A Resistless Process for the Production of Patterned, Vertically Aligned ZnO Nanowires

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A Resistless Process for the Production of Patterned, Vertically Aligned ZnO Nanowires. Mikhail Ladanov1, 2, 3, Kranthi Kumar Elineni2, Manoj Ram2, 3, Nathan D. Gallant2, Ashok Kumar2, 3, Garrett Matthews4 1

Department of Electrical Engineering, University of South Florida, Tampa, FL, United States. Department of Mechanical Engineering, University of South Florida, Tampa, FL, United States. 3 Nanotechnology Research and Education Center, University of South Florida, Tampa, FL, United States. 4 Department of Physics, University of South Florida, Tampa, FL, United States. 2

ABSTRACT ZnO nanostructures have attracted a great deal of interest because of their biocompatibility and outstanding optical and piezoelectric properties. Their uses are widely varying, including as the active element in sensors, solar cells, and nanogenerators. One of the major complications in device development is how to grow ZnO nanowires in well aligned and patterned films with predefined geometrical shape and aspect ratio. Controlled growth is required to achieve the optimal density of nanowires and to produce a defined geometric structure for incorporation in the device. In this work, we have presented a method by which vertically aligned ZnO nanowires could be grown in defined patterns on surfaces without the use of resists. We used a hydrothermal method to grow ZnO nanowires on a substrate through growth modifiers that was pre-patterned with a seeding solution by means of microcontact printing. This method produced vertically aligned ZnO nanowires of predefined size and shape with pattern resolution high enough for the production of rows of single nanowires. The nanowires were characterized by using scanning electron microscopy (SEM) and X-ray diffraction spectroscopy (XRD) techniques. INTRODUCTION Recently, ZnO nanostructures have attracted great attention. ZnO is a II-VI semiconductor with a wide direct band gap of 3.37 eV and large exciton binding energy of 60 meV making it suitable for application in UV lasers[1], light emitting diodes[2], sensors[3], nanogenerators[4-6] and solar cells[7]. Many methods have been used to prepare ZnO nanowires, including using chemical vapor deposition[3, 8], metal–organic chemical deposition[8, 9], pulsed laser deposition[10], physical vapor deposition[11, 12], vapor-liquid-solid methods[6, 13] as well as the hydrothermal method[1, 14, 15] used in this work. The latter is one of the most simple and cost effective methods, making it straightforward to scale up production[1, 14, 16]. Patterned growth of ZnO nanowires using hydrothermal methods have been studied extensively[17, 18] as it is a simple way to produce spatially distributed nanowires for device fabrication. The use of microcontact printing (µCP)[19] has become common for the modification of surfaces with monolayer domains, though its use as a method for patterning nanowire growth has not been well explored.

In this paper we have demonstrated vertically aligned and patterned ZnO nanowires on silicon substrates. These structures were produc