High-resolution Transmission Electron Micrographs Research Articles

Magnetoelectric coupling of manganese ferrite–potassium niobate lead-free composite ceramics synthesized by solid state reaction method

Lead-free composite ceramics xMnFe2O4-(1 − x) KNbO3 with the composition of x = 0.20, 0.30 and 0.40 were synthesized by the solid state reaction method to obtain the composites of ferrite and ferroelectric to achieve magnetoelectric coupling. A confirmation study for the formation of spinel cubic MnFe2O4 ferrite ceramic and orthorhombic KNbO3 ferroelectric ceramic was performed by X ray diffraction. The strain in the composite for various compositions was estimated using W–H method to understand the variation of multiferroic features of the ceramic composites. The Transmission Electron Micrograph and High Resolution Transmission Electron Micrograph images reveal the existence of ferrite and ferroelectric phases. Weak magnetic behavior is exhibited by the ferrite-ferroelectric composites as compared to ferrite MnFe2O4. The 20:80 composite possesses the highest magnetic parameters among the compositions. The 40:60 composite recorded the maximum Pr and Ec values. The enhanced ME coupling between magnetic and ferroelectric phases is shown for 40:60 composite and the same is good for the lead free multifunctional device. All the composite samples show low current leakage.

Microwave-assisted synthesis of hybrid organo-layered double hydroxides containing cholate and deoxycholate

Abstract Organic–inorganic layered double hydroxides (LDHs) were obtained by using a microwave-assisted method to intercalate cholate or deoxycholate ion into an Mg, Al mixed LDH. Based on the X-ray diffraction and Raman spectra for the resulting LDHs, a treatment time of only 1 h sufficed to ensure complete intercalation of the organic anions. This makes the proposed synthetic method more expeditious than existing alternatives for the same purpose. Based on the baseline spacing for the organo-LDHs, the organic anions were intercalated with no cross-over between their molecular chains. The interlayer distance of the solids was confirmed by high-resolution transmission electron micrographs (HR-TEM). As revealed by thermogravimetric monitoring measurements, and confirmed by Raman spectra, the decomposition temperature for the LDHs increased considerably upon intercalation of the organic anion.

Investigations of surface spin canting in Ni-Zn nanoferrite and its development as magnetic core for microwave applications

• Achieved high saturation magnetization of 80.3 emu/gm for a crystallite size of 42 nm. • Low surface spin canting angle observed is the cause for such high magnetization. • Initial permeability dispersion shows that the material would be suitable as magnetic core up to 18 GHz. Nanoparticles of nickel zinc ferrite Ni 0.65 Zn 0.35 Fe 2 O 4 having an average crystallite size of 42 nm, synthesized by sol–gel method were found to exhibit the highest value of saturation magnetization along with high dc resistivity. The observed variations in saturation magnetization and crystallite size as a function of annealing temperature were elucidated considering the core surface magnetic interactions and the particle shape of the nanoferrite using low temperature in-field Mössbauer measurements and the high-resolution transmission electron micrographs. With the attainment of valuable magnetization and resistivity, the usefulness of the material as magnetic core for high frequency applications has been investigated by studying the frequency dependence of initial permeability. Interestingly, the results support that the material would be suitable as magnetic core up to 18 GHz.

Identifying Atoms in High Resolution Transmission Electron Micrographs Using a Deep Convolutional Neural Net

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Synthesis of Ag/AgCl Nanoparticles and their action on Human Serum albumin: A fluorescence study

Abstract We report a one-step green synthesis of multifunctional silver nanoparticles AgNPs (Ag/AgCl NPs) using aqueous stem extracts of D. trifoliata and S. alba. Optimization results revealed that the maximum rate of synthesis could be achieved with 1.5 × 10−3 M and 2 × 10−3 M AgNO3 solution at room temperature in 4 h and 2 h respectively. The synthesized AgNPs were characterized by UV–vis spectroscopy, the bands were observed at 445 nm and 450 nm. High resolution transmission electron micrographs (HR-TEM) showed mostly spherical particles having diameters ranging from 20 to 60 nm. Energy dispersive x-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) confirmed elemental silver and chlorine, X-Ray diffraction (XRD) revealed the formation of face centered cubic. Interaction between human serum albumin (HSA) and AgNPs were studied at different temperatures. The Stern Volmer quenching constant, binding constant, number of binding sites thermodynamic parameters were calculated. Thermodynamic parameters (ΔG0, ΔH0 & ΔS0) hint that the binding process occurs spontaneously. Circular dichroism indicates that α helicity of HSA decreases due to the interaction with AgNPs. AgNPs showed potent antioxidant and anti-inflammatory activity. Our results reveal promising approach for alternative nano drug development.

Structural, optical, electronic and magnetic properties of multiphase ZnO/Zn(OH)2/ZnO2 nanocomposites and hexagonal prism shaped ZnO nanoparticles synthesized by pulse laser ablation in Heptanes

We have studied structural, optical, electronic and magnetic properties of undoped well crystalline hexagonal and non-hexagonal ZnO system. X-ray diffraction (XRD) and high resolution transmission electron micrographs (HRTEM) of air annealed at 550 °C (sample-d) confirmed the presence of hexagonal (wurtzite) single phase ZnO. Raman analysis detected the vibrations of fundamental and second order phonons of Zn and oxygen related species. In Photoluminescence (PL) spectra, we observed that the intensity of UV peak decreases as annealing temperature increases. Broad PL visible band of samples shifted towards lower wavelength due to annealing effects. Fitting of broad PL spectra confirmed the existence of Zinc interstitial (Zni), Zinc vacancy (VZn) and oxygen vacancy (Vo) defects. To determine the Zn interstitial and vacancy defects Auger peaks were de-convoluted from X-ray photoelectron spectroscopy (XPS) survey scan. Oxygen vacancies are estimated by fitting of asymmetric XPS O-1s spectra. Incomplete oxidation of magnetization versus temperature in the presence of applied field showed the presence of irreversibility in 550 °C annealed-sample. Zn clusters and secondary phases are may be reason of room temperature ferromagnetism in non-hexagonal samples (a-c). While, complex defect (zinc and oxygen vacancies) as observed in electronic and PL data may be responsible for inducing, promoting and stabilizing room temperature ferromagnetism in well crystalline hexagonal ZnO nanoparticles (sample-d).

Monoclinic to cubic phase transformation and photoluminescence properties in Hf1−xSmxO2 (x = 0–0.12) nanoparticles

Bulk hafnium oxide (HfO2) exhibits the monoclinic phase at room temperature which transforms to tetragonal and cubic phases at 1700 and 2600 °C, respectively, under ambient conditions. For the first time, we observe a monoclinic to stable cubic phase transformation at room temperature in nanoparticles of HfO2 by incorporating Sm3+ ions up to 12 at. %. Although the monoclinic structure is retained at 1 at. % of Sm, a mixed phase of monoclinic and cubic is observed at intermediate Sm concentration (5–11 at. %). Le-Bail profile refinement of X-ray diffraction patterns confirms the monoclinic to cubic phase transformation with increasing Sm3+ ion concentration. While the significant difference in ionic radii of Sm3+ and Hf4+ ion induces strain in the lattice above 9 at. %, a lower valency of Sm produces oxygen vacancy leading to 8-fold coordination with Sm3+ ion and stabilizes the cubic phase at room temperature. Not only the particle size obtained from transmission electron micrograph (TEM) matches well with the size calculated from the Williamson-Hall plot, the lattice spacing estimated from high resolution TEM also confirms the monoclinic and cubic phases in HfO2 and Hf0.88Sm0.12O2, respectively. Apart from phase transformation induced by Sm3+ ions, photoluminescence studies demonstrate an excellent emission in near green and red regions in Hf1−xSmxO2 nanoparticles. A schematic energy band diagram has been proposed based on the excitation and emission processes involved in HfO2 and Hf0.99Sm0.01O2 nanoparticles.

Chemical vapor transport synthesis of a selenium-based two-dimensional material

Selenium-based layered materials, and in particular transition-metal diselenides (TMDSs), have intriguing properties in the monolayer limit. Materials such as MoSe$_{2}$, WSe$_{2}$, and NbSe$_{2}$ display striking features such as spin-valley coupling at the valence-band edges and offer great potential for optoelectronics applications. Although a dozen of other TMDSs have been realized or proposed, whether two-dimensional chalcogens are possible or not is still an open challenge. In this work, we show the chemical vapor transport synthesis of a novel, atomically thin selenium-based material on oxidized silicon substrates. This new member of the two-dimensional materials family has a unique Raman spectrum similar to that of bulk selenium and has an optical gap of $\sim $1.57 eV at room temperature determined by the photoluminescence. No transition metals are found in the stoichiometry of the crystals. Analysis of high-resolution transmission electron micrographs of the monolayers reveals a distinctive set of hexagonal spots indicating a sixfold symmetry of the lattice. Atomic force microscopy measurements show the monolayer thickness to be $\sim $0.75 nm.

Structural features of Qingdao petroleum coke from HRTEM lattice fringes: Distributions of length, orientation, stacking, curvature, and a large-scale image-guided 3D atomistic representation

Structural features of a green Qingdao petroleum coke (produced at ∼ 500 °C) were investigated by image analysis of high-resolution transmission electron micrographs, XRD, and matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF MS). The fringe length distribution was comprised mostly of fringes <20 Å, with a peak at 5–7 Å. The MALDI-TOF MS data also indicated an abundance of low molecular weight material 250–300 Da. The coke had considerable preferential orientation within the field of view of the micrograph. However, the degree of ordering was poor with fringe stacking occurring for ∼20% for the fringes, with a mean of 2.11 fringes. XRD also indicated low ordering as expected for a lower quality, low temperature coke. The poor nanostructure-level order was a result of small fringe lengths, with curvature (present in 42% of the fringe) likely contributing. It is thus a partially ordered system, with order varying over length scales. An image-guided construction strategy capable of controlling the degree of order (utilizing Fringe3D and Vol3D) was used to construct an atomistic structural representation (C3717H1830N54O134S109) incorporating many experimental parameters. The structure was comprised of preferentially orientated molecules, but with the observed limited stacking, incorporating both curvature frequency and extent.

Zn-doped SnO2 nanostructures: structural, morphological and spectroscopic properties

SnO2 is a promising material for optoelectronic, catalytic and sensing applications and is highly sensitive to the small amount of impurities that can change its properties drastically. In the present work, co-precipitation method was employed to synthesize pure and Zn-doped SnO2nanostructures. The effect of Zn doping (1, 3 and 5% molar ratio) on crystallographic and spectroscopic properties of SnO2 nanostructures has been studied. The X-ray diffraction results revealed that SnO2 possesses tetragonal rutile crystal structure with predominant (110) plane and the same structure was retained after doping with Zn. Raman shifts also confirmed the typical feature of the tetragonal rutile phase in all samples. Fourier transform infrared spectra revealed stretching mode of Sn–O bond and vibrational mode of O–Sn–O bond complementing the Raman spectroscopy results. Field emission scanning electron micrographs confirmed the variation in morphology of synthesized samples with Zn-dopant concentration. High-resolution transmission electron micrographs showed that the synthesized nanostructures were nearly spherical and average particle size varies between ~20–26 nm. UV–Visible results revealed that the band gap of the synthesized SnO2 nanoparticles increased with increase in Zn content. Photoluminescence spectroscopic results showed that emission intensity increased with increase in Zn content. The increased intensity of emission peaks may be ascribed to the development of defect states in the band gap of Zn-doped SnO2 nanoparticles.

Microwave Assisted Synthesis of Palladium Nanoparticles in an Aqueous Emulsion of Copolymer: Application to Catalysis

Palladium nanoparticles were prepared in a few minutes using polyol assisted-microwave process. This synthesis based on the reduction of metal salt (k2PdCl4) in ethylene glycol medium in presence of an aqueous emulsion of copolymers (latex) as a reducing and stabilizer agent. The products were characterized by UV–Vis spectroscopy infrared spectroscopy transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, selected area electron diffraction patterns, and high-resolution transmission electron micrographs. We have found spherical homogeneous Pd nanoparticles with narrow particles size distributions. In addition, we used Pd-latex-EG nanofluid emulsion for catalyzing organic reactions including Suzuki, Heck and the Sonogashira reactions. As a result, we have successfully demonstrated the crucial effect of latex copolymer for reducing and capping Pd nanoparticle. We point out that the presence of the polymer molecules don’t affect the catalytic effect which mainly due to the Pd metallic nanoparticles.

Controlled Growth, Microstructure, and Properties of Functional Si Quantum Dot Films via Plasma Chemistry and Activated Radicals

Control of plasma and radical generation and associated energy deposition near the growing thin films are still the main challenges in materials fabrication in the plasma-assisted deposition of Si quantum dot (QD) thin film. To control and enhance the material’s performance concerning film properties and application durability, we prepare 2.6 nm sized Si QDs with a fully ordered structure and entrapped them in amorphous silicon nitride using advanced dual frequency capacitively coupled plasmas. Raman and XRD analyses consistent with the high-resolution transmission electron micrographs reveal that the QD size can be controlled and altered from ∼2.6 to 4.0 nm simply by changing the operating pressure, which affects the film’s crystallinity in a broad range from 60% to 72% and the resulting microstructure. Further, a broad visible range ∼ 1.8–3.0 eV photoluminescence, with intense intensity and narrow to broad widths, is observed from Si QDs films. It is also seen that the observed photoluminescence feature...

Fascinating improvement in physical properties of Cd/Co nanoferrites using different rare earth ions

Cadmium-cobalt-rare-earth nanoferrite samples of composition Cd0.7Co0.3Fe2O4 and Cd0.7Co0.3R0.05Fe1.95O4 (R = Ce, Sm, Gd, Er) were prepared by citrate auto combustion method. All samples were characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), High Resolution Transmission Electron Micrographs (HRTEM), Energy Dispersive X ray Spectroscopy (EDAX) and Atomic Force Microscope (AFM). XRD confirmed the formation of cubic spinel structure with the appearance of small peaks designated as secondary phases. The average crystallite sizes were found to be between 40.3 and 22.1 nm for pure and Gd doped samples respectively. The magnetic properties were studied by carrying out the hysteresis of the investigated samples at room temperature and at 100 K. The magnetic parameters, such as the saturation magnetization, coercivity Hc, squareness and loop area are markedly affected by increment of rare earth ions at the expense of Fe3+ ions in a spinel structure. The increase in magnetization of the nano ferrite samples at 100 K, may be clarified by annihilation of a nonmagnetic layers (surface dead layers) due to the rare earth doping. Greater than nearly nine-fold increase in coercivity was observed in pure and Ce, Sm doped compared to the Gd and Er samples. The data for Hc, Ms and Mr of lanthanide doped ferrites suggest their suitability in applications like magnetic targeting and separators.

Environmental benignity of a pesticide in soft colloidal hydrodispersive nanometric form with improved toxic precision towards the target organisms than non-target organisms

Mosquito-borne diseases are of major concern as they cause devastating health effects, morbidity, and mortality in the human population. Conventional pesticides have failed to curb the mosquito population due to the development of insensitivity in mosquitoes. Hence, higher dosages of pesticides along with their toxic solubilizers have been employed, which have led to raise in pesticide pollution load, environmental toxicity, and human health concerns. As a realisation for the requirement of alternative pesticides, the present study has involved in the formulation of a hydrodispersive nanometric colloidal form of deltamethrin (NDM), a type-II pyrethroid pesticide, from its hydroimmisicible parental form (PDM). The mean hydrodynamic diameter of the droplets was found to be 30.6±4.6nm by dynamic light scattering study (DLS). High-resolution transmission electron micrographs have revealed the spherical structure of the droplets with a size range of 35–40nm. The NDM was found to possess sedimentation resistance, intrinsic and hydrodispersive stability. The toxicity of NDM and PDM was comparatively investigated on target organisms (Culex tritaeniorhynchus and Culex quinquefasciatus mosquitoes) and non-target organisms (Allium cepa – Bioindicator of toxicants and Rhizobium sp. – Soil bacteria). As comparative to PDM, NDM has exerted higher efficacy on adult mosquito and larval population, even at low-level concentrations. However, in the case of non-target organisms, the NDM toxicity was lower than PDM. Comprehensively, the study has concluded the potential advantage of formulating conventional pesticides into nanometric soft colloidal form for the improved toxic precision on target organisms (mosquitoes). This ensures the ability of NDM to combat against the mosquito population even at lower concentrations, thereby reducing the pesticide exposure load towards the environment and human population.

Nonstoichiometry and phase stability of Al and Cr substituted Mg ferrite nanoparticles synthesized by citrate method

The spinel ferrite Mg0.7Cr0.3Fe2O4, and Mg0.7Al0.3Fe2O4 were prepared by the citrate technique. All samples were characterized by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), High Resolution Transmission Electron Micrographs (HRTEM), Energy Dispersive X ray Spectroscopy (EDAX) and Atomic Force Microscope (AFM). XRD confirmed the formation of cubic spinel structure of the investigated samples. The average crystallite sizes were found to be between 24.7 and 27.5nm for Al3+ and Mg2+ respectively. The substitution of Cr3+/Al3+ in place of Mg2+ ion initiates a crystalline anisotropy due to large size mismatch between Cr /Al and Mg2+, which creates strain inside the crystal volume. According to VSM results, by adding Al3+ or Cr3+ ions at the expense of Mg2+, the saturation magnetization increased. The narrow hysteresis loop of the samples indicates that the amount of dissipated energy is small, which is desirable for soft magnetic applications. Magnetic dynamics of the samples were studied by measuring magnetic susceptibility versus temperature at different magnetic fields. The band gap energy, which was calculated from near infrared (NIR) and visible (VIS) reflectance spectra using the Kubelka-Munk function, decreases with increasing the particle size. Furthermore, the band gaps were quite narrow (1.5–1.7eV), hence the investigated samples could act as visible light driven photo catalysts. To sum up the addition of trivalent Al3+, and Cr3+ ions enhanced the optical, magnetic and structure properties of the samples. Mg0.7 Cr0.3Fe2O4 sample will be a better candidate for the optical applications and will also be a guaranteeing hopeful for technological applications.

Microstructure and Creep Properties of Silicon- and/or Germanium-Bearing Near-α Titanium Alloys

The effects of Si and/or Ge addition on the microstructure and creep properties at 650°C and 137 MPa were investigated in near-α Ti–Al–Sn–Zr–Mo alloys. Si and/or Ge addition decreased the minimum creep strain rate owing to the solid solution of Si and Ge in the matrix and the precipitation of silicide, germanide, and their solid solutions. The decrease in the minimum creep strain rate in the alloy with 1 wt% Ge without Si was the most significant because of the formation of very fine germanide precipitates. In addition, a marked shift in the lattice parameters of the α and β phases was detected for the alloy with 4 wt% Ge. The Moiré fringe patterns at the α/β interfaces in the alloys were investigated using high-resolution transmission electron micrographs to discuss the alloying effect on the structure of the interfaces.

Development of multiferroic polymer nanocomposite from PVDF and (Bi0.5Ba0.25Sr0.25)(Fe0.5Ti0.5)O3

Thin films of some polymer–ceramics multiferroic nanocomposites (in 0–3 connectivity) of compositions (1 − x)PVDF–x((Bi0.5Ba0.25Sr0.25)(Fe0.5Ti0.5)O3 (x = 0.05,0.1,0.15)) have been prepared using a standard solution casting method. The basic structure and surface morphology of the materials were studied using X-ray diffraction and scanning electron microscopy technique respectively. Structural investigation confirms the presence of polymeric electro active β-phase of matrix (PVDF) and nano filler perovskite phase of the incorporated nano-ceramics. The high resolution transmission electron micrograph of the prepared nano-ceramic thin film composite has shown distinct and uniformly distributed particles (with less agglomeration). This has been observed in SEM micrographs also. The flexible nano-composites fabricated with polymer (PVDF), bismuth ferrite (BiFeO3) and ferroelectric (BST) exhibit high dielectric constant and low tangent loss. The electric response investigated by impedance spectroscopy technique in terms of electric circuit has provided some interesting results on contributions of grain and grain boundary in the restive characteristics of the composites. The study of ac conductivity as a function of frequency obeys Jonscher’s power law. The experimentally obtained first order magnetoelectric coefficient (αME) is found to encouraging for multifunctional application. The improved conductivity and dielectric properties suggest some promising applications in the embedded capacitors.

Nanoparticle Precursor into Polycrystalline Bi2Fe4O9: An Evolutionary Investigation of Structural, Morphological, Optical, and Vibrational Properties

Mullite-type Bi2Fe4O9 was synthesized using a polyol-mediated method. X-ray powder diffraction (XRD) revealed that the as-synthesized sample is nanocrystalline. It transformed into a rhombohedral perovskite-type BiFeO3 followed by a second transformation into mullite-type Bi2Fe4O9 during heating. Each structural feature, from as-synthesized into crystalline phase, was monitored through temperature-dependent XRD in situ. The locally resolved high resolution transmission electron micrographs revealed that the surface of some heated samples is covered by 4–13 nm sized particles which were identified from the lattice fringes as crystalline Bi2Fe4O9. XRD and Raman spectra demonstrate that the nucleation of both BiFeO3 and Bi2Fe4O9 might simultaneously commence; however, their growth and ratios are dependent on temperature. The diffuse UV/vis reflectance spectra showed fundamental absorption edges between 1.80(1) and 2.75(3) eV. A comparative study between the “derivation of absorption spectrum fitting method” (DASF) and the Tauc method suggests Bi2Fe4O9 to be a direct band gap semiconductor.

Charge Transfer States in Dilute Donor-Acceptor Blend Organic Heterojunctions.

We study the charge transfer (CT) states in small-molecule blend heterojunctions comprising the nonpolar donor, tetraphenyldibenzoperiflanthene (DBP), and the acceptor, C70, using electroluminescence and steady-state and time-resolved photoluminescence spectroscopy along with density functional theory calculations. We find that the CT exciton energy blue shifts as the C70 concentration in the blend is either decreased or increased away from 50 vol %. At 20 K, the increase in CT state lifetime is correlated with the increasing diameter of C70 nanocrystallites in the blends. A quantum confinement model is used to quantitatively describe the dependence of both CT energy and lifetime on the C70 or DBP domain size. Two discrete CT emission peaks are observed for blends whose C70 concentration is >65%, at which point C70 nanocrystallites with diameters >4 nm appear in high-resolution transmission electron micrographs. The presence of two CT states is attributed to coexistence of crystalline C70 and amorphous phases in the blends. Furthermore, analysis of CT dissociation efficiency versus photon energy suggests that the >90% dissociation efficiency of delocalized CT2 states from the crystalline phase significantly contributes to surprisingly efficient photogeneration in highly dilute (>80% C70) DBP/C70 heterojunctions.

Growth of L1-ordered crystal in FePt and FePd thin films on MgO(001) substrate

Formation of L10-oredered structure from disordered A1 phase has been investigated for FePt and FePd films on MgO(001) substrates employing a two-step method consisting of low temperature deposition at 200 °C followed by high-temperature annealing at 600 °C. L10-(001) variant crystal with the c-axis perpendicular to the substrate grows preferentially in FePd films whereas L10-(100), (010) variants tend to be mixed with the L10-(001) variant in FePt films. The structure analysis by X-ray diffraction indicates that a difference in A1 lattice strain is the influential factor that determines the resulting L10-variant structure in ordered thin films. Misfit dislocations and anti-phase boundaries are observed in high-resolution transmission electron micrographs of 10 nm-thick Fe(Pt, Pd) film consisting of L10-(001) variants which are formed through atomic diffusion at 600 °C in a laterally strained FePt/PeFd epitaxial thin film. Based on the experimental results, a nucleation and growth model for explaining L10-variant formation is proposed, which suggests a possibility in tailoring the L10 variant structure in ordered magnetic thin films by controlling the alloy composition, the layer structure, and the substrate material.