Electron Microscopy Based Characterization of Semiconductor Nanowires
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- Institutt for fysikk 
One-dimensional semiconductor structures have attracted a large research interest, mainly for the purpose of novel or improved opto-electronic properties and applications. In this work, semiconductor nanowires grown using the vapor-liquidsolid method are characterized using electron microscopy based techniques, in order to understand and improve nanowire synthesis and nanowire-based devices. Methods and tools have also been developed to improve and expedite such characterizations. One area of focus in the work has been on nanowire interfaces, especially the interface between GaAs nanowires and graphene substrates. Here, the symmetry and lattice mismatch have been considered, and the consequences this has on nanowire epitaxy on graphene. In addition, the study has focused on in situ characterization of nanowires and their interfaces, both in focused ion beam systems and in electron microscopes, with the goal of correlating the functional properties with the observed composition and structural features. Here, both the electrical properties of the nanowires and the dynamic behavior under heat-treatment have been studied. The main findings of the work include the proof of GaAs nanowire growth directly on few-layer graphene, as well as the quantitative description of the solid state replacement of GaAs nanowires by Au during heat-treatment. Additionally, techniques to characterize the mechanical and electrical characteristics of the nanowire–substrate interface have been further developed. Large contributions to collaborative, open source analysis software have also been made. These developed tools were essential for obtaining more informative results from the experimental data.