Indium Tin Oxide Nanoparticles Prepared by Chemical Vapor Synthesis
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Indium Tin Oxide Nanoparticles prepared by Chemical Vapor Synthesis Joachim U. Brehm, Markus Winterer and Horst Hahn Institute of Materials Science, Darmstadt University of Technology Darmstadt, D-64287, Germany Günther Michael and Andreas Gutsch Degussa AG Hanau, D-63403, Germany ABSTRACT Nanoparticles of indium oxide, tin oxide and indium oxide doped with tin oxide (ITO) have been prepared by Chemical Vapor Synthesis, CVS (a modified CVD process), starting with In-(tmhd)3 as precursor. A modification of the CVS process using a novel radio-frequency reaction zone has been developed in order to avoid the rapid decomposition of the nanocrystalline indium oxide particles at high temperatures. These oxides are candidates for applications as transparent conducting oxides, catalysts and gas sensors. Structural characterization by high resolution scanning and transmission electron microscopy and X-ray-diffraction has been used to determine the phase, grain size, grain size distribution and crystallinity of the nanoparticles. The specific surface area, and particle or agglomerate size of the powders have been measured by nitrogen sorption. Agglomerate sizes in aqueous dispersions have been determined by photon correlation spectroscopy. Zeta-potentials were measured. As well CVS powders exhibit a narrow size distribution with an average size of about 5 nm.
INTRODUCTION Optically transparent and electrically conducting oxides were first discovered by Badeker [1] in 1907. He found that films of cadmium became transparent, but remained electrically conductive after oxidation. Fifty years later SnO2 and Sn-doped In2O3 where found to be transparent conducting oxides (TCO´s) when deposited as thin films. Since then indium tin oxide (ITO) has become the most commonly used TCO in industrial applications. Applications are in flat panel displays, low-emissivity windows, solar cells, transparent heating elements for windscreens, gas sensors, and antistatic coatings [2]. Today ITO films are prepared by sputtering or CVD processes. Advantages of these techniques are the possibilities of coating large areas at good film and thickness uniformity. Disadvantage is the relatively high substrate temperature. Therefore, redispersible powders of nanosized TCO´s are of interest. There have been a number of successive reports on synthesizing these by wet chemical processes and bv Physical Vapor Synthesis called synthesis methods. Here we present the synthesis of indium oxide, tin oxide and ITO by Plasma-Assisted Chemical Vapor Synthesis (PA-CVS).
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Figure 1. Experimental setup of the PA-CVS system, (T1 was about 200-220°C, T2 20°C higher than T1, the evaporation temperature of the Sn-precursor was 80°C)
EXPERIMENTAL DETAILS Indium oxide was synthesized using Indium-tetramethyl-heptanedionate (In-tmhd3) as solid precursor (Chempur GmbH, Karlsruhe, Germany) and tin oxide using tin-IV t-butoxide, a liquid precursor (Inorgtech Ltd., Mildenhall, UK). Figure 1 shows a schematic drawing of the experimental setup of the reactor. Argon (200 sccm
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