Shubhra Kala

A dual-deposition setup for fabricating nanoparticle-thin film hybrid structures

This report describes a dual-deposition setup for fabricating well-defined nanoparticles-thin film structures. The setup consists of a particle synthesis section for the gas phase generation of size-selected nanoparticles and a deposition section for the sequential growth of thin film and nanoparticle layers on substrates using vacuum evaporation and atmospheric pressure electrostatic precipitator techniques, respectively. The setup has been used to deposit Pd nanoparticles-Pr thin film structures. Average sizes and size distributions of Pd nanoparticles measured online during the particle synthesis by means of electrical mobility analysis have been compared with those of nanoparticle samples deposited on Pr thin film and other substrates and measured by high resolution scanning electron microscopy and transmission electron microscopy techniques. The setup is useful for depositing a variety of nanoparticles-thin film structures.

Magnitude and time response of electronic and topographical changes during hydrogen sensing in size selected palladium nanoparticles

In this study, size dependence of electronic and topographical effects during Pd-H interaction has been investigated by studying H sensing in thin films of size selected and monosized nanoparticles having 15, 20, and 25 nm diameter. By separating the contributions of electronic changes due to H adsorption and topographical changes due to lattice expansion to hydrogen sensing, it has been shown that the magnitude and response time of these changes are sensitive functions of nanoparticle size and measurement temperature. The temperature dependence of saturated resistance corresponding to these changes provides important information about the nature of electronic and topographical changes.

Metal-semiconductor pair nanoparticles by a physical route based on bipolar mixing

In this report a methodology is described and demonstrated for preparing Au-Ge pair nanoparticles with known compositions by extending and modifying the basic steps normally used to synthesize nanoparticles in carrier gas. For the formation of pair nanoparticles by bipolar mixing, two oppositely charged aerosols of nanoparticles having the desired size are produced with the help of two differential mobility analyzers. Then both are allowed to pass through a tube, which provides sufficient residence time to result in nanoparticle pair formation due to Brownian collisions influenced by Coulomb forces. The effect of residence time on the formation of nanoparticle pairs as well as the influence of diffusion and discharging is described. Subsequently, necessary modifications to the experimental setup are demonstrated systematically. The kinetics of nanoparticles pair formation in a carrier gas is also calculated and compared with measurements made with the help of an online aerosol size analysis technique. This synthesis of nanoparticle pairs can be seen as a possible route towards Janus-type nanoparticles.

Nanotracks as transport routes for enhanced and reversible hydrogen diffusion in swift heavy ion irradiated Pd–Pr layers

This study reports an all-round enhancement in the hydrogenation properties of Pd–Pr layers due to ion tracks formed on irradiation with 120MeV Ag+10 ions. About 17.8% increase in the hydrogen stoichiometry value during loading, near maximal removal (about 31%) during deloading, and increase in the active layer thickness are observed on ion irradiation. Nonequilibrium structural change during ion-induced shock wave generation results in the formation of nanotracks throughout the film thickness, which provide two-way transport routes for H diffusion. This study thus provides an effective methodology of improving the hydrogenation properties of materials.

Synthesis and Film Formation of Monodisperse Nanoparticles and Nanoparticle Pairs

The use of well-defined nanoparticles for functional film applications is described. The advantages of applying size-fractionation, e.g. by means of mobility analysis, are described together with the technological obstacles which have to be overcome. The synthesis of Au and Ge nanoparticles by means of spark discharge is described. To prepare alloy nanoparticles, two different approaches have been utilized. Au-Ge pair nanoparticles are formed by bipolar mixing after separate size selection of both materials. The synthesis of AuGe alloyed nanoparticles is also performed by co-sparking from two different electrodes. The development of an electrostatic precipitator for functional film formation is described.

Size-selected rare earth and palladium nanoparticles for hydrogen induced switching and sensing applications

This manuscript describes the effect of using nanoparticles of Pd and rare earth in switchable mirror devices. Overall improvements in the hydrogenation properties observed in Pr and Pd nanoparticle layers and size selected nanoparticles over the normally used thin films have been described.

Optical properties of Pr thin film and nanoparticle layers during hydrogen loading and deloading

Changes in the optical properties of Pd capped Pr thin film and nanoparticle layers prepared by vacuum evaporation and inert gas evaporation techniques, respectively, have been studied as a function of time during hydrogen loading and deloading. These samples were characterized by transmission electron microscopy, atomic force microscopy, x-ray diffraction, and spectrophotometery techniques. Absorption spectra of Pr thin film and nanoparticles samples in metal, and hydrogen loaded and deloaded states have been reported. It is observed that filling of octahedral sites in the dihydride phase results in changes in absorption coefficient values at 1.5–2.0eV and H content in the trihydride phase causes shift of the absorption edge. Enhanced surface area, loose topography, a larger number of interparticle boundaries due to small sizes, relatively loose adhesion to the substrate, and smaller structural changes in nanoparticle layers result in larger and faster changes in the optical properties during loading in ...