Preparation of Shape and Size-Controlled Zinc Oxide Nanostructures by Chemical Spray Pyrolysis Technique
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Preparation of Shape and Size-Controlled Zinc Oxide Nanostructures by Chemical Spray Pyrolysis Technique Tatjana Dedova, Malle Krunks, Arvo Mere, Jelena Klauson, and Olga Volobujeva Department of Materials Science, Tallinn University of Technology, Ehitajate tee 5, Tallinn, 19086, Estonia
ABSTRACT Highly structured layers comprising zinc oxide rods, tripods or platelets were fabricated by spray pyrolysis method at temperatures of 510-550 °C. Zinc chloride solution was pulverized onto the preheated substrates of glass and ITO, SnO2, ZnO covered glass using a pneumatic spray set-up. ZnO layers were characterized by scanning electron microscopy and Raman spectroscopy. C-axis orientated ZnO nanorod arrays of well-developed hexagonal rods with length from some hundreds of nanometers up to some microns and diameter from 70 nm up to 200-300 nm were prepared on glass and metal oxide coated glass substrates. Alcoholic solutions allow deposit thinner rods and reduce the deposition temperature. By increasing the solution concentration the nanorods are developing into the tripods on glass substrates and into the platelet-shape crystals on metal oxide covered substrates. Strong and narrow E2 Raman bands indicate that ZnO structured layers prepared by spray pyrolysis technique are of high crystal quality. INTRODUCTION One-dimensional semiconductor nanostructures are attracting a great interest for future nanoscale electronic and optoelectronic devices [1]. ZnO nanostructures have potential applications in solar cells, gas sensors, short-wavelength light emitting and field effect devices, Schottky diodes, etc [2]. In addition, ZnO nanorod arrays are of specific interest for use as substrates in solar cells due to their high surface area and specific crystalline orientation [3,4]. So far, many methods have successfully been employed to grow ZnO nanorod arrays, such as vapour-liquid-solid (VLS) [5], chemical vapour deposition (CVD) methods [2,6,7] and wet chemical low temperature techniques [8,9]. In this work a simple spray pyrolysis technique has been applied to prepare ZnO rods. Compared to other methods, spray pyrolysis has the following advantages such as simple and inexpensive apparatus, possibility to cover large areas, and easily scalable to industrial production. In our previous work [10] we have demonstrated the possibility to obtain high quality c-axis orientated ZnO rods by spray on glass substrates. However, for applications in electronic devices, nanostructures should be grown on conductive transparent electrodes instead of bare glass. In present study we investigated the formation of ZnO nanostructures onto different substrates: glass, conductive oxides as ITO, SnO2 and sprayed ZnO “seed” layers covered glass substrates. The influence of precursor concentration, growth temperature and nature of solvent on growth of ZnO nanostructured layers is reported here.
EXPERIMENTAL ZnO nanostructured layers were prepared by spraying a solution of zinc chloride (Aldrich, high purity) with a concentration of 0.05 t
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