Chemical Vapor Functionalization of ZnO Nanocrystals
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1260-T01-05
Chemical Vapor Functionalization of ZnO Nanocrystals Moazzam Ali1, Marty D. Donakowski2 and Markus Winterer1 1
Nanoparticle Process Technology and Center for Nanointegration Duisburg-Essen (CeNide), University Duisburg-Essen, Duisburg 47057, Germany 2
Department of Chemistry, University of Minnesota, 207 Pleasant St. SE, Minneapolis MN 55455-0431 (USA) ABSTRACT Chemical Vapor Functionalization (CVF) is a method in which nanocrystals undergo in situ functionalization in the gas phase. In CVF, two reactors are used in series. The first reactor consists of a hot quartz tube (1073 K) where ZnO nanocrystals are synthesized in the gas phase from diethylzinc and oxygen. The second reactor, connected at the exit of the first one and kept at lower temperature (673 K), is used as functionalization chamber. At the connecting point of the two reactors, vapors of organic functionalizing agents are injected which react with the surface of ZnO nanocrystals. ZnO nanocrystals have been functionalized by 1-hexanol, n-hexanoic acid, n-hexanal and 1-hexylamine. Functionalized ZnO nanocrystals have been characterized by Dynamic Light Scattering, X-ray Diffraction and Diffuse Reflectance Infrared Fourier Transform Spectroscopy. INTRODUCTION In the last few years, the interest in printable electronics has substantially increased. The advantage of printable electronics is the feasibility of large-scale production of finely tuned patterns, even on flexible substrates. The ink required for printing, especially for inkjet printing, plays an important role in the quality and reliability of the final products. The preparation of different types of nanoparticulate inks – Indium-tinoxide (ITO), Si, ZrO2 – by different methods has been reported earlier [1-3]. In the investigation presented here, a new functionalization technique – Chemical Vapor Functionalization (CVF) – is developed for the preparation of zinc oxide (ZnO) nano-inks. The advantage of CVF is that the production is continuous and an industrial scale-up of the process is possible. ZnO nanocrystals produced by Chemical Vapor Synthesis (CVS) contain no functionalizing/capping agents (organic functional groups) [4], which makes it difficult to prepare stable colloidal dispersions (inks) from the powder. Typically, stable dispersions of ZnO nanocrystals are prepared by mixing ZnO nanocrystals with functionalizing agents in an appropriate solvent and applying ultrasonic treatment or other comminution techniques for a rather long period of time (around 60 minutes). Ultrasonic treatment not only helps the functionalization of the nanocrystals but it also breaks the agglomerates [4]. The advantage of CVF is that the functionalization of ZnO nanocrystals is performed in situ, which removes one processing step and also decreases the degree of aggregation. ZnO is a material known for various intrinsic point defects [5]. In CVS, ZnO nanocrystals are synthesized under non-equilibrium conditions, which may further increase the defect density [6].
The presence of oxygen vacancies i
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