International Journal of Nanoscience

In this work, we report the influence of silver nanoparticles of different size on the optical behavior of the europium-doped hydroxyapatite nanorods. The presence of ionic, plasmonically visible and silent (ultra-small) silver nanoparticles on the surface of europium-doped apatite and its influence on its luminescent behavior were discussed. It was found that ionic silver exhibited a concentration-dependent enhancement in emission at the excitation of europium. For plasmonically visible and silent silver nanoparticles, the emission observed was due to the contribution of the ligand passivating the europium-doped hydroxyapatite nanoparticle surface. These nanoparticles due to its luminescent and biocompatible nature can be used for bioimaging applications.

Thin film memristor behavior depends on the choice of top and bottom electrode material and metal oxide layer. In the present work, the influence of the top and bottom electrode layers on the electric field-induced resistance switching phenomena of TiO₂-based MIM was studied. Au/TiO₂/NiCr and NiCr/TiO₂/Au structures were fabricated by depositing TiO₂ active layer by reactive dc magnetron sputtering technique between thermally evaporated NiCr and Au electrodes. TiO₂ layer was sputtered with a cathode power of 150W keeping the other deposition parameters constant. TiO₂ films were analyzed by X-ray diffractometer, field emission scanning electron microscopy and UV–Visible spectrophotometer to investigate their structural, morphological and optical behavior. Structural studies of the films reveal that the samples were amorphous. And the $I$–$V$ analysis for the fabricated MIM structure was analyzed.

Optical nonlinearity of 4-dimethyl aminopyridinium dihydrogen phosphate (DMAPDP) was studied using continuous wave of diode pumped Nd:YAG laser (532nm, 50mW). The nonlinear refractive index, nonlinear absorption coefficient and nonlinear optical (NLO) susceptibility of the sample were found to be in the order of 10${}^{-8}$cm²/W, 10${}^{-3}$cm/W and 10${}^{-6}$ esu respectively. The observed self defocusing effect was used to demonstrate the optical limiting action at 532nm. Initially, XRD analysis showed that DMAPDP crystallizes in triclinic crystal system with centrosymmetric space group $P\overline{1}$. Thermal studies explored that the material undergoes an irreversible endothermic transition at 192${}^{\circ }$C which correspond to the decomposition of material. SEM image portrays the formation of nanoparticles with grain size in the range of 45–170nm. Hence 4-dimethyl aminopyridinium dihydrogen phosphate nanoparticles can be used as potential candidate for optical limiting applications.

The spray pyrolysis technique was employed to deposit V₂O₅ thin films on a glass substrate. By varying the precursor solution volume from 10mL to 50mL in steps of 10mL, films of various thicknesses were prepared. Orthorhombic polycrystalline V₂O₅ films were inferred from the XRD pattern irrespective of precursor solution volume. The micro-Raman studies suggested that annealed V₂O₅ thin film has good crystallinity. The effect of precursor solution volume on morphological and optical properties were analysed and reported.

2-Amino-5-nitropyridinium halides (2A5NPBr)/(2A5NPCl) were synthesized by dissolving 2-amino-5-nitropyridine in hydrobromic/hydrochloric acid. Nanoparticles of 2A5NPBr and 2A5NPCl were attained by hydrothermal method. For comparison and estimation of mechanical properties, single crystals of the samples were grown by slow evaporation process. SEM analysis shows the formation of nanoparticles of 2A5NPBr and 2A5NPCl with average grain size of 50 and 100nm, respectively. UV-Vis analysis reveals that the materials possess low cut-off wavelength and a wide optical transmission window. By Vickers test, the Meyer index (n) was estimated to be 1.33 for 2A5NPBr and 2.49 for 2A5NPCl crystals. The SHG efficiency of 2A5NPBr and 2A5NPCl nanoparticles was calculated to be 1.5 and 4.3 times that of well known NLO material KDP. The role of cations in demonstrating the desired NLO properties were discussed in detail.

The present work deals with NiO/Si₃N₄ layers formed by depositing nickel oxide (NiO) thin films over silicon nitrate (Si₃N${}_4)$ thin films. NiO films were coated on Si₃N₄-coated Si substrate using magnetron sputtering method by changing duration of coating time and were analyzed using X-ray diffractometer, field emission-scanning electron microscopy, UV–Vis spectrophotometer and four-point probe method to study the influence of thickness on physical properties. Crystallinity of the deposited films increases with increase in thickness. All films exhibited spherical-like structure, and with increase in deposition time, grains are coalesced to form smooth surface morphology. The optical bandgap of NiO films was found to decrease from 3.31eV to 3.22eV with upsurge in the thickness. The film deposited for 30min exhibits temperature coefficient resistance of $-$1.77%/${}^{\circ }$C as measured at 80${}^{\circ }$C.

Bismuth oxide was prepared using hydrothermal route and the effect of pH on the phase of Bi₂O₃ reported. Phase pure $\alpha$-Bi₂O₃ was prepared at the pH of 13 and its phase purity was confirmed from the X-ray diffraction pattern. At the pH of 10, 11 and 12 the hydrothermal synthesis yields Bi(OH)₃, ($\alpha$, $\gamma$-Bi₂O₃) & Bi₂O₄ and mixture of $\alpha$-Bi₂O₃ & Bi₂O₄, respectively. The optical band gaps were calculated from reflectance spectra using the Kubelka–Munk relation and the values decrease from 3.050(3) to 2.686(3) eV with the increase in pH value. Photoluminescence intensity decrease with the increase of pH value indicated the increase in the charge separation efficiency. In the application point of view, the photocatalytic activity of the samples was evaluated for methyl orange and among the four samples, $\alpha$-Bi₂O₃ degraded 67% within 4h. The degradation of dye was analyzed using pseudo first-order kinetics and the rate constant value was 0.0045(3) min${}^{-1}$ with the correlation coefficient of 0.983.

A computational study on adsorption and dissociation mechanisms of H₂ molecule on ZnO cluster was analysed using Density Functional Theory (DFT) approach in Gaussian 09 software. The stable sites for hydrogen adsorption were inferred from the adsorption energy and bond length. Further investigations such as Mulliken charge, HOMO–LUMO energy gap and intrinsic reaction coordinate (IRC) were performed for the stable adsorption sites. It infers that the (ZnO)₆ cluster has the highest binding energy of 1.851eV (O-site) and the least binding energy of $-$3.865eV (O-site), showing most favorable size for both adsorption and dissociation of H₂ molecule. The IRC plot clearly shows the dissociation mechanism of hydrogen on the ZnO cluster.

This research work describes the fabrication of polymer blend nanocomposite membranes using the solution casting method. These membranes were fabricated with Poly (Vinylidene Fluoride) (PVdF) as host, Poly (Ethylene Glycol) (PEG) in steps of 2wt.% as blending polymer and Montmorillonite (MMT) nanoclay particles in steps of 3wt.% which were used as received. The protonated MMT was synthesized through an ion exchange process with column chromatographic technique. The prepared membrane’s performance was investigated using different characterization techniques of Thermo Gravimetric Analysis (TGA), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), water uptake, IEC and electrochemical impedance spectroscopy. Thermal stability was decreased while adding PEG into PVDF but it is controlled with the addition of MMT on PVDF/PEG blend matrix. Moreover, It is noticed that, the increase of water uptake, IEC by the increasing additive concentration of PEG and MMT. XRD studies reveal the increased amorphous phase with uniform exfoliation of nanoclay particles. The highest proton conductivity value of 0.127S cm${}^{-1}$ is obtained with 9wt.% of MMT in the PVdF/PEG/MMT composite membranes at room temperature with 100% Relative Humid (RH) condition and 10 V.% of sulfonation. The blended nanocomposite membranes fulfill the requirements of proton exchange membrane for fuel cell application.

In this computational study, the interaction between a single layer graphene sheet and a gold nanoparticle is investigated employing molecular dynamics (MD) simulation at room temperature. The interactions between the graphene and gold nanoparticle were explored for three different types of gold nanoparticle, namely, bare gold nanoparticle, methyl terminated alkane thiol-coated gold nanoparticle and hydroxy terminated alkane thiol-coated gold nanoparticle. The interactions between the graphene and gold nanoparticle have resulted in the adsorption of gold nanoparticle on the surface of graphene. The structural properties of the graphene–gold hybrid nanostructures were found to be influenced by the capping layer of the gold nanoparticle.

Zinc oxide (ZnO) thin films have been synthesized by thermally oxidizing the direct current magnetron sputtered zinc (Zn) films at 500${}^{\circ }$C for different annealing time periods (3–5h) in ambient air. Influence of annealing time on the structural, morphological, optical and electrical properties of ZnO films was studied using X-ray diffractometer, field emission-scanning electron microscopy (FE-SEM), UV–Vis spectrophotometer and two-probe method, respectively. ZnO films exhibited hexagonal crystal structure with (1 0 1) as preferential orientation plane, and the crystallite size of the films increased from 30nm to 83nm on increasing the annealing time. Pebble-like surface morphology was observed from the FE-SEM micrographs. Optical band gap of the films varied between 3eV and 3.5eV for different annealing times. Electrical resistance of the ZnO films was decreased with increase in the annealing time, which is due to the improvement in the crystallinity.

Biotemplate-based zinc oxide nanocomposite was effectively prepared via simple chemical precipitation route. The functional groups of amino (–NH₂), hydroxyl (–OH) and O–Zn–O were confirmed and characterized by FTIR spectroscopy. The structural and morphological properties were confirmed by XRD, UV–Vis DRS, HR-SEM and TEM analyses. The elemental composition of carbon, nitrogen, zinc and oxygen was confirmed by energy-dispersive X-ray analysis (EDAX) and Brunauer–Emmett–Teller high surface area of materials was estimated to be 52.49m²/g, respectively. Thermogravimetric analysis (TGA) shows that biotemplate on zinc oxide nanocomposite has higher thermal stability than chitosan matrix. The results demonstrate that biotemplate on zinc oxide matrix causes immobilization effect among the two components. Therefore, chitosan–ZnO nanocomposite has a microcrystalline morphological structure and also good thermal stability, so it can be a promising material for sensors, medical, tissue engineering and wastewater treatment applications.

The copper telluride (Cu₂Te) thin film of thickness 240nm was coated on a microscopic glass substrate by thermal evaporation technique. The prepared films were annealed at 150${}^{\circ }$C and 250${}^{\circ }$C for 1h. The annealing effect on Cu₂Te thin films was examined with different characterization methods like X-ray Diffraction Spectroscopy (XRD), Scanning Electron Microscopy (SEM), Ultra Violet–Visible Spectroscopy (UV–VIS) and Photoluminescence (PL) Spectroscopy. The peak intensities of XRD spectra were increased while increasing annealing temperature from 150${}^{\circ }$C to 250${}^{\circ }$C. The improved crystallinity of the thin films was revealed. However, the prepared films are exposed complex structure with better compatibility. Moreover, the shift in band gap energy towards higher energies (blue shift) with increasing annealing temperature is observed from the optical studies.

Zinc oxide (ZnO) films have been sputter coated over glass substrates at different cathode powers. Influence of cathode power on physical characteristics of ZnO samples was analyzed using X-ray diffractometer (XRD), field emission-scanning electron microscopy (FE-SEM), UV-Visible spectrophotometer and four-point probe (FPP) method. XRD patterns exhibited $c$-axis-oriented ZnO and enhanced crystallinity with increase in cathode power due to the increase in adatom mobility. Uniformly arranged spherical grains were observed from FE-SEM images. The grain size increased from 25 to 40nm with increase in power. All samples exhibited high electrical resistance (G$\mathrm{\Omega }$) which is compatible for piezoelectric application.