Controlling the polarity of ZnO nanowires in addition to the uniformity of their structural morphology in terms of position, vertical alignment, length, diameter, and period is still a technological and fundamental challenge for real-world device integration. In order to tackle this issue, we specifically combine the selective area growth on prepatterned polar c-plane ZnO single crystals using electron-beam lithography, with the chemical bath deposition. The formation of ZnO nanowires with a highly controlled structural morphology and a high optical quality is demonstrated over large surface areas on both polar c-plane ZnO single crystals. Importantly, the polarity of ZnO nanowires can be switched from O- to Zn-polar, depending on the polarity of prepatterned ZnO single crystals. This indicates that no fundamental limitations prevent ZnO nanowires from being O- or Zn-polar. In contrast to their catalyst-free growth by vapor-phase deposition techniques, the possibility to control the polarity of ZnO nanowires grown in solution is remarkable, further showing the strong interest in the chemical bath deposition and hydrothermal techniques. The single O- and Zn-polar ZnO nanowires additionally exhibit distinctive cathodoluminescence spectra. To a broader extent, these findings open the way to the ultimate fabrication of well-organized heterostructures made from ZnO nanowires, which can act as building blocks in a large number of electronic, optoelectronic, and photovoltaic devices.

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A multidisciplinary approach has been used to study Au occurrences within pyrite and arsenopyrite in four refractory Au ores from Colombia, France (Le Châtelet and Villeranges) and Portugal (Neves Norte). The Au was characterized by optical and scanning electron microscopy and analysed using electron and ion microprobes to determine Au distribution, with particular attention to spectral interferences in electron and ion microprobes, background measurements in electron probes, and quantitative analysis using external standardization in ion probes. The ionic emission rate is proven to be dependent on the Au status; combined Au has a greater ion emission than metallic Au. Invisible Au occurrences are closely linked to As distribution. Gold bonding in arsenopyrite, examined by transmission electron microscopy, is shown to be dispersed within the FeAsS crystal structure. Typical growth patterns and As-Au diffusion zoning in pyrite and arsenopyrite may account for the very irregular distribution of Au in these minerals.

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