© 2018, IJSRPAS All Rights Reserved 69 International Journal of Scientific Research in _______________________________ Research Paper . Physics and Applied Sciences Vol.6, Issue.6, pp.69-79, December (2018) E-ISSN: 2348-3423 MnO 2 -ZnO Hexagonal Nanomaterials: Characterization and High Performance Humidity Sensing Application Vikas Kumar Verma 1* , Narendra Kumar Pandey 2 1,2 Sensors and Materials Research Laboratory, Department of Physics, University of Lucknow, Lucknow, India *Corresponding Author Email: vikasverma37@gmail.com Available online at: www.isroset.org Received: 25/Nov/2018, Accepted: 10/Dec/2018, Online: 31/Dec/2018 Abstract---MnO 2 doped nanostructured zinc oxide was synthesized by solid state reaction route. The prepared material was characterized by X-ray diffraction, scanning electron microscope and UV-Vis absorption spectroscopy. The doping of MnO 2 in ZnÒ enhanced the crystallization and decreased the crystallite size. Surface morphology of the sensing material showed that the hexagonal shaped particles were uniformly distributed in zinc oxide that left large number of pores. These pores acted as humidity adsorption sites. With increase in the concentration of MnO 2 , the pores also increased. The optical band gap of pure ZnO was 4.05 eV. The value of band gap decreased with increase in the MnO 2 doping concentration. The average sensitivity of undoped zinc oxide was 3400 KΩ/%RH. The sensitivity of the sensing element increased with increase in the doping concentration. Sensitivity of MnO 2 doped ZnO composite is more than four times the sensitivity of pure zinc oxide at annealing temperature 600 o C. Keywords---Humidity Sensor; Zinc oxide; X-ray diffraction; Scanning electron microscopy; UV-Vis Spectroscopy. I. INTRODUCTION Humidity plays an important role in human life. Its tremendous importance is due to the fact that its vapour consists of highly reactive dipolar molecules which get condensed on or evaporate from surface even with slight variation in temperature of the environment. It, therefore, becomes necessary to measure and control the humidity. The humidity is one of the most frequently measured quantities and its measurement is complex and an old problem too [1-2]. Humidity sensors convert the amount of water (H 2 O) vapour into a measurable parameter. Humidity sensors based on different working principles have been developed and utilized in various applications [3–4]. Surface morphology has an important role in sensing properties. Researchers are developing cutting edge humidity sensors that show superb sensitivity, low hysteresis, and other amazing properties. Scientists are focusing more and more on impedance or resistive type humidity sensors due to low cost and better performance. The nano-grained ceramic materials provide opportunities for enhancing the performance of sensors because of their high surface to volume ratio. To enhance the sensing properties, therefore, it is essential to manipulate and control surface morphology so that high surface to volume ratio is available for effective sensing. To enhance sensing efficiency, some additives are used that play catalytic role. In the past few decades, metal oxide ceramic materials have attracted much attention of researchers due to their significant applications in microelectronic circuits, fuel cells, sensors, catalysts, optoelectronic devices and coatings for the passivation of surfaces with rust [5-11]. Zinc oxide (ZnO) is a versatile semiconductor with direct band gap of gap of ~3.37 eV and a large exciting binding energy of ~60 meV [12-13] at room temperature (RT). For photonic crystals ZnO is a promising candidate as functional components, gas sensors [14-15], light emitting diodes , solar cells, varistors and photo electrochemical cells [16-20]. ZnO nanomaterials has been synthesized with various structures and properties viz, nanoparticles, nanorods, nanocombs, nanowires, and tetrapod nanostructures [21-25]. Doping of selective element into ZnO is the primary method for manipulating and controlling its properties such as band gap or electrical conductivity, carrier concentration, etc. Studies have focused on the doping of transition metals Mn, Ni, Fe, Co and Cr into ZnO due to the potential applications in spintronics [26]. ZnO materials are believed to be non-toxic, bio-safe and biocompatible [27]. Doped and undoped ZnO nanostructures have the possibility of being applied for nano devices to detect gas and humidity because the response to different gases is related to a great extent to