SAED Images Research Articles

Phase transformation of ZrO2:Tb3+ nanophosphor: Color tunable photoluminescence and photocatalytic activities

The current study involves synthesis of a series of Tb3+ doped ZrO2 nanophosphors by solution combustion method using oxalyl dihydrazide as fuel. The as-formed ZrO2:Tb3+ nanophosphors having different concentrations of Tb3+ (1–11mol%) were characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–Visible spectroscopic techniques and the materials were subjected to photoluminescence and photocatalytic dye decolorization studies. The PXRD analysis indicates the formation of tetragonal symmetry up to 5mol% concentration of Tb3+. Further increase in Tb3+ concentration has lead to cubic phase formation and the same was confirmed by Rietveld refinement analysis. SEM images revealed that material was highly porous in nature comprising of large voids and cracks with irregular morphology. TEM and SAED images clearly confirm the formation of high quality tetragonal nanocrystals. The emissive properties of nanophosphors were found to be dependent on Tb3+ dopant concentration. The green emission of the material was turned to white emission with the increase of Tb3+ ion concentration. The photocatalytic activities of these nanophosphors were probed for the decolorization of Congo red under UV and Sunlight irradiation. All the photocatalysts showed enhanced activity under UV light compared to Sunlight. The photocatalyst with 7mol% Tb3+ showed enhanced activity attributed to effective separation of charge carriers due to phase transformation from tetragonal to cubic. The influence of crystallite size and PL on charge carrier trapping–recombination dynamics was investigated. The study successfully demonstrates synthesis of tetragonal and cubic ZrO2:Tb3+ green nanophosphors with superior photoluminescence and photocatalytic activities.

Molecular self ordering and charge transport in layer by layer deposited poly (3,3‴-dialkylquarterthiophene) films formed by Langmuir-Schaefer technique

The performance of π-conjugated polymer based electronic devices is directly governed by the molecular morphology of polymer aggregation, the extent to which a molecule is electronically coupled (self ordered and interacted) to neighboring molecules, and orientation. The well electronic coupled and crystalline/ordered polymer films have the potential to enhance the charge transport properties up to a benchmark. However, there is insufficient knowledge about the direct formation of large area, oriented, crystalline, and smooth films. In this study, we have presented Langmuir Schaefer technique to obtain the large area, oriented, crystalline, and smooth film of Poly (3,3‴-dialkylquarterthiophene) (PQT-12) polymer. The effect of self ordering and orientation of PQT-12 polymer on optical, morphological, and charge transport properties has been investigated. The prepared films have been characterized by UV-vis spectroscopy, Raman spectroscopy, transmission electron microscopy (TEM), selected area diffractions pattern (SAED), and atomic force microscopy (AFM) techniques. UV-vis spectra, TEM, SAED, and AFM images of monolayer films reveal the formation of well ordered and electronically coupled polymer domains. Layer by layer deposited films reveal the change in the orientation, which is confirmed by Raman spectra. Electronic properties and layer dependent charge transport properties are investigated using sandwiched structure Al/PQT-12/ITO Schottky configuration with perpendicular to the deposited films. It is observed that the charge transport properties and device electronic parameters (ideality factor and turn on voltage) are significantly changing with increasing the number of PQT-12 layers. Our study also demonstrates the charge transport between polymer crystallites and cause of deviation of ideal behavior of organic Schottky diodes. It may be further explored for improving the performance of other organic and optoelectronic devices.

Linking Catalyst Phase with CNT Morphology and its Subsequent Field Emission Characteristics: An Optimization Study

The effect of phase transition in catalyst nanoparticles due to increasing growth temperatures and its effect over the morphology and field emission of carbon nanotubes (CNT) films is reported here. Thin Fe film coated Si substrates are used to obtain Fe nanoparticles under hydrogen and argon plasma treatment. For this, three different microwave powers (400, 500 and 650 watts) in a microwave plasma enhanced CVD system is used. TEM images of plasma annealed films shows Fe nanoparticles of size ranging from 10 nm to 70 nm. The SAED images of these Fe nanoparticles shows additional diffraction rings for the films annealed at higher microwave power (i.e., higher growth temperatures). Acetylene and hydrogen plasma is used for 2 minutes to deposit the CNT films over three different sized Fe nanoparticles. High resolution TEM (HRTEM) images are used to further investigate any effect of growth temperature on catalyst encapsulated in the CNTs. The field emission studies and Kelvin probe measurements are carried out to examine the suitability of films for its field emission application. It is established that, only under specific optimized growth parameters CNT film must be grown for its usefulness as efficient field emitters.

Effect of Mn2+ Doping on Structural, Morphological and Optical Properties of ZnS Nanoparticles by Chemical Co-Precipitation Method

Zinc Sulphide (ZnS) nanoparticles doped with different concentrations of Mn 2+ (0%, 2%, 4%, 6%, 8%, 10%) have been synthesized by chemical co-precipitation method using polyvinyl alcohol (PVA) as a capping agent to control the particle growth. The structural characterizations of as synthesized nanoparticles are determined by X-ray diffraction (XRD) which showed cubic zinc blende structures with average crystallite sizes of the range 2.3 nm - 2.1 nm. There is no phase transformation due to Mn 2+ doping and this characteristic has been observed in all the synthesized powder. Scanning electron microscopy (SEM) and energy dispersive X- ray (EDX) analysis show the morphology and elemental analysis of as synthesized nanoparticles.TEM images confirms the spherical shape of the nanoparticles. HRTEM and SAED images show the crystalline nature and confirm the cubic nature of ZnS nanoparticles. Absorption study has been carried out by using UV-Vis spectrophotometer to determine the band gap of ZnS:Mn nanoparticles and they showed a blue shift with respect to the bulk. The effect of Mn 2+ substitution on the photoluminescence properties of doped samples is also studied and doped ZnS:Mn showed enhanced luminescence property compared with that of the undoped ZnS nanoparticles. Radius of the synthesized nanoparticles has been evaluated from the absorption spectrum by using the Effective Mass Approximation (EMA) formula. Fourier Transform Infrared Spectra (FTIR) is recorded in an FTIR spectrometer to verify the presence and effect of capping agent.

Role of Cu Substitution on the Pseudocapacitive Performance of Nano-platelet Shaped Spinels, NixCuzCoyO4 {x=1-z, y=2-z, z=0.2}

AB2O4 type 3d transition metal nano-platelets NixCuzCoyO4 {x=1-z, y=2-z, z=0.2}, exhibiting pseudocapacitance behavior in aqueous electrolytes has been examined as a positive electrode in an asymmetric hybrid cell against a double layer coke carbon. Synthesis of these single phase spinels has been accomplished via a modified solvothermal route which yields individual nano-platelets (∼50nm size) as confirmed by STEM, high resolution TEM (HRTEM) and SAED images. It is evident from XPS analysis that the copper substitution occupies both tetrahedral and octahedral coordination in the host spinel. Indexed XRD patterns reveal Cu substitution affects the cell volume as compared with pristine spinel. It has been found that substitution of up to 20 mol% Ni or Co by Cu leads to a significant increase of specific capacitance (Fg−1) compared to pristine counterpart (NiCo2O4). More pronounced effects on the capacitance have been realized specifically with Cu substitution at Ni site (octahedral, called A-site herein after) namely Ni0.8Cu0.2Co2O4 rather than Co site (tetrahedral, called B-site) of NiCo1.8Cu0.2O4 spinels. The former composition delivers an average capacitance of up to 458Fg−1 whereas only a 244Fg−1 was deduced from the latter. A hybrid asymmetric aqueous cell comprised of Ni0.8Cu0.2Co2O4(+)//activated carbon (AC) (-) electrode couple renders ∼72Fg−1 of cell capacitance with a good cycle stability (over 1000 cycles) within a potential window of 1.5V. It has been deduced that the hybrid cell delivers a power density of 12kWkg−1 and energy density of 7Whkg−1 at room temperature.

A facile route to synthesis of CoPt magnetic nanoparticles

The face-centered tetragonal (FCT) ordered L10 CoPt nanoparticles (NPs) are prepared by the sol–gel method. Their structure and magnetic properties are characterized by the X-ray diffraction (XRD), the transmission electron microscope (TEM) and the vibrating sample magnetometer (VSM). The results indicate that the CoPt NPs heated at 400°C are the disordered face-centered cubic (FCC) structure, whereas the samples annealed at the temperature above 600°C exhibit an ordered FCT structure. TEM images show the increase of the particle size as the annealing temperature increases. SAED images show the appearance of the L10 phase at 800°C, and the maximum coercivity is 254,720.3A/m.

Three-dimensional bubble field resolution using synthetic aperture imaging: application to a plunging jet

A methodology for resolving three-dimensional (3D) bubble fields using 3D synthetic aperture imaging (SA imaging) is developed and applied to the bubbly flows induced by a turbulent circular plunging jet. 3D SA imaging involves capturing entirely in-focus images in an array of cameras with multiple viewpoints, then reprojecting the images into the measurement volume and combining them post capture. The result is a stack of synthetically refocused images that span the measurement volume with each refocused image having a narrow focus on a particular plane. In this paper, bubble shadow images are captured by projecting diffuse backlight onto the measurement volume. 3D SA imaging is ideally suited to investigate optically dense multiphase flows due to the ability to reconstruct volumes that contain partial occlusions. Instantaneous bubble sizes and locations in the plunging jet bubble fields are extracted from the volumes using two feature extraction algorithms and presented for various jet heights. The data are compared with existing literature on bubble penetration depth and size distributions. A scaling law for the integrated air concentration as a function of depth below the free-surface is proposed. Coupled with scaling laws for a parameter describing the radius of the bubble cone and radial concentration profiles, this new scaling law can be used to determine the entire air concentration profile given a minimal number of single-point measurements.

Controlled synthesis of CdS micro/nano leaves with (0001) facets exposed: enhanced photocatalytic activity toward hydrogen evolution

Two-dimensional CdS micro/nano leaves have been synthesized via a controlled hydrothermal process. The dimensions of the leaves is in the range of 4–6 μm and the thickness of the leaves is 30–50 nm. The surface of the leaves is smooth and composed of several parallel laminar layers with multi-steps. The SAED and HRTEM images indicated that the surface of the leaves was mainly composed of (0001) plane and all the leaves had single-crystallinity. The morphology of the as-prepared products could be controlled by adjusting the concentration of hydrofluoric acid (HF). The effects of HF concentration, reaction temperature and time were investigated. A possible formation mechanism is proposed based on the intrinsic crystal structure and selected adsorption processes. In addition, the as-prepared CdS pinnate leaves showed enhanced photocatalytic activity toward hydrogen evolution under visible light irradiation. The efficiency of micro/nano leaves was more than 6 times greater than normal CdS microparticles.

Crystal Structure of Reduced and of Oxidized Peroxiredoxin IV Enzyme Reveals a Stable Oxidized Decamer and a Non-disulfide-bonded Intermediate in the Catalytic Cycle

Peroxiredoxin IV (PrxIV) is an endoplasmic reticulum-localized enzyme that metabolizes the hydrogen peroxide produced by endoplasmic reticulum oxidase 1 (Ero1). It has been shown to play a role in de novo disulfide formation, oxidizing members of the protein disulfide isomerase family of enzymes, and is a member of the typical 2-Cys peroxiredoxin family. We have determined the crystal structure of both reduced and disulfide-bonded, as well as a resolving cysteine mutant of human PrxIV. We show that PrxIV has a similar structure to other typical 2-Cys peroxiredoxins and undergoes a conformational change from a fully folded to a locally unfolded form following the formation of a disulfide between the peroxidatic and resolving cysteine residues. Unlike other mammalian typical 2-Cys peroxiredoxins, we show that human PrxIV forms a stable decameric structure even in its disulfide-bonded state. In addition, the structure of a resolving cysteine mutant reveals an intermediate in the reaction cycle that adopts the locally unfolded conformation. Interestingly the peroxidatic cysteine in the crystal structure is sulfenylated rather than sulfinylated or sulfonylated. In addition, the peroxidatic cysteine in the resolving cysteine mutant is resistant to hyper-oxidation following incubation with high concentrations of hydrogen peroxide. These results highlight some unique properties of PrxIV and suggest that the equilibrium between the fully folded and locally unfolded forms favors the locally unfolded conformation upon sulfenylation of the peroxidatic cysteine residue.

Green synthesis and characterization of gold nanoparticles using extract of anti-tumor potent Crocus sativus

In the present study, we have explored anti-tumor potent Crocus sativus (saffron) as a reducing agent for one pot size controlled green synthesis of gold nanoparticles (AuNps) at ambient conditions. The nanoparticles were characterized using UV–vis, scanning electron microscope (SEM), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) and FTIR analysis. The prepared AuNPs showed surface Plasmon resonance centered at 549 nm with average particle size of 15±5 nm. Stable, spherical and triangular crystalline AuNPs with well-defined dimensions were synthesized using anti-tumor potent Crocus sativus (saffron). Crystalline nature of the nanoparticles is confirmed from the HR-TEM, SAED and SEM images, and XRD patterns. From the FTIR spectra it is found that the biomolecules are responsible for capping in gold nanoparticles.

Synthesis and enhanced photoluminescence in novel Au coreAu–Ag shell nanoparticles embedded Nd 3+-doped antimony oxide glass hybrid nanocomposites

Au coreAu–Ag shell nanoparticles and Nd 3+ ions co-doped in a novel antimony(III) oxide based dielectric (glass) matrix were synthesized for the first time, by a new very simple single-step methodology involving selective thermo-chemical reduction without employing any external reducing agent. They were characterized by the evolution of UV–vis–NIR absorption and photoluminescence spectra, XRD patterns, TEM and SAED images. XRD and SAED indicate the building of core–shell nanoparticles through the formation of (1 1 1) and (2 0 0) planes whereas TEM advocates the generation of spherical and spheroidal particles of 22–107 nm sizes with various core morphologies. Photoluminescence upconversion exhibits two major emission bands of Nd 3+ ions at 540 (green) and 649 (deep-red) nm which undergo about 5-fold intensity enhancement by the nanoparticles. Such enhancement is attributed to the local field effect induced by plasmonic Au–Ag nanoparticles to Nd 3+ ions. These nanocomposites are promising for many nanophotonics applications.

Synthesis and optical properties of Cr doped ZnS nanoparticles capped by 2-mercaptoethanol

Nanoparticles of Zn 1− x Cr x S ( x=0.00, 0.005, 0.01, 0.02 and 0.03) were prepared by a chemical co-precipitation reaction from homogenous solutions of zinc and chromium salts. These nanoparticles were sterically stabilized using 2-mercaptoethanol. Here a study of the effect of Cr doping on structural, morphological and optical properties of nanoparticles was undertaken. Elemental analysis, morphological, structural and optical properties have been investigated by energy dispersive analysis of X-rays (EDAX), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM) and UV–visible spectroscopy .EDAX measurements confirmed the presence of Cr in the ZnS lattice. XRD showed that ZnS:Cr nanoparticles crystallized in zincblende structure with preferential orientation along (1 1 1) plane. The average sizes of the nanoparticles lay in the range of 3–6 nm and lattice parameters were in the range of 5.2–5.4 Å. Lattice contraction was observed with an increase of Cr concentration. The particle size and lattice parameters obtained from TEM and SAED images were in agreement with the XRD results. The absorption edge shifted to lower wavelengths with an increase in Cr concentration as per UV–Vis spectroscopy. The band gap energy values were in the range of 3.85–4.05 eV. This blueshift is attributed to the quantum confinement effect.

Synthesis and characterization of polycrystalline ZnO/HZSM-5 nanocomposites

Polycrystalline ZnO/HZSM-5 nanocomposites were synthesized by the impregnation method using a home prepared HZSM-5 zeolite as porous support and Zn(C5H7O2)2 or Zn(NO3)2 as zinc precursors. As-prepared samples were characterized by ICP, XRD, SEM (EDS), TEM (SAED), BET and DRS techniques. A small amount of sub-nanometeric ZnO clusters were introduced into the channels of HZSM-5 zeolite. These ZnO clusters exhibited absorption band onset at about 280 nm, different from ZnO particles at about 370 nm. The significant blue shift possesses high quantum size effect in sub-nanometeric ZnO clusters. SAED and TEM images revealed that the ZnO nanoparticles, supported on the surface of HZSM-5 zeolite, were identified as polycrystalline structure with the particle size of about 20-25 nm. XRD results provided evidence of the strong host-guest interactions between HZSM-5 framework and ZnO structure. The samples prepared by Zn(C5H7O2)2 were more porous and smaller than those prepared from the Zn(NO3)2. This was confirmed by SEM and XRD results.

Ga2O3 nanowires grown on GaN–Ga2O3 core–shell nanoparticles using a new method: Structure, morphology, and composition

Ga2O3 nanowires grown on GaN–Ga2O3 core–shell nanoparticles were prepared through heat-treating GaN powder method which comprises a pre-nitridation process in the flow of N2 gas and a post-oxidation process in the air at 1200°C. XRD and EDS patterns indicated that the heat-treated GaN powders were a powder mixture of GaN and Ga2O3. SEM, TEM, HRTEM and SAED images revealed that some nanowires that grow out from the edge of the GaN–Ga2O3 core–shell nanostructures with atomically smooth interfaces were monoclinic Ga2O3. Large blue-shifts in vibration frequency of Ga–N bonds observed in the FTIR spectrum could be contributed to size confinement effect and internal strains in GaN nanoparticles.

Synthesis and luminescence of CePO4 and CePO4:Tb hollow and core–shell microspheres composed of single-crystal nanorods

Lanthanide phosphate microspheres composed of single-crystalCePO4 and CePO4:Tb nanorods were successfully synthesized, respectively, using thefunctionalized composite aggregate as a template, which is composed of P123,H6P4O13 andCe3+, andalso as a resource of reaction species with high chemical potential. The shape and the phase structureof the CePO4 nanocrystal can be easily controlled via adjusting reaction temperature, monomerconcentration and annealing temperature. SEM images show the sphericalsuperstructure composed of nanorods. HRTEM and SAED images reveal thesingle-crystalline nature of nanorod and TEM images show the hollow interiorsof the superstructure. XRD patterns indicate that the crystal structure of thenanorods is hexagonal before and monoclinic after annealing. The formationmechanism was proposed. Strong UV and green luminescence were observed for theCePO4 and CePO4:Tb microspheres, respectively. The synthesis method can be extended to thefabrication of NRHS and core–shell microspheres of other rare-earth or dopedLnPO4 materials for wide applications.

Selective synthesis of plate-like and shrub-like micro-scale copper crystallites

Copper (Cu) plate-like and shrub-like micro-scale crystallites were synthesized by a facile hydrothermal method using formaldehyde (HCHO) as the reducing agent in NaOH aqueous solution at 180 °C. The X-ray diffraction patterns indicate that the as-synthesized Cu crystallites were well crystallized and with pure phase. FESEM and TEM images reveal that the final plate-like products consist of lager numbers of triangular and hexagonal plates with the edge length ranging from 0.5 to 4 μm and with the thickness ranging from 250 to 350 nm, and the shrub-like products are composed of some dendrites. SAED and HRTEM images prove that the Cu plates are singe crystals and covered by {1 1 1} facets. The effect of capping agent, NaOH concentration, reaction time and temperature on the morphologies of the final products has been investigated, and their possible formation mechanisms were also discussed.

Nacrite in the Lodève Permian Basin: a TEM and fluid-inclusion study

Nacrite, a two-layer polytype of kaolin (space group C c ) generally formed at high temperature, was found in the Lodeve Basin, France. It occurs in dolomite cavities in the Cambrian basement of the Permian basin, as authigenic, euhedral, up to millimetre-sized crystals, associated with barite deposits of hydrothermal origin. Formation of the mineral deposits is attributed to subbasinal fluid discharge and trapping during a Late Permian extensional regime. Textural relations suggest that nacrite and barite formed contemporaneously. The combination of transmission electron microscopy (TEM) images and electron diffraction patterns (SAED) confirm the two-layer periodicity of nacrite. In low-magnification images, nacrite displays a lamellar structure defined by a high density of planar defects parallel to (001). Each lamella is from 1.4 to 600 mm thick. SAED and high-resolution images imply that these planar defects are “twin” boundaries. Fluid inclusions occurring in barite are mostly one-phase, but coexist with rare two-phase inclusions. Ice-melting temperatures indicate the presence of a high-salinity brine (up to 25 wt% NaCl equiv.), whereas heating runs indicate formation at low temperature, approximately 80 to 100°C. Oxygen isotope data for nacrite are consistent with that low temperature range. These data imply that the occurrence of nacrite rather than other kaolin-family polytypes can not generally be used as a qualitative geothermometer that implies formation at relatively high temperatures.