V. Ganesan

Publications (16)15.83 Total impact

• Article: Highly conductive and transparent laser ablated nanostructured Al: ZnO thin films

  R. Vinodkumar, I. Navas, S.R.Chalana, K.G. Gopchandran, V. Ganesan, Reji Philip, V.P. Mahadevan Pillai
  Applied Surface Science 257,708-716, 2010. 01/2010;
• Article: 2. Effect of ITO buffer layers on the structural, optical and electrical properties of ZnO multilayer thin films prepared by pulsed laser deposition technique

  R. Vinodkumar, K.J. Lethy, D. Beena, A.P. Detty, I. Navas, U.V. Nayar, V. P. Mahadevan Pillai, V. Ganesan, V.R. Reddy
  Solar Energy Materials & Solar Cells 94 (2010) 68–74. 01/2010;
• Article: Effect of zinc oxide doping on the structural and optical characterization of nanostructured molybdenum oxide films.

  I Navas, R Vinodkumar, K J Lethy, M Satyanarayana, V Ganesan, V P Mahadevan Pillai
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  ABSTRACT: Undoped and zinc oxide (ZnO) doped molybdenum oxide (MoO3) films were prepared by RF magnetron sputtering technique. The influence of doping and post annealing temperature on the structural and optical properties of these films were investigated systematically using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDAX), scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-VIS spectroscopy and photoluminescence spectroscopy (PL). The XRD patterns indicate the presence of stoichiometric orthorhombic alpha-MoO3 phase in the annealed (573 and 673 K) undoped molybdenum oxide films and in ZnO doped molybdenum oxide film (annealed at 673 K). The crystalline grain size in the films was investigated using Debye Scherrer formula and corrected using Hall-Williamson equation. The SEM and AFM images revealed the distribution of nano leafs, nanorods and nanograins. Nanorods of length 1.4 microm and diameter 149 nm can be observed in ZnO doped films. The optical band gap energy was found to increase with increase in annealing temperature and particle size. These nanostructures show a room temperature PL emission in the UV and visible region.
  Journal of Nanoscience and Nanotechnology 09/2009; 9(9):5254-61. · 1.56 Impact Factor
• Article: Structural and optical characterization of pulsed laser‐ablated potassium lithium niobate thin films

  V. Jayasree, R. Ratheesh, P. Prabhakar Rao, Peter Koshy, V. Ganesan, V. U. Nayar, V. P. Mahadevan Pillai
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  ABSTRACT: Thin films of potassium lithium niobate (K3Li2Nb5O15: KLN) have been prepared on glass substrate, as a function of substrate temperature, using a pulsed laser-deposition (PLD) technique for the first time. Grazing-incidence X-ray diffraction (GIXRD) analysis suggests that KLN films can be grown successfully at a substrate temperature as low as 300 K. The anomalous behavior of the decline of crystalline structure with increase in substrate temperature is explained. The atomic force microscopic (AFM) and scanning electron microscopic (SEM) images show an agglomerated growth mode for the films deposited at a substrate temperature of 300 K and a decrease in grain size with increase in substrate temperature. The films deposited at higher substrate temperatures show ring-like structures. The AFM analysis shows that the rms surface roughness of the film decrease with increase in substrate temperature. The UV–Vis transmission spectra suggest that the nature of the transition in the films is directly allowed. A blue shift in optical bandgap is observed for the films compared to bulk material. The changes in the optical bandgap with substrate temperature are also discussed.
  Physica Status Solidi (A) Applications and Materials 07/2009; 206(12):2801 - 2808. · 1.46 Impact Factor
• Article: Transparent and low resistive nanostructured laser ablated tungsten oxide thin films by nitrogen doping: I. Nitrogen pressure

  K J Lethy, Satish Potdar, V P Mahadevan Pillai, V Ganesan
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  ABSTRACT: Nitrogen incorporated tungsten oxide films are deposited on heated quartz substrates (973 K) for various nitrogen background pressures (namely, pN2 = 0.04, 0.08, 0.12, 0.17 and 0.20 mbar) by the pulsed laser deposition technique. The prepared films are characterized by using techniques such as x-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), atomic force microscopy (AFM), scanning electron microscopy, micro-Raman spectroscopy, UV–visible spectroscopy and temperature dependent dc electrical resistivity studies. XRD measurements revealed the presence of tungsten sub-oxide and WO3 phases depending on the nitrogen ambient pressure. Nitrogen incorporation in the films is confirmed through EDX analysis. Morphological features consisting of densely packed, void-free grains with a distinct grain boundary are portrayed through the AFM images of the films. The WO3 lattice distortion due to nitrogen incorporation is discussed using micro-Raman spectra of the films. Band gap narrowing, moderate transmittance in the visible range and the very low resistivity exhibited by the films prepared at pN2 = 0.12 mbar are imperative as far as solar cell applications are considered. A comparably higher visible transmittance with a band gap of 3.141 eV and a low resistivity obtained for the N : WO3 films prepared at a nitrogen ambient of 0.17 mbar is among the best reported for the coexistence of transparency in the visible range and conductivity in tungsten oxide films, which make them significant for micro-electronic applications.
  Journal of Physics D Applied Physics 04/2009; 42(9):095412. · 2.54 Impact Factor
• Article: 12. Growth and characterization of molybdenum oxide nanorods by RF magnetron sputtering and subsequent annealing.

  I. Navas, R. Vinodkumar, K. J. Lethy, A. P. Detty, V. Ganesan, V. Sathe, V. P. Mahadevan Pillai
  J. Phys. D: Appl. Phys. 42 (2009) 175305. 01/2009;
• Source

  Available from: Jayasree R S

  Article: 1. Effect of thermal annealing on the structural and optical properties of nanostructured zinc oxide thin films prepared by pulsed laser ablation

  R. Vinodkumar, K.J. Lethy, D. Beena, M. Satyanarayana, R.S. Jayasree, V. Ganesan, V.U. Nayar, V. P. Mahadevan Pillai
  Solar Energy Materials and Solar Cells, 93 (2009) 74-78. 01/2009;
• Article: Bandgap renormalization in titania modified nanostructured tungsten oxide thin films prepared by pulsed laser deposition technique for solar cell applications

  K. J. Lethy, D. Beena, V. P. Mahadevan Pillai, V. Ganesan
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  ABSTRACT: Pure and titania modified W O ₃ films are prepared using pulsed laser ablation technique in an oxygen ambient of 0.12 mbar at a substrate temperature of 873 K . Titania incorporation effects on the microstructure, optical, and electrical properties on the tungsten oxide films are systematically investigated using techniques such as x-ray diffraction, atomic force microscopy, scanning electron microscopy, energy dispersive x-ray spectroscopy, micro-Raman spectroscopy, and UV-visible absorption spectroscopy measurements. The resistivity measurements of the pure and titania modified W O ₃ films are done at room temperature. The variation of resistivity with temperature for the range of 170–450 K is also investigated. The microstructural analysis indicates that titania addition strongly perturbs the tungsten oxide lattice and suppresses the grain growth. Optical measurements revealed a bandgap renormalization in tungsten oxide films for higher titania concentrations. Bandgap values of the films decrease from 3.17 eV for pure W O ₃ to 2.7 eV for 10 wt % Ti O ₂ modified W O ₃ films. The shifting of photoresponse of W O ₃ films to visible range by titania incorporation throw light on the feasibility of their application in visible-light-driven photocatalysis and in solar cells. All the films show semiconducting behavior in their temperature dependence of resistivity.
  Journal of Applied Physics 09/2008; · 2.17 Impact Factor
• Article: Nanostructured tungsten oxide thin films by the reactive pulsed laser deposition technique

  K.J. Lethy, D. Beena, R. Vinod Kumar, V.P. Mahadevan Pillai, V. Ganesan, V. Sathe, D.M. Phase
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  ABSTRACT: Preparation of nanostructured tungsten oxide thin films using the reactive pulsed laser ablation technique is reported. The structural, morphological, optical and electrical properties of deposited films are systematically studied by changing the ambient oxygen pressure (pO2). Structural dependence of tungsten oxide films on ambient oxygen pressure is discussed using grazing incidence X-ray diffraction (GIXRD) and micro-Raman spectra. The section analysis using atomic force microscopy exposed the smooth surface features of the deposited films. The blue shift in optical bandgap with an increase in ambient oxygen pressure is expounded in terms of electronic band structure of tungsten oxide. The influence of oxygen pressure on optical constants like extinction coefficient, band edge sharpness, refractive index and optical bandgap is also conveyed. The temperature variation of electrical resistance for films deposited at 0.12mbar furnishes evidence for its semiconducting nature.
  Applied Physics A 05/2008; 91(4):637-649. · 1.63 Impact Factor
• Article: Enhanced photoemission from nanoscale agglomerations in Li co-activated Y2O3:Eu3+ thin films

  K.M. Nissamudeen, R.G. Abhilash Kumar, V. Ganesan, K.G. Gopchandran
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  ABSTRACT: Nanostructured Y2O3:Eu3+ and Li+ co-activated Y2O3:Eu3+ thin film phosphors have been deposited on fused amorphous quartz, silicon (1 1 1) and alumina (0 0 0 1) substrates using reactive pulsed laser deposition technique. Crystal structure, morphology and optical properties of the films were studied using GIXRD, SEM, AFM, UV–vis and photoluminescence. X-ray diffraction investigations indicate that the structural properties of these films strongly depend on substrate temperature, oxygen partial pressure and Li+ co-activation. An increase in photoluminescence with deviation in lattice constant was observed for all the films. AFM images show nanoscale agglomerations in Li co-activated films, prepared at 873 K under an oxygen partial pressure of 0.002 mbar, and photoluminescence studies indicate intense photoemission from these films. Dependence of asymmetric ratio of the photoluminescence spectra of Li co-activated Y2O3:Eu3+ thin films on the substrate temperature and Li co-activation are reported. Using CIE chromaticity diagram, x chromaticity values are determined from the photoluminescence spectra of Y2O3:Eu3+ and Li co-activated Y2O3:Eu3+ thin films deposited at different substrate temperatures and is discussed.
  Journal of Alloys and Compounds.
• Article: Highly conductive and transparent laser ablated nanostructured Al: ZnO thin films

  R. Vinodkumar, I. Navas, S.R. Chalana, K.G. Gopchandran, V. Ganesan, Reji Philip, S.K. Sudheer, V.P. Mahadevan Pillai
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  ABSTRACT: Al doped ZnO thin films are prepared by pulsed laser deposition on quartz substrate at substrate temperature 873 K under a background oxygen pressure of 0.02 mbar. The films are systematically analyzed using X-ray diffraction, atomic force microscopy, micro-Raman spectroscopy, UV–vis spectroscopy, photoluminescence spectroscopy, z-scan and temperature-dependent electrical resistivity measurements in the temperature range 70–300 K. XRD patterns show that all the films are well crystallized with hexagonal wurtzite structure with preferred orientation along (0 0 2) plane. Particle size calculations based on XRD analysis show that all the films are nanocrystalline in nature with the size of the quantum dots ranging from 8 to 17 nm. The presence of high frequency E2 mode and longitudinal optical A1 (LO) modes in the Raman spectra suggest a hexagonal wurtzite structure for the films. AFM analysis reveals the agglomerated growth mode in the doped films and it reduces the nucleation barrier of ZnO by Al doping. The 1% Al doped ZnO film presents high transmittance of ∼75% in the visible and near infrared region and low dc electrical resistivity of 5.94 × 10−6 Ω m. PL spectra show emissions corresponding to the near band edge (NBE) ultra violet emission and deep level emission in the visible region. Nonlinear optical measurements using the z-scan technique shows optical limiting behavior for the 5% Al doped ZnO film.
  Applied Surface Science.
• Article: Microstructural, optical and spectroscopic studies of laser ablated nanostructured tantalum oxide thin films

  Renju R. Krishnan, K.G. Gopchandran, V.P. MahadevanPillai, V. Ganesan, Vasant Sathe
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  ABSTRACT: Thin films of tantalum oxide (Ta2O5) have been prepared by pulsed laser deposition technique at different substrate temperatures (300–973 K) under vacuum and under oxygen background (pO2 = 2 × 10−3 mbar) conditions. The films are annealed at a temperature of 1173 K. The as-deposited films are amorphous irrespective of the substrate temperature. XRD patterns show that on annealing, the films get crystallized in orthorhombic phase of tantalum pentoxide (β-Ta2O5). The annealed films deposited at substrate temperatures 300 K and 673 K have a preferred orientation along (0 0 1) plane, whereas the films deposited at substrate temperatures above 673 K show a preferred orientation along (2 0 0) crystal plane. The deposited films are characterized using techniques such as grazing incidence X-ray diffraction (GIXRD), atomic force microscopy (AFM), micro-Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy and UV–visible spectroscopy. FTIR and micro-Raman measurements confirm the presence of Ta–O, Ta–O–Ta and O–Ta–O bands in the films. Grain size calculations from X-ray diffraction and AFM show a decrease with increase in substrate temperature. The variation of transmittance and band gap with film growth parameters are also discussed.
  Applied Surface Science.
• Article: Effect of ITO buffer layers on the structural, optical and electrical properties of ZnO multilayer thin films prepared by pulsed laser deposition technique

  R. Vinodkumar, K.J. Lethy, D. Beena, A.P. Detty, I. Navas, U.V. Nayar, V.P. Mahadevan Pillai, V. Ganesan, V.R. Reddy
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  ABSTRACT: ZnO/ITO/ZnO/ITO/ZnO five layer thin films are fabricated by pulsed laser deposition on quartz substrate kept at a substrate temperature (Ts) 873 K at a background oxygen pressure (pO2) of 0.05 mbar for different deposition duration for ZnO layers (5, 10, 15 and 20 min) while keeping a constant deposition time for ITO layers. The structural, optical and electrical properties of the as-deposited thin films have been investigated by GIXRD, AFM, UV–visible spectra, photoluminescence spectra and temperature-dependent electrical resistivity measurements (10–300 K) using four-probe technique. XRD patterns of the films show a polycrystalline nature. From the AFM images, the average grain size and mean surface roughness are estimated and the particles are densely packed in the film. A high transmittance is observed for all the films in the visible and IR region. The PL spectra show that the emission is in the UV and visible region due to the near band edge and deep level transitions of ZnO. The electrical resistivity of all the films are calculated and are very low compared to the reported values of as deposited ZnO thin films. The co-existence of very high transmittance in the visible region and very low dc resistivity enables these films suitable for optoelectronic device fabrications. The structural, optical and electrical studies reveal that ITO buffer layers improve the crystalline quality, optical and electrical properties of ZnO multilayered thin films.
  Solar Energy Materials and Solar Cells.
• Article: Photoluminescence in laser ablated nanostructured indium oxide thin films

  D. Beena, K.J. Lethy, R. Vinodkumar, A.P. Detty, V.P. Mahadevan Pillai, V. Ganesan
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  ABSTRACT: Nanocrystalline indium oxide films have been deposited using pulsed laser ablation technique at different substrate temperatures and the films are post-annealed at different temperatures. The structural, optical and electrical properties of the films are investigated by XRD, SEM, AFM, UV–vis spectra, photoluminescence spectra and electrical conductivity measurements. X-ray diffractograms of the as-deposited and post-annealed films A–C show that films are amorphous at lower substrate temperatures and transform to mixture of amorphous and crystalline phases. The grain size determination based on Debye Scherrer's formula shows that the average grain size of the crystallites in the films ranges from 6 to 32 nm. Dislocation density, biaxial strain, lattice strain and lattice stress of the films are also calculated. SEM micrographs show that all the films are densely packed with the crystallites in the nanodimensions. SEM images show porous nanocrystalline nature for the films of samples B and C which make them suitable for gas sensing. The as-deposited samples show decrease in resistivity with increase in substrate temperature and the lowest resistivity obtained is 6.6 × 10−5 Ω m for the as-deposited films at substrate temperature 773 K. Efficient photoluminescence emission is observed in all the films and this can be attributed to higher values of rms surface roughness exhibited by these films. In2O3 films exhibit a PL emission property in the UV region at room temperature which suggests possible applications in nanoscale optoelectronic devices in the future.
  Journal of Alloys and Compounds 489(1):215-223. · 2.29 Impact Factor
• Article: Influence of europium oxide doping on the structural and optical properties of pulsed laser ablated barium tungstate thin films

  N. Venugopalan Pillai, V.P. Mahadevan Pillai, R. Vinodkumar, I. Navas, V. Ganesan, Peter Koshy
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  ABSTRACT: Nanostructured Eu2O3 doped Barium tungstate (BaWO4) crystallites are successfully synthesized using pulsed laser deposition (PLD) technique. The influence of different Eu2O3 doping concentrations (1,2,3 & 5 wt.%) on the structural, surface morphological and optical properties are systematically studied using XRD, micro-Raman, SEM, AFM, UV–vis and photoluminescence spectroscopy. All the films are polycrystalline with tetragonal scheelite structure. The vibrational analysis of the atoms in BaWO4 is studied by micro-Raman spectra using factor group analysis. The surface morphological analysis by SEM and AFM reveals the presence of fine nanoparticles with distinct grain boundaries in all the films. The band gap energy variation in the Eu2O3 doped BaWO4 films is in accordance with the variation of the sizes of nano particles in the films. The films with higher Eu3+ doping concentrations (≥2 wt.%) show a PL emission peak centered around 614 nm when excited at 394 nm which can be attributed to the 5D0 → 7F2 (0–2) transition of Eu3+ ion.Research highlights▶ Study on the influence europium oxide doping on the structural and optical properties of laser ablated barium tungstate thin films is new. ▶ The surface morphological analysis by SEM and AFM reveals the presence of fine nanoparticles with distinct grain boundaries in all the films. ▶ The films with higher Eu3+ doping concentrations (≥2 wt.%) show a PL emission peak centered around 614 nm when excited at 394 nm which can be attributed to the 5D0 → 7F2 (0–2) transition of Eu3+ ion ▶ The observation of PL emission in these films is a new result which can have large practical applications and also it shows that BaWO4 can act as host material for europium ion. ▶ Detailed analysis of the Raman spectra of BaWO4 films are presented.
  Journal of Alloys and Compounds 509(6):2745-2752. · 2.29 Impact Factor
• Article: Influence of reactive oxygen ambience on the structural, morphological and optical properties of pulsed laser ablated potassium lithium niobate thin films

  V. Jayasree, R. Ratheesh, V. Ganesan, V.R. Reddy, C. Sudarsanakumar, V.P. Mahadevan Pillai, V.U. Nayar
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  ABSTRACT: The effect of oxygen ambience on the structure and properties of potassium lithium niobate (K3Li2Nb5O15: KLN) films prepared on glass substrates by pulsed laser ablation technique (PLD) are studied. The influence of annealing on the properties of vacuum deposited films is also investigated. The Gracing Incidence X-ray Diffraction (GIXRD) data suggests the tetragonal structure for the KLN film whose grain sizes increase on thermal annealing. The Atomic Force Microscopic (AFM) analysis reveals the four-fold symmetric nature of the grains in the films. Self assembly of grains in the form of rings and rods are observed in AFM images of the films deposited in an oxygen ambience of 2 Pa. The films deposited at higher oxygen ambience show a blue shift in optical band gap. The direct current (DC) resistance measurement on the films deposited at non-reactive ambience reveals resistivity in the range of kΩ m.
  Thin Solid Films 517(2):603-608. · 1.89 Impact Factor