Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
8 results
Search Results
Item Third-order nonlinear optical properties of Mn doped ZnO thin films under cw laser illumination(Elsevier B.V., 2013) Nagaraja, K.K.; Pramodini, S.; Santhosh Kumar, A.; Nagaraja, H.S.; Poornesh, P.; Kekuda, D.We report the measurements of third-order nonlinear optical properties of undoped zinc oxide and manganese doped zinc oxide thin films with different doping concentrations investigated using z-scan technique. Thin films were prepared by radio frequency magnetron sputtering using a compound target on glass substrate at room temperature. The structural properties of the deposited films were analysed by X-ray diffraction studies. The atomic force microscope analysis of the deposited films reveals that the grain size and roughness of the films depend on the Mn concentration. The direct energy band gap of the deposited film increases with the increase in Mn concentration in the films. The nonlinear optical measurements were carried out using a cw He-Ne laser at 633 nm wavelength. The z-scan results reveal that the films exhibit self-defocusing nonlinearity. The third-order nonlinear optical susceptibility ?(3) is found to be of the order of 10-3 esu. The films investigated here exhibit good optical power limiting at the experimental wavelength. © 2012 Elsevier B.V. All rights reserved.Item Effect of Sn doping on structural, optical, electrical and wettability properties of oriented ZnO nanorod arrays(2013) Santhosh Kumar, A.; Nagaraja, K.K.; Nagaraja, H.S.Herein we present a modified sol gel route for the one step fabrication of oriented ZnO nanorod arrays. The method is seed layer free, and nanorods directly attach to a substrate. We also present the effect of tin (Sn) content on the crystallinity, microstructural, optical and electrical properties of the ZnO nanorod arrays. Thermo gravimetric (TG) curves of gel precursors showed that most of the organic groups and other volatiles were removed at about 450 C. X-ray diffraction patterns confirmed that the films were polycrystalline in nature with (002) preferred orientation. The texture coefficient, grain size, dislocation density and lattice parameters of the ZnO arrays were determined. The SEM micrographs revealed that the undoped and 1 at.%Sn doped films were composed of nanorods and the concentration of 2 at.%Sn doping hindered the rod like structure growth and modulated into granular nature. UV-visible transmission spectroscopy indicated that the transparency of the films increased with Sn content. On Sn doping, the films also exhibited a red shift and slight shrinkage of band gap. The electrical studies revealed that 1 at.% of Sn doping enhanced electrical conduction in ZnO films and beyond that the distortion caused in the lattice reduced the conductivity. The contact angle of the ZnO nanostructures varied between 91 and 115 depending upon the Sn content. Therefore, 1 at.%Sn doping into ZnO nanorods improves the crystallinity, electrical conductivity and water contact angle. © 2013 Springer Science+Business Media New York.Item Influence of Sn doping on photoluminescence and photoelectrochemical properties of ZnO nanorod arrays(Kluwer Academic Publishers, 2014) Santhosh Kumar, A.S.; Huang, N.M.; Nagaraja, H.S.Herein, the nanostructured Sn containing ZnO is directly synthesized on the surface of substrate by modified sol gel approach under low-temperature condition. The samples are characterized by scanning electron microscopy (SEM), x-ray diffraction (XRD), Raman-scattering, photoluminescence (PL) and photoelectrochemical analyses. The SEM micrographs show that the undoped and 1 at. % Sn doped films are composed of nanorods and the concentration of 2 at. % Sn doping hinders the rod-like structure's growth and modulates into granular nature. The investigations of XRD reveal that the synthesized undoped and Sn doped ZnO nanorods possess a perfect hexagonal growth habit of wurtzite zinc oxide, along the (002) direction of preference. The Raman spectra demonstrate that the vibrational mode of E1(LO), which is very weak in undoped and 1at. % Sn doped ZnO, is strongly enhanced with 2 at. % Sn doping into ZnO lattice. PL spectra show that strong UV emission in pure and 1 at. % Sn doped ZnO, while there is dominant green emission in 2 at. % Sn doped ZnO. Moreover, all the samples are photo electrochemically active and exhibit the highest photocurrent of 28 ?A for the 1 at. % Sn doped ZnO nanorod arrays in 0.2M Na2SO4 electrolyte, on light irradiation. Time dependent photoresponse tests are carried out by measuring the photocurrent under chopped light irradiation. © 2014 The Korean Institute of Metals and Materials and Springer Science+Business Media Dordrecht.Item Structural, linear, and nonlinear optical properties of radio frequency-sputtered nitrogen-doped ZnO thin films studied using z-scan technique(Institute of Physics Publishing custserv@iop.org, 2014) Nagaraja, K.K.; Pramodini, S.; Santhosh Kumar, A.S.; Nagaraja, H.S.; Poornesh, P.The third-order nonlinear optical properties of undoped and nitrogen-doped ZnO thin films were evaluated using the z-scan technique. The films were sputter-deposited on glass substrates using radio frequency power. The He-Ne continuous wave laser operating at 633 nm was used as an irradiation source. A change in the growth mode in the nitrogen-doped films was observed. The grain size and roughness were found to be dependent on the nitrogen concentration, as shown by atomic force microscopy analysis. The optical band gap was determined and found to increase with nitrogen concentration in the films. Both nonlinear absorption and refraction nonlinearities were exhibited by the deposited films. The nonlinear refractive index n2, the nonlinear absorption coefficient ?eff and the third-order nonlinear optical susceptibility ?(3) were determined and found to be largest. Multiple diffraction ring patterns were observed when the samples were made to interact with the laser beam and were attributed to refractive index change and thermal lensing. Further, optical power-limiting experiments were performed to determine the optical-limiting threshold and clamping values for undoped and nitrogen-doped ZnO films. © 2014 Astro Ltd.Item Preparation, characterization and photoelectrochemical properties of hydrophilic Sn doped TiO2 nanostructures(Elsevier, 2014) Santhosh Kumar, A.S.; Nagaraja, K.K.; Huang, N.M.; Nagaraja, H.S.Abstract Hydrophilic Sn doped TiO2 nanostructured thin films have been fabricated using a sol-gel method, and followed by calcination at 450 C. The samples are characterized by means of XRD, Raman, SEM and contact angle measurements. The XRD and Raman studies revealed that, the higher Sn doping content (3 at%) leads to the formation of mixed phases of TiO2. SEM micrographs revealed that all samples are porous in nature. The contact angle of TiO2 nanostructured films varied between 19 and 37 depending upon the Sn content. All the samples are photoelectrochemically active and 2% Sn doping significantly enhances the photoelectrochemical ability of TiO 2 film. The highest photocurrent density of 20 ?A cm-2 is measured for 2 at% Sn doped TiO2 in 0.2 M Na2SO 4 electrolyte, on light irradiation. Time dependent photoresponse tests have been carried out by measuring the photocurrent under chopped light irradiation. © 2014 Elsevier B.V.Item Influence of annealing on the linear and nonlinear optical properties of Mn doped ZnO thin films examined by z-scan technique in CW regime(Elsevier B.V., 2016) Nagaraja, K.K.; Pramodini, S.; Poornesh, P.; Rao, A.; Nagaraja, H.S.We present the studies on the influence of annealing on the third-order nonlinear optical properties of RF magnetron sputtered manganese doped zinc oxide (MZO) thin films with different doping concentration. It is revealed that the incorporation of Mn into ZnO and annealing lead to prominent changes in the third order nonlinearity. Nonlinear optical measurements were carried out by employing the z-scan technique using a continuous wave (CW) He-Ne laser of 633 nm. The z-scan results reveal that the films exhibit self-defocusing thermal nonlinearity. The third-order nonlinear optical susceptibility ?(3) was found to be of the order of 10-3 esu and 10-2 esu for annealed MZO thin films at 200 °C and 400 °C respectively. The dependence of grain size on the observed nonlinearity was revealed by atomic force microscopy analysis. Optical limiting studies were carried out for a range of input power levels and an optical limiting of about ?8 mW was observed indicating the possible application for photonic devices. © 2016 Elsevier B.V. All rights reserved.Item Cerium doping of FeS2 for the effective hydrogen evolution reaction (HER) electrocatalysis(Taylor and Francis Ltd., 2025) Hegde, A.P.; Gonde, A.; Kumawat, A.; Mukesh, P.; Lakshmisagar, G.; Kumar, A.; Nagaraja, H.S.Crafting and developing nanostructured electrocatalyst materials that are both active and stable plays a pivotal role in the shift toward economically viable hydrogen production through electrochemical water splitting, paving the way for the future replacement of fossil fuels. Such materials need to be cost-effective, simple to produce, and durable. In this context, the current research delves into improving the hydrogen evolution reaction (HER) electrocatalytic performance by incorporating cerium (Ce) into iron disulfide (FeS2) catalysts, using an uncomplicated hydrothermal fabrication approach. The study systematically examines the effects of various Ce doping levels on electrocatalytic activity. Notably, the catalyst with 15% Ce doping demonstrated exceptional efficiency, reducing the overpotential to 369 mV at 100 mA cm?2 current density. This enhanced performance can be attributed to the reduction in total charge-transfer resistance and a significant increase in the electrochemical active surface area (ECSA). Furthermore, the durability assessment of the 15% Ce-doped sample revealed its ability to sustain its catalytic activity for over 100 h under a continuous HER operation at 300 mA cm-2, with low performance-falloff. These results highlight the potential of Ce-dopping of FeS2 catalysts as a formidable choice for achieving efficient and long lasting HER electrocatalysis. © 2025 Taylor & Francis Group, LLC.Item Enhancing conductivity of Bi2O3 through ‘Fe3+’ doping for pseudocapacitor application(Springer Science and Business Media Deutschland GmbH, 2025) G, L.S.; Bhat, K.S.; Mukesh, P.; Hegde, A.P.; Kumar, A.; Brijesh, K.; Nagaraja, H.S.Binary metal oxides have emerged as pSromising materials for advanced electrochemical energy storage systems due to their superior performance characteristics. In this study, we focus on bismuth oxide (Bi?O?), a material renowned for its high theoretical capacity, wide potential range, and exceptional power density, as a potential candidate for supercapacitors. Iron doping was employed as a strategy to enhance its electrochemical performance and modulate the band gap, thereby improving conductivity and charge storage efficiency. Fe-doped bismuth oxide (Fe-Bi?O?) was synthesized via a solvothermal method with varying iron concentrations (2%, 4%, and 6%), followed by annealing. The pure and iron-doped bismuth oxide samples revealed a combination of monoclinic and cubic phases and a prominent micro-sheet architecture. The introduction of iron doping led to a noticeable reduction in the band gap, highlighting its role in fine-tuning the electronic properties for enhanced energy storage capabilities. The electrochemical evaluation highlighted the 4% Fe-Bi?O? sample as the optimal composition, achieving a remarkable specific capacity of 904 F g?1, a substantial improvement over 101 F g?1 for pristine Bi?O?, at 1 A g?1 in a 2 M KOH electrolyte. Moreover, this sample exhibited outstanding cyclic stability, retaining 104 F g?1 after 2000 cycles at 10 A g?1. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.