V. P. Mahadevan Pillai

University of Kerala, Tiruvananantapuram, Kerala, India

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Publications (129)157.81 Total impact

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    Sajan Ambadiyil · K.S. Soorej · V.P. Mahadevan Pillai ·
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    ABSTRACT: Security documents like certificates, land revenue documents, etc., have only the individual's name, address, and in some cases a photo as means of personal identification. This makes criminal impersonation an easy task. This paper proposes a method for creating a unique ID based on the core point of the fingerprint of an individual. The minutia features of the fingerprint are extracted with the core point as the reference. The numerical value thus generated is used to create the unique ID in the form of a QR code and this is printed in the security documents. There are current technologies to convert a fingerprint to barcode but the method proposed in this paper is more suitable for use in security documents.
    Procedia Computer Science 12/2015; 46:507-516. DOI:10.1016/j.procs.2015.02.075
  • S. R. Chalana · V. Ganesan · V. P. Mahadevan Pillai ·
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    ABSTRACT: Silver incorporated zinc sulfide thin films are prepared by RF magnetron sputtering technique and the influence of silver incorporation on the structural, optical and luminescence properties is analyzed using techniques like grazing incidence X-Ray diffraction (GIXRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), micro-Raman spectroscopy, UV-Vis spectroscopy and laser photoluminescence spectroscopy. XRD analysis presents hexagonal wurtzite structure for the films. A reduction of crystallinity of the films is observed due to Ag incorporation. The Raman spectral analysis confirms the reduction of crystallinity and increase of strain due to the Ag incorporation. AFM analysis reveals a rough surface morphology for the undoped film and Ag incorporation makes the films uniform, dense and smooth. A blue shift of band gap energy with increase in Ag incorporation is observed due to quantum confinement effect. An absorption band (450-650 nm region) due to surface plasmon resonance of the Ag clusters present in the ZnS matrix is observed for the samples with higher Ag incorporation. The complex dielectric constant, loss factor and distribution of volume and surface energy loss of the ZnS thin films are calculated. Laser photoluminescence measurements gives an intense bluish green emission from the ZnS films and a quenching of the PL emission is observed which can be due to the metal plasmonic absorption and non-radiative energy transfer due to Ag incorporation.
    AIP Advances 10/2015; 5(10):107207. DOI:10.1063/1.4933075 · 1.52 Impact Factor
  • R. Sreeja Sreedharan · R. Vinodkumar · I. Navas · Radhakrishna Prabhu · V. P. Mahadevan Pillai ·
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    ABSTRACT: The effects of Pr doping on the structural, morphological, optical and non-linear optical properties have been investigated. X-ray diffraction and Raman analysis reveals the formation of highly c-axis-oriented films with hexagonal wurtzite structure of ZnO. Atomic force microscopy and scanning electron microscopy images reveal the formation of grains with well-defined grain boundaries. The Pr-doped films present excellent optical transparency in the visible region. The photoluminescence spectra show both UV and visible emissions and the intensity of the visible emission increases with Pr doping. Nonlinear optical properties of the Pr-incorporated ZnO nanostructures have been investigated using the open aperture Z-scan technique. It is interesting to note that 1 wt.% praseodymium-incorporated ZnO film shows saturable absorption, whereas the 5 wt.% praseodymium-incorporated ZnO shows reverse saturable absorption and the high value of non-linear absorption coefficient (β) for 5 wt.% Pr-doped ZnO film suggests the suitability of these films for optoelectronic device applications.
    JOM: the journal of the Minerals, Metals & Materials Society 09/2015; DOI:10.1007/s11837-015-1632-0 · 1.76 Impact Factor
  • Sibimol Luke · S.K. Sudheer · V.P. Mahadevan Pillai ·

    Optik - International Journal for Light and Electron Optics 09/2015; DOI:10.1016/j.ijleo.2015.08.190 · 0.68 Impact Factor
  • S. Ambadiyil · Jayan K. G. · R. Prabhu · V P M Pillai ·

    SPIE Optics + Optoelectronics 2015, Prague, Czech Republic; 04/2015
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    ABSTRACT: Tantalum doped indium oxide films are prepared by RF magnetron sputtering technique and the films are annealed in air at 300 °C. The effect of Ta doping on the structural, morphological, and optical properties of the annealed films are studied using techniques like X-ray diffraction (XRD), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), EDX analysis, micro-Raman, UV-visible and photoluminescence spectroscopy and electrical measurements. The XRD patterns present a cubic bixbyite structure for all the films with preferred orientation along the (222) plane. The lattice constant estimation presents a reduction in lattice size with Ta doping. The W-H plot shows a tensile strain for all the films and also indicates the presence of strain induced broadening of the XRD peaks. The Raman spectra present all the characteristic modes of In2O3 cubic bixbyite phase. FESEM and AFM images show the uniform and dense distribution of smaller grains in the films. All the films show high transmittance (above 85%) in the 400-900 nm region. Electrical measurement shows a systematic increase of carrier concentration and electrical conductivity with increase in Ta doping concentration. Band gap energy increases with increase in Ta doping concentration. All the films show intense PL emission in the UV region.
    Materials Science in Semiconductor Processing 03/2015; 37. DOI:10.1016/j.mssp.2015.02.033 · 1.96 Impact Factor
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    ABSTRACT: Silver/tungsten oxide multi-layer films are deposited over quartz substrates by RF magnetron sputtering technique and the films are annealed at temperatures 200, 400 and 600°C. The effect of thermal annealing on the phase evolution of silver tungstate phase in Ag/WO3 films is studied extensively using techniques like X-ray diffraction, micro-Raman analysis, atomic force microscopy and photoluminescence studies. The XRD pattern of the as-deposited film shows only the peaks of cubic phase of silver. The film annealed at 200°C shows the presence of XRD peaks corresponding to orthorhombic phase of Ag2WO4 and peaks corresponding to cubic phase of silver with reduced intensity. It is found that, as annealing temperature increases, the volume fraction of Ag decreases and that of Ag2WO4 phase increases and becomes highest at a temperature of 400°C. When the temperature increases beyond 400°C, the volume fraction of Ag2WO4 decreases, due to its decomposition into silver and oxygen deficient phase Ag2W4O13. The micro-Raman spectra of the annealed films show the characteristic bands of tungstate phase which is in agreement with XRD analysis. The surface morphology of the films studied by atomic force microscopy reveals that the particle size and r.m.s roughness are highest for the sample annealed at 400°C. In the photoluminescence study, the films with silver tungstate phase show an emission peak in blue region centered around the wavelength 441nm (excitation wavelength 256nm). Copyright © 2015 Elsevier B.V. All rights reserved.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 02/2015; 145. DOI:10.1016/j.saa.2015.01.125 · 2.35 Impact Factor
  • Jaison Joseph · R.B. Tangsali · V.P. Mahadevan Pillai · R.J. Choudhary · D.M. Phase · V. Ganeshan ·
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    ABSTRACT: Patterned nano crystalline ZnFe2O4 thin film was fabricated on quartz substrate by pulse laser deposition. XRD and Raman spectroscopic techniques were employed for structural characterization of the film. Silencing of a small number of prominent ferrite XRD peaks in thin film signify mild textured film growth. The observed XRD peak position swing with respect to the target material in thin film indicates formation of lateral strain in opposite directions during film growth. The thin film XRD peak position shift with target material data as reference is explained by suggesting an appropriate film growth model. Designated ferrite Raman emission peaks originated from film surface authenticates the stoichiometric and structural stability of ferrite material. AFM images indicate specific pattern formation with nanogranular morphology. Magnetic property measurements of the thin film revealed enhanced properties which are explained on the basis of texture, lattice strain, and surface features that are originated from patterned thin film growth.
    Materials Research Bulletin 01/2015; 61:475-480. DOI:10.1016/j.materresbull.2014.10.061 · 2.29 Impact Factor
  • Anand N. · Binu Madhavan · S. K. Sudheer · V. P. Mahadevan Pillai ·

    102nd Indian Science Congress Physical Sciences Section, Mumbai; 01/2015
  • Jaison Joseph · R.B. Tangsali · V.P. Mahadevan Pillai · R.J. Choudhary · D.M. Phase · V. Ganeshan ·
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    ABSTRACT: Nanoparticles of Mn0.2Zn0.8Fe2O4 were chemically synthesized by co-precipitating the metal ions in aqueous solutions in a suitable alkaline medium. The identified XRD peaks confirm single phase spinal formation. The nanoparticle size authentication is carried out from XRD data using Debye Scherrer equation. Thin film fabricated from this nanomaterial by pulse laser deposition technique on quartz substrate was characterized using XRD and Raman spectroscopic techniques. XRD results revealed the formation of high degree of texture in the film. AFM analysis confirms nanogranular morphology and preferred directional growth. A high deposition pressure and the use of a laser plume confined to a small area for transportation of the target species created certain level of porosity in the deposited thin film. Magnetic property measurement of this highly textured nanocrystalline Mn–Zn ferrite thin film revealed enhancement in properties, which are explained on the basis of texture and surface features originated from film growth mechanism.
    Physica B Condensed Matter 01/2015; 456:293–297. DOI:10.1016/j.physb.2014.09.015 · 1.32 Impact Factor
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    ABSTRACT: Light Detection and Ranging (LIDAR) which is analogous to Radio Detection And Ranging (RADAR), has become an important and unique technology for atmospheric research and applications. The technology is widely used for the remote sensing of the Earth’s atmosphere, oceans, vegetation and the characteristics of Earth’s topography. Remote sensing of atmosphere, for its structure, composition and dynamics, is one of the proven applications of the lidar systems. More importantly the lidar technique is applied for the study of clouds, aerosols and minor constituents in the atmosphere. It provides the information on the above with good spatial and temporal resolutions and accuracy. The high altitude cirrus clouds which play an important role in the Earth’s radiative budget and global climate can be studied by using the LIDAR system. These clouds absorb long-wave outgoing radiation from Earth’s surface while reflecting part of the incoming short-wave solar radiation. Lidar measurements are useful in deriving the altitude, top height, bottom height and the optical properties of cirrus clouds, which are essential in understanding the cloud-radiation effects. The optical depth, the effective lidar ratio and the depolarization of the clouds are also derived by inverting the lidar signals from the cirrus clouds. In this paper we present the results on the lidar derived optical and microphysical properties of the cirrus clouds at a tropical station Gadanki (13.5°N, 79.2°E) India during two year period from 2009 to210. The seasonal variations of the cloud properties during the observation period are presented and discussed with reference to earlier period.
    11/2014; XL-8:253-256. DOI:10.5194/isprsarchives-XL-8-253-2014
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    ABSTRACT: MoO3 nanostructures have been grown in thin film form on five different substrates by RF magnetron sputtering and subsequent annealing; non-aligned nanorods, aligned nanorods, bundled nanowires, vertical nanorods and nanoslabs are formed respectively on the glass, quartz, wafer, alumina and sapphire substrates. The nanostructures formed on these substrates are characterized by AFM, SEM, GIXRD, XPS, micro-Raman, diffuse reflectance and photoluminescence spectroscopy. A detailed growth model for morphology alteration with respect to substrates has been discussed by considering various aspects such as surface roughness, lattice parameters and the thermal expansion coefficient, of both substrates and MoO3. The present study developed a strategy for the choice of substrates to materialize different types MoO3 nanostructures for future thin film applications. The gas sensing tests point towards using these MoO3 nanostructures as principal detection elements in gas sensors.
    Nanoscale 10/2014; 6(22). DOI:10.1039/c4nr04529g · 7.39 Impact Factor
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    ABSTRACT: Zinc oxide is a wide, direct band gap II-VI oxide semiconductor. Pure and Eu-doped ZnO films are prepared by RF Magnetron sputtering at different doping concentrations (0.5, 1, 3 and 5 wt %). The films are annealed at 500 0C in air for two hours. The structural, morphological and optical properties of the films are characterized using XRD, micro-Raman, AFM, UV-Visible and photoluminescence spectroscopy. The thickness of the films is measured using stylus profilometer. XRD analysis shows that all the films are highly c-axis oriented exhibiting a single peak corresponding to (002) lattice reflection plane of hexagonal wurtzite crystal phase of ZnO. The micro-Raman spectra analysis reveals the presence of E2 high mode in all the samples which is the intrinsic characteristic of hexagonal wurtzite structure of ZnO. The appearance of LO modes indicates the formation of defects such as oxygen vacancies in the films. AFM micrographs show uniform distribution of densely packed grains of size with well defined grain boundaries. All the films exhibit very high transmittance (above 80%) in the visible region with a sharp fundamental absorption edge around 380 nm corresponding to the intrinsic band edge of ZnO. All the films show PL emission in the UV and visible region.
    IOP Conference Series Materials Science and Engineering 08/2014; 64(1):012027. DOI:10.1088/1757-899X/64/1/012027
  • K. Sathesh Kumar · P Srinivasan · V. P. Mahadevan Pillai ·
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    ABSTRACT: Single crystals of para amino hippuric acid (PAHA) were grown by slow evaporation technique. The spectral and its structural properties of the crystals were studied by FT-IR, micro-Raman and factor group analysis. The optical transparency in the UV-Visible regions was found to be good for non-linear optics (NLO) applications. Thermogravimetric analysis (TGA) and Differential Thermal Analysis (DTA) showed that the compound decomposes beyond 300°C. The dielectric behavior of the compound predicts low dielectric loss at high frequency applied whereas in the case of mechanical behavior of the specimen hardness increases with increasing applied load. After certain weight increase, hardness gets saturated in the region of ⩾110. Relative second harmonic efficiency of the compound is found to be 1.8 times greater than that of potassium di-phosphate reference.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 05/2014; 132C:263-270. DOI:10.1016/j.saa.2014.04.150 · 2.35 Impact Factor
  • Anand N. · Binu Madhavan · S. K. Sudheer · V. P. Mahadevan Pillai ·

    International Conference on Advanced Trends in Engineering and Technology; 03/2014
  • Reji K. Dhaman · V. Krishnakumar · V. P. Mahadevan Pillai · M. Satyanarayana · K. Raghunath ·
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    ABSTRACT: The study on the optical characteristics of aerosol is carried out using the dual polarization lidar observations from the tropical inland station Gadanki (13.5A degrees N, 79.2A degrees E) for the period of observation during the year 2010. The summer and monsoon observation days show high scattering ratio at the tropical tropopause layer (TTL) and at the lower stratosphere region. The depolarization ratio is also high at this altitude due to the transport of particulates to the TTL layer by the active convection prevailing at the period. The study reveals more dependable values of scattering ratio that are seasonal and range-dependent.
    Pramana 01/2014; 82(2). DOI:10.1007/s12043-014-0697-6 · 0.65 Impact Factor
  • K. Sathesh Kumar · P. Srinivasan · V.P. Mahadevan Pillai ·

    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 01/2014; 132:263–270. · 2.35 Impact Factor
  • Navas Illyaskutty · Heinz Kohler · Thomas Trautmann · Matthias Schwotzer · V. P. Mahadevan Pillai ·
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    ABSTRACT: Nanostructured molybdenum oxide (MoO3) gas sensitive layers were prepared via RF magnetron sputtering and controlled post deposition annealing on Au and Pt inter-digitated electrodes (IDE), which are integrated onto alumina substrates. Sensitivity test measurements towards hydrogen and ethanol vapour at different concentrations in synthetic air under non-humid and humid ambience at isothermal (200 degrees C and 300 degrees C) conditions are presented. Extremely different response behaviour to the analytes depending on morphology of the sensing layer, operating temperature, background humidity and electrode material was observed. The humid ambience does not significantly change the sensitivity to H-2, however, it drastically diminishes the sensitivity to ethanol. At higher temperature (300 degrees C), influence of electrode material (catalytic effect of Pt from the Pt-IDE) on the gas sensing performance of MoO3 layer is identified. Non-dissociative and dissociative adsorption of analytes on the sensing layer, reaction of the adsorbed analyte species with lattice oxygen and diffusion effects due to different layer morphologies were taken into account in order to account the diverse sensing behaviour.
    Sensors and Actuators B Chemical 10/2013; 187:611-621. DOI:10.1016/j.snb.2013.05.092 · 4.10 Impact Factor
  • Source
    R Vinodkumar · I Navas · K Porsezian · V Ganesan · N V Unnikrishnan · V. P. Mahadevan Pillai ·
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    ABSTRACT: ZnO thin films are grown on quartz substrates at various substrate temperatures (ranging from 573 to 973K) under an oxygen ambience of 0.02mbar by using pulsed laser ablation. Influence of substrate temperature on the structural, morphological, optical and electrical properties of the ZnO thin films are investigated. The XRD and micro-Raman spectra reveal the presence of hexagonal wurtzite structure of ZnO with preferred orientation (002). The particle size is calculated using Debye-Scherer equation and the average size of the crystallites are found to be in the range 17-29nm. The AFM study reveals that the surface morphology of the film depends strongly on the substrate temperature. UV-Visible transmittance spectra show highly transparent nature of the films in visible region. The calculated optical band gap energy is found to be decrease with increase in substrate temperatures. The complex dielectric constant, the loss factor and the distribution of the volume and surface energy loss of the ZnO thin films prepared at different substrate temperatures are calculated. All the films are found to be highly porous in nature. The PL spectra show very strong emission in the blue region for all the films. The dc electrical resistivity of the film decreases with increase in substrate temperature. The temperature dependent electrical measurements done on the film prepared at substrate temperature 573K reveals that the electric conduction is thermally activated and the activation energy is found to be 0.03911eV which is less than the reported values for ZnO films.
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 09/2013; 118C:724-732. DOI:10.1016/j.saa.2013.08.090 · 2.35 Impact Factor
  • J. R. Rani · G. Anoop · Meera Gopal · V. Ganesan · V. P. Mahadevan Pillai ·
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    ABSTRACT: Ytterbium (Yb) and Praseodymium Oxide (Pr2O3) doped Si nanorings with diameter varying from 40 to 90 nm and average width of 17 nm are grown by pulsed laser deposition. Atomic Force Microscopy (AFM) reveals several interesting self-assembled forms of polycrystalline as well as amorphous type of silicon nanorings. It is observed that the structure, average diameter and width of the rings strongly depend on the nature of dopants. The strong resputtering due to the high laser fluence could be the reason for the formation of ring like structures. As observed in the log α versus log hν plot, the band gap values of doped silicon nanorings varies with the nature of dopants. For Yb doped Si film, the slope of log α versus log hν plot is found to be 1.65 indicating a direct—forbidden transition in this film. The various dopants in the deposited thin films results in different crystal lattice mismatch which will cause different values of strain and stress in the films. Due to the inner stress, the lattice plane spacing decreases and the X-ray Diffraction (XRD) peaks shift to higher 2 values. Present study shows evidence for the strong quantum confinement effect along the width of ring like quantum states. Z scan studies shows that excited state absorption (ESA) and saturation absorption (SA) behavior of the films which again depends on the nature of dopants and for Pr doped Si nanorings, the observed Im χ(3) is 2.996 × 10–8 esu.
    08/2013; 5(8):869-876. DOI:10.1166/asem.2013.1375