Electron microscopy and physical studies of a new tungsten doped indium oxide transparent conductor

Advanced electron microscopy techniques - HREM and EFTEM - were used to study a new transparent conductive material: Indium Tungsten Oxide (IWO, in this work), which was synthesized from an aerosol. Indium oxide thin films doped with tungsten were deposited by spray pyrolysis for several %W concentration using (NH4)10W(12)O(41) and InCl3 dissolved in ethanol as starting compounds. The W6+ ions fulfill the electronic and structural requirements to work like a donor impurity in In,03 materials. The solution was sprayed onto silicon and glass substrates kept at 525 degrees C. Structural analysis was carried out from X-ray diffraction and selected area electron diffraction results reveal the structure of In2O3 with very small variations in crystallographic parameters. From electron microscopy observations, the nanostructured nature of the IWO compound was derived and from EFTEM micrographs the distribution of W reveals an increasing concentration in grain boundaries. Also scanning electron and atomic force microscopy techniques were used in order to determine the morphological and topological characteristics of the films. Also the number of carrier increases when W grows up to 5% weight and remains constant close to eta(e)=28 x 10(19) cm(-3). The mobility grows up 2% W weight and the decreases monotonically. The optical transmittance of the IWO was close to 78% for all the cases. From XPS studies, low intensity signals form W orbitals were detected. The identified signals correspond to W-4d(5/2) and to W-4f(7/2) which were found very close to 250 and 37 eV respectively. These signals correspond to W atoms surrounded by 0 atoms in a similar configuration to the one reported for WO. (c) 2007 Elsevier B.V. All rights reserved.