S Kasiviswanathan

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.

Thermal stability of silver selenide thin films formed from the solid-state reaction of Ag-Se diffusion couples on Si substrates covered with a thin Cr film, is investigated. Glancing angle X-ray diffraction (GXRD), XPS, atomic force microscopy (AFM) and Rutherford backscattering spectrometry (RBS) are used to characterize the as-deposited films and those annealed at 100, 200, 300, and 400 °C. The results reveal the formation of polycrystalline orthorhombic silver selenide films that remain stable without compositional change upon thermal annealing, in marked contrast to the agglomeration exhibited by silver selenide films deposited on Si without Cr film. The improvement in the thermal stability is attributed to compressive stress relief by a grainy morphology with large surface area, the formation of which is promoted by partially oxidized Cr adhesion film. © 2008 John Wiley & Sons, Ltd.

Effect of heat treatment on silver selenide films grown from diffusion-reaction of Ag and Se films on Cr-buffered Si substrates was investigated up to 400 °C. X-ray diffraction (XRD), Scanning electron microscopy (SEM), Secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) were used to characterize the films. XRD patterns of the films showed stress assisted change in preferential orientation of the films upon annealing: the films annealed at 200 °C exhibited a strong orientation along (2 0 0) plane, which changed to (0 1 3) after annealing at 300 and 400 °C. Dynamic SIMS measurements showed that Cr is confined to the interface and that there is no diffusion of Cr into silver selenide. © 2007 Elsevier B.V. All rights reserved.

In2O3 thin films were grown by direct current reactive sputtering. Structural investigations using X-ray diffraction and transmission electron microscopy confirmed the single-phase and polycrystalline nature of the films. Rutherford backscattering spectrometry study of the interface of In2O3 films with Si indicated the formation of ∼20 nm thick intermediate region consisting of silicon, oxygen and indium. Annealing at 875 K in oxygen atmosphere led to an increase in interface layer thickness. Broadening of the interface and diffusion of silicon into In2O3 were observed in films annealed in argon at 875 K. Oxygen-to-indium atomic concentration ratio in the as-grown films was ∼1.44, which was found to vary depending upon the annealing conditions. However, films deposited over Si/SiO2 showed a sharp interface between the In2O3 film and SiO2. © 2005 Elsevier B.V. All rights reserved.

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.

Single-particle tunnelling experiments have been performed on polycrystalline BiSrCaCuO : Pb using break junction configuration in the temperature range 4·2 K ≤ T ≤ Tc. A single peak at V = ± 60 mV, ascribed to a gap feature, has been observed in the conductance spectra at 4·2 K from which a ratio of 2Δ(0)/KBTC = 6·2 (± 0·5) is obtained. The temperature dependence of Δ is compared with the BCS theory. Alternative non-BCS mechanisms may also have to be invoked to obtain satisfactory agreement between the measured values and theory. Attempts to fit the experimental data by considering lifetime smearing Dynes model have resulted in Δ = 25 meV and Γ = 4 ·1 meV.

Thermal stability of silver selenide thin films grown on silicon substrates by the solid state reaction of Se and Ag films is studied. The as-deposited as well as films annealed at different temperatures for 60 min in argon were investigated using X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS) and scanning electron microscopy (SEM) measurements. Analysis of the XRD and RBS data of as-deposited films indicated the formation of single phase orthorhombic silver selenide from the reaction of Ag and Se films at room temperature. RBS spectra of films annealed at 473 K and above showed features characteristic of agglomerated morphology. SEM images showed the smooth morphology of the as-deposited films to evolve into a discontinuous island state with annealing temperature. The results suggest that above ∼ 473 K, the films are thermally unstable and agglomerate through holes generated at grain boundaries. © 2006 Elsevier B.V. All rights reserved.

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.

Indium based transparent conducting oxides doped with magnetic elements have been studied intensively in recent years with a view to develop novel ferromagnetic semiconductors for spin-based electronics. In the present work, we have grown manganese doped indium tin oxide (Mn:ITO) thin films, onto Si and Si/SiO2 substrates by DC reactive sputtering of a composite target containing indium-tin alloy and manganese, in a gas mixture of oxygen and argon. Glancing angle X-ray diffraction (GXRD) studies reveal the polycrystalline nature of the films. Magnetic measurements carried out using vibrating sample magnetometer (VSM) suggest that the films are ferromagnetic at room temperature, with a saturation magnetization of ∼22.8 emu/cm3. The atomic percentages of In, Sn, Mn and O, as estimated using Rutherford backscattering spectrometry (RBS) are 37.0, 4.0, 1.6 and 57.4, respectively. RBS measurements reveal that the interface of the films with Si substrate has a ∼30 nm thick intermediate layer. This layer consists of oxygen, silicon, indium, tin and manganese, in the ratio 1:0.56:0.21:0.07:0.03, indicative of diffusion of elements across the interface. The films on Si/SiO2, on the other hand, have a sharp interface. © 2007 Elsevier B.V. All rights reserved.

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.