CONICET | Buscador de Institutos y Recursos Humanos

INTRODUCTIONThe broadband semiconductor nanostructures, mainly in the form of nanowires (NWs), nanobars, nanoparticles (NPs) and nanolayers, introduce a wide range of possibilities with promising innovative applications in different fields such as photonics, spintronics and optoelectronics1.In particular, ZnO nanostructures have been drawing increasing attention. ZnO is a n-type semiconductor with a direct wide band gap of 3.37 eV, which crystallizes in the hexagonal structure of wurzite, composed of monoatomic planes of O2- or Zn2+ tetrahedral coordinated that alternate along the axis of hexagonal symmetry (c). This property leads into faster growth along that axis, originating elongated nanostructures of nanobar or nanowire type, which make it potentially useful for the design of different nanotechnological devices.The potential of nanotechnology depends mainly on the ability to manipulate atoms and nanoparticles during the fabrication process of nanostructures. The flux of electrically charged nanoparticles can be controlled simply and efficiently through electric fields. In the electrophoretic technique (EDP), particles which have acquired electric charge in the liquid they suspend, move under the action of an electric field towards the electrode (substrate) with opposite charge2. EPD technique does not demand costly or sophisticated equipment, which is an enormous advantage for its application in the development of low-cost devices.Experimental results using EPD technique show that morphology and quality obtained in the deposition are strongly dependent upon substrate type and its surface morphology3. ZnO nanowires were successfully obtained by the use of substrates on which Au nanoclusters had been previously deposited4. In the present work, we investigate the influence of the cluster size and separation between Au nanoclusters on the properties of ZnO nanostructures grown by EPD. And also, with the aim of growing ZnO nanowires through EPD without the use of Au nanoclusters, boron doped Si substrates were used. EXPERIMENTAL STUDYThe growth of nanostructures was carried out through EPD, from a low concentration colloidal suspension of ZnO NPs in 2-propanol5. The size of the NPs obtained in the colloidal suspension was estimated from absorbance and photoluminescence measurements, which yielded an average diameter of 5 nm with a narrow size distribution, between 4 and 6 nm. The substrates used were commercial Si wafers and Si wafers where an Au nanolayer is deposited by sputtering and annealed at different conditions to produce distinct morphological nanometer-sized Au clusters. The ZnO nanostructures obtained were characterized by scanning electronic (SEM) and transmission microscopy, energy dispersive X-Ray spectroscopy, X-Ray diffraction and photoluminescence spectroscopy.RESULTS AND DISCUSSIONThe growth of thin films and novel nanostructures was carried out at room temperature through EPD, from a ZnO NPs colloidal suspension.The results of all the characterizations are discussed in detail in order to find a better understanding of the way in which the ZnO nanostructure grows by EPD, and also how the type of substrate affects the structural and photoluminescent properties of the obtained nanostructures.CONCLUSIONThe results show that the deposition of Au nanoclusters on the silicon substrate induces a vertical alignment of the ZnO nanoparticles which allows the formation of nanowires without the use of templates. This particular growth is probably due to increased electric field intensity near the Au nanocluster4. The obtained samples on boron doped Si substrates without Au nanoclusters showed novel nanostructures, like bunches of ZnO nanowires6.The influence of substrate and growing process parameters on quality, properties and morphology of the nanostructures produced, allows a glimpse of possible applications on the design of devices based on low-cost nanotechnology.REFERENCES[1] R.S. Hegde, et al. Nanoelectronics Devices, Circuits and Systems. Advanced Nanomaterials 289-315 (2019) [2] Ferrari B., et al. J. Eur. Ceram. Soc. 30, 1069 (2010)[3] Besra, L., et al. Prog. Mater Sci. 52, 1-61 (2007) [4] C. Sandoval, et al. Mater. Sci. Eng. B 187, 21 (2014)[5] D.W. Bahnemann, et al. J. Phys. Chem. 91, 3789 (1987)[6] O.A. Espindola, et al. ECI Symposium Series, (2017)