Manvendra Kumar

Growth mechanism and optical property of CdS nanoparticles synthesized using amino-acid histidine as chelating agent under sonochemical process

Using amino-acid histidine as chelating agent, CdS nanoparticles have been synthesized by sonochemical method. It is found that by varying the ultrasonic irradiation time, we can tune the band gap and particle size of CdS nanoparticles. The imidazole ring of histidine captures the Cd ions from the solution, and prevents the growth of the CdS nanoparticles. The deviation in the linear relation in between cube of radius of nanoparticles and ultrasonic irradiation time confirms the growth of CdS nanoparticles occur via two process; one is the diffusion process of the reactants as well as reaction at the surface of the crystallite. CdS nanoparticles synthesized using histidine as organic chelating agent have band edge emission at approximately 481 nm and have greater photoluminescence intensity with blue-shift to higher energy due to typical quantum confinement effect.

Size effect on electronic sputtering of LiF thin films

Electronic sputtering in polycrystalline LiF thin film by 120MeV Ag25+ is investigated. The sputter yields of Li and F for the different thicknesses (10–265nm) of films are measured with online elastic recoil detection analysis technique. A reduction in sputter yield, from ∼2.3×106 to 2.2×104 atoms/ion, is observed with increase in the film thickness. The trend in the experimental results can be explained in terms of size effect in thin film following inelastic thermal spike model. The confinement of energy in the film having smaller grains and lower thickness results in higher temperature causing higher sputtering yield.

Fractal and multifractal characteristics of swift heavy ion induced self-affine nanostructured BaF2 thin film surfaces.

Fractal and multifractal characteristics of self-affine surfaces of BaF2 thin films, deposited on crystalline Si ⟨1 1 1⟩ substrate at room temperature, were studied. Self-affine surfaces were prepared by irradiation of 120 MeV Ag(9+) ions which modified the surface morphology at nanometer scale. The surface morphology of virgin thin film and those irradiated with different ion fluences are characterized by atomic force microscopy technique. The surface roughness (interface width) shows monotonic decrease with ion fluences, while the other parameters, such as lateral correlation length, roughness exponent, and fractal dimension, did not show either monotonic decrease or increase in nature. The self-affine nature of the films is further confirmed by autocorrelation function. The power spectral density of thin films surfaces exhibits inverse power law variation with spatial frequency, suggesting the existence of fractal component in surface morphology. The multifractal detrended fluctuation analysis based on the partition function approach is also performed on virgin and irradiated thin films. It is found that the partition function exhibits the power law behavior with the segment size. Moreover, it is also seen that the scaling exponents vary nonlinearly with the moment, thereby exhibiting the multifractal nature.

Red luminescent manganese-doped zinc sulphide nanocrystals and their antibacterial study

Water soluble, uniform-sized ZnS:Mn2+ nanocrystals (NCs) have been prepared using a simple co-precipitation method with a methanol and water binary mixture as a reaction medium. The structure of the prepared ZnS:Mn2+ NCs is cubic with a mean size distribution of 3-5 nm. Photoluminescence (PL) studies showed emission at ∼612 nm, which is 22 nm red shifted as compared with the reported literature. This red shift could be attributed to the observed distortion in the imaged lattice plane. The capping effect of pepsin, citric acid and biotin on the optical properties of ZnS:Mn2+ NCs has been examined and the maximum enhancement in PL Intensity was found in the case of biotin. The synthesised ZnS:Mn2+ NCs were characterized by X-ray Diffraction (XRD), transmission electron microscopy (TEM), X-ray photoemission spectroscopy (XPS) for investigation of their structural properties. Because of the high PL intensity, biotin capped ZnS:Mn2+ NCs were further investigated for their anti-bacterial activity against gram negative and gram positive bacteria. These NCs show broad spectrum antibacterial activity against both types of bacteria having an MIC value of 100 ng ml-1 for B. subtilis.

Highly Stabilized Monodispersed Citric Acid Capped

Nanophosphors of ZnO:Cu2+ were synthesized by a chemical technique based on coprecipitation method. The synthesized nanophosphors were annealed at different temperatures (100-400°C) in steps of 100°C for 4 h. A reduction in photoluminescence intensity was observed with increase in the annealing temperature. Further, these nanophosphors were capped with citric acid, which results in enhancement in the luminescence intensity. These surface-modified ZnO nanoparticles were found to be remarkably stable. The reduction in luminescence with annealing temperature occurred due to removal of surface defects and intrinsic impurities, while the citric acid reduced the unsaturated bond density and passivated the surface, resulting in reduction in the number of surface trap sites for nonradiative recombination processes to occur, enhancing the luminescence intensity. Currently, LEDs giving UV emission have been combined with broadband visible green phosphors to make white-light LEDs. Thus, green luminescent ZnO:Cu2+ nanoparticles can be seen as necessary and critical constituent for white light generation from UV LEDs, underlying the findings and importance of current investigations. Besides this citric acid capped ZnO:Cu2+ nanophosphors can also be used in biological (drug delivery system, bioimaging, etc.) and biosensors.

\hbox{ZnO:Cu}^{2+}

Eu3+ doped yttrium aluminum garnet (YAG) nanoparticles were synthesized by sol-gel method. The samples were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy including vacuum ultraviolet (VUV) PL spectroscopy. XRD confirmed that each and every phases of YAG were present, indicating very good quality of sample. The crystallite size, estimated by XRD, increased from 10 to 30 nm with annealing temperatures and significant changes in morphology with annealing temperature was also found in TEM study. The particles were in spherical shape initially but agglomeration of particles started at higher temperatures resulting in hierarchical nanostructures having dimension more than 50 nm. The annealed YAG:Eu3+ hierarchical nanostructures showed strong red luminescence under VUV excitation, corresponding to D50→F72 transition. PL spectra also showed significant increase in luminescence intensity with the increase in annealing temperature. Time evo...

Nanoparticles: Synthesis and Characterization for Their Applications in White Light Generation From UV LEDs

Fractal characterization of surface morphology can be useful as a tool for tailoring the wetting properties of solid surfaces. In this work, rippled surfaces of Si (100) are grown using 200 keV Ar+ ion beam irradiation at different ion doses. Relationship between fractal and wetting properties of these surfaces are explored. The height-height correlation function extracted from atomic force microscopic images, demonstrates an increase in roughness exponent with an increase in ion doses. A steep variation in contact angle values is found for low fractal dimensions. Roughness exponent and fractal dimensions are found correlated with the static water contact angle measurement. It is observed that after a crossover of the roughness exponent, the surface morphology has a rippled structure. Larger values of interface width indicate the larger ripples on the surface. The contact angle of water drops on such surfaces is observed to be lowest. Autocorrelation function is used for the measurement of ripple wavelength.

Properties of sol-gel derived YAG:Eu3+ hierarchical nanostructures with their time evolution studies

Histidine functionalised CdS quantum dots (QDs) have been synthesised by sonochemical method. Transmission Electron Microscopy (TEM) observation shows that the histidine functionalised CdS QDs are well-defined, nearly spherical particles. The X-ray diffraction pattern indicates formation of cubic phase of CdS/histidine QDs. The absorption spectra confirm quantum confinement of histidine functionalised CdS QDs. The photoluminescence property of CdS/histidine QDs is found better than that of CdS QDs. Histidine functionalised CdS QDs, in which histidine acts as a biocompatibiliser, can find potential applications in the biological fields.

Fractal characterization and wettability of ion treated silicon surfaces

Swift heavy ions induced structural and magnetic modifications of Co/Ti multilayers have been studied with 120 MeV Ag9+ ions at different ion fluences. The decrease in 1st Bragg peak intensity of X-ray reflectivity spectra confirms an increase in Co-Ti mixing at the interfaces, whereas X-ray diffraction (XRD) measurements reveal amorphization of the crystalline Co layer. XRD also indicates a shift in peak position towards a lower angle, confirming the development of tensile stress upon irradiation whereas an increase in the peak width suggests the reduction in the grain size. Vibrating sample magnetometer measurements show a reduction in Mr/Ms due to Co-Ti interface mixing and formed bcc-Co3Ti metastable phase. The X-ray absorption fine structure (XAFS) technique has been utilized to obtain variation in Co-Co and Co-Ti bond distances as a function of ion fluences. Quantitative estimation of Co3Ti phase generated due to ion irradiation has also been obtained using Co K-edge XAFS fitting.

Histidine functionalised biocompatible CdS quantum dots synthesised by sonochemical method

The band alignment of Zn0.9Co0.1O/ZnO thin film heterostructure was investigated using photoelectron spectroscopy. The ZnO, Zn0.9Co0.1O and Zn0.9Co0.1O/ZnO thin film heterostructure has been prepared using RF ion beam sputtering, The band offset of prepared heterostructure were calculated form valance band maximum and core level peaks. The valance band and conduction band offset for Zn0.9Co0.1O/ZnO heterostructure thin film were found to be 0.36 eV and 0.51 eV, respectively, which indicates type-II band alignment in the Zn0.9Co0.1O/ZnO heterostructure.