V. P. Mahadevan Pillai

University of Kerala, Tiruvananantapuram, Kerala, India

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Publications (121)140.73 Total impact

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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 · 2.13 Impact Factor
  • Anand N., Binu Madhavan, S. K. Sudheer, V. P. Mahadevan Pillai
    102nd Indian Science Congress Physical Sciences Section, Mumbai; 01/2015
  • 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 01/2015; 46:507-516. DOI:10.1016/j.procs.2015.02.075
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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 · 1.28 Impact Factor
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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; DOI:10.1039/c4nr04529g · 6.74 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 · 2.13 Impact Factor
  • Anand N., Binu Madhavan, S. K. Sudheer, V. P. Mahadevan Pillai
    International Conference on Advanced Trends in Engineering and Technology; 03/2014
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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 · 0.72 Impact Factor
  • K. Sathesh Kumar, P. Srinivasan, V.P. Mahadevan Pillai
    Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 01/2014; 132:263–270. · 2.13 Impact Factor
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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 · 3.84 Impact Factor
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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 · 2.13 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
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    ABSTRACT: A novel ZnO incorporated MoO3 nanostructured thin film system exhibiting high sensitivity and selectivity to ethanol has been developed. The MoO3:ZnO nanostructures exhibit enhanced ethanol sensing performance in non-humid and humid (75% r.H. at 21 °C) atmospheres compared to the pure MoO3 layer; with increase in ZnO concentrations, the sensitivity and stability increased, and the response/recovery time decreased. The response (Gethanol/Gair) of the 25% MoO3:ZnO sensor at an operating temperature of 300 °C against 500 ppm ethanol is up to 171 under non-humid and 117 under humid (75% r.H.) conditions. By comparing the response of the 25% ZnO added MoO3 sensor toward various gases (H2, CO, C3H6, CH4 and C2H5OH), distinctive selectivity to ethanol is observed. The ethanol sensitivity action over MoO3 nanostructures can be ascribed to the catalytic oxidation of ethanol to acetaldehyde, and the enhancement of gas sensing response of the MoO3:ZnO system can be attributed to more active centers that are obtained from the enhanced oxygen vacancy defects induced by ZnO. The presence of a humid atmosphere has a dramatic influence on the sensor performance towards ethanol; the sensitivity diminishes drastically due to the partial site precluding nature of the adsorbed hydroxyl groups to the analyte. The ZnO incorporated MoO3 nanostructure based sensing layers in the present work show significantly superior ethanol sensing performance to the works previously reported for various metal oxide systems.
    06/2013; 1(25):3976-3984. DOI:10.1039/C3TC30408F
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    ABSTRACT: OBJECTIVES: A quantitative volumetric analysis of caudate nucleus can provide valuable information in early diagnosis and prognosis of patients with Alzheimer's diseases (AD). Purpose of the study is to estimate the volume of segmented caudate nucleus from MR images and to correlate the variation in the segmented volume with respect to the total brain volume. We have also tried to evaluate the caudate nucleus atrophy with the age related atrophy of white matter (WM), gray matter (GM) and cerebrospinal fluid (CSF) in a group of Alzheimer's disease patients. METHODS: 3D fast low angle shot (3D FLASH) brain MR images of 15 AD patients, 15 normal volunteers and 15 patients who had normally diagnosed MR images were included in the study. Brain tissue and caudate nuclei were segmented using the statistical parametric mapping package and a semi-automatic tool, respectively and the volumes were estimated. Volume of segmented caudate nucleus is correlated with respect to the total brain volume. Further, the caudate nucleus atrophy is estimated with the age related atrophy of WM, GM and CSF in a group of AD patients. RESULTS: Significant reduction in the caudate volume of AD patients was observed compared to that of the normal volunteers. Statistical analysis also showed significant variation in the volume of GM and CSF of AD patients. Among the patients who had normal appearing brain, 33% showed significant changes in the caudate volume. We hypothesize that these changes can be considered as an indication of early AD. CONCLUSION: The method of volumetric analysis of brain structures is simple and effective way of early diagnosis of neurological disorders like Alzheimer's disease. We have illustrated this with the observed changes in the volume of caudate nucleus in a group of patients. A detailed study with more subjects will be useful in correlating these results for early diagnosis of AD.
    European journal of radiology 05/2013; 82(9). DOI:10.1016/j.ejrad.2013.03.012 · 2.16 Impact Factor
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    J. R. Rani, V. P. Mahadevan Pillai, G. Anoop, Meera Gopal, V. Ganeshan
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    ABSTRACT: Tin oxide (SnO2)-doped Si nanorings of diameter in the range of 100 nm to 170 nm with an average width of 25 nm are synthesized by off-axis laser ablation (PLD) and are characterized by different techniques. The AFM observations show that the surface morphological features of films depend on the tin oxide concentration. The bandgap energies of undoped quantum dots are found to be 2.29 eV, while it decreases to 2.15 eV and 1.5 eV for 3 wt.% and 0.1 wt.% SnO2-doped samples, respectively. The increase in the value of bandgap energy can be attributed to size reduction of particles. The Raman spectra of SnO2-doped films are characterized by a broad Raman band with intensity maximum around 478 cm-1. Raman spectrum shows frequency shift which may be due to changes in the Si–O bond length or Si–O–Si bond angle. The activation energy at higher temperature is found to be 16.99 meV for 3SnSi209, 21 meV for 0.1SnSi209 and 18.1 meV for undoped silicon which shows that defect levels are present in all the samples, the conduction is due to the presence of holes. The synthesized films exhibit PL peak in the visible region. The PL emission peak and PL intensity depend on dopants and it is concluded that luminescence does not originate from localized states in gap but from extended states. The size and shape of nanostructures depend on the SnO2 concentration and the doping effects can be used as a significant guideline for tuning the electronic and optical properties of Si.
    Nano brief reports and reviews 02/2013; 8(1). DOI:10.1142/S1793292013500082 · 1.26 Impact Factor
  • S. Karpagam, S.K. Sudheer, V.P.M. Pillai
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    ABSTRACT: A new method for Discrete Gyrator Transform (DGT) based image encryption and decryption using Double Random Phase Mask (RPM) is proposed. In the present work encryption and decryption has been done using Gyrator Transform (GT) a kind of discrete algorithm using convolution operation. The proposed method uses DGT to reduce the computational load. The robustness of the proposed algorithm to blind decryption in terms of different key values has been calculated. Numerical simulations and some analysis for security have been presented to verify its validity and efficiency.
    Fiber Optics in Access Network (FOAN), 2013 4th International Workshop on; 01/2013
  • B. Soumya, S.K. Sudheer, V.P. Mahadevan Pillai
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    ABSTRACT: Photonic Crystal Fibers (PCFs) are a new class of optical waveguides which offer exceptional light guiding mechanism and deliver significantly improved performance compared to conventional optical fibers. In the present investigation, we propose an solid core PCF for three different values of air filling fraction. The proposed PCF is simulated by using COMSOL Multiphysics. The nonlinearity of proposed PCF is found to be varying with respect to its air filling fraction and a nonlinear coefficient of 148 W-1Km-1 is obtained for PCF with air filling fraction of 0.7. The variation of other parameters like effective refractive index, confinement loss and effective area with respect to wavelength and air filling fraction is also investigated. The supercontinuum spectrum is generated using the designed highly nonlinear fiber and the effect of pump power on the generated output spectrum is studied and results shows that the bandwidth of output spectrum increases with pump power provided its pulse width remains constant.
    Fiber Optics in Access Network (FOAN), 2013 4th International Workshop on; 01/2013
  • N. Anand, S.K. Sudheer, V.P. Mahadevan Pillai
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    ABSTRACT: Design and analysis of a Nonlinear Photonic Crystal Fiber having low confinement loss, low birefringence and low effective mode area has been presented using COMSOL Multiphysics software. The suggested design has a central hole filled with Nematic Liquid Crystal (NLC) surrounded by air holes and a Perfectly Matched Layer (PML). Results show that by using circular holes of small diameter and materials with considerable refractive index difference, the nonlinearity and confinement increases, but the effective area and birefringence properties of the fiber decreases.
    Fiber Optics in Access Network (FOAN), 2013 4th International Workshop on; 01/2013
  • B. Soumya, S.K. Sudheer, V.P. Mahadevan Pillai
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    ABSTRACT: Here, we designed a highly nonlinear and low loss Photonic Crystal Fiber (PCF) structure with square lattice using COMSOL multiphysics. Propagation properties of proposed PCF has been analysed. The analysis has been carried out using finite element method. The proposed fiber obtained low confinement loss, minimum dispersion for wide range of wavelength. Results shows that the proposed PCF gives large negative dispersion for a wide range of wavelength and this makes it suitable for dispersion compensating applications and also it gives high nonlinear coefficient of 117 W-1Km-1. The square lattice PCF structure with elliptical holes is also designed and its birefringence property is compared with PCF with circular holes. Results shows that PCF with elliptical holes shows high birefringence as compared to other and such high birefringent PCF can be used for polarization maintaining applications.
    Fiber Optics in Access Network (FOAN), 2013 4th International Workshop on; 01/2013