Novel 3D nano-antennas of self-assembled zinc oxide on silver nanowires

Date
2016
Authors
Sanchez, John Eder
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Abstract

The manipulation of geometrical and structural arrangement of nano-devices, especially nanoantennas (nantennnas), is highly desirable for a precise controlling and monitoring of the multidirectional radiation pattern generated from the active elements on nanoantenna (nantenna) applications. Here we report the epitaxial growing of ZnO nanorods preferentially oriented along the [0001] direction on pentagonal faces (010) of Ag nanowires (Ag/ZnO). The Ag/ZnO nanosystem, resembling an hierarchal aerial antenna, was obtained using an innovative microwave irradiation process. There, the combination of chemical synthesis along accelerated micro wave irradiation digestion process, allows us to control precisely the morphology and distribution of the Ag/ZnO nanostructure. Because of the high order arrangement exhibited for the nanosystem as well as high rate of reproducibility in the production process, we opted to tested the nanostructures in a set of experiments ranging from the bulk properties down to in-situ nanoscale; in order to gain valuable information from the experiments and with the aim to give a real application to the nanomaterial. In this order, first, we described the far and near electric field generated for the nantenna obtained from electrical radiation patterns resulting from phase map reconstruction using off-axis electron holography. It is important to notice that knowing the properties at nanoscale level, it will give key insight of mechanism through which the metal-semiconductor (Ag-ZnO) behaves in opto-electronic applications. In fact, using electric numerical approximations methods for a finite number of ZnO nanorods on Ag nanowires it was shown that the electric radiation intensities maps match closely the experimental results obtained with electron holography. Additionally, to reinforce the understanding of how the metal-semiconductor (Ag-ZnO) nanostructures could be used as an active element on photo-signal reception/transmitter generation it was investigated the photo - catalytic activity by employing dynamic UV-vis spectrometry. There, it was determined a kinetic constant of photodegradation around k=0.0037 min-1 which is related with the capability of the nano-system to convert a photo-excitation signal onto a converted electrical stimulated signal. Moreover, studies of Raman spectroscopy shown the main activated vibrational modes corresponding to frequencies in the THz range, those were found to be characteristic of longitudinal and transversal modes with particularly two enhanced bands near to the infrared region (1200 cm-1) assigned to be optical overtones originated from the high ordered distribution contributing to the vibrational frequency of the whole system. Additionally, thermo-electric and electrical measurements were performed on the nanosystem ZnO NRs for testing the thermo-electrical properties by measuring the thermal coefficient of resistance (TCR) for the material in bulk. Particularly, for in-situ electrical measurements a single multi-pentagonal nanostructure of ZnO NRs was nano-manipulated to create a simple electrical circuit containing the nanostructure as a pasive element to measure directly the response current vs voltage to obtain the conductivity of the material by using emphin-situ TEM. Furthermore, because of the high directionality exhibited for the multi-pentagonal arrangement, studies of the growth mechanism along the active/contact faces of the heterojunction have been performed by mapping dynamical electron diffraction patterns under fin-situ precession electron diffraction (PED) to understand the coupling mechanism between the metal-semiconductor system. Indeed, the orientation phase maps, retrieved from PED, shown a preferential axis of growing (0001) of ZnO NRs along the expose faces (001) of silver nanowires. For completeness, x-ray diffraction in Brang-Bretano configuration shown the characteristic phases for both ZnO and Silver. The understanding of both opto-electronic properties as well as the mechanisms through which the contact metal-semiconductor behaves at nanoscale level undoubtedly will allow us to elucidate the receiving/transmitting mechanism on future nanoantennas applications.

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Keywords
Electron Holography, Nano-optic, Nanoantennas, Nanomanipulation, Precession Electron Diffraction, ZnO
Citation
Department
Physics and Astronomy