scholarly journals The role of curvature in silica mesoporous crystals

2012 ◽  
Vol 2 (5) ◽  
pp. 634-644 ◽  
Author(s):  
Keiichi Miyasaka ◽  
Alfonso Garcia Bennett ◽  
Lu Han ◽  
Yu Han ◽  
Changhong Xiao ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Liquid Crystal ◽  
Biological Membrane ◽  
Porous Silica ◽  
Mesoporous Structure ◽  
Synthesis Conditions ◽  
Interface Curvature ◽  
Silica Wall

Silica mesoporous crystals (SMCs) offer a unique opportunity to study micellar mesophases. Replication of non-equilibrium mesophases into porous silica structures allows the characterization of surfactant phases under a variety of chemical and physical perturbations, through methods not typically accessible to liquid crystal chemists. A poignant example is the use of electron microscopy and crystallography, as discussed herein, for the purpose of determining the fundamental role of amphiphile curvature, namely mean curvature and Gaussian curvature, which have been extensively studied in various fields such as polymer, liquid crystal, biological membrane, etc. The present work aims to highlight some current studies devoted to the interface curvature on SMCs, in which electron microscopy and electron crystallography (EC) are used to understand the geometry of silica wall surface in bicontinuous and cage-type mesostructures through the investigation of electrostatic potential maps. Additionally, we show that by altering the synthesis conditions during the preparation of SMCs, it is possible to isolate particles during micellar mesophase transformations in the cubic bicontinuous system, allowing us to view and study epitaxial relations under the specific synthesis conditions. By studying the relationship between mesoporous structure, interface curvature and micellar mesophases using electron microscopy and EC, we hope to bring new insights into the formation mechanism of these unique materials but also contribute a new way of understanding periodic liquid crystal systems.

Electron Microscope Characterization of Pulse Annealed Semiconductors

1980 ◽  
Vol 2 ◽  
Author(s):  
A. G. CULLIS
Keyword(s):  
Electron Microscopy ◽  
Defect Structure ◽  
Device Fabrication ◽  
Fabrication Technology ◽  
The Past ◽  
Semiconductor Structures ◽  
Pulse Processing ◽  
Processing Techniques

ABSTRACTThe pulse processing techniques that have assumed prominence over the past few years offer various important advantages for device fabrication technology. However, the usefulness of each individual method depends substantially upon the specific annealing mechanism involved. This article demonstrates the role of electron microscopy in elucidating such mechanisms and in analysing annealed semiconductor structures of importance to both research workers and semiconductor technologists. The range of laser and electron beam pulse annealing methods is covered and defect structure transitions observed are related to the solid and liquid phase processes occurring. Characteristic impurity trapping and segregation phenomena are described.

Laser investigations on the role of cholesterol in some liquid crystal biological membrane models

2002 ◽  
Author(s):  
Mihaela A. Ghelmez ◽  
Elena Slavnicu ◽  
Bogdan Dumitru ◽  
Andreea-Rodica P. Sterian ◽  
C. Molnar ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Biological Membrane ◽  
Membrane Models

Synthesis and Characterization of Flower-Like Hematite Nanostructures

2011 ◽  
Vol 287-290 ◽  
pp. 169-172
Author(s):  
Hong Wang ◽  
Xi Yang He ◽  
Ying Wang
Keyword(s):  
Electron Microscopy ◽  
Average Length ◽  
Critical Role ◽  
Average Diameter ◽  
Synthesis And Characterization ◽  
Hydrothermal Route ◽  
X Ray ◽  
Scanning Electron

The flower-like α-Fe2O3superstructures were fabricated by a novel hydrothermal route and sequential annealing at 600 °C for 1 h using FeCl3×6H2O as the starting precursor. The structures and morphologies of the synthesized flower-like superstructures have been characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM). It is revealed that the flower-like α-Fe2O3nanostructures consist of nanorods with the average diameter of about 70 nm and an average length of about 200nm growing from the centers. The critical role of urea in the hydrothermal synthesis of the flower-like nanostructures is discussed.

scholarly journals Colloidal Cu2ZnSnS4-based and Ag-doped Nanocrystals: Synthesis and Raman Spectroscopy Study

2021 ◽  
Vol 22 (2) ◽  
pp. 260-268
Author(s):  
V. Dzhagan ◽  
O. Kapush ◽  
S. Budzulyak ◽  
N. Mazur ◽  
E. Gavryliuk ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Structural Characterization ◽  
Critical Role ◽  
Partial Substitution ◽  
Optical Absorption Spectroscopy ◽  
Synthesis Conditions ◽  
Synthetic Routes ◽  
New Generation

Cu2ZnSnS4 (CZTS) is one of the promising materials for absorber layers of new-generation thin film solar cells. Various synthetic routes of materials preparation and structural characterization have been explored so far. Further tuning of the CZTS properties is realized via partial substitution of the cations. Here we have used an affordable and scalable method of synthesizing colloidal CZTS nanocrystals (NC) in an aqueous solution. Variation of the synthesis parameters, in particular pH of the solution, was employed to improve the crystallinity of the NCs. Furthermore, CZTS NCs with partial substitution of Cu for Ag were also successfully synthesized. Raman spectroscopy was employed as a prime tool of structural characterization of the NCs obtained, along with optical absorption spectroscopy and ab initio DFT lattice dynamics calculations. An experimentally observed slight upward shift of the main phonon Raman peak upon increase of the Ag content in (AgxCu1-x)2ZnSnS4 NCs is in agreement with the trend predicted by DFT calculation. No pure Ag2ZnSnS4 NCs could be formed, indicating a critical role of Cu in forming the kesterite structure NCs under given synthesis conditions in an aqueous medium.

Structural Characterization of Molecular Beam Epitaxy Grown GaInNAs and GaInNAsSb Quantum Wells by Transmission Electron Microscopy

2004 ◽  
Vol 817 ◽  
Author(s):  
Tihomir Gugov ◽  
Mark Wistey ◽  
Homan Yuen ◽  
Seth Bank ◽  
James S. Harris
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Quantum Wells ◽  
Phase Segregation ◽  
Dark Field ◽  
Lower Growth ◽  
Transmission Electron ◽  
Material Uniformity

AbstractIn the past decade, the quaternary GaInNAs alloy has emerged as a very promising material for lasers in the 1.2-1.6 μm range with application in telecommunication fiber-optic networks. While most of the challenges in growing high quality laser material with emission wavelength out to 1.3 μm have been successfully resolved, extending the emission beyond 1.3 μm has proven to be quite difficult. Achieving emission out to 1.5 μm requires higher In (up to 40%) and N (up to 2%) compositions. This makes the growth of this thermodynamically unstable alloy quite difficult with phase segregation occurring even at lower growth temperatures. Recently, adding small amounts of antimony has dramatically improved the quality of the material and high luminescence has been demonstrated at wavelengths beyond 1.5 μm. In this study, high-resolution transmission electron microscopy (HRTEM) was used in a novel way in conjunction with dark-field (DF) TEM to elucidate the role of antimony in improving the material quality. The results show that antimony improves the material uniformity via reduction of the local compositional fluctuations of indium.

scholarly journals Growth and Characterization of Ni Nano-Micro Structures in the Presence of Ethylenediamine

Crystals ◽  
2018 ◽  
Vol 8 (11) ◽  
pp. 397 ◽  
Author(s):  
Lingxiao Chen ◽  
Hang Liu ◽  
Linghao Liu ◽  
Yifan Zheng ◽  
Haodong Tang ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Alkaline Conditions ◽  
Naoh Solution ◽  
Micro Structures ◽  
Scanning Electron

Ni nano-micro structures have been synthesized via a solution reduction route in the presence of ethylenediamine (EDA) under strong alkaline conditions. The phase composition, morphology, and microstructure of the resulting products are investigated by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The presence of EDA plays an important role in the formation of Ni nano-micro structures, and microflowers or microspheres assembled from nanosized horns can be produced by changing the amount of EDA. The size of Ni nano-micro structures is dependent on the NaOH concentration, and long chains assembled from Ni nano-micro structured microspheres can be obtained by reducing the amount of NaOH solution used. The role of both EDA and NaOH in the reduction of Ni (II) to Ni, as well as in the growth of Ni nano-micro structures, has been discussed, and a possible formation mechanism of these Ni nano-micro structures has been proposed based on the experimental results.

Synthesis and Characterization of CdSe Microspheres via Solvothermal Process

2010 ◽  
Vol 654-656 ◽  
pp. 1142-1145
Author(s):  
Juan Yang ◽  
Chuang Liang Zang ◽  
Xiao Nong Cheng
Keyword(s):  
Electron Microscopy ◽  
Heat Treating ◽  
Reducing Agent ◽  
Wurtzite Structure ◽  
Mixed Solution ◽  
X Ray Diffraction ◽  
Zinc Blende ◽  
Transmission Electron

CdSe particles with the wurtzite structure have been synthesized via solvothermal method using a mixed solution of triethylenetetramine (TETA) and de-ionized water (DIW) without adding a reducing agent. It was found that the ball-like CdSe precursor with the zinc-blende phase could be transformed to the wurtzite structure after heat-treating at 580 °C in Ar atmosphere and the obtained microspheres were composed of small CdSe particles. The experimental results were compared with that obtained without TETA and it was speculated that TETA in the mixed solution played a role of reducing agent and solvent. Both the as-prepared products and the annealed powders were systematically characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared absorbance spectroscopy (FTIR).

CHARACTERIZATION OF DIFFERENT REGIMES IN NONLINEAR LIQUID CRYSTAL MODELS

2012 ◽  
Vol 21 (03) ◽  
pp. 1250042 ◽  
Author(s):  
I. ORQUÍN-SERRANO ◽  
F. R. VILLATORO ◽  
A. FERRANDO ◽  
P. FERNÁNDEZ DE CÓRDOBA ◽  
H. MICHINEL
Keyword(s):  
Liquid Crystal ◽  
Liquid Crystals ◽  
Critical Role ◽  
Optical Power ◽  
Initial Position ◽  
Optical Field ◽  
Planar Cells ◽  
Nonlocal Nonlinear

The range of validity of two models for nonlocal nonlinear optics in Nematic Liquid Crystals (NLC) is studied. Particularly the influence of the optical power and the initial position of the beam over its trajectory is studied when launching the beam with an offset in a planar cell. The main difference between both models is the dependence of the orientational angle with the optical field, either linear or nonlinear. The results demonstrate the critical role of the nonlinearity in the propagation of nematicons in NLC planar cells.

scholarly journals Characterization of a ‘Bacteroidetes’ symbiont in Encarsia wasps (Hymenoptera: Aphelinidae): proposal of ‘Candidatus Cardinium hertigii’

2004 ◽  
Vol 54 (3) ◽  
pp. 961-968 ◽  
Author(s):  
Einat Zchori-Fein ◽  
Steve J. Perlman ◽  
Suzanne E. Kelly ◽  
Nurit Katzir ◽  
Martha S. Hunter
Keyword(s):  
Electron Microscopy ◽  
16S Rdna ◽  
Sequence Similarity ◽  
Phylogenetic Analyses ◽  
16S Rdna Sequence ◽  
Rdna Sequences ◽  
16S Rdna Sequences

Previously, analysis of 16S rDNA sequences placed a newly discovered lineage of bacterial symbionts of arthropods in the ‘Bacteroidetes’. This symbiont lineage is associated with a number of diverse host reproductive manipulations, including induction of parthenogenesis in several Encarsia parasitoid wasps (Hymenoptera: Aphelinidae). In this study, electron microscopy and phylogenetic analysis of the 16S rRNA and gyrB genes of symbionts from Encarsia hispida and Encarsia pergandiella are used to describe and further characterize these bacteria. Phylogenetic analyses based on these two genes showed that the Encarsia symbionts are allied with the Cytophaga aurantiaca lineage within the ‘Bacteroidetes’, with their closest described relative being the acanthamoeba symbiont ‘Candidatus Amoebophilus asiaticus’. The Encarsia symbionts share 97 % 16S rDNA sequence similarity with Brevipalpus mite and Ixodes tick symbionts and 88 % sequence similarity with ‘Candidatus A. asiaticus’. Electron microscopy revealed that many of the bacteria found in the ovaries of the two Encarsia species contained a regular, brush-like array of microfilament-like structures that appear to be characteristic of the symbiont. Finally, the role of this bacterium in parthenogenesis induction in E. hispida was confirmed. Based on phylogenetic analyses and electron microscopy, classification of the symbionts from Encarsia as ‘Candidatus Cardinium hertigii’ is proposed.

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