TEM Analysis of Long-Period Polytypes in SiC—S

Author(s):  
S. Shinozaki ◽  
J. W. Sprys

In reaction sintered SiC (∽ 5um average grain size), about 15% of the grains were found to have long-period structures, which were identifiable by transmission electron microscopy (TEM). In order to investigate the stability of the long-period polytypes at high temperature, crystal structures as well as microstructural changes in the long-period polytypes were analyzed as a function of time in isothermal annealing.Each polytype was analyzed by two methods: (1) Electron diffraction, and (2) Electron micrograph analysis. Fig. 1 shows microdensitometer traces of ED patterns (continuous curves) and calculated intensities (vertical lines) along 10.l row for 6H and 84R (Ramsdell notation). Intensity distributions were calculated based on the Zhdanov notation of (33) for 6H and [ (33)3 (32)2 ]3 for 84R. Because of the dynamical effect in electron diffraction, the observed intensities do not exactly coincide with those intensities obtained by structure factor calculations. Fig. 2 shows the high resolution TEM micrographs, where the striped patterns correspond to direct resolution of the structural lattice periodicities of 6H and 84R structures and the spacings shown in the figures are as expected for those structures.

2013 ◽  
Vol 745-746 ◽  
pp. 551-554 ◽  
Author(s):  
Ming Hui Wang ◽  
Hua Jian Li ◽  
Wan Jiang

TiB2/TiN nanocomposites were in-situ fabricated by spark plasma sintering (SPS) technique using Ti and BN powders as starting materials. The phase constituents and microstructures of the samples were analyzed by X-ray diffraction (XRD) techniques, scanning electron microscopy (SEM) and transmission electron microscope (TEM), respectively. The results showed that the average grain size of TiB2 and TiN was 1m and 300nm respectively. Furthermore, high resolution TEM analysis indicated that the as-prepared TiB2/TiN nanocomposites had very clean grain boundaries, and no amorphous phase or oxide layer was observed.


Nanomaterials ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1485 ◽  
Author(s):  
Marta Rubio-Camacho ◽  
Yolanda Alacid ◽  
Ricardo Mallavia ◽  
María José Martínez-Tomé ◽  
C. Reyes Mateo

Multifunctional nanoparticles have been attracting growing attention in recent years because of their capability to integrate materials with different features in one entity, which leads them to be considered as the next generation of nanomedicine. In this work, we have taken advantage of the interesting properties of conjugated polyelectrolytes to develop multicolor fluorescent nanoparticles with integrating imaging and therapeutic functionalities. With this end, thermosensitive liposomes were coated with three recently synthesized polyfluorenes: copoly-((9,9-bis(6′-N,N,N-trimethylammonium)hexyl)-2,7-(fluorene)-alt-1,4-(phenylene)) bromide (HTMA-PFP), copoly-((9,9-bis(6′-N,N,N-trimethylammonium)hexyl)-2,7-(fluorene)-alt-4,7-(2- (phenyl)benzo(d) (1,2,3) triazole)) bromide (HTMA-PFBT) and copoly-((9,9-bis(6′-N,N,N- trimethylammonium)hexyl)-2,7-(fluorene)-alt-1,4-(naphtho(2,3c)-1,2,5-thiadiazole)) bromide (HTMA-PFNT), in order to obtain blue, green and red fluorescent drug carriers, respectively. The stability, size and morphology of the nanoparticles, as well as their thermotropic behavior and photophysical properties, have been characterized by Dynamic Light Scattering (DLS), Zeta Potential, transmission electron microscope (TEM) analysis and fluorescence spectroscopy. In addition, the suitability of the nanostructures to carry and release their contents when triggered by hyperthermia has been explored by using carboxyfluorescein as a hydrophilic drug model. Finally, preliminary experiments with mammalian cells demonstrate the capability of the nanoparticles to mark and visualize cells with different colors, evidencing their potential use for imaging and therapeutic applications.


2014 ◽  
Vol 917 ◽  
pp. 3-9
Author(s):  
Muhammad Ayoub ◽  
Ahmad Zuhairi Abdullah

Mesoporous material SBA-15 was synthesized using P123 and TEMOS as the templates. Lithium in the form of LiOH was loaded over a previously prepared SBA-15. The basic strength of the prepared samples of SBA-15 was found to increase but the mesoporous structure was severely destroyed. The mesoporous structure of the prepared SBA-15 was retained after coating it with 30 wt. % magnesium prior to LiOH loading. The stability of mesoporous structure was strongly influenced by the extent of magnesium coating. It was also noted that this structure was also affected by LiOH loading and significantly destroyed structure when magnesium coating value exceeded 20 %. These samples were thoroughly characterized for their surface area, pore volume, pore size, basic strength, SAXRD patterns and transmission electron microscopic (TEM) analysis.


2009 ◽  
Vol 1184 ◽  
Author(s):  
Peter Moeck ◽  
Sergei Rouvimov ◽  
Edgar Rauch ◽  
Stavros Nicolopoulos

AbstractStrategies for the structurally identification of nanocrystals from Precession Electron Diffraction (PED) patterns in a Transmission Electron Microscope (TEM) are outlined. A single-crystal PED pattern may be utilized for the structural identification of an individual nanocrystal. Ensembles of nanocrystals may be fingerprinted structurally from “powder PED patterns”. Highly reliable “crystal orientation & structure” maps may be obtained from automatically recorded and processed scanning-PED patterns at spatial resolutions that are superior to those of the competing electron backscattering diffraction technique of scanning electron microscopy. The analysis procedure of that automated technique has recently been extended to Fourier transforms of high resolution TEM images, resulting in similarly effective mappings. Open-access crystallographic databases are mentioned as they may be utilized in support of our structural fingerprinting strategies.


1995 ◽  
Vol 398 ◽  
Author(s):  
W. Sinkler ◽  
C. Michaelsen ◽  
R. Bormann

ABSTRACTInverse melting of bcc Nb4sCr55 is investigated using transmission electron microscopy, high-resolution TEM and electron diffraction. It is shown that the transformation to the amorphous phase initiates at the bcc grain boundaries. The transformation results in an increase in incoherence, evidenced by a loss of bend contours. Some anisotropy is found in the amorphous phase produced by inverse melting, which is associated in HRTEM with preferentially oriented but discontinuous and distorted fringes. The results are consistent with the production of an amorphous phase by inverse melting.


2013 ◽  
Vol 19 (6) ◽  
pp. 1575-1580 ◽  
Author(s):  
Xiaohong Shao ◽  
Huajie Yang ◽  
Jeff T.M. De Hosson ◽  
Xiuliang Ma

AbstractTransmission electron microscopy characterization of two major long-period stacking ordered (LPSO) phases in Mg–Zn–Y alloy, i.e., 18R- and 14H-LPSO are reported. The space group and atomic-scale microstructures of both compounds were determined using a combination of electron diffraction, convergent beam electron diffraction, high-resolution transmission electron microscopy, and Z-contrast scanning transmission electron microscopy. The 18R-LPSO phase is demonstrated to have a point group and space group 3m and R3m (or 3m and R3m), with the lattice parameter a = 1.112 nm and c = 4.689 nm in a hexagonal coordinate system. The 14H-LPSO phase has a point group 6/mmm and a space group P63 /mmc, and the lattice parameter is a = 1.112 nm and c = 3.647 nm. In addition, insertion of extra thin Mg platelets of several atomic layers, results in stacking faults in the LPSO phase. These results may shed some new light on a better understanding of the microstructure and deformation mechanisms of LPSO phases in Mg alloys.


1993 ◽  
Vol 317 ◽  
Author(s):  
Rajiv Ahuja ◽  
Hamish L. Fraser

ABSTRACTThis paper presents the results of a detailed study of titanium - aluminum thin film multilayers fabricated using UHV Magnetron sputtering. Transmission electron Microscopy (TEM) techniques have been used to characterize the structure of these multilayers and to study the various structural transitions as a function of the composition modulation wavelength (CMW). Evidence is presented which indicates the existence of a titanium based fcc structure in these films, below a critical CMW. At even smaller values of CMW, both the Ti and Al layers adopt the hep structure and are coherent with each other. The evolution of thin film microstructure has been studied using high resolution TEM (HRTEM) and an attempt is made to rationalize the stability of different phases based on the energetics of atomic stacking.


2018 ◽  
Vol 5 (11) ◽  
pp. 2836-2855 ◽  
Author(s):  
W. Wan ◽  
J. Su ◽  
X. D. Zou ◽  
T. Willhammar

This review presents various TEM techniques including electron diffraction, high-resolution TEM and scanning TEM imaging, and electron tomography and their applications for structure characterization of zeolite materials.


1999 ◽  
Vol 595 ◽  
Author(s):  
J.H. Mazur ◽  
M. Benamara ◽  
Z. Liliental-Weber ◽  
W. Swider ◽  
J. Washburn ◽  
...  

AbstractAlxGa1−xN {x=30% (doped and undoped), 45% (doped)} thin films were grown by MOCVD on ∼2 µm thick GaN layer using Al2O3 substrate. These films were designed to be the active parts of HFETs with nsí product of about 1016(Vs)−1. The layers were then studied by means of transmission electron microscopy (TEM) techniques. In this paper, it is shown that the AlxGa1−xN layer thickness was non-uniform due to the presence of Vshaped defects within the AlxGa1−xN films. The nucleation of these V-shaped defects has taken place about 20 nm above the AlxGa1−xN/aN interface. Many of these Vshaped defects were associated with the presence of the threading dislocations propagating from the GaN/Al2O3 interface. We show that the density of these V-shaped defects increases with the doping level and also with the Al mole fraction in the films. The formation mechanism of the V-shaped defects seems to be related to the concentration of dopants or other impurities at the ledges of the growing film. This suggestion is supported by high resolution TEM analysis. The growth front between the V-shaped defects in the lower Al concentration thin films was planar as compared with F99W3.77 the three-dimensional growth in the doped, higher Al concentration film. This interpretation of the origin of the V-shaped defects is consistent with the observed lowering of the Schottky barrier height in n-doped AlGaN/Ni Schottky diodes.


2002 ◽  
Vol 754 ◽  
Author(s):  
J.L. Soubeyroux ◽  
J.M. Pelletier ◽  
B. Van de Moortèle ◽  
T. Epicier

ABSTRACTThe formation of the primary crystals appearing during isothermal annealing of the Zr46.8Ti8.2Cu7.5Ni10Be27.5 (Vit4) bulk metallic glasses has been studied by in-situ neutron diffraction, DSC, high resolution TEM and electron diffraction. We have evidenced that the primary phase appearing on the isothermal plateau at 620 K is quasicrystalline and is beryllium free. Moreover, we have prepared an alloy with the composition determined by EDX (without beryllium), and studied the formation of quasicrystals in this alloy. A comparison is done between the quasicrystalline phases appearing during the annealing of Vit4 and the quasicrystals prepared without beryllium in an amorphous alloy prepared by melt spinning. In particular they have the same intensities and peak positions in the diffraction studies.


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