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Ravichandran K.,AVVM Sri Pushpam College Autonomous | Rajkumar P.V.,AVVM Sri Pushpam College Autonomous | Sakthivel B.,AVVM Sri Pushpam College Autonomous | Swaminathan K.,RKM Vivekananda College Autonomous | Chinnappa L.,Rajah Serfoji Government College Autonomous
Ceramics International | Year: 2014

ZnO thin films were deposited using a successive ionic layer adsorption and reaction (SILAR) method from three different precursors viz. zinc acetate, zinc sulfate and zinc chloride. All the films were annealed in air and vacuum ambiences at 350 °C and characterized for their structural, optical, photoluminescence, electrical and surface morphological properties. The XRD profiles show that the crystalline quality of the films is improved after annealing in both the environments. It is found that the preferential orientation changes from (002) plane to (100) plane after atmospheric annealing for the films prepared from zinc acetate and zinc sulfate precursors, whereas no transition in preferential orientation is observed for films deposited from zinc chloride. Vacuum annealing does not affect the preferential orientation of all the three sets of films, but the intensities of diffraction peaks are increased remarkably. The films fabricated from zinc acetate and zinc sulfate precursors exhibit good average optical transmittance of 80% in the visible region after annealing whereas that deposited from zinc chloride exhibits only 70% transmittance. Compared with as-deposited and air annealed films, the vacuum annealed films exhibit lower electrical resistivity. An increase in the optical band gap and improvement in the surface morphology are also observed after annealing under both the ambiences for all the films, irrespective of the precursor used. The photoluminescence studies support the results on crystalline quality and optical band gap. © 2014 Elsevier Ltd and Techna Group S.r.l.

Ravichandran K.,P.A. College | Snega S.,P.A. College | Jabena Begum N.,P.A. College | Swaminathan K.,RKM Vivekananda College Autonomous | And 4 more authors.
Superlattices and Microstructures | Year: 2014

Fluorine doped ZnO nanopowders were synthesized from starting solutions having different doping levels of F (0, 5,., 20 at.%) using a simple soft chemical route and the effects of the doping level on the structural, optical, surface morphological and antibacterial properties were investigated. The XRD studies reveal that all the products have preferential orientation along the (1 0 1) plane. The PL studies show that all the samples exhibit strong visible emission with a peak at 425 nm. The enhancement in the visible emission indicates an increasing number of surface defects caused by the doping of F. The obtained FTIR spectra confirm the incorporation of F into ZnO lattice. From the SEM studies, it is observed that the ZnO nanowires formed at 10 at.% of F doping level exhibit excellent antibacterial activities. Antibacterial activity of F doped ZnO nanopowders against Staphylococcus aureus was found to be significantly higher than that against the Escherichia coli and Pseudomonas aeruginosa micro-organisms. All the physical properties were corroborated well with the findings related to antibacterial activity. Finally, we conclude that, the analysis of all the results shows that F doping level of 10 at.% is optimal in all respects and is suitable for antibacterial applications. © 2014 Elsevier Ltd. All rights reserved.

Ravichandran K.,P.A. College | Karthika K.,P.A. College | Sakthivel B.,P.A. College | Jabena Begum N.,P.A. College | And 3 more authors.
Journal of Magnetism and Magnetic Materials | Year: 2014

Manganese (Mn) doped ZnO nanopowders (0, 2, 4, 6, 8 and 10 at%) were synthesized using a simple soft chemical route and their structural, optical, surface morphological, magnetic and antibacterial properties were investigated. Structural studies show that the nanopowders exhibit hexagonal wurtzite structure of ZnO. No other secondary phases like MnO2, MnO, Mn 3O4 and Mn2O3 are observed. The blue shift observed in the photoluminescence spectra beyond the Mn doping level of 6 at% shows that there is an increase in the carrier concentration, caused by the interstitial incorporation of Zn and Mn in the ZnO matrix. From the antibacterial studies, it is found that ZnO:Mn nanopowders with higher Mn doping level (8 and 10 at%) exhibit good antibacterial efficiency against Escherichia coli (E. coli) bacteria. The magnetization curves obtained using vibrating sample magnetometer (VSM) show a sign of strong room temperature ferromagnetic behavior when the Mn doping level is 6 at% and a weak room temperature ferromagnetic behavior, when the Mn doping level is below 6 at%. Beyond 6 at% they are found to exhibit antiferromagnetic and paramagnetic properties, when the Mn doping levels are 8 and 10 at%, respectively. The SEM images indicate that there is a gradual decrease in the grain size with increase in the Mn doping level. The EDAX profile clearly confirms the presence of expected elements in the final product, in appropriate proportions. © 2014 Elsevier B.V. All rights reserved.

Ravichandran K.,P.A. College | Mohan R.,P.A. College | Begum N.J.,P.A. College | Swaminathan K.,RKM Vivekananda College Autonomous | Ravidhas C.,Bishop Heber College
Journal of Physics and Chemistry of Solids | Year: 2013

Undoped and simultaneously (Sn+F) doped ZnO thin films were fabricated using a simplified spray pyrolysis technique and the effects of Sn doping level on their electrical, structural, optical and surface morphological properties were studied. The XRD patterns confirmed the hexagonal wurtzite structure of ZnO. The minimum electrical resistivity of 0.45×10-2 Ω cm was obtained for ZnO films having Sn+F doping levels of 8+20 at%. All the films exhibited average optical transmittance of 85% in the visible region, suitable for transparent electrode applications. The overall quality of the fabricated films was confirmed from photoluminescence (PL) studies. The PL and surface morphological studies along with the elemental analysis showed the increase of Sn diffusion into the ZnO lattice which was consistent with the concentration of Sn in the starting solution. The results of the analysis of physical properties of simultaneously doped ZnO films proved that these films might be considered as promising candidates for solar cells and other opto-electronic applications. © 2013 Elsevier Ltd.

Ravichandran K.,P.A. College | Snega S.,P.A. College | Jabena Begum N.,P.A. College | Rene Christena L.,SASTRA University | And 2 more authors.
Philosophical Magazine | Year: 2014

ZnO nanopowders simultaneously doped with fluorine (20 at.%) and magnesium (4, 8, 12 and 16 at.%) (ZnO:F:Mg) have been synthesized using an inexpensive simple soft chemical route for the first time. The effect of Mg doping level on certain physical properties and antibacterial activities of ZnO:F:Mg nanopowders has been investigated and reported. XRD studies showed that the products have the hexagonal wurtzite structure of ZnO. Fourier transform infrared spectra authenticate the presence of MgO stretching vibration, which is responsible for the increased antibacterial activity of the synthesized samples. The antibacterial activity of ZnO:F:Mg nanopowders was found to be enhanced with increase in Mg doping level as it causes a reduction in the grain size. © 2014 Taylor & Francis.

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