Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
93 results
Search Results
Item Aluminum doped ZnO thin films by RF sputtering of coaxial ZnO and Al targets(2011) Nagaraja, K.K.; Santhosh Kumar, A.S.; Nagaraja, H.S.Transparent conducting aluminum doped zinc oxide (AZO) films were deposited on glass substrates by radio (RF) frequency magnetron sputtering employing zinc oxide and aluminum targets. The targets are fixed coaxially in one cathode, by using a center hollow aluminum disc. Gas pressure was kept constant and the sputter power was varied. The nature of AZO film was found to be polycrystalline with hexagonal structure and a preferred orientation along c-axis. The Al content in the films is determined using EDXA analysis and it is found to vary with the applied power. Surface morphology of the films was found to be uniform and has fine grained structure. Electrical resistivity of the deposited films was found to be as low as 26×10-4Ω-cm for the film deposited at 250 W. The average transparencies up to 85% in the visible region were obtained for all the films. Optical band gap of the films show a slight blue shift as indicated by the (αhν)2 v/s hν plots. In the present investigation we have controlled Al content in the films by adjusting the power to the coaxial targets. The value of resistivity was found to decrease with the amount of Al present in the sample. © 2011 American Institute of Physics.Item Growth and temperature dependent electrical properties of ZnO nanostructures(2013) Santhosh Kumar, A.; Nagaraja, K.K.; Nagaraja, H.S.Zinc oxide (ZnO) nanostructured films are grown using Polyvinyal alcohol (PVA)-citric acid modified sol gel process and the effect of (0, 1, and 2Wt%) PVA content on growth, crystallanity, microstructure and electrical properties are investigated. The XRD patterns confirm that the films are polycrystalline nature. 1 Wt% assisted grown samples are found to be good crystallanity with (002) preferred orientation. The SEM micrographs confirm that the 1 Wt% PVA assisted grown films are composed of vertically oriented ∼1.2 μm length nanorods. The temperature dependent electrical resistivity of the films has been measured using the four-probe method. The electrical resistivity found to be 7.08 ω-cm at room temperature for vertically oriented nanorods composed films, which are grown using 1Wt% PVA. © 2013 AIP Publishing LLC.Item Polymer assisted preparation and characterization of ZnO and Sn doped ZnO nanostructures(Institute of Physics Publishing custserv@iop.org, 2015) Santhosh Kumar, A.S.; Nagaraja, K.K.; Nagaraja, H.S.Zinc oxide (ZnO) and tin doped ZnO are wide band gap semiconducting materials with excellent optoelectronic properties. In the present study ZnO and Sn: ZnO films are prepared using polymer assisted sol gel process. The thermal behaviour of the dried gel sample studied using DTA and TG analysis. TG-DTA result shown that most of the organic of PVA and CH3COO group of zinc acetate and other volatiles are removed below 500°C. The effect of Sn on the crystallinity, microstructral properties of the deposited films was investigated. XRD patterns of undoped and Sn doped ZnO films indicate enhanced intensities for the peak corresponding to (002) plane, resulting preferential orientation along the c-axis. The SEM images confirm that the grown films are composed of nanorods. © Published under licence by IOP Publishing Ltd.Item Fabrication and characterization of ZnO/AI/ZnO multilayers by simultaneous DC and RF magnetron sputtering(Institute of Physics Publishing custserv@iop.org, 2015) Nagaraja, K.K.; Santhosh Kumar, A.S.; Nagaraja, H.S.The present investigation reports the fabrication and characterization of multilayered transparent electrodes by simultaneous DC and RF magnetron sputtering on glass substrates. The multilayer structure consists of three layers (ZnO/Al/ZnO). The influence of Al layer thickness on the electrical and optical properties was investigated. Optimum thickness of Al was determined for high transmittance and good electrical conductivity. High quality films having resistance as low as 25 Ω/sq with optical transmittance upto 65% were obtained at room temperature. © Published under licence by IOP Publishing Ltd.Item The effect of etching time on structural properties of Porous silicon at the room temperature(Elsevier Ltd, 2016) Ramesh, M.; Nagaraja, H.S.Nano-porous silicon (PS) layers have been prepared by electrochemical etching of (100) silicon wafer in the solution of hydrofluoric acid (HF) and ethanol (C2H5OH). In this paper, XRD and FTIR confirm the formation of PS. The size of crystallites in the porous Si layers was found from XRD, which isaround ~2.4 nm. The evolution of morphology of PS as a function of etching time is imaged using SEM. The average pore-diameter has been calculated from the image j software, which is in the range of 238-1117nm. The Raman spectra reveal that the peak intensities sharply increase with etching time due to presence of nancrystals on the surface of PS. It was observed that the peak of Raman signal was around ~520.5cm-1. Luminescence studies revealedthat the strong photoluminescence emission was observed at about ~660nm. It possesses a broad red emission band on the surface of PS due to the growth of Si=O bonds and the formation of silicon hydrides (SiHx), which is caused to trapped electron states at the interface between the crystalline Si and SiO2. © 2016 Elsevier Ltd.Item Hydrazine sensing properties of microwave synthesized graphene/ZnO composites(American Institute of Physics Inc. subs@aip.org, 2016) Moolayadukkam, M.; Nagaraja, H.S.; Bhat, K.U.This paper reports the synthesis of graphene/ ZnO nanocomposite using microwave method and its application in sensing of hydrazine. The morphological characteristics of the samples are studied using Scanning Electron Microscope (SEM). The formation of the composite is further confirmed by the X-ray Diffraction (XRD). Energy Dispersive X-ray Analysis (EDAX) shows the presence of carbon indicating the presence of graphene. The hydrazine sensing property of the electrode is studied using cyclic voltammometry (CV) and Chronoamperometry (CA) studeis. © 2016 Author(s).Item Structural and magnetic studies of tin doped α-Fe2O3 (α-SnxFe2-xO3) nanoparticles prepared by microwave assisted synthesis(American Institute of Physics Inc. subs@aip.org, 2016) Bindu, K.; Chowdhury, P.; Ajith, A.; Nagaraja, H.S.Hematite (α-Fe2O3) doped with tetravalent ions have potential applications in various fields such as gas sensors, memories, energy storage devices because of their electrical and magnetic properties. Microwave assisted synthesis was used to prepare Tin doped α-Fe2O3 [α-SnxFe2-xO3]. The structural and morphological studies were investigated using X-ray diffraction (XRD) and Scanning electron microscopy (SEM). XRD patterns revealed that α-Fe2O3 and α-SnxFe2-xO3 were having rhombohedral structure. The compositional study was done by Energy dispersive X-ray Spectroscopy (EDS). The magnetic properties were studied by Vibrating Sample Magnetometry (VSM). Results shows that the prepared samples were found to be antiferromagnetic in nature and the results are discussed in detail. © 2016 Author(s).Item Effect of Composition on Designed Tandem Absorber to Achieve Selective Properties for High Temperature Solar Thermal Applications(Elsevier Ltd, 2017) Jyothi, J.; Nagaraja, H.S.; Barshilia, H.C.We have designed a tandem absorber comprising of five layers namely:TiAlC / TiAlCN / TiAlSiCN / TiAlSiCO / TiAlSiO on stainless steel substrate by DC unbalanced magnetron sputtering system.Tandem absorber shows a high absorptance of 0.961 with an emittance of 0.15 by careful optimization of flow rates and thicknesses of the individual layers. Further, the detailed effects of reactive gas flow rates and thicknesses of each individual layers on the optical properties were studied. Growth rate and thicknesses of each individual layers of the tandem absorber were studied by cross-section FESEM images. The tandem absorber shows long term thermal stability when annealed in vacuum at 600°C for more than 750 h under cyclic heating conditions, indicating suitability of the tandem absorber for solar thermal high temperature applications. © 2017 Elsevier Ltd. All rights reserved.Item Corrosion Behaviour and Characterization of Thermal Sprayed Coating of Nickel Chromium Cermet on Low Carbon Steel(Elsevier Ltd, 2018) Amudha, A.; Shashikala, H.D.; Nagaraja, H.S.Corrosion is the major problem faced by Navy, especially when pumps, ship impellers and other components have to work in harsh environments like sea water. Therefore, high corrosion resistant metal ceramic matrix 75Cr3C2- 25 (NiCr) cermet has been one of the good choices for coating. In this study, we are discussing the HVOF (High Velocity Oxy Fuel) coating of 75Cr3C2-25(NiCr) on the low carbon steel substrate, IS 2062 grade B. The as coated samples were annealed at 600°C for 1 hour, 2hour and 3hours. The electrochemical tests were conducted for corrosion evaluation. Structural analysis was done by using X-Ray diffraction technique. Microstructure and thickness of the coating was studied using Scanning Electron Microscopy (SEM). Density measurement studies were done on as-coated and annealed coupons. © 2017 Elsevier Ltd.Item Electrochemical corrosion behaviour of nickel chromium-chromium carbide coating by HVOF process(American Institute of Physics Inc. subs@aip.org, 2018) Amudha, A.; Nagaraja, H.S.; Shashikala, H.D.To overcome the corrosion problem in marine industry, coatings are one of the most economical solutions. In this paper, the corrosion behaviour of 25(NiCr)-75Cr3C2 cermet coating on low carbon steel substrate by HVOF process is studied. Different phases such as Cr7C3 and Cr3C2, along with Ni and chromium oxide(Cr3O2) constituents present in the coating were revealed by X-Ray Diffraction (XRD) analysis. The morphology of the coating obtained by scanning electron microscope (SEM) gave confirmation for the XRD analysis. Electrochemical corrosion techniques such as Linear Polarization Resistance (LPR) and Electrochemical Impedance Spectroscopy (EIS) were used to study the corrosion behaviour of the cermet in 3.5wt% NaCl electrolyte solution. The corrosion current density of the coated sample and substrate were found to be 6.878μA/cm-2 and 21.091μA/cm-2 respectively. The Nyquist Impedance spectra were used to derive an equivalent circuit to analyze the interaction between the coating and electrolyte. The Bode Impedance plots obtained by EIS for the coating showed a typical passive material capacitive behaviour, indicated by medium to low frequency with phase angle approaching -60o, suggesting that a stable film is formed on the tested material in the electrolyte used. © 2018 Author(s).