy (STEM) will be discussed. The magnetic domain structure of soft magnetic FeCo based nanocrystalline alloys was investigated by Lorentz microscopy and off-axis electron holography. A strong correlation between the microstructure of the alloys and the structure of the magnetic domains was found. INTRODUCTION Nanostructured materials from almost all classes of materials are of great interest because the reduced dimensionality may drastically change the physical properties. In general these properties are a function of size, shape, arrangement, structure and chemical composition of the nanosized materials. Transmission electron microscopy (TEM) allows a detailed insight into the material characteristics. In order to correlate microstructure, microchemistry and materials properties the various TEM techniques for imaging, diffraction and spectroscopy have to be combined. The classical diffraction contrast method of conventional TEM is applied to analyse the size, shape and arrangement of nanosized structures, where a quantitative analysis often requires image simulations of diffraction contrast for theoretical structure models. An alternative and powerful method is the three-dimensional reconstruction of the shape of nanostructures from two-dimensional phase mapping by means of electron holography. Furthermore, electron holography and Lorentz microscopy are useful for the evaluation of structure/magnetic property relationships. Quantitative high-resolution transmission electron microscopy (qHRTEM) provides
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