S. S. Verma

Refractive Index Sensitivity Analysis of Ag, Au, and Cu Nanoparticles

The localized surface plasmon resonance (LSPR) spectrum of noble metal nanoparticles is studied by quasi-static approximation. Taking the sensitivity of LSPR shape to the size and shape of nanoparticle along with surrounding refractive index, parameters like refractive index sensitivity and sensing figure of merit have been determined. In the present analysis from the sensing relevant parameters, it is concluded that Ag represents a better sensing behavior than Au and Cu over the entire visible to infrared regime of EM spectrum.

Scattering Efficiency and LSPR Tunability of Bimetallic Ag, Au, and Cu Nanoparticles

Scattering efficiencies of Ag–Cu, Ag–Au, and Au–Cu alloy nanoparticles are studied based on Mie theory for their possible applications in solar cells. The effect of size (radius), surrounding medium, and alloy composition on the scattering efficiency at the localized surface plasmon resonance (LSPR) wavelengths has been reported. In the alloy nanoparticles of Ag1−xCux, Au1−xCux and Ag1−xAux; the scattering efficiency gets red-shifted with increase in x. Moreover, the scattering efficiency enhancement can be tuned and controlled with both the alloy composition and the surrounding medium refractive index. A linear relationship which is in good agreement to the experimental observations between the scattering efficiency and metal composition in the alloys are found. The effect of nanoparticle size and LSPR wavelength (scattering peak position) on the full width half maxima and scattering efficiency has also been studied. Comparison of Au–Ag, Au–Cu, and Ag–Cu alloy nanoparticles with 50-nm radii shows the optical response of Ag–Cu alloy nanoparticle with wide bandwidth in the visible region of the electromagnetic spectrum making them suitable for plasmonic solar cells. Further, the comparison of Ag–Cu alloy and core@shell nanoparticles of similar size and surrounding medium shows that Cu@Ag nanoparticle exhibits high scattering efficiency with nearly the same bandwidth.

DDA simulations of noble metal and alloy nanocubes for tunable optical properties in biological imaging and sensing

The selection of nanoparticles for achieving efficient contrast in biological imaging and sensing is based on their optical properties. In the present study, discrete dipole approximation (DDA) simulated Ag, Au and their alloy nanocubes of various edge length spectra are used to investigate the surface plasmon resonance (SPR) wavelength, resonant line-width, relative contribution of scattering in extinction, and sensitivity of the SPR peak position to the refractive index of the embedding medium. The optical properties are significantly altered by the nanocube alloy composition. The scattering to absorption ratio is enhanced and tuned in the visible regime by alloying the metals, which may be useful for biological imaging. The sensitivity of the SPR peak position to the bulk refractive index is enhanced in alloys compared to pure metals. According to the sensing figure of merit (FOM), there exists an optimum alloy nanocube edge length and spectral region to obtain the best sensing performance. Such endeavours have the potential to improve the sensing performance of the nanoparticles with tunable SPR wavelength of the desired spectral regime.

To study the direct transformation of methane into methanol in the lower temperature range

Abstract A considerable industrial interest has always existed in the catalytic as well as non-catalytic transformation of methane (CH 4 ) gas into methanol (CH 3 OH) as an intermediate product due to its wide applications. The purpose of the present computational study was to study the homogeneous reaction kinetics of methane and to analyze the effect of operating parameters, viz. temperature, residence time and CH 4 /O 2 input ratio on direct oxidation of CH 4 into CH 3 OH in the lower temperature range suitable to catalytic conversion. It is found that a higher conversion of methane into methanol can be achieved by controlling the operating parameters to their optimum values. A combination of input values as CH 4 /O 2 ratio=0.005/0.995, OH=5 ppm and T =100 °C was concluded to be optimum for direct oxidation of methane into methanol. The combination of reactions R 1 (CH 3 OH=CH 3 +OH) and R 15 (CH 4 +OH=CH 3 +H 2 O) was mainly found responsible for the formation of methanol under the present operating conditions. Though the contribution of direct oxidation of CH 4 into CH 3 OH is very small (≈1% at the maximum) with suitable operating parameters, this advantage can be coupled with other optimum catalytic conversion conditions to enhance the production of methanol.

Simulated study of plasmonic coupling in noble bimetallic alloy nanosphere arrays

The plasmonic coupling between the interacting noble metal nanoparticles plays an important role to influence the optical properties of arrays. In this work, we have extended the Mie theory results of our recent communication to include the effect of particle interactions between the alloy nanoparticles by varying interparticle distance and number of particles. The localized surface plasmon resonance (LSPR) peak position, full width at half maxima (FWHM) and scattering efficiency of one dimensional (1D) bimetallic alloy nanosphere (BANS) arrays of earlier optimized compositions i.e. Ag0.75Au0.25, Au0.25Cu0.75 and Ag0.50Cu0.50 have been studied presently by using discrete dipole approximation (DDA) simulations. Studies have been made to optimize size of the nanosphere, number of spheres in the arrays, material and the interparticle distance. It has been found that both the scattering efficiency and FWHM (bandwidth) can be controlled in the large region of the electromagnetic (EM) spectrum by varying the nu...

Solar-assisted liquid metal MHD power generation: A state of the art study

Abstract The research and development of LMMHD energy conversion (EC) systems which started in the 1960s has already come a long way and is heading towards commercialization. Design and development of such systems has to deal with a number of questions relating to single- and two-phase flows of molten metals, including different patterns of two-phase flow, interphase, phenomena, heat transfer, performance of LMMHD components and compatibility of liquid metals with other fluids and with confinement materials. Liquid metal MHD (LMMHD) power conversion systems proposed many years ago are gaining increasing attention in their various proposed modes, consisting of single-phase or two-phase fluid flow for a wide range of heat sources, e.g. solar energy, waste heat, nuclear energy, etc. Liquid metal MHD (LMMHD) power systems have been recently proposed for direct electrical energy conversion of low grade thermal sources of energy, like solar energy. Solar-powered LMMHD power generation systems are very attractive regarding efficiency and cost per unit of installed power. Theoretical and experimental investigations carried out in the various aspects of these systems are presented. A state of the art review of activities in the solar-powered LMMHD power systems field which have taken place so far is described here.

Searching for Alternative Plasmonic Materials for Specific Applications

The localized surface plasmon resonance (LSPR) based optical properties such as light scattering, absorption, and extinction efficiencies of multimetallic and metal-semiconductor nanostructures will be studied. The effect of size, surrounding medium, interaction between the particles, composition of the particles, and substrate on LSPR peak position, its line width, and maxima of cross-sections will also be discussed to optimize the selected systems for various applications like plasmonic sensors and biomedical applications and to enhance the efficiency of solar cells. Therefore, by varying all these factors, the LSPR peak of multimetallic and metal-semiconductor nanostructures can be tuned over the entire UV-visible to infrared (IR) region of the electromagnetic spectrum. Moreover the optical properties of underlying semiconductor materials can be enhanced by combining the semiconductor with noble metal nanoparticles.

Eco-friendly alternative refrigeration systems

Refrigeration applications at the domestic, commercial and industrial levels are becoming an integral part of the present day living. The demand and supply of refrigeration systems is increasing day by day with the changing lifestyle. The existing compressor-based refrigeration (i.e., mechanical refrigeration) system has reached the maximum level of innovation. For the last few decades, there has not been any significant increase in the efficiency (i.e., coefficient of performance, COP) of the system. Moreover, with the increasing awareness of environmental degradation, the production, use and disposal of ChloroFluoro Carbons (CFCs) and HydroChloroFluoroCarbons (HCFCs) as refrigerants in mechanical refrigeration system has become a subject of great concern. However, such systems are being developed using more ecofriendly refrigerants viz., air, CO2, NH3, etc. Besides, efforts are being directed to develop other types of refrigeration technologies e.g., magnetic refrigeration, thermoelectric refrigeration (discussed in Part 1) and thermoacoustic refrigeration (discussed in Part 2), which will be moreecofriendly, cost effective, efficient, simple in design, convenient and reliable.

Optimum liquid fuel mixture for MHD power generators

Abstract Electrical conductivity of the seeded combustion products of various liquid fuel mixtures is evaluated analytically, assuming combustion to take place under stoichiometric conditions in enriched air, to investigate the suitability of the fuels for magnetohydrodynamic (MHD) power generators. Calculations have also been carried out to study the dependence of the conductivity of the fuel mixtures on their cost in order to obtain an optimum fuel mixture with a reasonable conductivity of about 10 mho/m at minimum cost.

Optimum gaseous fuel combination for MHD utility

In the present work, the electrical conductivity of the seeded (with K) combustion products of various gaseous fuel mixtures has been analytically evaluated when the fuel combinations are burnt in oxygen enriched air. The dependence of their electrical conductivity on the percentage of enriched air is investigated in order to obtain an optimum gaseous fuel combination which gives a desired electrical conductivity (⋍10 mho/m) for MHD utility at minimum cost. It is found that the gaseous combinations of WG-LPG and WGC3H8, when burnt under stoichiometric conditions in 30% enriched air at atmospheric pressure, are the optimum fuel combinations that satisfy these conditions.