scholarly journals Fabrication and Characteristics of Yb-Doped Silica Fibers Produced by the Sol-Gel Based Granulated Silica Method

Fibers ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 82 ◽  
Author(s):  
Ali El Sayed ◽  
Soenke Pilz ◽  
Hossein Najafi ◽  
Duncan Alexander ◽  
Martin Hochstrasser ◽  
...  
Keyword(s):  
Significant Contribution ◽  
Transmission Loss ◽  
Sol Gel ◽  
Fiber Material ◽  
Fiber Properties ◽  
Silica Fibers ◽  
Transmission Electron ◽  
Excess Concentration ◽  
Scanning Transmission ◽  
High Degree

Combining the sol-gel method for fiber material production with the granulated silica method for preform assembly results in a robust method that offers a high degree of freedom regarding both the composition and the geometry of the produced fiber. Using this method, two types of Yb-doped silica glass composition, that feature an excess in P concentration with respect to Al, have been prepared. The elemental distributions in a fiber core were analyzed by scanning transmission electron microscopy (STEM). The elemental mapping shows a similar localization of Al, P and Yb through the microstructure. In addition, the influence of the variation in the co-dopant concentration, with respect to Yb, on the fiber properties has been investigated. The results show an increase in the refractive index step and in the fiber’s transmission loss as the excess concentration of P increases. A significant contribution to the losses can be assigned to the existence of impurities such as iron, which was detected in our samples by mass spectrometer. Single exponential fluorescence decays with lifetimes of around 0.88 ms were measured for the two compositions. Finally, pumping at 976 nm a laser slope efficiency of 67% at 1031 nm was achieved for one of the fiber compositions.

A Transmission Electron Microscopy Study of CoFe2O4 Ferrite Nanoparticles in Silica Aerogel Matrix Using HREM and STEM Imaging and EDX Spectroscopy and EELS

2010 ◽  
Vol 16 (2) ◽  
pp. 200-209 ◽  
Author(s):  
Andrea Falqui ◽  
Anna Corrias ◽  
Peng Wang ◽  
Etienne Snoeck ◽  
Gavin Mountjoy
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Silica Aerogel ◽  
Sol Gel ◽  
Interlayer Spacing ◽  
Microscopy Study ◽  
Nanocomposite Materials ◽  
Electron Microscopy Study ◽  
Transmission Electron ◽  
Scanning Transmission

AbstractMagnetic nanocomposite materials consisting of 5 and 10 wt% CoFe2O4 nanoparticles in a silica aerogel matrix have been synthesized by the sol-gel method. For the CoFe2O4-10wt% sample, bright-field scanning transmission electron microscopy (BF STEM) and high-resolution transmission electron microscopy (HREM) images showed distinct, rounded CoFe2O4 nanoparticles, with typical diameters of roughly 8 nm. For the CoFe2O4-5wt% sample, BF STEM images and energy dispersive X-ray (EDX) measurements showed CoFe2O4 nanoparticles with diameters of roughly 3 ± 1 nm. EDX measurements indicate that all nanoparticles consist of stoichiometric CoFe2O4, and electron energy-loss spectroscopy measurements from lines crossing nanoparticles in the CoFe2O4-10wt% sample show a uniform composition within nanoparticles, with a precision of at best than ±0.5 nm in analysis position. BF STEM images obtained for the CoFe2O4-10wt% sample showed many “needle-like” nanostructures that typically have a length of ∼10 nm and a width of ∼1 nm, and frequently appear to be attached to nanoparticles. These needle-like nanostructures are observed to contain layers with interlayer spacing 0.33 ± 0.1 nm, which could be consistent with Co silicate hydroxide, a known precursor phase in these nanocomposite materials.

scholarly journals Obtaining and Characterization of TiO2-GO Composites for Photocatalytic Applications

2020 ◽  
Vol 2020 ◽  
pp. 1-9 ◽  
Author(s):  
D. K. Calvo Ramos ◽  
M. Vega González ◽  
R. A. Esparza Muñóz ◽  
J. Santos Cruz ◽  
F. J. De Moure-Flores ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Uv Radiation ◽  
Uv Light ◽  
Sol Gel ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission

Titanium dioxide (TD) and graphene oxide (GO) were synthesized by sol-gel and improved Hummers method, respectively. This study shows the results of the incorporation through four different conditions (sol-gel, sol-gel and ultrasonic, annealed, and UV radiation, C1 to C4, respectively). It was observed that a homogeneous incorporation of TD on sheets of GO was obtained satisfactorily. The composites of TiO2/GO were characterized using different techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS), Raman spectroscopy, and infrared spectroscopy (IR). The photocatalytic activity of the composites was determined from the degradation of the dye azo tartrazine using UV and solar radiation. The best incorporation of TD nanoparticles on GO was obtained with condition C3 (thermal incorporation method) at a temperature of 65°C. This shows a uniformity in the size and shape of the TD as well as an excellent adherence to the sheet of GO. This addition is accomplished by ionic bonding in the presence of electrostatic Coulomb forces. The C3 composite degraded the tartrazine dye using UV radiation and sunlight. With the latter, the degradation time was three times faster than using UV light.

Structural and Chemical Characterization of Yb2O3-ZrO2 System by HAADF-STEM and HRTEM

2009 ◽  
Vol 15 (1) ◽  
pp. 46-53 ◽  
Author(s):  
C. Angeles-Chavez ◽  
P. Salas ◽  
L.A. Díaz-Torres ◽  
E. de la Rosa ◽  
R. Esparza ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Crystalline Structure ◽  
Sol Gel ◽  
Tetragonal Zirconia ◽  
Chemical Characterization ◽  
Dark Field ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission

AbstractZrO2:Yb3+ nanocrystalline phosphors with high concentrations of ytterbium ions were prepared using the sol-gel method. X-ray diffraction, high-angle annular-dark-field scanning transmission electron microscopy (HAADF-STEM), energy dispersive X-ray spectroscopy, and high-resolution transmission electron microscopy (HRTEM) were used to characterize the nanocrystalline phosphors annealed at 1000°C. Unit-cell distortion and changes in the crystalline structure of the monoclinic zirconia to tetragonal zirconia, and subsequently cubic zirconia, were observed with increased Yb concentration. Yb ions were randomly distributed into the lattice of the crystalline structure. No segregation of Yb2O3 phase was observed. The substitution of Zr atoms by Yb atoms on different crystalline phases was confirmed by the experimental results and theoretical simulations of HRTEM and HAADF-STEM.

Template-Assisted Fabrication of Double-Shelled Nanotubes Composed of Inner Shell Pb(Zr0.52Ti0.48)O3 and Outer Shell TiO2 by Sol-Gel Process with Spin-Coating Technique

2011 ◽  
Vol 1292 ◽  
Author(s):  
Y. C. Choi ◽  
S. Y. Cho ◽  
S. D. Bu
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Spin Coating ◽  
Sol Gel ◽  
Outer Shell ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Sol Gel Process ◽  
Scanning Transmission ◽  
Diffraction Patterns

ABSTRACTDouble-shelled nanotubes composed of inner shell Pb(Zr0.52Ti0.48)O3 (PZT) and outer shell TiO2 are successfully fabricated by a spin coating of each sol-gel solution on porous anodic alumina template. Field emission transmission electron microscopy images show that they have a ~ 10 nm wall thickness. The selected area electron diffraction patterns show that they have two mixed crystalline phases of tetragonal PZT and anatase TiO2. The analyses of scanning transmission electron microscopy equipped with energy dispersive X-ray spectroscopy confirm their uniform distribution of each element.

Electron Microscopy Studies and Image Simulation of the YBa2Cu3O7−x/ BaF2 Interface

1994 ◽  
Vol 357 ◽  
Author(s):  
J. L. Lee ◽  
J. Silcox
Keyword(s):  
Significant Contribution ◽  
Wide Band ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Interface Plane ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Contrast Mechanism ◽  
Annular Dark Field ◽  
Z Contrast

AbstractImages of the YBa2Cu3OT7−x (YBCO) / BaF2 interface obtained with a scanning transmission electron microscope (STEM) show a relatively wide (∼40 Å) band of contrast at the interface, despite attempts to orient the interface plane parallel to the beam. Simulation of STEM annular dark field (ADF) images of several different interface geometries suggests that strain is the dominant cause of this wide band of contrast at the interface. In particular, it is the dislocations which run normal to the beam direction which make a significant contribution to the width of the contrast band in the case of this YBCO / BaF2 interface. A line scan taken across the interface using energy dispersive X-ray spectrometry (EDX) suggests that there is no significant Ba concentration at the interface, indicating that Z-contrast is not the primary contrast mechanism in these ADF images of the YBCO / BaF2 interface.

scholarly journals Fundamental material property trends in the La0.8-xNdxCa0.2FeO3-δ series: crystal structure and thermal expansion

2021 ◽  
Author(s):  
Christian Berger ◽  
Edith Bucher ◽  
Judith Lammer ◽  
Christina Nader ◽  
Werner Sitte
Keyword(s):  
Thermal Expansion ◽  
Sol Gel ◽  
Rietveld Analysis ◽  
Homogeneous Distribution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Thermal Expansion Coefficients ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
A Site

AbstractCompounds from the series La0.8-xNdxCa0.2FeO3-δ (0.1 ≤ x ≤ 0.7) were synthesised by a sol–gel route. X-ray diffraction and Rietveld analysis showed that materials with 0 ≤ x ≤ 0.6 crystallize as single-phase orthorhombic perovskites. The smaller ionic radius of Nd3+ compared to La3+ leads to a decrease in unit cell volume with increasing x. Elemental mapping by high-resolution scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy confirms the homogeneous distribution of the A-site elements (La, Nd and Ca) in the perovskite (ABO3) lattice. The thermal expansion behaviour of La0.8-xNdxCa0.2FeO3-δ (0 ≤ x ≤ 0.6) was characterized by dilatometry at 30 ≤ T/°C ≤ 1000 and 1 × 10–3 ≤ pO2/bar ≤ 1. The thermal expansion coefficients of La0.8-xNdxCa0.2FeO3-δ, which were determined in regions I (40–530 °C) and II (530–990 °C), respectively, are almost independent of the Nd concentration in the range of (0 ≤ x ≤ 0.6) and increase slightly with decreasing pO2. The transition from orthorhombic to trigonal modification, which is observed for La0.8Ca0.2FeO3-δ at approx. 740 °C, is suppressed for all Nd-substituted compounds with x ≥ 0.1.

scholarly journals Facile fabrication of mesostructured natural rubber/silica nanocomposites with enhanced thermal stability and hydrophobicity

2019 ◽  
Vol 14 (1) ◽  
Author(s):  
Supphathee Chaowamalee ◽  
Chawalit Ngamcharussrivichai
Keyword(s):  
Natural Rubber ◽  
Photoelectron Spectroscopy ◽  
Self Assembly ◽  
Sol Gel ◽  
X Ray ◽  
Silica Nanocomposites ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Silica Wall ◽  
Adsorption Desorption

AbstractNatural rubber (NR)/hexagonal mesoporous silica (HMS) nanocomposites (NRHMS) with enhanced thermal and hydrophobic properties were facilely prepared via in situ sol–gel formation with pH adjustment using a low sulphuric acid (H2SO4) acid concentration. The effect of the amount of 0.5 M H2SO4 (2.5–10 g) added into the pre-synthesis mixture on the physicochemical properties of the obtained NRHMS nanocomposites was investigated. With a small addition of H2SO4 solution, the fabricated NRHMS nanocomposite possessed an improved wormhole-like mesostructure arrangement with a thicker silica wall, which retarded the thermal decomposition of the NR phase, as deduced from the auto-oxidation of NR by thermogravimetric analysis. The H2O adsorption–desorption measurement revealed an increased hydrophobicity of the NRHMS composites, explained by the acid-catalyzed bridging of free silanol groups to siloxane bonds, which was supported by the X-ray photoelectron spectroscopy analysis. Scanning transmission electron microscopy with energy dispersive X-ray spectroscopy elemental mapping revealed a good dispersion of the NR phase within the mesostructured silica. However, a high amount of added H2SO4 solution led to silica–NR phase separation due to the decreased hydrophobic interaction between the silica precursor and rubber chain, as well as an agglomeration of the NR phase itself. The mechanism of NRHMS nanocomposite formation under pH-controlled conditions was proposed to proceed via a cooperative self-assembly route.

scholarly journals Direct Observation of Cationic Ordering in Double Perovskite Sr2FeReO6 Crystals

2013 ◽  
Vol 19 (S5) ◽  
pp. 25-28 ◽  
Author(s):  
Si-Young Choi ◽  
Jong Bong Lim ◽  
Yuichi Ikuhara ◽  
Danilo Suvorov ◽  
Jae-Ho Jeon
Keyword(s):  
Scanning Transmission Electron Microscopy ◽  
Double Perovskite ◽  
Antiphase Boundary ◽  
Dark Field ◽  
High Angle ◽  
The Poor ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
High Degree

AbstractTwo kinds of Sr2FeReO6 (SFRO) samples, pristine SFRO and Re-excess SFRO, were prepared and we visualized the local atomic structure in terms of cationic ordering in the prepared SFRO samples via high-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM). HAADF-STEM results demonstrated the high degree of cationic ordering maintains in both the pristine SFRO and Re-excess SFRO samples. On the other hand, defective structures such as antiphase boundary and Re-deficient phase were observed dominantly in the pristine SFRO, and thus the poor magnetic property in the pristine SFRO is attributed to those defective structures related with the frustrated Fe/Re ordering.

The High Resolution Scanning Transmission Electron Microscope

1974 ◽  
Vol 32 ◽  
pp. 316-317
Author(s):  
A. V. Crewe
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
High Vacuum ◽  
Scanning Transmission Electron Microscope ◽  
Ultra High Vacuum ◽  
Resolving Power ◽  
Imaging Characteristics ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
The Moment

The high resolution STEM is now a fact of life. I think that we have, in the last few years, demonstrated that this instrument is capable of the same resolving power as a CEM but is sufficiently different in its imaging characteristics to offer some real advantages.It seems possible to prove in a quite general way that only a field emission source can give adequate intensity for the highest resolution^ and at the moment this means operating at ultra high vacuum levels. Our experience, however, is that neither the source nor the vacuum are difficult to manage and indeed are simpler than many other systems and substantially trouble-free.

Resolution Attainable With the Present Day STEM

1973 ◽  
Vol 31 ◽  
pp. 230-231 ◽  
Author(s):  
J. S. Wall ◽  
J. P. Langmore ◽  
H. Isaacson ◽  
A. V. Crewe
Keyword(s):  
Spherical Aberration ◽  
Focal Length ◽  
Incident Beam ◽  
Scanning Transmission Electron Microscope ◽  
Aperture Size ◽  
Magnetic Lens ◽  
Peak Intensity ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Half Angle

The scanning transmission electron microscope (STEM) constructed by the authors employs a field emission gun and a 1.15 mm focal length magnetic lens to produce a probe on the specimen. The aperture size is chosen to allow one wavelength of spherical aberration at the edge of the objective aperture. Under these conditions the profile of the focused spot is expected to be similar to an Airy intensity distribution with the first zero at the same point but with a peak intensity 80 per cent of that which would be obtained If the lens had no aberration. This condition is attained when the half angle that the incident beam subtends at the specimen, 𝛂 = (4𝛌/Cs)¼

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