Satyabrata Mohapatra

Au–ZnO: A tunable localized surface plasmonic nanocomposite

In this letter, we report the thermal processing controlled tunability of localized surface plasmon resonance (LSPR) of Au nanoparticles embedded in ZnO matrix. Au–ZnO nanocomposite films were prepared by atom beam cosputtering and were annealed from 200to600°C in Ar. A regular redshift ∼110nm (from 505to615nm) in LSPR peak with increase in annealing temperature up to 600°C is observed. Transmission electron microscopy results confirm the formation of Au nanoparticles supported by ZnO nanorods at annealing temperature of 600°C. The Au–ZnO nanocomposite exhibits significant enhancement in the Raman signal for C70 molecules.

Formation of Self-organized Silver Nanocup-Type Structures and Their Plasmonic Absorption

The present work reports on the formation of extremely low volume, silver nanocup-type structures on the surface by annealing of ultra-thin silver film on quartz in inert environment. Atomic force microscopy studies together with scanning electron microscopy confirmed the formation of Ag nanocup-type structures at the surface. A basic physical model for the formation of nanocups in terms of buckling and Oswald ripening due to surface-induced morphological instability and diffusional mass transport under thermal treatment is demonstrated. Surface plasmon resonance absorptions of nanocup structures are studied and preliminary experiment for observing the surface-enhanced Raman scattering of fullerene C70 molecules has been shown.

Gold-silica nanocomposites for the detection of human ovarian cancer cells : a preliminary study

We report the structural and optical properties of Au nanoparticles embedded in a silica matrix synthesized by atom beam co-sputtering. The presence of surface plasmon resonant absorption indicates the formation of Au nanoparticles. Transmission electron microscopy (TEM) studies show the presence of Au nanoparticles with an average size ranging from ~1.8 to 5.4 nm with narrow size distributions depending on the relative areas of Au and SiO2. We discuss the process of nucleation and growth of Au nanoparticles in the nanocomposite films formed by co-sputtering. The present method of nanoparticle synthesis is compared with other ion beam based techniques such as ion implantation and ion beam mixing. Preliminary experiments for the detection of human ovarian cancer cells using these Au nanoparticles are described.

Enhanced photocatalytic activity of Ag–ZnO hybrid plasmonic nanostructures prepared by a facile wet chemical method

Summary We report the synthesis of Ag–ZnO hybrid plasmonic nanostructures with enhanced photocatalytic activity by a facile wet-chemical method. The structural, optical, plasmonic and photocatalytic properties of the Ag–ZnO hybrid nanostructures were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), photoluminescence (PL) and UV–visible absorption spectroscopy. The effects of citrate concentration and Ag nanoparticle loading on the photocatalytic activity of Ag–ZnO hybrid nanostructures towards sun-light driven degradation of methylene blue (MB) have been investigated. Increase in citrate concentration has been found to result in the formation of nanodisk-like structures, due to citrate-assisted oriented attachment of ZnO nanoparticles. The decoration of ZnO nanostructures with Ag nanoparticles resulted in a significant enhancement of the photocatalytic degradation efficiency, which has been found to increase with the extent of Ag nanoparticle loading.

Structural, optical and photocatalytic properties of flower-like ZnO nanostructures prepared by a facile wet chemical method

Summary Flower-like ZnO nanostructures were synthesized by a facile wet chemical method. Structural, optical and photocatalytic properties of these nanostructures have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence (PL) and UV–vis absorption spectroscopy. SEM and TEM studies revealed flower-like structures consisting of nanosheets, formed due to oriented attachment of ZnO nanoparticles. Flower-like ZnO structures showed enhanced photocatalytic activity towards sun-light driven photodegradation of methylene blue dye (MB) as compared to ZnO nanoparticles. XRD, UV–vis absorption, PL, FTIR and TEM studies revealed the formation of Zn(OH)2 surface layer on ZnO nanostructures upon ageing. We demonstrate that the formation of a passivating Zn(OH)2 surface layer on the ZnO nanostructures upon ageing deteriorates their efficiency to photocatalytically degrade of MB.

Effects of swift heavy ion irradiation on structural, optical and photocatalytic properties of ZnO-CuO nanocomposites prepared by carbothermal evaporation method.

Summary ZnO–CuO nanocomposite thin films were prepared by carbothermal evaporation of ZnO and Cu, combined with annealing. The effects of 90 MeV Ni7+ ion irradiation on the structural and optical properties of ZnO–CuO nanocomposites were studied by using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), UV–visible absorption spectroscopy and Raman spectroscopy. XRD studies showed the presence of ZnO and CuO nanostructures in the nanocomposites. FESEM images revealed the presence of nanosheets and nanorods in the nanocomposites. The photocatalytic activity of ZnO–CuO nanocomposites was evaluated on the basis of degradation of methylene blue (MB) and methyl orange (MO) dyes under sun light irradiation and it was observed that swift heavy ion irradiation results in significant enhancement in the photocatalytic efficiency of ZnO–CuO nanocomposites towards degradation of MB and MO dyes. The possible mechanism for the enhanced photocatalytic activity of ZnO–CuO nanocomposites is proposed. We attribute the observed enhanced photocatalytic activity of ZnO–CuO nanocomposites to the combined effects of improved sun light utilization and suppression of the recombination of photogenerated charge carriers in ZnO–CuO nanocomposites.

A study on the formation of Ag nanoparticles on the surface and catcher by ion beam irradiation of Ag thin films

Irradiation of Ag thin films with 100 MeV Ag ions leads to the formation of Ag nanoparticles on the surface as well as on the catcher, due to electronic energy loss mediated sputtering of Ag. The experimentally determined sputter yield of Ag is found to be three orders of magnitude higher than the values expected for bulk Ag, which is explained on the basis of the inelastic thermal spike model. The confinement of energy in the nanoparticles having size smaller than the electron mean free path (λ) and higher surface coverage area results in a higher sputtering yield. Transmission electron microscopy was performed to study the size distribution of nanoparticles on the catcher. The variation of sputtered particle yield with the number of constituent atoms follows an inverse power law with the value of exponent (δ) ~ 0.33, at a fluence of 1 × 1013 ions cm−2. With increase in fluence up to 1 × 1014 ions cm−2, an additional value of exponent of δ ≈ 1 arises. The size of Ag nanoparticles is decreased with increased fluence due to ion-induced sputtering. The irradiated sample is found to have partially embedded nanoparticles showing localized surface plasmon resonance.

Smoothing, roughening and sputtering: the complex evolution of immiscible Fe/Bi bilayer system

In this work, swift heavy ion (SHI) induced surface smoothing, roughening and sputtering of thermally immiscible Fe/Bi bilayer system has been investigated. The pristine and irradiated samples were analysed by Rutherford backscattering spectrometry (RBS), grazing angle x-ray diffraction (XRD), atomic force microscopy and scanning electron microscopy including x-ray dispersive energy analyzer. RBS analysis revealed that steepness of the low energy edge of the Bi signal increases at a fluence of 3 ? 1013?ions?cm?2, beyond which the slope of the rear edge decreases. The increased steepness is due to smoothing induced at initial fluence; however, the decrease in the slope of rear edge beyond 3 ? 1013?ions?cm?2 fluence is a result of surface roughening. XRD reveals the increase in the crystalline nature of Bi after irradiation at 3 ? 1013?ions?cm?2. Irradiation at higher fluences from 6 ? 1013 to 1 ? 1014?ions?cm?2 leads to a decrease in the crystalline nature of Bi. Surface roughness of pristine and irradiated samples from AFM analysis revealed that initially roughness decreases with a fluence of 3 ? 1013?ions?cm?2. However, at higher fluences, beyond 3 ? 1013?ions?cm?2, the agglomeration of smaller grains has been observed due to the shear flow mechanism, which results in surface roughening. The observed behaviour of surface smoothing and roughening under SHI irradiation may be explained on the basis of the thermal spike model.

Crater formation in gold nanoislands due to MeV self-ion irradiation

The modification of gold nanoislands, grown on silicon substrates under high-vacuum conditions, by MeV self-ion irradiation has been studied by using scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and x-ray reflectivity. Upon irradiation with 1.5 MeV Au2+, two types of craters are observed on the Au islands: Empty craters and craters with a central hillock. The contribution of plastic flow, pressure spike, and sputtering to the crater formation during the ion impacts on the gold islands is analyzed. Thermal spike confinement within the gold islands is also proposed to be one of the possible reasons for crater formation in nanoislands.

Synthesis of Au nanoparticles in partially oxidized Si matrix by atom beam sputtering

Nanocomposite thin films containing Au nanoparticles embedded in a partially oxidized Si matrix were synthesized by the atom beam co-sputtering technique. Transmission electron microscopy studies revealed formation of Au nanoparticles in as-deposited films. The size distribution of Au nanoparticles was tailored by varying the metal fraction in the nanocomposite films. Increasing the metal fraction has been found to result in the formation of Au nanoparticles with a relatively narrower size distribution. The processes involving irradiation with energetic sputtered atoms arriving at the substrate are considered in nucleation and growth of Au nanoparticles at room temperature. The advantages of atom beam sputtering over ion implantation and ion beam mixing are also discussed.