Vol. 128, Issue 5, May 2011, pp.100-114

New Method for Fabrication of Co₃O₄ Thin Film Sensors: Structural, Morphological and Optoelectronic Properties

^aVikas Patil, ^aShailesh Pawar, ^aManik Chougule, ^aBharat Raut, ^aRamesh Mulik, ^bShashwati Sen

^aMaterials Research Laboratory, School of Physical Sciences, Solapur University,

Solapur-413255, M. S., India

^b Crystal Technology Section, Bhabha atomic Research Centre, Mumbai, India

E-mail: drvbpatil@gmail.com

Received: 16 April 2011   /Accepted: 20 May 2011   /Published: 28 May 2011

Abstract: Nanocrystalline Co₃O₄ thin films have been deposited by spin coating technique and then have been analyzed to test their application in NH₃ gas-sensing technology. In particular, spectrophotometric and conductivity measurements have been performed in order to determine the optical and electrical properties of Co₃O₄ thin films. The structure and the morphology of such material have been investigated by X ray diffraction and Scanning electron microscopy.

The X-ray diffraction studies confirmed that the films grown by this technique have good crystalline cubic spinel structure and present a random orientation. The morphology of the sol gel derived Co₃O₄ shows nanocrystalline grains with some overgrown clusters .The optical band gap has been determined from the absorption coefficient. We found that the optical band gap energy decreases from 2.58 eV to 2.07 eV with increasing annealing temperature between 400-700 ^oC. These mean that the optical quality of Co₃O₄ films is improved by annealing.

The dc electrical conductivity of Co₃O₄ thin films were increased from 10^-4 to 10^-2(Ω cm)^-1 with increase in annealing temperature. The electron carrier concentration (n) and mobility (μ) of Co₃O₄ films annealed at 400-700 ^oC were estimated to be of the order of 2.4 to 4.5 x 10¹⁹ cm^-3 and 5.2 to 7.0 x 10^-5 cm² V^-1 s^-1 respectively. It is observed that Co₃O₄ thin film annealing at 700 ^oC after deposition provide a smooth and flat texture suited for optoelectronic applications. Gas sensing properties showed that the Co₃O₄ films (at 700 ^oC) were sensitive as well as fast in responding to NH₃. A high sensitivity for ammonia indicates that the Co₃O₄ films are selective for this gas.

Keywords: Co₃O₄ sensor, Structural properties, Optical properties, Electrical properties

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