Physical and optical properties of HfO2 NPs – Synthesis and characterization in finding its feasibility in opto-electronic devices

HfO₂ nanoparticles (HfO₂ NPs) with different precursors (NaOH, H₂O, ethanol) were synthesized by a simple co-precipitation method. FTIR and EDX spectroscopy analysis shows the Stoichiometries composition of HfO₂ NPs. X-ray diffraction pattern analysis revealed that the as prepared and calcined HfO₂ NPs are respectively amorphous and polycrystalline nature. TEM analysis confirms that the morphology of the calcined HfO₂ NPs is spherical in shape with less agglomeration. The crystallite size was evaluated to be 51 nm, 37 nm and 30 nm respectively, for the precursors NaOH, H₂O and ethanol used for HfO₂ NPs. SEM analysis shows spherical, rock and sponge like surface morphology respectively, for the precursors NaOH, H₂O and ethanol used for HfO₂ NPs. UV–visible spectroscopy analysis revealed that the optical band gap energy of NaOH, H₂O and ethanol precursors used HfO₂ NPs were respectively 5.50 eV, 5.52 eV and 5.50 eV. The observed optical properties indicated the feasibility of utilizing these NPs as anti reflection layers in solar cells and for the construction of poultry farms to save energy. The estimated dielectric constant value indicated that these NPs could be used to prepare dielectric layers in thin film transistor.     

Novel synthesis of hafnium oxide nanoparticles by precipitation method and its characterization

Hafnium oxide nanoparticles (HfO₂ NPs) have been successfully synthesized by means of a novel precipitation method and were characterized by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Field emission scanning electron microscopy (FESEM), UV–visible, Fourier transform infrared (FTIR) and laser Raman spectroscopy. The XRD and Raman analysis revealed the presence of pure monoclinic HfO₂ NPs. FESEM image showed that the HfO₂ NPs were of spherical shape with an average particle size of about 20 nm. The optical band gap of the HfO₂ NPs was found to be 6.12 eV. Advantages of this method were simple and low cost of synthesis of HfO₂ NPs includes the small and narrow particle size distribution.     

Solution-deposited GdCeOx thin films: Microstructure,band structure,and dielectric property

The microstructural and electrical properties of solution-deposited GdCeO_x dielectric thin films with different mixing ratios were studied. The Ce incorporation enhanced the degree of crystallization and the refractive index of the Gd₂O₃ film, reduced the hysteresis and increased the dielectric constant. According to reflective electron energy loss spectroscopy and X-ray photoelectron spectroscopy analyses, the bandgap of the GdCeO_x film gradually decreased with increasing Ce/(Gd + Ce) atomic ratio, which was primarily affected by the reduction of the valence band offset.     

Effect of reduced graphene oxide (rGO) on structural,optical, and dielectric properties of Mg(OH)2/rGO nanocomposites

In this paper, we report the synthesis of Mg(OH)₂ NPs and Mg(OH)₂–rGO nanocomposites (NCs) by microwave assisted co-precipitation method. The crystal phase, structural morphology and functional groups of the as-synthesized samples were analyzed by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR). Raman spectroscopy was used to study the defects in the samples. Raman spectroscopy and the SEM results validate the growth of Mg(OH)₂ NPs on the rGO nanosheets. The chemical composition of the prepared samples was analyzed by EDAX. Optical properties of the as-synthesized samples were studied by UV–visible spectroscopy and the energy band gap was calculated by Tauc relation which shows a decrease in band gap with an increase in the amount of Graphene Oxide (GO) in the NCs. The dielectric properties were studied as a function of frequency over a range of 50 Hz to 5 MHz at room temperature. The value of dielectric constant decreases with an increase in frequency, this could be due to the existence of a polarization process at the border of the rGO sheets and Mg(OH)₂ NPs. The value of dielectric loss shows a decreasing trend with an increase in frequency whereas the larger value of AC conductivity in Mg(OH)₂–rGO NCs as compared to Mg(OH)₂ NPs approves the restoration of sp² network in the graphene sheets.     

The effect of molybdenum on optical properties of ZnO nanoparticles in Ultraviolet–Visible region

Zn_1?xMo_xO (x = 0.0, 0.01, 0.03, and 0.05) nanoparticles (NPs) are synthesized by using gelatin, via the sol-gel method. A calcination temperature of 600 °C is maintained for 2 h. The influence of molybdenum concentration on the structural and optical properties of these NPs is demonstrated. Synthesized NPs are characterized using X-ray diffraction (XRD), UV–vis spectroscopy, and transmission electron microscopy (TEM). XRD patterns reveal the crystallite nature of samples that exist in the hexagonal wurtzite phase. TEM images manifest the existence of nearly spherically-shaped NPs. The UV–vis spectroscopy results showed that the absorption edge of ZnO nanoparticles is red-shifted by adding molybdenum. Finally, the optical parameters of the refractive index and permittivity of the synthesized samples were calculated using Kramers-Kronig relations using the UV–vis spectra.     

Structural,electrical, and rheological properties of palladium/silver bimetallic nanoparticles prepared by conventional and ultrasonic-assisted reduction methods

Polyvinylpyrrolidone stabilized Pd/Ag bimetallic nanoparticles (NPs) with average particle sizes of 9 and 6 nm were synthesized by simultaneous reduction in the presence and absence of ultrasound waves, respectively. The prepared NPs were characterized by six methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution-TEM (HRTEM), UV–vis spectroscopy, scanning tunneling microscopy (STM), and energy dispersive X-ray (EDX) analysis. The rheological properties of Pd/Ag NPs in ethylene glycol as a base fluid with various mass fractions of NPs from 2% to 5% at different temperatures were studied experimentally and theoretically. The experimental results showed that viscosity of Pd/Ag NPs in ethylene glycol increases with increasing particle mass fraction and decreases with increasing temperature. A maximum of 31.58% increase in viscosity of ethylene glycol at 20 °C was observed when 5% Pd/Ag NPs was added. Measurement of the electrical conductivity of nanofluids of Pd/Ag bimetallic NPs in distilled water at different mass fractions and temperatures was performed. A 3841% increase in electrical conductivity of distilled water at 25 °C was observed when 1% Pd/Ag NPs was added. Both the rheological and electrical properties of Pd/Ag bimetallic NPs were measured in ethylene glycol and distilled water, respectively for the first time.     

Structural phase analysis,band gap tuning and fluorescence properties of Co doped TiO2 nanoparticles

This paper reports on structural and optical properties of Co (0, 3, 5 & 7 mol%) doped TiO₂ (titania) nanoparticles (NPs) synthesized by employing acid modified sol–gel method. The crystalline phase of the pure and doped NPs was observed with X-ray diffraction (XRD) followed by Raman scattering technique. Field emission scanning electron microscope and transmission electron microscopy give the morphological details. Fourier transform infrared spectra indicate the bonding interactions of Co ions with the titania lattice framework. Optical studies were attained with UV–visible absorption and fluorescence emission spectroscopy. XRD analysis reveals that all prepared samples have pure anatase phase with tetragonal symmetry devoid of any other secondary phase. The average crystallite size of all samples was calculated using Scherrer’s formula and was found to vary from 8 to 10 nm with doping concentration of Co. The Raman spectroscopy further confirmed the formation of TiO₂ in anatase structure in both pure and Co doped TiO₂ NPs. The most intense Raman active E_g peak of TiO₂ NPs shifted to higher energy on doping. Both UV–visible and fluorescence spectra show a blue shift in their absorption and band edge emission subsequently on increasing with Co percentage in titania host matrix, wherever there is an indication of quantum confinement effect with widening of band gap on decreasing in NPs size. There is also a possibility of strong Coulomb interaction effect on the optical processes involving the Co ions. However, the intensities of different emission spectra are not the same but decrease profoundly for doping samples due to concentration quenching effect.     

Extending LaMer's mechanism using open system for increasing forced and controlled growth of Au nano particles: Desired decreasing Fe3O4 nano particles size during simultaneous synthesis in optimized conditions

The most effective parameters were found to obtain Au/Fe₃O₄ nano particles (NPs)-oleylamine composite. Having Au NPs with the controlled maximum mean size under the forced conditions was the main aim of this study. We used the continuous flow rates of oleylamine 75% to produce Au NPs under an open system by extended LaMer mechanisms. This process decreased the mean size of Fe₃O₄ NPs synthesized simultaneously, by classic LaMer mechanism. The Fe₃O₄ NPs production was carried out without continuous adding of any iron reactant, viz. as a closed system. In the absence of gold ions, the mean size of the synthesized Fe₃O₄ NPs using 2.5 ml/min oleylamine was about 35.0 nm at 2.0 ± 0.5 °C after 120 min. This mean size was decreased to 27.2, 21.4, 16.8 and 8.7 nm, when Au NPs were simultaneous prepared using 0.5, 0.75, 1.5 and 2.5 ml/min of oleylamine, respectively, at the same conditions. Surface Plasmon Resonance (SPR) adsorption was used to evaluate Au NPs production at first 30 min, while Small Angle X-ray Scattering (SAXS) method was used to monitor the reaction progression for near-real time analysis of increasing the growth of Au NPs up to 280 min, at the optimum conditions. Changing the properties of Fe₃O₄ NPs during processes was determined by studying Magnetization, Potentiometric titration, Inductive heating and Zeta potential.     

New strategy to prepare platinum salts by electrochemical methods and subsequent synthesis of platinum nanoparticles

As shown in the literature, most of Pt nanoparticles (NPs) were synthesized from precursors of commercial Pt salts. However, the impurity of the commercial Pt salts is a concerned issue. In this work, we report a new pathway based on electrochemical methods to prepare Pt-containing complexes with high purity in aqueous solutions from bulk Pt substrates. Experimental results indicate that Pt complexes with higher concentration can be obtained in 0.1 N HCl by using square-wave oxidation–reduction cycles (ORCs) under a frequency of 8 Hz with a step potential of 6.3 mV. Moreover, concentrations of other heavy metals of Hg and Cr in 65 ppm Pt complexes-containing solution are just 0.65 and 0.78 ppb, respectively. These Pt complexes were further reduced to Pt NPs by using NaBH₄ and poly(vinylpyrrolidone) (PVP) as reducing agent and stabilizer, respectively. The concentration and the particle size of synthesized Pt (1 1 1) NPs are ca. 60 ppm and smaller than 5 nm, respectively.     

A facile method to prepare size-tunable silver nanoparticles and its antibacterial mechanism

The antibacterial effect of silver nanoparticles (denoted as Ag NPs) is closely related to size. This could partly explain why size controllable synthesis of Ag NPs for bactericidal application is drawing much attention. Thus, we establish a facile and mild route to prepare size-tunable Ag NPs with highly uniform morphologies and narrow size distributions. The as-prepared Ag NPs with averaged sizes of 2, 12 and 32?nm were characterized by transmission electron microscopy (TEM), ultraviolet–visible absorption spectroscopy (UV–vis), X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The antimicrobial effect of the as-prepared Ag NPs with different particles size was assessed by broth dilution and disk diffusion as well as measurement of optical density (OD₆₀₀). Moreover, their antibacterial mechanism was discussed in relation to morphology observation of microorganism by scanning electron microscopy (SEM) and to concentration detection of Ag⁺ by stripping voltammetry. It was found that the parameters such as reactant molar ratio, reaction time, dropping speed, and most of all, pH of the reactant solutions, have significant influences on size-regulation of Ag NPs. The as-prepared Ag NPs exhibit excellent antibacterial properties, and their antimicrobial activities increase with decreasing particles size. Besides, two kinds of mechanisms, i.e., contact action and release of Ag⁺, are responsible for the antimicrobial effect of Ag NPs.     

LaBr3:Ce crystal: The latest advance for scintillation cameras

Recent availability of LaBr₃:Ce crystal is attracting researchers for the development of new advanced SPECT e PET systems. The crystal shows excellent energy resolution values good radiation absorption properties and speed. At present, LaBr₃:Ce crystal is available with continuous shape covering 5×5 cm² area with a thickness up to 1 in. With the aim of analysing the imaging performances of LaBr₃:Ce for Single Photon Emission Tomography (SPET), we tested three continuous crystals with the same detection area of 5×5 cm² and various thicknesses ranging between 4 and 10 mm. Three small scintillation cameras were assembled by coupling LaBr3:Ce crystal to Hamamatsu H8500 Flat panel PMT. The results show very good imaging performances for single photon emission application with superior energy and spatial resolution up 7.5% and 0.9 mm, respectively, and a detection efficiency up to 95% at 140 keV photon energy.     

Bio-directed synthesis of gold nanoparticles using Ananas comosus aqueous leaf extract and their photocatalytic activity for LDPE degradation

A bio-directed synthesis of gold nanoparticles (Au NPs) was developed via the reduction of hydrogen tetrachloroaurate (III) (HAuCl₄·3H₂O) solution by the aqueous leaf extract of Ananas comosus. The polyphenol stabilized Au NPs were characterized by UV–visible, Fourier transform infrared (FTIR), powder X-ray diffraction (PXRD)/selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM) and energy-dispersive X-ray spectroscopy (EDX) analyses. The HRTEM images revealed that Au NPs were well dispersed with spherical structures. The size ranges from 7.39 to 32.09 nm with average particle size of 18.85 ± 6.74 nm. The peaks of XRD analysis at (2θ) 37.96°, 44.06°, 64.54°, 77.50° and 81.73° were respectively assigned to (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) planes of the face-centered cubic (fcc) lattice of gold. The photocatalytic potential of Au NPs was studied through the solid-phase degradation of low-density polyethylene (LDPE) film. The photoinduced degradation of LDPE@Au nanocomposite film was higher than that of the pure LDPE film. The weight loss of LDPE@Au (1.0 wt%) nanocomposite film steadily increased and reached 51.4 ± 4.8% in 240 h under solar light irradiation, compared to the photo-induced LDPE with only 8.6 ± 0.7%. However, LDPE film with 1.0% Au NPs gave a weight loss value of 4.72 ± 0.71 under the dark condition at the end of 240 h. Thus, LDPE film with 1.0% Au NPs showed a degradation efficiency of 90.8% under solar irradiation after 240 h. The sustainability of the nanoparticles was confirmed through reusability in the photocatalytic degradation reaction up to five consecutive cycles without substantial loss in its catalytic performance.     

Synthesis and photoluminescence of Ca1-xTiO3:xEu3+ nanoparticles

Ca_1-xTiO₃:xEu³⁺ nanoparticles (NPs) with the size ranging from 27 nm to 135 nm were prepared by means of a chemical co-precipitation method. The structural and optical properties of the NPs were investigated, and the influence of Eu doping content and sintering temperature on the photoluminescence of the Ca_1-xTiO₃:xEu³⁺ NPs were examined. An obvious red emission band centered at 615 nm were observed under the excitation with 395 nm for the Ca_1-xTiO₃:xEu³⁺ NPs. X-ray photoelectron spectroscopy analyses suggest that Eu³⁺ is incorporated into not only the Ca-site, but also Ti-site of CaTiO₃ crystal lattice. Our study shows the promise of the Ca_1-xTiO₃:xEu³⁺ NPs as a red nanophosphor.     

Size effect of Au seeds on structure of Au–Pt bimetallic nanoparticles

Au–Pt bimetallic nanoparticles (NPs) were synthesized by a seeded growth method. Au NPs with different sizes were obtained by reducing HAuCl₄ with butyllithium, and AuPt bimetallic NPs were synthesized by reducing H₂PtCl₆ with oleylamine using the pre-synthesized Au NPs as seeds. The size of Au seeds was found to be a key factor on the structure of Au–Pt bimetallic NPs. Using big Au NP seeds (8 nm or 12 nm) resulted in the formation of Au–Pt dendritic structures. While relatively small Au NPs (3 nm) were used as seeds, the fast atomic diffusion inside relatively small bimetallic NPs will result in an Au–Pt alloy formation.     

Na0.5Li0.5CoO2 nanopowders: Facile synthesis,characterization and their application for the removal of methylene blue dye from aqueous solution

In this paper, delafossite-type Na_0.5Li_0.5CoO₂ nanoparticles (NPs) with an average particle size of 50 nm were successfully synthesized by sol–gel method. Prepared NPs were characterized by differential thermal analysis, powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and scanning tunneling microscopy. The nanoparticles showed the excellent adsorption properties towards methylene blue dye (MBD) as a reactive dye. The kinetics of removal of MBD in aqueous solutions was studied in a series of experiments which were varied in the amount of NPs, contact time, pH, and temperature. The experimental data were fitted very well in the pseudo-second order kinetic model and the Freundlich adsorption isotherm model. 92% of dye was successfully removed in 10 min using 0.02 g Na_0.5Li_0.5CoO₂ NPs in a pH = 11. Thermodynamic study indicates that the adsorption of MBD is feasible, and spontaneous in nature.     

Hydrothermal synthesis and indication of room temperature ferromagnetism in CeO2 nanowires

Bundle of CeO₂ nanowires have been successfully synthesized by a simple hydrothermal process using Ce(NO₃)₃·6H₂O as cerium source and NaH₂PO₄·2H₂O as mineralizer, into which no surfactant or template was introduced. The synthesized nanowires were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy and magnetization measurements. The XRD results indicated that CeO₂ nanowires have fluorite structure. Magnetization measurements indicate that CeO₂ nanowires exhibit room temperature ferromagnetism with remanent magnetization (M_r) and coercivity (H_C) of about 7.44 × 10^? 4 (emu/g) and 27.19 Oe, respectively, which may results due to the presence of defects in the CeO₂ nanowires.     

Toward uniform ZnO nanoparticles embedded in SiO2 by post Xe irradiation

Uniform ZnO nanoparticles (NPs) have been created by Zn ion implantation and post Xe ion irradiation. Irregularly shaped ZnO NPs with a broad size distribution of 5–30 nm have been tailored to spherical shape with a narrow size distribution of 3–5 nm. The optical properties of the ZnO NPs have been modified clearly after Xe ion irradiation. Furthermore, Rutherford back-scattering spectrometry results give the evidence that Xe irradiation can cause the diffusion and reprecipitation of the Zn NPs. The present study shows the interest of using heavy ion irradiation to tailor size and shape distribution of the embedded NPs in SiO₂.     

Starch-stabilized synthesis of ZnO nanopowders at low temperature and optical properties study

Zinc oxide nanoparticles (ZnO–NPs) were synthesized via the sol–gel method in starch media. Starch was used as a stabilizer to control of the mobility of zinc cations and then control growth of the ZnO–NPs. Because of the special structure of the starch, it permits termination of the particle growth. Thermogravimetry analysis (TGA) was applied on dried gel to obtain the certain calcination temperature(s) of the ZnO–NPs. The dried gel was calcined at different temperatures of 400, 500, and 600 °C. Several techniques such as X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and high-magnification transmission electron microscopy (TEM) were used to characterize the ZnO–NPs. The ZnO–NPs calcined at different temperatures exhibited a hexagonal (wurtzite) structure with sizes from 30 to 50 nm. The optical properties of the prepared samples were investigated using UV–vis spectroscopy. The results showed that starch is a suitable stabilizer in the sol–gel technique, and this method is a reasonable and facile method to prepare ZnO–NPs for large-scale production.     

Synthesis and luminescence properties of YAG:Ce nanopowder prepared by the Pechini method

Cerium-doped yttrium aluminum garnet (YAG:Ce) powder was synthesized by the Pechini method with aluminum nitride, yttrium nitride, citric acid and ethylene glycol as the starting materials. Structure, morphology and luminescence spectra were investigated by using X-ray diffraction, thermogravimetric and differential thermal analysis, scanning electron microscopy, Fourier transform infrared spectroscopy and photoluminescence spectroscopy measurements. The pure YAG phase was formed after heat treatment at 800 °C for 3 h and no intermediate phase was observed. The average size of the particles was about 70 nm. The photoluminescence spectrum of the crystalline YAG:Ce phosphors showed the green-yellow emission with 5d → 4f transition as the most prominent group.The increase of the ethylene glycol:citric acid molar ratio, resulted in a powder with smaller particle size and better luminescence properties.     

Green and eco-friendly synthesis of cobalt-oxide nanoparticle: Characterization and photo-catalytic activity

Cobalt-oxide nanoparticles (NPs) were fabricated using Punica granatum peel extract from cobalt nitrate hexahydrate at low temperature. The synthesized cobalt-oxide NPs were characterized using X-ray powder diffraction, scanning electron microscopy, energy-dispersive X-ray, atomic force microscopy, fourier transform infrared spectroscopy and UV-visible techniques. The cobalt-oxide NPs were in highly uniform shape and size was in the size of 40–80 nm. Photo-catalytic activity (PCA) of the synthesized NPs was evaluated by degrading Remazol Brilliant Orange 3R (RBO 3R) dye and a degradation of 78.45% was achieved (dye conc. 150 mg/L) using 0.5 g cobalt-oxide NPs for 50 min irradiation time. In view of eco-benign and cost-effective nature, the present investigation revealed that P. granatum could be used for the synthesis of cobalt-oxide NPs for photo-catalytic applications.