Browsing by Author "Nagaraja, K.K."

Now showing 1 - 20 of 24

Aluminum doped ZnO thin films by RF sputtering of coaxial ZnO and Al targets
(2011) Nagaraja, K.K.; 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�10-4?-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 (?h?)2 v/s h? 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.
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 26Ã—10-4Î©-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 (Î±hÎ½)2 v/s hÎ½ 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. Â© 2011 American Institute of Physics.
Continuous wave laser probed thermal nonlinearity in TiO2 and TiO2-dye nano colloidal
(Elsevier Ltd, 2021) Pramodini, S.; Aravinda, L.S.; Nagaraja, K.K.; Poornesh, P.
Herein, we report on the nonlinear optical studies on the nano colloidal solutions of titanium dioxide (TiO2), TiO2-dye and acid blue dye in distilled water under continuous wave laser using the z-scan technique. The phase and structural properties of the sol–gel synthesized TiO2 nanoparticles at different temperatures were analyzed by x-ray powder diffraction (XRD) studies. The transmission electron microscopy (TEM) images confirmed that with an increase in calcination temperature, crystallite size increases. Further, the Fourier transform infrared (FTIR) spectra validate the synthesized TiO2 nano particle's structure. The results from the z-scan reveal self-defocusing and reverse saturable absorption (RSA) behaviors of nano colloidal. The real and imaginary parts of third-order nonlinear optical susceptibility ?(3) were determined and estimated as 10?6 esu. Also, the optical limiting behavior of the samples is studied; a clamping of around ~ 4 mW is observed for the TiO2-dye nano colloidal. © 2021 Elsevier Ltd
Conversion of microfiltration membrane into nanofiltration membrane by vapour phase deposition of aluminium for desalination application
(2011) Padaki, M.; Isloor, A.M.; Nagaraja, K.K.; Nagaraja, H.S.; Pattabi, M.
Preparation and modification of NF membrane are challenging aspects in research. In the present work, we have synthesised Polysulfone (PSf) microfiltration membrane and reduced the pore size to nano level by physical vapour deposition (PVD) of aluminium metal. Membrane pore size was reduced from micro pore to nano pore, which rejected 42.22% of NaCl from the solution with 164L/m2h. And also water permeation decreases from 1.10324-10-10 to the 9.141-10-12. The SEM and AFM pictures showed the surface modification and metal deposition in the pores. The performance of the membrane was studied by dead end flow cell using 3.5% of NaCl solution, in which PVD membrane showed 42.22% of rejection with 16.4L/m2h flux. Thermal analysis from DSC showed Tg of 265°C. Contact angle measurement, and water uptake were also reported. © 2011 Elsevier B.V.
Effect of annealing on the structural and nonlinear optical properties of ZnO thin films under cw regime
(2013) Nagaraja, K.K.; Pramodini, S.; Poornesh, P.; Nagaraja, H.S.
We report on the studies of the effects of annealing on the structural and third-order nonlinear optical properties of ZnO thin films deposited on quartz substrates by the RF magnetron sputtering technique. The films were annealed in the temperature range 400-1000 °C. The third-order nonlinear optical studies were carried out using the z-scan technique under continuous wave (cw) He-Ne laser irradiation at 633 nm wavelength. The effects of annealing on the structural properties were examined using x-ray diffraction and atomic force microscopy (AFM). The (0 0 2) preferred orientation increased with increase in annealing temperature up to 800 °C. The crystalline phases of SiO2 were observed at higher annealing temperatures. The appearance of an extraneous phase was confirmed by AFM images and optical transmittance spectra. The samples exhibited nonlinear absorption and nonlinear refraction under the experimental conditions. The negative sign of the nonlinear refractive index n2 indicated that the films exhibit self-defocusing property due to thermal nonlinearity. The nonlinear refractive index n2, the nonlinear absorption coefficient ?eff and the third-order optical susceptibility ?(3) were found to be of the highest orders. The estimated value of third-order optical susceptibility ?(3) was of the order of 10-3 esu. Multiple diffraction rings were observed when the samples were exposed to the laser beam. The appearance of rings was due to the refractive index change and thermal lensing. With increase in laser intensity, the variations of the self-diffraction ring patterns were studied experimentally. The films also exhibited strong optical limiting properties under cw laser excitation, and reverse saturable absorption was the dominant process leading to the observed nonlinear behaviour. © 2013 IOP Publishing Ltd.
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.
Fabrication and characterization of ZnO/AI/ZnO multilayers by simultaneous DC and RF magnetron sputtering
(2015) Nagaraja, K.K.; 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 ?/sq with optical transmittance upto 65% were obtained at room temperature. � Published under licence by IOP Publishing Ltd.
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 Î©/sq with optical transmittance upto 65% were obtained at room temperature. Â© Published under licence by IOP Publishing Ltd.
Fabrication and performance evaluation of hybrid supercapacitor electrodes based on carbon nanotubes and sputtered TiO2
(Institute of Physics Publishing michael.roberts@iop.org, 2016) Aravinda, L.S.; Nagaraja, K.K.; Nagaraja, H.S.; Bhat, K.U.; Badekai Ramachandra, B.R.
We report a simple and eco-friendly method for the fabrication of a titanium dioxide/functionalized multiwalled carbon nanotube (TiO2/FMWCNT) composite electrode for use in supercapacitors. The nanocomposite electrodes were formed by depositing titanium dioxide onto FMWCNTs using reactive magnetron sputtering, thus providing a green roue for the formation of the binder-free composite electrode. It is shown that the electrochemical performance of the fabricated electrodes can be altered by tuning the thickness of the titanium dioxide overlayer. The integrated nanocomposite electrode showed an improved specific capacitance of 90 Fg-1 in two-electrode configuration. © 2016 IOP Publishing Ltd.
Growth and temperature dependent electrical properties of ZnO nanostructures
(2013) Kumar, A.S.; 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 ?m 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 ?-cm at room temperature for vertically oriented nanorods composed films, which are grown using 1Wt% PVA. � 2013 AIP Publishing LLC.
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 âˆ¼1.2 Î¼m 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 Ï‰-cm at room temperature for vertically oriented nanorods composed films, which are grown using 1Wt% PVA. Â© 2013 AIP Publishing LLC.
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.
Magnetic domain studies of cobalt nanostructures
(2012) Nagaraja, H.S.; Nagaraja, K.K.; Rossignol, F.; Dumas-Bouchiat, F.; Champeaux, C.; Catherinot, A.
The pulsed laser deposition technique associated with a low energy cluster beam is used to deposit cobalt thin films with a thickness 100-200 nm and cobalt dots of a diameter 100-200 nm on silicon substrates. The deposited thin films of Co are composed of clusters of a size 10- 50 nm, with very few large grains as revealed by atomic force microscopy. The observations performed by magnetic force microscopy on as-grown thin films reveal randomly distributed out-of-plane magnetic domain structures. These magnetic domains are aligned linearly by applying an external magnetic field either perpendicular or parallel to the substrate during the deposition. In addition, the effect of film thickness and roughness on multidomains is reported. The increase of roughness resulted in the decrease of magnetic domain width from 200 to 100 nm. This decrease is accompanied by the appearance of instability in the stripe domain pattern. Well separated cobalt dots of diameter in the range of 100-200 nm are also deposited on silicon substrates, which show arc-like multidomains. The domains seem to be oriented along the long axis of the dots. The domain structure of Co nanodots is similar to that of Co thin films indicating strong magnetic coupling of clusters. © Springer Science+Business Media, LLC 2012.
Magnetron sputtered MoO3/carbon nanotube composite electrodes for electrochemical supercapacitor
(Elsevier B.V., 2013) Aravinda, L.S.; Nagaraja, K.K.; Bhat, K.; Badekai Ramachandra, B.
Molybdenum oxide (MoO3) has been deposited on multiwalled carbon nanotubes (MWCNTs) using DC reactive magnetron sputtering of molybdenum for supercapacitor applications. The deposits of MoO3 have been developed under different intervals of time. The structure and surface morphology of the deposits have been characterized by means of X-ray diffraction (XRD) analysis and field emission scanning electron microscopy (FESEM). X-ray diffraction peaks of the composite films reveal the formation of crystalline structure of MoO3. The electrochemical performance of the composite films was studied using cyclic voltammetry (CV), galvanostatic charge discharge and electrochemical impedance spectroscopy measurements. The composite film exhibits maximum specific capacitance of 70 F g-1 at a scan rate of 10 mV s-1 in 1 M Na2SO4 electrolyte. The nanocomposite electrode material shows specific capacitance which is almost four fold increase with respect to that of bare MWCNTs. The effect of coating duration on specific capacitance has been studied. The nanocomposite film is found to display good cycleability, even up to 1000 cycles. © 2013 Elsevier Inc. All rights reserved.
Poly(ionic liquid)-Based charge and size selective loose nanofiltration membrane for molecular separation
(Elsevier B.V., 2021) Naik, N.S.; Padaki, M.; Isloor, A.M.; Nagaraja, K.K.; Vishnumurthy, K.A.
Separation of chemicals using membranes in smaller size regimes is a much-complicated process. An ideal membrane for molecular separation should be more hydrophilic with well-defined pore sizes for ensuring the selectivity to give a maximum solvent flux. Here, we report a poly(itaconic acid-co-styrene-co-sulfobetaine vinylimidazole) (PIL)/PSf blend selective filtration membrane with nanochannels for superior molecular separation. FESEM images showed asymmetrical membrane structure with a dense upper layer on the hallow spherical sphere, though contact angle measurements reported improved membrane hydrophilicity. Newly developed loose nanofiltration membranes showed a superior removal performance of synthetic dyes based on their size and charge, such as congo red (2.5 × 0.7 nm2 size, 99%) and Eriochrome Black T (1.5 × 0.8 nm2 sizes, 99%). The passage of methyl orange (1.1 × 0.4 nm2) demonstrating an excellent molecular separation capability due to their stable networks of interconnected nanochannel and thin selective layer. The overall results are promising and paving the way for environmental friendly and energy-efficient separation of chemicals through membranes in industrial applications. © 2021
Polymer assisted preparation and characterization of ZnO and Sn doped ZnO nanostructures
(2015) 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.
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 500Â°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. Â© Published under licence by IOP Publishing Ltd.
Polymer assisted synthesis and characterization of fine ZnWO4
(2013) Santhoshkumar, A.; Nagaraja, K.K.; Nagaraja, H.S.
Zinc tungstate is a scintillator with excellent photocatalytic and photoluminescent properties. In the present study, fine sized ZnWO4 particles with monoclinic wolframate structure are prepared by chemical precipitation route assisted by polymer evaporation. The DTA/TGA and XRD techniques are employed to investigate the thermal behaviour and crystallite size evaluation of ZnWO4.The particle size and morphology of the powder that is heat treated at different temperature was characterized by SEM. The stretching and bending frequencies of the ZnWO4 is studied using FTIR. The result shows that the process provides a technically simple route for the precipitation of fine sized powder with narrow particle distribution. © (2013) Trans Tech Publications, Switzerland.
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.
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.