Metal-semiconductor hybrid nanoparticles: Halogen induced shape control, hybrid synthesis and electrical transport

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Kapitel 2, Halogen induced shape control of CdSe nanoparticles:
Due to their special size dependent optical and electronic properties semiconductor nanoparticles find application in photovoltaics [18, 19], (photo)catalysis [1, 12], light emitting devices [20] and biological labelling [21, 22], among others [23].
In these contexts, the shape of the nanoparticles may become important due to physical properties depending on the dimensionality of quantum confinement in the nanostructure or simply their packing behaviour [3, 24, 25, 26]. Apart from their morphology, an aspect that is critical for applications is the passivation of the nanoparticle surface by stabilisers.
Owing to the successful implementation of nanoparticles partially capped by or post synthetically treated with halides into solar cells with increased efficiency [27, 28], incorporation of atomic halogen ligands has attracted much attention recently [29, 30, 31, 32, 33]. In addition to enhancing physical properties in nanoparticle arrays, halides show interesting effects on the shaping of nanoparticles. With metal nanoparticles they are deliberately employed to control the growth with influences on the shape formation [34, 35]. For semiconductor nanoparticles, several cases of wurtzite structures with hexagonal bullet, pyramid, pencil or diamond shape were reported which had in common that chloride precursors were present [36, 37, 38]. A few studies showed an increase of morphological uniformity in branched cadmium chalcogenides with wurtzite arms growing on seeds of deviating crystal structures when halides were added [39, 38, 40]. Juárez and co-workers observed how traces of 1,2-dichloroethane employed as solvent for carbon nanotubes added in situ to a synthesis of CdSe nanorods induced a shape evolution [15, 16]. Hexagonal pyramidal nanoparticles with wurtzite structure evolved, which then formed composites with the nanotubes. Chloroalkanes were furthermore reported to aid the