Humidity Sensing Property of Zinc Oxide Film Deposited by PLD
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1074-I05-27
Humidity Sensing Property of Zinc Oxide Film Deposited by PLD Shobhna Dixit, K. C. Dubey, K. P. Mishra, Atul Srivastava, R. K. Shukla, and Anchal Srivastava Department of Physics, University of Lucknow, University Road, Lucknow, 226007, India ABSTRACT This paper reports structural, morphological, optical and humidity sensing characteristics of pulsed laser deposited ZnO film. The XRD pattern reveals predominant amorphous structure of the film. Scanning electron micrograph indicates formation of ZnO rods in micron size. Transmission increases gradually in the UV-VIS region. For studying the humidity sensing characteristics of the film, base of a right angled isosceles glass prism has been coated. Chopped light from a polarized He-Ne laser incident on the entry face of the prism gets reflected from the base – film – humid air interfaces and then emergent light is collected by the detector placed in front of the exit face of the prism. The least change in relative humidity which could be measured using the present configuration is 1.06RH%. Further the film is annealed at 4000C for four hours and its humidity sensing behavior is investigated in the similar manner which now shows a reversed trend. The sensitivity to humidity has decreased and the least change which could be detected now is 1.16RH%.
INTRODUCTION Zinc oxide is a non toxic, physically and chemically stable material found in abundance in nature. It has material properties that make it well – suited to applications in UV light emitters [1], transparent conducting electrodes [2-7], SAW devices [8, 9], piezoelectric transducers [10] and gas sensing [11, 12] devices. Transparency in the visible region and refractive index value higher than that of glass is particularly suitable for using ZnO in optical sensing. Also ZnO shows good adherence to many substrates. Moreover it is biosafe and biocompatible and hence can be used for biomedical applications as well. In this paper we report our study on zinc oxide thin film deposited by pulsed laser technique on glass substrate. Humidity sensing capability of the film besides its structural, morphological and transmission characteristics has also been presented. Most of the gas sensors [13, 14] and humidity sensors [15-17] reported earlier operate on the principle of modulation in some electrical parameters of the film due to chemisorption of gas/vapor molecules on the sensor surface. Unlike earlier reports in literature which are based on electrical properties of the film we have exploited the change in optical properties i.e. refractive index of the film occurring upon adsorption of vapor molecules. The opto-electronic sensing configuration [18-19] used for the experiment has been developed in our laboratory.
FABRICATION OF THE SENSING ELEMENT Pelletization of Zinc Oxide powder (99.999%, Aldrich Chemical Company Inc.) calcined for four hours at 8000C, is done at room temperature, by using uniaxial die press. The pellet is then sintered and polished. The substrates- glass slide and a right angled isoscel
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