Scanning Transmission Electron Microscopy Observations Research Articles

Hollow spherical carbonized polypyrrole/sulfur composite cathode materials for lithium/sulfur cells with long cycle life

Hollow carbonized polypyrrole (PPy) spheres are synthesized using poly(methyl methacrylate–ethyl acrylate–acrylic acid) latex spheres as sacrificial templates. The hollow spherical carbonized PPy/sulfur composite cathode materials are prepared by heating the mixture of hollow carbonized PPy spheres and element sulfur at 155 °C for 24 h. Scanning electron microscope (SEM) and transmission electron microscope (TEM) observations show the hollow structures of the carbonized PPy spheres and the homogeneous distribution of sulfur on the carbonized PPy shells. The hollow spherical carbonized PPy/sulfur composite with 60.9 wt.% S shows high specific capacity and excellent cycling stability when used as the cathode materials in lithium/sulfur cells, whose initial specific discharge capacity reaches as high as 1320 mA h g−1 and the reversible discharge capacity retains 758 mA h g−1 after 400 cycles at 0.2C. The excellent electrochemical properties benefit from the hollow structures and the flexible shells of the carbonized PPy spheres.

Characterization of Sc2O3&CeO2-Stabilized ZrO2 Powders Via Co-Precipitation or Hydrothermal Synthesis

As the presence of Sc₂O₃ and CeO₂ is known to largely enhance the ionic conductivity in the temperature range of 600-800°C, compared with the conventional yttria-stabilized ZrO₂, Sc₂O₃&CeO₂-stabilized ZrO₂ provide its applicability as electrolytes in solid oxide fuel cells. The current study introduces the methodology to synthesize Sc₂O₃&CeO₂-stabilized ZrO₂ powders by using co-precipitation technique or high-temperature hydrothermal reaction, and further describes the structural characterization of the zirconia powders synthesized by the above-mentioned two methods. The co-precipitation technique was found to allow obtaining powders of cubic phase, whereas high-temperature hydrothermal synthesis results in the presence of a monoclinic phase as well. The scanning transmission electron microscope observations also confirm that the size of the synthesized ZrO₂ powders in this study is found to be much smaller than that of commercially available powders.

Effects of surfactants, solvents and time on the morphology of MgO nanoparticles prepared by the wet chemical method

Magnesium oxide nanoparticles with different morphologies, including sphere, flower-like, sheet, rod-like and plate shapes have been synthesized in different solvents and surfactants. During this study, magnesium hydroxide nanostructure was prepared in aqueous and organic solvents using magnesium acetate and ammonia solution as precursors. The phase purity was confirmed by XRD. Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) observations show that the solvents, surfactants and time affect the morphology of magnesium oxide produced. It was found that having solvent changed from DMSO to H2O in the presence of polyvinyl alcohol 72000, altered the morphology from rod-like to nanosheet. It was also observed that by changing calcination temperature from 500°C to 750°C in the presence of polyethylene glycol 400 altered the morphology from sphere to pyramid. Finally, the effects of solvents, surfactants and time on the morphology and crystallite size of the magnesium oxide have been investigated.

Three-dimensional hierarchical Ag/AgI/BiOI microspheres with high visible-light photocatalytic activity

Three-dimensional (3D) hierarchical Ag/AgI/BiOI microspheres were prepared by microwave-assisted solvethermal process and subsequently in situ photo-assisted reduction approach. A reactive ionic liquid 1-butyl-3-methylimidazolium iodine([Bmim]I) was employed as I source in the presence of surfactant polyvinylpyrrolidone (PVP). The scanning electron microscope(SEM) and transmission electron microscopy (TEM) observations revealed that the obtained Ag/AgI/BiOI had three-dimensional hierarchical frameworks assembled by nanoflakes. Nitrogen sorption analysis showed that the Ag/AgI/BiOI microspheres exhibited a large Brunauer–Emmett–Teller specific surface area of 73.63m2/g. The obtained Ag/AgI/BiOI showed excellent photocatalytic activity for the decomposition of methylene blue (MB) and o-nitrophenol (OPN) under visible light irridiation, which can be ascribed to the surface plasmon resonance (SPR) effect caused by the silver nanoparticles present in the composite photocatalyst.

Self-assembly fabrication of ZnO hierarchical micro/nanospheres for enhanced photocatalytic degradation of endocrine-disrupting chemicals

ZnO hierarchical micro/nanospheres were successfully synthesized via a facile and surfactant-free chemical solution route. The field emission scanning electron microscopy and transmission electron microscopy observations showed that the ZnO micro/nanospheres were assembled by large amounts of interleaving nanosheets with the thickness of about 17nm. The X-ray diffraction, energy dispersion X-ray and Raman results revealed that the as-synthesized products were well-crystalline and possessing wurtzite hexagonal phase pure ZnO. Under UV irradiation, the ZnO micro/nanospheres showed an enhanced photocatalytic performance compared with the ZnO nanorods and commercial TiO2 in the degradation of phenol. The photocatalytic enhancement of ZnO micro/nanospheres was attributed to their unique hierarchical porous surface structure and large surface area which can enhance the electron–hole separation and increased the yield of hydroxyl radical quantities as evidenced by the photoluminescence spectra. By using a certain of radical scavengers, hydroxyl radical was determined to play a pivotal role for the phenol degradation. Moreover, the as-synthesized ZnO micro/nanospheres could be easily recycled without any significant loss of the photocatalytic activity. Other endocrine-disrupting chemicals such as resorcinol, bisphenol A and methylparaben were also successfully photodegraded under identical conditions. These characteristics showed the practical applications of the ZnO micro/nanospheres in environmental remediation.

Structural Properties, Interface Modes and Magnetophonon Resonances in the Double Quantum Well Structure

The Double Quantum Well structure (DQWs) of special engineering providing a rectangular shape of QW's, is investigated. The Scanning Transmission Electron Microscopy (STEM) observations confirmed a high quality of interfaces and smooth change of the In-content in a rectangular shape QW. Micro-Raman experiment enabled to detect interface phonons in DQWs which are manifested in Magnetophonon Resonance. This contribution of interface phonons in the electron magneto-transport is important because as could be expected, the role of these phonons will increase in case of electron transport in the Double Quantum Wires fabricated from DQWs investigated.

Drug-Loaded Zein Nanofibers Prepared Using a Modified Coaxial Electrospinning Process

This study investigated the preparation of drug-loaded fibers using a modified coaxial electrospinning process, in which only unspinnable solvent was used as sheath fluid. With zein/ibuprofen (IBU) co-dissolving solution and N, N-dimethylformamide as core and sheath fluids, respectively, the drug-loaded zein fibers could be generated continuously and smoothly without any clogging of the spinneret. Field emission scanning electron microscopy and transmission electron microscopy observations demonstrated that the fibers had ribbon morphology with a smooth surface. Their average diameters were 0.94±0.34 and 0.67±0.21 μm when the sheath-to-core flow rate ratios were taken as 0.11 and 0.25, respectively. X-ray diffraction and differential scanning calorimetry verified that IBU was in an amorphous state in all fiber composites. Fourier transform infrared spectra showed that zein had good compatibility with IBU owing to hydrogen bonding. In vitro dissolution tests showed that all the fibers could provide sustained drug release files via a typical Fickian diffusion mechanism. The modified coaxial electrospinning process reported here can expand the capability of electrospinning in generating fibers and provides a new manner for developing novel drug delivery systems.

Morphology Observation of Latex Particles with Scanning Transmission Electron Microscopy by a Hydroxyethyl Cellulose Embedding Combined with RuO4 Staining Method

Imaging of latex particles, especially those with low glass transition temperature (Tg) has been a challenging issue. Different sample preparation methods for characterization of the morphology of a poly(n-butyl acrylate)/polystyrene two-phase latex are discussed and compared in this study. A method via hydroxyethyl cellulose embedding combined with ruthenium tetraoxide (RuO4) staining for scanning transmission electron microscope (STEM) observation is developed. By using this method, the spherical shape of latex particles can be maintained without deformation. The degree of incorporation of RuO4 into latex particles and cellulose matrix is different, which makes latex particles readily identifiable from cellulose matrix under STEM. A series of latexes with different structures such as copolymer latex and organic-inorganic hybrid latex were also successfully investigated by this method. The results indicate this specimen preparation method can be applied to study the morphology of a wide range of latex systems.

Electron Microscopy Study of Preferential Variant Selection in CoPt Alloy Ordered under a Magnetic Field

Transmission electron microscope (TEM) and scanning transmission electron microscope (STEM) observations were carried out to investigate microstructure formation and variant selection process in L10-type ordered CoPt alloy upon a two-step ordering heat-treatment. The first step corresponds to nucleation process carried out under a magnetic field of 10T and the second step represents growth process without magnetic field. After the first step of ordering, ordered domains of about 5nm in size were observed and fraction of the preferred variant with the c-axis parallel to applied magnetic field was slightly higher than that of the other two variants. Formation of tweed microstructure along f011gL10 was confirmed at the initial stage of ordering. This structure is considered to be derived from the periodic alignment of interface between two ordered variants with twin relation. At the early stage of the second step of ordering, numerous micro-twins were formed through tweed microstructure and the volume fraction of the preferred variant was increased accompanying with modulation of twins, while that of other two variants was decreased. After the second step of ordering, the twins were vanished and single variant was obtained. [doi:10.2320/matertrans.MAW201313]

Atomistic observation of electron irradiation-induced defects in CeO2

ABSTRACTWe have investigated the atomistic structure of radiation-induced defects in CeO2 formed under 200 keV electron irradiation. Dislocation loops on {111} habit planes are observed, and they grow accompanying strong strain-field. Atomic resolution scanning transmission electron microscopy (STEM) observations with high angle annular dark-field (HAADF) and annular bright-field (ABF) imaging techniques showed that no additional Ce layers are inserted at the position of the dislocation loop, and that strong distortion and expansion is induced around the dislocation loops. These results are discussed that dislocation loops formed under electron irradiation are non-stoichiometric defects consist of oxygen interstitials.

LaPO4:Eu microstructures constructed by nanorods with triangular pores in the ends: a simple mixed-solvothermal synthesis, growth mechanism and optical property

Flowerlike LaPO4:Eu microstructures built up of nanorods with triangular pores in the ends have been successfully synthesized by a simple water–ethyleneglycol (EG) mixed solvothermal route in the presence of appropriate amounts of concentrated HNO3 and Eu2O3. Lanthanum nitrate (La(NO3)3) and monopotassium phosphate (KH2PO4) were used as the La3+ ion and the PO43− ion source, respectively. X-Ray powder diffraction (XRD) analyses showed that the product was a mixture of hexagonal and monoclinic phases and could be converted to pure monoclinic phase after calcining at 400 °C for 2 h. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy observations exhibited that the morphology of the product did not change before and after calcination. The optical properties and the thermal stability of the flowerlike LaPO4:Eu microstructures were studied. Experiments showed that the presence of appropriate amounts of concentrated HNO3 had a crucial role in the formation of flowerlike LaPO4:Eu microstructures. Based on a time-dependent shape evolution experiment, a possible growth mechanism of the flowerlike LaPO4:Eu microstructures was proposed.

Evidence of oxygen vacancy induced room temperature ferromagnetism in solvothermally synthesized undoped TiO2 nanoribbons

We report on the oxygen vacancy induced ferromagnetism (FM) at and above room temperature in undoped TiO2 nanoporous nanoribbons synthesized by a solvothermal route. The origin of FM in as-synthesized and vacuum annealed undoped nanoribbons grown for different reaction durations followed by calcinations was investigated by several experimental tools. X-Ray diffraction pattern and micro-Raman studies reveal the TiO2(B), TiO2(B)-anatase, and anatase-rutile mixed phases of TiO2 structure. Field emission scanning electron microscopy and transmission electron microscopy observations reveal nanoribbons with uniform pore distribution and nanopits/nanobricks formed on the surface. These samples exhibit strong visible photoluminescence associated with oxygen vacancies and a clear ferromagnetic hysteresis loop, both of which dramatically enhanced after vacuum annealing. Direct evidence of oxygen vacancies and related Ti(3+) in the as-prepared and vacuum annealed TiO2 samples are provided through X-ray photoelectron spectroscopy analysis. Micro-Raman, infrared absorption and optical absorption spectroscopic analyses further support our conclusion. The observed room temperature FM in undoped TiO2 nanoribbons is quantitatively analyzed and explained through a model involving bound magnetic polarons (BMP), which include an electron locally trapped by an oxygen vacancy with the trapped electron occupying an orbital overlapping with the unpaired electron (3d(1)) of Ti(3+) ion. Our analysis interestingly shows that the calculated BMP concentration scales linearly with concentration of oxygen vacancies and provides a stronger footing for exploiting defect engineered ferromagnetism in undoped TiO2 nanostructures. The development of such highly porous TiO2 nanoribbons constitutes an important step towards realizing improved visible light photocatalytic and photovoltaic applications of this novel material.

Microscopic observations of osteoblast growth on micro-arc oxidized β titanium

Titanium alloys are widely used in orthopedic and dental implants, owing to their excellent physical properties and biocompatibility. By using the micro-arc oxidation (MAO), we generated anatase-rich (A-TiO2) and rutile-rich (R-TiO2) titanium dioxide coatings, individually on β-Ti alloy, in which the latter achieved an enhanced in vitro and in vivo performance. Thoroughly elucidating how the osteoblasts interact with TiO2 coatings is of worthwhile interest. This study adopts the focused ion beam (FIB) to section off the TiO2 coated samples for further scanning electron microscope (SEM) and transmission electron microscope (TEM) observation. The detailed crystal structures of the TiO2 coated specimens are also characterized. Experimental results indicate osteoblasts adhered more tenaciously and grew conformably with more lamellipodia extent on the R-TiO2 specimen than on the A-TiO2 and raw β-Ti specimens. FIB/SEM cross-sectional images of the cell/TiO2 interface revealed micro gaps between the cell membrane and contact surface of A-TiO2 specimen, while it was not found on the R-TiO2 specimen. Additionally, the number of adhered and proliferated cells on the R-TiO2 specimen was visually greater than the others. Closely examining EDS line scans and elemental mappings of the FIB/TEM cross-sectional images of the cell/TiO2 interface reveals both the cell body and interior space of the TiO2 coating contain nitrogen and sulfur (the biological elements in cell). This finding supports the assumption that osteoblast can grow into the porous structure of TiO2 coatings and demonstrating that the R-TiO2 coating formed by MAO serves the best for β-Ti alloys as orthopedic and dental implants.

Microstructure and martensitic transformation in the Fe-Mn-Al-Ni shape memory alloy with B2-type coherent fine particles

Microstructure and martensitic transformation yielding a magnetic change were investigated for Fe43.5Mn34Al15Ni7.5 alloy with B2-type fine precipitates. Thermoelastic martensitic transformation from the ferromagnetic parent phase to the weak magnetic martensite with a nano-twinned fcc structure was confirmed. High-angle annular dark-field scanning transmission electron microscopic observation revealed that a β particle of about 10 nm maintains coherency with the matrix martensite phase, even though distorted due to the martensitic transformation. The martensitic transformation temperatures decreased about 75 K by application of a magnetic field of 70 kOe and magnetic field-induced reverse martensitic transformation was confirmed.

Preparation of Freestanding Zn Nanocrystallites by Combined Milling at Cryogenic and Room Temperatures

The present investigation reports the preparation of freestanding nanocrystalline Zn by combined mechanical milling at cryogenic and room temperatures. The cryomilling is used as an effective means of rapid fracturing. The detailed scanning electron microscopy and transmission electron microscopy observations indicate that the minimum crystallite size is 6 ± 2 nm after 3 hours of cryomilling. The crystallite size increases to 30 ± 2 nm after 3 hours of room temperature milling of the cryomilled powder due to deformation-induced sintering. Detailed theoretical analysis allows us to obtain a diagram of size of the nanoparticles formed vs temperature to explain the experimental findings.

High energy-resolution electron energy-loss spectroscopy study on the near-infrared scattering mechanism of Cs0.33WO3 crystals and nanoparticles

The optical and dielectric properties of cesium-doped hexagonal tungsten trioxide (Cs0.33WO3) bulk crystal and nanoparticles, which are employed in solar heat-shielding filter, were investigated by high energy-resolution electron energy-loss spectroscopy (HR-EELS). The EELS spectrum of a Cs0.33WO3 crystal showed a prominent peak at 1.2 eV and a subpeak at 1.7 eV. On the basis of the dielectric function derived from the EELS spectrum, the peaks at 1.2 eV and 1.7 eV were assigned to the volume plasmon excitation of the carrier electrons and electronic excitation, respectively. The EELS spectra of the edge region of individual Cs0.33WO3 nanoparticles exhibited a surface dipole plasmon peak at 0.88 eV and a shoulder structure at 1.4 eV, which corresponded with the optical scattering spectrum. Therefore, it was confirmed that the optical scattering of the filter in the near-infrared region resulted from a surface dipole mode of the plasmon oscillation of the nanoparticles. The peak energies in the experimental spectra of the nanoparticle could not be reproduced by the derived dielectric function of the Cs0.33WO3 crystal. On the basis of the EELS and annular dark-field scanning transmission electron microscopy observations, this inconsistent result was attributed to Cs atom deficiency in the surface region of the nanoparticles.

Fabrication of erbium-doped spherical-like ZnO hierarchical nanostructures with enhanced visible light-driven photocatalytic activity

Erbium-doped spherical-like ZnO hierarchical nanostructures (Er/ZnO) were newly synthesized via a facile and surfactant-free chemical solution route. Field emission scanning electron microscopy and transmission electron microscopy observations showed that the assemblies were composed of large amounts of interleaving nanosheets with the thickness of about 15nm. X-ray diffraction and energy dispersive X-ray results revealed that Er ion was successfully doped into ZnO. The Er doping increased the visible light absorption and a red shift appeared in UV–vis diffuse reflection spectra for Er/ZnO. Photoluminescence spectra showed that the improvement of visible emission in the Er/ZnO was a result of oxygen vacancy of defect increased by addition of Er in ZnO. The photocatalytic tests revealed that Er/ZnO was a new promising photocatalyst in remediation of water contaminated by organic pollutants under visible light irradiation.

Luminescent and magnetism properties of YPO4:Eu3+ octahedron microcrystals

The large-scale novel YPO4:Eu3+ octahedron microcrystals have been synthesized successfully under a facile hydrothermal condition. Field emission scanning electron microscopy and transmission electron microscopy observations indicate that the obtained YPO4:Eu3+ octahedron microcrystals have a diameter of about 1–2μm with smooth surface. The luminescent properties with three main emission bands centered at 582, 587 and 610nm indicate that the YPO4:Eu3+ octahedron microcrystals possess the 5D0–7F0, 5D0–7F1 and 5D0–7F2 transitions from Eu3+. The magnetism property of the synthetic YPO4:Eu3+ octahedron microcrystals is also investigated, and the room temperature ferromagnetism is observed.

Liposomes self-assembled from electrosprayed composite microparticles

Composite microparticles, consisting of polyvinylpyrrolidone (PVP), naproxen (NAP) and lecithin (PC), have been successfully prepared using an electrospraying process and exploited as templates to manipulate molecular self-assembly for the synthesis of liposomes in situ. Field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) observations demonstrate that the microparticles have an average diameter of 960 ± 140 nm and a homogeneous structure. X-ray diffraction (XRD) patterns, differential scanning calorimetry (DSC) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) results verify that the building blocks NAP and PC are scattered in the polymer matrix in a molecular way owing to the very fast drying of the electrospraying process and the favorable secondary interactions among the components. FESEM, scanning probe microscope (SPM) and TEM observations demonstrate that the liposomes can be achieved through molecular self-assembly in situ when the microparticles contact water thanks to ‘like prefers like’ and by means of the confinement effect of the microparticles. The liposomes have an encapsulation rate of 91.3%, and 80.7% of the drug in the liposomes can be freed into the dissolution medium in a sustained way and by a diffusion mechanism over a period of 24 h. The developed strategy not only provides a new, facile, and effective method to assemble and organize molecules of multiple components into liposomes with electrosprayed microparticles as templates, but also opens a new avenue for nanofabrication in a step-by-step and controllable way.

Sulfonated poly(ether sulfone ether ketone ketone)/sulfonated poly(ether sulfone) blend membranes with reduced methanol permeability

Proton exchange membranes were prepared by blending sulfonated poly(ether sulfone ether ketone ketone) (SPESEKK) with sulfonated poly(ether sulfone) (SPES). The morphology, tensile strength, proton conductivity and methanol permeability of the blend membranes were investigated. The scanning electron microscope and transmission electron microscope observation indicates the good dispersion of the SPES in SPESEKK polymer matrix. The addition of SPES also enhances the tensile strength of the SPESEKK membrane. The blend membrane shows lower methanol diffusivity and higher proton conductivity with comparison to the pure SPESEKK membrane, ascribing to the inhabitation of the player SPES to methanol permeation and facilitation of the increment of sulfonic acid groups to the proton transport. The SPESEKK/SPES 5 : 5 membrane exhibits an appreciable tensile strength of 52.3 MPa and a reduced methanol permeability of 6.6 × 10−7 cm2 s−1. This SPESEKK/SPES composite membrane shows a potential feasibility as a promising electrolyte for direct methanol fuel cells.