Now showing 1 - 10 of 33
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    Effective Medium-Based Plasmonic Waveguides for Tailoring Dispersion
    (15-09-2015)
    Balasubrahmaniyam, M.
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    Abhilash, T.
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    We propose a waveguide configuration with a plasmonic grating for tailoring dispersion characteristics. The unit-cell of the plasmonic grating encompasses the subwavelength distribution of metal nanowires forming a highly resonant effective medium. The configuration enables independent control of the coupling between the plasmonic and waveguide modes via the resonant strength of the effective medium. Numerical simulations show that the line shapes of the coupled modes can be varied from Fano to electromagnetically induced transparency-like. Furthermore, we use the structure to enhance the group index from 250 to 850 and to broaden the associated band from 40 to 180 meV.
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    Low temperature magnetic and electrical transport behavior of Co 58.5 Ga 41.5 alloy
    (24-06-2015)
    Yasin, Sk Mohammad
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    Saha, Ritwik
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    Rao, T. V.Chandrasekhar
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    Nigam, A. K.
    The electrical transport and magnetic properties of Co 58.5 Ga 41.5 binary alloy have been investigated in the temperature range 2-300 K. Analysis of field and temperatures dependence magnetization data suggests a reentrant magnetic behavior with Curie temperature (T C ) ∼90 K. Temperature dependence of resistivity shows large residual resistivity values which is sensitive to the applied magnetic field. The temperature and field dependent resistivity behavior indicates the presence of spin fluctuations at low temperature. Magnetoresistance (MR) of 17 % has been observed at 2 K in 90 kOe field, which follows a power law with exponent varying form 0.5 at low temperature to linear behavior at higher temperature. The temperature variation of magnetization and MR can be understood on the basis of ferromagnetic matrix with finite spin clusters.
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    Correlation of Mn charge state with the electrical resistivity of Mn doped indium tin oxide thin films
    (13-09-2010)
    Kumar, S. R.Sarath
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    Hedhili, Mohamed Nejib
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    Alshareef, H. N.
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    Correlation of charge state of Mn with the increase in resistivity with Mn concentration is demonstrated in Mn-doped indium tin oxide films. Bonding analysis shows that Mn 2p3/2 core level can be deconvoluted into three components corresponding to Mn2+ and Mn4+ with binding energies 640.8 eV and 642.7 eV, respectively, and a Mn2+ satellite at ∼5.4 eV away from the Mn2+ peak. The presence of the satellite peak unambiguously proves that Mn exists in the +2 charge state. The ratio of concentration of Mn2+ to Mn4+ of ∼4:1 suggests that charge compensation occurs in the n-type films causing the resistivity increase. © 2010 American Institute of Physics.
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    Enhanced short wave IR third order nonlinearity of gold nanoparticle embedded ZnO thin films
    (01-01-2013)
    Ali, S. Akbar
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    Kalanoor, B. S.
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    Patra, Anuradha
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    Gold nanoparticle embedded ZnO thin films have been studied at the fundamental and second harmonic wavelengths of a picosecond laser by Z-scan technique. The films exhibit the effect of saturable absorption and selfdefocusing. Large value third order nonlinear susceptibility (∼10 -8 esu) has been observed at 1064 nm. Fast relaxation time measurements have been performed with the diffraction of the probe beam with laser-induced transient grating technique. Figure of merit values for optical switching applications have been obtained. One of the samples has been tested for passive mode-locking applications in combination with the standard saturable absorber, IR26. © 2013 Optical Society of America.
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    Gold nanoparticles embedded zinc oxide films as possible optical filters
    (01-08-2011)
    Patra, Anuradha
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    Multilayered structures of gold nanoparticles (AuNPs) embedded Zno films were prepared by sandwiching Au nanoparticles in between magnetron sputtered Zno films. More than 80% transmittance in visible region was observed for Zno film. For structures consisting of single and double layers of AuNPs, transmittance at ∼600 nm was reduced to ∼25% and ∼6%, respectively. AuNPs embedded sandwiches showed a huge reduction in UV Photoluminescence that was prominent in pure Zno films, and was attributed to the interband absorption in Au. © 2011 World Scientific Publishing Company.
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    Spectral response of nanocrystalline ZnO films embedded with Au nanoparticles
    (01-12-2012)
    Patra, Anuradha
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    Manivannan, A.
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    The optical response of a two-phase composite consisting of Au nanoparticles (AuNPs) in a nanocrystalline ZnO thin film matrix has been systematically studied and analyzed by the Bergman-Milton spectral density formalism. The real and imaginary parts of the effective dielectric function exhibited anomalous dispersion and absorption, respectively, at the characteristic localized surface plasmon resonance (LSPR) wavelength. A multilayer structure consisting of two AuNP-ZnO composite films separated by a thin ZnO film displayed a twofold increase in the absorption at LSPR (with negligible change in FWHM), which is attributed to the increase in the number density of the AuNPs resulting from the nanocrystalline nature of the ZnO film. The results have been used to correlate the spectral density function to the morphology of AuNPs in a ZnO matrix. © 2012 Optical Society of America.
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    Spin correlations and magnetic order in Co-Ga alloys: A comprehensive study
    (11-08-2015)
    Yasin, Sk Mohammad
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    Saha, Ritwik
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    Nigam, A. K.
    Low temperature magnetic properties of binary CoxGa100-x alloy with Co concentration in the range 54 ≤ x ≤; 61.5 at% have been investigated. From the temperature and magnetic field dependent magnetization measurements magnetic phase diagram has been identified. Cluster spin glass like features are noticed in x = 54, 55 compositions, while the compositions x > 57 exhibit double magnetic transition i.e., at higher temperatures paramagnetic (PM) - ferromagnetic (FM) and at lower temperatures FM-SG like transition. The critical concentration is identified to be near x = 57 composition where discernible spontaneous magnetization emerges and the long range ferromagnetic order develops above this composition in addition to the spin glass transition (or mixed magnetic phase). Analysis of temperature dependence magnetization data in the different temperature ranges for the compositions x = 60 and 61.5 indicate that the mean field models are not suitable to understand the phase transition. Magnetic isotherms in the critical region were analyzed using non-mean-field approach and the critical exponents (γ = 1.31 and β = 0.337) found to be close to 3D Heisenberg model suggesting the importance of short range magnetic order. The data satisfies magnetic equation of state characteristic of a second order phase transition. The results obtained from the present study corroborate well with the phenomenological interacting spin cluster model.
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    Studies on interface between In 2 O 3 and CuInTe 2 thin films
    (01-10-2017)
    Ananthan, M. R.
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    Malar, P.
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    Osipowicz, Thomas
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    Interface between dc sputtered In 2 O 3 and stepwise flash evaporated CuInTe 2 films were studied by probing Si/In 2 O 3 /CuInTe 2 and Si/CuInTe 2 /In 2 O 3 structures with the help of glancing angle X-ray diffraction, Rutherford backscattering spectrometry and micro-Raman spectroscopy. The results showed that in Si/In 2 O 3 /CuInTe 2 structure, a ∼20 nm thick interface consisting of In, Cu and O had formed between In 2 O 3 and CuInTe 2 and was attributed to the diffusion of Cu from CuInTe 2 into In 2 O 3 film. On the other hand, in Si/CuInTe 2 /In 2 O 3 structure, homogeneity of the underlying CuInTe 2 film was found lost completely. An estimate of the masses of the constituent elements showed that the damage was caused by loss of Te from CuInTe 2 film during the growth of In 2 O 3 film on Si/CuInTe 2 .
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    SPR: A promising platform for thermal transport studies
    (18-07-2013)
    Abhilash, T.
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    Balasubrahmaniyam, M.
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    A theoretical model has been adopted to simulate the effect of temperature on surface plasmon resonance (SPR) of a gold film by modeling its dielectric functions at various temperatures. A two-prism experimental arrangement that uses Kretschmann configuration in angular interrogation mode has been used to study SPR. Reflectivity measurements as a function of temperature have been performed at different positions of the resonance spectrum. Observed intensity variations reveal a considerable sensitivity of the reflectivity towards temperature which can further be utilized for extracting thermal transport properties. © 2013 AIP Publishing LLC.
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    Localized surface plasmon resonance in Au nanoparticles embedded dc sputtered ZnO thin films
    (01-02-2015)
    Patra, Anuradha
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    Balasubrahmaniyam, M.
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    Laha, Ranjit
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    Malar, P.
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    Osipowicz, T.
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    Manivannan, A.
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    The plasmonic behavior of metallic nanoparticles is explicitly dependent on their shape, size and the surrounding dielectric space. This study encompasses the influence of ZnO matrix, morphology of Au nanoparticles (AuNPs) and their organization on the optical behavior of ZnO/AuNPs-ZnO/ZnO/GP structures (GP: glass plate). These structures have been grown by a multiple-step physical process, which includes dc sputtering, thermal evaporation and thermal annealing. Different analytical techniques such as scanning electron microscopy, glancing angle X-ray diffraction, Rutherford backscattering spectrometry and optical absorption have been used to study the structures. In-situ rapid thermal treatment during dc sputtering of ZnO film has been found to induce subtle changes in the morphology of AuNPs, thereby altering the profile of the plasmon band in the absorption spectra. The results have been contrasted with a recent study on the spectral response of dc magnetron sputtered ZnO films embedded with AuNPs. Initial simulation results indicate that AuNPs-ZnO/Au/GP structure reflects/absorbs UV and infrared radiations, and therefore can serve as window coatings.