Transmission electron microscopy characterization of composite nanostructures
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High Angle Annular Dark Field (HAADF) and Electron Energy Loss Spectroscopy (EELS) were investigated as characterization tools for chemical element localization in novel nanostructures. The studied nanostructures were Pt-Au core-shell bimetallic nanoparticles and semiconductor doped layers. Pt-Au bimetallic nanoparticles were synthesized by the polyol method and characterized with the techniques previously mentioned. EDS results confirmed the bimetallic nature of the synthesized nanoparticles. HAADF was determinant in the identification of core-shell nanoparticles. This was possible due to the presence of strain fields in the interface between the core and the shell elements produced by the difference in their lattice parameter. The presence of these strain fields produced an anomalous contrast on the HAADF images, which enabled the identification of this interface, and hence of the core-shell nanostructures. UV-Visible absorption spectra (experimental and simulated) in combination with EXAFS results allowed the identification of Au on the viii shell of the nanoparticles and Pt in the core. HAADF was proved to be a useful technique for core-shell nanoparticles identification. Several doped semiconductor nanostructures were also studied; B doped Si FinFET nanostructures, As doped Si samples and Ge1-xCx thin layers. For the case of the B doped Si FinFET nanostructures strain fields produced by the implantation of B atoms into the Si lattice allowed a qualitative determination of the 2-dimensional B dopant profile with the use of HAADF, just as in the case of the core-shell nanoparticles. In the As doped Si samples, EELS is proposed as a quantitative characterization tool for the determination of dopant concentrations based on the relationship described in the freeelectron gas model between the characteristic plasmon peak energy and the electron density. Promising results obtained in the present study indicate the feasibility of using EELS as a quantitative tool for dopant concentration studies. Finally, a proper analysis of the EELS results allowed the observation of preferential segregation of C atoms to the interface between the Ge1-xCx thin layers and the Si substrate where these layers were grown. We interpret this result as a mechanism of strain relaxation in Ge1-xCx layers grown directly on Si substrates.