Dixit, Ambesh

We investigated the effect of Au nanoparticles in Zinc o xide semiconductor matrix for enhanced absorption. Apart from ZnO optical absorption at 360 n m, the matrix also shows plasmonic absorption at 560 nm.

Zirconium carbide-nitride absorber (ZrC-ZrN) and zirconium reflector tandem structures were prepared on glass and aluminum substrate, in conjunction with zirconium oxide (ZrOx) anti-reflection coatings, using DC/RF magnetron sputtering system. The solar absorption properties of zirconium carbide-nitride absorber layers were optimized by controlling nitrogen flow during synthesis process for optimal solar thermal response. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) measurements were carried out on fabricated absorber-reflector tandem structures to understand the structure-property correlation. We absorbed strong dependence of zirconium nitride fraction on solar thermal performance. We observed enhanced solar absorptance α ∼ 0.86 and thermal emittance ϵ ∼ 0.05 at room temperature for structures fabricated with optimized synthesis parameters. The optimized structures are stable up to 150 °C in the air without any significant degradation in their solar performance.

Adsorption characteristics of carbon nanotubes (CNTs) intercalated with nickel is a subject of growing experimental and theoretical interest. In this manuscript adsorption of hydrogen gas on the surface of nickel intercalated multiwall carbon nanotubes (MWNTs) has been studied. It is expected that metal catalysts like nickel can have possible pattern of atoms and molecules on the surface of MWNTs with varying parameters like diameters, concentration of nickel & MWNTs for sorption kinematics. Distribution and strong interaction of Ni with the MWNTs could support. Thus, adsorption capacity of the hydrogen via the spillover effect is expected. Ni doped MWNTs composites have been examined by using X-ray diffraction (XRD), Fourier Transform (FT-IR) infrared spectroscopy, Sorption kinetics (Sievert's spectrometer), and Scanning Electron Microscopy (SEM).

Ni-Co/Nanoporous Al2O3/Aluminum spectrally selective structures are grown using electrochemical anodization of alumina, followed by electrochemical pigmentation of Ni and Co metallic particles simultaneously. The pigmentation of Ni and Co particles into nanoporous anodized alumina (AA) is achieved using the reduction of metal ions in the aqueous electrolyte. The measured absorptivity and emittance are ∼ 0.90 ± 0.05 and 0.14 ± 0.04, respectively. These structures are subjected to the ten identical thermal cycling upto 300°C in inert N2 and air ambient conditions. The optical performance suggests that absorptivity is nearly same with slight enhancement in the emittance values as compared to the structure without any heat treatment. The accelerated corrosion studies suggest that Ni-Co co-pigmented AA structures are relatively corrosion robust as compared to that of the AA structure.

Parabolic dish solar energy concentrator with aperture diameter 1.4 m and focal length 0.32 m is designed and fabricated to charge and store solar thermal energy in phase change material (PCM) based heat packs. Overall heat loss factor, heat duty, over all thermal efficiency, and optical efficiency factor are calculated using water sensible heating and cooling tests and values are 16.11 W m-2 K-1, 546.9 W, 49.2% and 0.62 respectively. The performance characteristic curve is generated using these parameters to understand its performance at different ambient temperatures and solar insolation. The fabricated concentrator has been used to charge 16 PCM heat packs with 150 g PCM in each heat pack, which took about 35 minutes for complete charging of PCM heat packs at average ambient temperature 39 °C and solar radiation flux density 715 W m-2 K-1. The charged heat packs are subjected to discharge studies at average ambient temperature about - 7 °C and observed heat release in the temperature range of 48 to 40 °C for 50 minutes, suggesting its applications for comfort and therapeutic applications in high altitude areas.

We will discuss a small novel hexagonal shaped geometry for ultra wideband (UWB) monopole antenna with notch characteristics. The self-similar nature of this fractal like geometry provides higher effective antenna length and wide operating bandwidth because of the onset of multiple resonances. Notch characteristics are introduced using a rectangular slot in the ground plane, which enhances the reflection coefficient over the entire UWB frequency operating range for the proposed device. The optimized 19 mm × 15 mm dimensions, for the proposed antenna are the smallest among such geometries, exhibiting a large bandwidth from 3.1 GHz to 11.7 GHz with VSWR < 2 over the entire frequency range. The proposed antenna demonstrates nearly omnidirectional radiation pattern, proper impedance matching, and good return loss over the entire UWB frequency range.

We used temperature-dependent neutron diffraction measurements on FeVO4 to understand the temperature driven anisotropy and observed that the maximum change for a&b lattice parameters in conjunction with a large contraction in angle β as a function of temperature. The least changes are observed for the c lattice parameter and in γ angle. From these structural parameters, it can be said that, FeVO4 exhibits large structural anisotropy with lowering temperature. The large change in lattice parameters in magnetic phases i.e. below 22K explains the strong magnetostructural coupling in FeVO4.

Phase Change Materials (PCMs) are being used in thermal energy storage systems because of their high energy storage density, and heat storage/release in small temperature range near melting temperature. Such requirements compel to design and develop materials with high latent heat of fusion for thermal energy storage applications. This will rely on characterization of materials to understand their thermal properties as a function of temperature. In this work, an experimental set-up is presented for measuring the thermodynamic properties of materials, such as, temperature-time response, latent heat of fusion, specific heat of solids and liquids, melting-solidification temperatures, degree of supercooling and enthalpy-temperature response of PCMs. The present experimental test set-up, including specific PCM container, is designed and fabricated for characterization of low temperature PCMs with melting temperature in the range of 0-100°C.

Structural and electronic properties of pristine and transition metal doped ZnS monolayer are investigated within the framework of density functional theory. The pristine ZnS monolayer is showing direct band gap of about 2.8 eV. The investigated transition metal doping showed the transition from non-magnetic semiconductor to a magnetic system e.g. magnetic semiconductor for Co doped ZnS and half metal for Ni doped ZnS monolayers. The Co doped ZnS monolayer showed higher formation energy, confirming the strong bonding than that of Ni doped ZnS monolayer. The electron difference density shows the charge sharing between transition metal (Ni and Co) and S, confirming the covalent bond formation.

CdTe quantum dots were synthesized using water as a solvent medium. Synthesized quantum dots were used to integrate into TiO2 nano-porous electrode using a combination of linker assisted direct adsorption and chemical bath deposition process. Sensitized electrodes were characterized to understand their physical and optical properties for photovoltaic application.