Browsing by Author "Santhosh Kumar, A.S."

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    A large-scale-oriented growth of ZnO nanorod array on glass substrate: Growth, structural and photoluminoscent properties
    (National Institute of Optoelectronics, 2014) Santhosh Kumar, A.S.; Nagaraja, H.S.
    We report a modified sol gel route for one step fabrication of large scale arrays of zinc oxide (ZnO) nanorods. The method is seed layer free, and nanorods are directly attached to a substrate. We studied the effect of PVA content on growth, crystallanity, orientation, microstructure and optical properties of ZnO. The XRD patterns confirm that samples grown with PVA have good crystallanity with (002) preferred orientation. The SEM micrographs show that the 1 Wt% PVA assisted grown films are covered with large scale oriented nanorod array. Raman spectrum represents that the 1 wt% PVA assisted grown ZnO nanostructures are highly crystalline with a hexagonal wurtzite phase. The room temperature PL spectrum exhibits a strong and sharp UV emission, which confirms that the grown arrays have good optical properties with few structural defects such as oxygen vacancies and zinc interstitials.
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    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.
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    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.
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    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.
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    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.
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    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.
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    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.