Transmission of light through magnetic nanocavities

The transmission of light through a metallic film stack on a transparent substrate, perforated with a periodic array of cylindrical holes/nanocavities, is studied. The structure is fabricated by using self-assembled nanosphere lithography. Since one layer in the film stack is made of a ferromagnetic metal (iron), exposure of the structure to a solution containing iron oxide nanoparticles causes nanoparticle accumulation inside the nanocavities. This changes the dielectric constant inside the nanocavities and thus affects the light transmission. Simulations are in good agreement with experiment, and show large sensitivity of the response to the amount of iron oxide nanoparticles deposited. This could be used in various sensor applications.     

Metamaterial-plasmonic absorber structure for high efficiency amorphous silicon solar cells

We show that a planar structure, consisting of an ultrathin semiconducting layer topped with a solid nanoscopically perforated metallic film and then a dielectric interference film, can highly absorb (superabsorb) electromagnetic radiation in the entire visible range, and thus can become a platform for high-efficiency solar cells. The perforated metallic film and the ultrathin absorber in this broadband superabsorber form a metamaterial effective film, which negatively refracts light in this broad frequency range. Our quantitative simulations confirm that the superabsorption bandwidth is maximized at the checkerboard pattern of the perforations. These simulations show also that the energy conversion efficiency of a single-junction amorphous silicon solar cell based on our optimized structure can exceed 12%.     

Influence of annealing environment on microstructure and magnetic properties of amorphous Co75Fe5Zr10B10 ribbons

Rapidly solidified amorphous Co₇₅Fe₅Zr₁₀B₁₀ ribbon has been subjected to heat treatment at temperature of 300 °C for 10 min under three different atmospheric conditions, such as; air, vacuum and hydrogen-blowing atmospheres. Although no significant change in bulk structure of the ribbons was observed through X-ray diffraction analysis, substantial changes in surface microstructures are seen through SEM microstructural investigations. It is observed that the magnetic softness (coercivity, initial permeability, longitudinal permeability ratio [(Δμ/μ)%], sensitivity factor of (Δμ/μ)%, etc.) of the hydrogen-blowing atmospheric annealed ribbons is enhanced, compared to the as quenched, air and vacuum annealed samples. Moreover, a comparative study between these low temperature annealed samples has been reported.     

Effect of precursor on epitaxially grown of ZnO thin film on p-GaN/sapphire (0 0 0 1) substrate by hydrothermal technique

Single crystalline ZnO thin film on p-GaN/sapphire (0 0 0 1) substrate, using two different precursors by hydrothermal route at a temperature of 90 °C were successfully grown. The effect of starting precursor on crystalline nature, surface morphology and optical emission of the films were studied. ZnO thin films were grown in aqueous solution of zinc acetate and zinc nitrate. X-ray diffraction analysis revealed that all the thin films were single crystalline in nature and exhibited wurtzite symmetry and c-axis orientation. The thin films obtained with zinc nitrate had a more pitted rough surface morphology compared to the film grown in zinc acetate. However the thickness of the films remained unaffected by the nature of the starting precursor. Sharp luminescence peaks were observed from the thin films almost at identical energies but deep level emission was slightly prominent for the thin film grown in zinc nitrate.     

Morphology and crystal quality investigation of hydrothermally synthesized ZnO micro-rods

Micro-structural and room and low temperature photoluminescence response of undoped one-dimensional ZnO were investigated. ZnO rods of different morphology and size were synthesized by controlling growth parameters through hydrothermal technique. The phase and microstructure analysis were carried out by X-ray diffraction and scanning electron microscopy. The room and low temperature photoluminescence spectra of the samples were studied. Near band edge sharp exciton emission peaks and broad defect-related peaks were observed. The ratio of band edge emission to deep level emission was controlled by tuning the initial concentration, pH and reaction time period. Optimal growth condition for growth of micro-rods with improved crystal quality was obtained with initial Zn²⁺ concentration of 0.5 M, at reaction temperature of 120 °C, pH of 9.9 and in a reaction time period of 6 h.     

Superconductivity of Metaphosphatecobalt(II) Salt at 173 K

An inorganically template metaphosphate of Co(II) complex has been synthesized and thermal properties have been studied at a low temperature up to 173?K from 298?K by the Differential Scanning Calorimeter (DSC). The specific heat capacity is measured in atmospheric O₂ at a heating rate of 283?K?min^?1 from 298?K and kept constant at 173?K for 4?minutes then reversed to 298?K again. The bulk critical temperature of superconductivity of metaphosphatecobalt(II) salt was found at 173?K.     

Thermal application of composites of iron and magnesium in thermosyphon solar water heating system

A novel and low-cost mixture of iron and magnesium have been synthesized and used as selective coatings for flat plate absorber in solar water heating system. The commercial black paint is fabricated with the mixture of composition Fe₃(PO₄)₂·0.1Mg₂P₂O₇·1.9 MgSO₄(FPM3A). The composition of the coating mixture has been characterized by various analytical techniques. Thermal studies of these mixtures were accomplished using differential scanning calorimetry and thermo-gravimetric analysis. From the thermal analysis, it has been observed that the mixtures can be used as thermal heat storage materials. The FPM3A-modified black paint has been tested in a thermosyphon solar water heater prototype. The average water temperature and efficiency of the flat plate absorber with FPM3A-modified black paint have increased by an average of 7.5° and around 12%, respectively, in comparison with that with commercial unprocessed black paint.     

Topographical heterogeneity in transparent PVA hydrogels studied by AFM

Physically crosslinked poly (vinyl alcohol) (PVA) hydrogels have a wide range of biomedical applications. Transparent and stable PVA hydrogels synthesized by freeze-thawing method are potential candidates to be used as tissue engineering scaffolds provided they exhibit suitable topographical roughness and surface energy. The effect of processing parameters i.e., polymer concentration and number of freeze-thaw cycles on the resulting topography of the freeze-thawed transparent hydrogels has been studied and quantified using non-contact mode of an atomic force microscope (AFM) and image analysis. Simultaneously captured phase contrast images have revealed significant information about morphological changes in the topographical features and crystallinity of the hydrogels. Topographical roughness was found to decrease as a function of number of freeze-thaw cycles.     

Effect of annealing temperature on optical band-gap of amorphous indium zinc oxide film

The effect of annealing temperature on the electrical and optical properties of indium zinc oxide (IZO) (In₂O₃:ZnO = 90:10 wt.%) thin films has been investigated. The IZO thin films were deposited on glass substrates by radio frequency magnetron sputtering and then subjected to annealing in a mixed ambient of air and oxygen at 100, 200 and 300 °C. All the IZO films were found to have amorphous structure. With the increase of the annealing temperature, the carrier concentration decreased and the resistivity increased. The average transmittance of IZO thin films decreased slightly with annealing temperature. Interestingly, a systematic reduction of the optical band-gap from 3.79 eV to 3.67 eV was observed with annealing temperature. The change in optical band-gap was observed to be caused predominantly by Burstein-Moss band-gap widening effect suggesting unusual absence of band narrowing effect. The effects on optical and electrical properties of IZO films have been discussed in detail.