TEM Investigation of Arsenic Precipitates in Semi-Insulating GaAs

1991 ◽  
Vol 225 ◽  
Author(s):  
S. Yegnasubramanian ◽  
M. A. Shahid
Keyword(s):  
Electron Diffraction ◽  
Dislocation Density ◽  
Pattern Analysis ◽  
Vertical Gradient ◽  
Fine Particulates ◽  
Growth Technique ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Low Dislocation Density ◽  
Vertical Gradient Freeze

ABSTRACTThis paper presents a TEM investigation of undoped, semi-insulating GaAs crystals grown by the VGF (vertical gradient freeze) technique for microstructure and defects characterization. Energy dispersive X-ray spectrometry (EDS) and selected area electron diffraction (SAD) were used to characterize for composition and lattice spacings, respectively. TEM images of dislocations decorated with precipitate particles are presented. The particles were found to be arsenic rich. Regions of fine particulates were identified and a Moire pattern analysis was carried out. The occurrence of such defects in the low dislocation density VGF GaAs of the present study suggests that these are material related and not necessarily dependent on the growth technique.

Bimolecular and Monomolecular Lipid Films: Selected Area Electron Diffraction

1969 ◽  
Vol 27 ◽  
pp. 338-339
Author(s):  
Robert M. Glaeser ◽  
David W. Deamer
Keyword(s):  
Electron Diffraction ◽  
Membrane Structure ◽  
Molecular Organization ◽  
Membrane Material ◽  
X Ray Diffraction ◽  
Membrane Systems ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Lipid Films ◽  
Ultimate Objective

In the investigation of the molecular organization of cell membranes it is often supposed that lipid molecules are arranged in a bimolecular film. X-ray diffraction data obtained in a direction perpendicular to the plane of suitably layered membrane systems have generally been interpreted in accord with such a model of the membrane structure. The present studies were begun in order to determine whether selected area electron diffraction would provide a tool of sufficient sensitivity to permit investigation of the degree of intermolecular order within lipid films. The ultimate objective would then be to apply the method to single fragments of cell membrane material in order to obtain data complementary to the transverse data obtainable by x-ray diffraction.

The structure of amorphous and polycrystalline materials using energy-filtered RDF analysis

1992 ◽  
Vol 50 (2) ◽  
pp. 1190-1191
Author(s):  
David Cockayne ◽  
David McKenzie
Keyword(s):  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Density Function ◽  
Electron Diffraction Pattern ◽  
Polycrystalline Materials ◽  
Nearest Neighbour ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Reduced Density ◽  
System F

The technique of Electron Reduced Density Function (RDF) analysis has ben developed into a rapid analytical tool for the analysis of small volumes of amorphous or polycrystalline materials. The energy filtered electron diffraction pattern is collected to high scattering angles (currendy to s = 2 sinθ/λ = 6.5 Å-1) by scanning the selected area electron diffraction pattern across the entrance aperture to a GATAN parallel energy loss spectrometer. The diffraction pattern is then converted to a reduced density function, G(r), using mathematical procedures equivalent to those used in X-ray and neutron diffraction studies.Nearest neighbour distances accurate to 0.01 Å are obtained routinely, and bond distortions of molecules can be determined from the ratio of first to second nearest neighbour distances. The accuracy of coordination number determinations from polycrystalline monatomic materials (eg Pt) is high (5%). In amorphous systems (eg carbon, silicon) it is reasonable (10%), but in multi-element systems there are a number of problems to be overcome; to reduce the diffraction pattern to G(r), the approximation must be made that for all elements i,j in the system, fj(s) = Kji fi,(s) where Kji is independent of s.

Heteroepitaxy and Characterization of Low-Dislocation-Density GaN on Periodically Grooved Substrates

2000 ◽  
Vol 639 ◽  
Author(s):  
T. Detchprohm ◽  
M. Yano ◽  
R. Nakamura ◽  
S. Sano ◽  
S. Mochiduki ◽  
...  
Keyword(s):  
Dislocation Density ◽  
New Method ◽  
Growth Technique ◽  
New Approach ◽  
Density Area ◽  
Low Dislocation Density ◽  
Dislocation Densities ◽  
Movpe Growth

ABSTRACTWe have developed a new method to prepare low-dislocation-density GaN by using periodically grooved substrates in a conventional MOVPE growth technique. This new approach was demonstrated for GaN grown on periodically grooved α-Al2O3(0001), 6H-SiC(0001)Si and Si(111) substrates. Dislocation densities were 2×107 cm−2 in low-dislocation-density area.

HRTEM Investigation of Precipitates in Al-Zn-In-Mg-Ti-Ce Anode Alloy

2011 ◽  
Vol 189-193 ◽  
pp. 1036-1039
Author(s):  
Jing Ling Ma ◽  
Jiu Ba Wen ◽  
Yan Fu Yan
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Electron Diffraction ◽  
Hexagonal Structure ◽  
Orientation Relation ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Transmission Electron ◽  
Scanning Electron

The precipitates of Al-5Zn-0.02In-1Mg-0.05Ti-0.5Ce (wt %) anode alloy were studied by scanning electron microscopy, X-ray microanalysis, high resolution transmission electron microscopy and selected area electron diffraction analyses in the present work. The results show that the alloy mainly contains hexagonal structure MgZn2 and tetragonal structure Al2CeZn2 precipitates. From high resolution transmission electron microscopy and selected area electron diffraction, aluminium, Al2CeZn2 and MgZn2 phases have [0 1 -1]Al|| [1 -10]Al2CeZn2|| [-1 1 0 1]MgZn2orientation relation, and Al2CeZn2 and MgZn2 phases have the [0 2 -1]Al2CeZn2|| [0 1 -10]MgZn2orientation relation.

Comparison of Simulated and Experimental Order Parameters in FePt—II

2011 ◽  
Vol 17 (3) ◽  
pp. 403-409 ◽  
Author(s):  
Karen L. Torres ◽  
Richard R. Vanfleet ◽  
Gregory B. Thompson
Keyword(s):  
Electron Diffraction ◽  
Order Parameter ◽  
Convergent Beam Electron Diffraction ◽  
Order Parameters ◽  
X Ray Diffraction ◽  
Chemical Order ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Convergent Beam ◽  
Good Agreement

AbstractEight FePt thin film specimens of various thicknesses, compositions, and order parameters have been analyzed to determine the robustness and fidelity of multislice simulations in determining the chemical order parameter via electron diffraction (ED). The shape of the simulated curves depends significantly on the orientation and thickness of the specimen. The ED results are compared to kinematical scattering order parameters, from the same films, acquired from synchrotron X-ray diffraction (XRD). For the specimens analyzed with convergent beam electron diffraction conditions, the order parameter closely matched the order parameter as determined by the XRD methodology. However, the specimens analyzed by selected area electron diffraction conditions did not show good agreement. This has been attributed to substrate effects that hindered the ability to accurately quantify the intensity values of the superlattice and fundamental reflections.

X-ray diffraction with a four-reflection monochromator

1987 ◽  
Vol 20 (6) ◽  
pp. 522-528 ◽  
Author(s):  
S. E. G. Slusky ◽  
A. T. Macrander
Keyword(s):  
Experimental Data ◽  
Indium Phosphide ◽  
Single Crystal ◽  
Simulated Data ◽  
Vertical Gradient ◽  
X Ray Diffraction ◽  
Rocking Curve ◽  
X Ray ◽  
Vertical Gradient Freeze

A formula is derived for simulating rocking-curve measurements made with an X-ray diffractometer fitted with a four-reflection monochromator. The derivation is carried out both graphically and algebraically. Results of a simulation using this formula are then compared with experimentally obtained rocking curves. The rocking curves were obtained using a diffractometer with a four-reflection monochromator that uses 440 reflections from two channel-cut germanium crystals. The experimental data comprise 200, 400, 600, 511, 711, 622, 422 and 444 reflections from thick single-crystal indium phosphide grown by the vertical-gradient freeze technique. The simulated data correlate well with the experimental data, although the simulations consistently show somewhat higher reflectivities and narrower linewidths than the experiment, indicating the existence of broadening mechanisms not included in the simulation that are affecting the experiment.

scholarly journals Gallium nitride films grown on AlN/sapphire templates

2020 ◽  
Author(s):  
Jin Wu
Keyword(s):  
Gallium Nitride ◽  
Dislocation Density ◽  
Carrier Concentration ◽  
Hall Mobility ◽  
High Quality ◽  
Rocking Curve ◽  
X Ray ◽  
Low Dislocation Density

High-quality GaN films were grown on AlN/c-sapphire templates by MOVPE with Hall mobility of 802 cm2/V.s and carrier concentration of 8.1x1016/cm3 at 300K have achieved. The film low dislocation density of 5x107 cm-2 and X-ray rocking curve FWHM of 101 and 250 arcsec for the (0004) and (20-24) reflections were also obtained, respectively.

Sublimation Growth of Bulk AlN Crystals on SiC Seeds

2013 ◽  
Vol 740-742 ◽  
pp. 95-98 ◽  
Author(s):  
E.N. Mokhov ◽  
A.A. Wolfson ◽  
A.O. Avdeev ◽  
S.S. Nagalyuk ◽  
D. P. Litvin ◽  
...  
Keyword(s):  
Surface Layer ◽  
Dislocation Density ◽  
High Purity ◽  
Bulk Crystals ◽  
Considerable Decrease ◽  
Vapor Source ◽  
X Ray ◽  
Low Dislocation Density ◽  
Sandwich Method ◽  
Sublimation Growth

AlN bulk crystals were grown by the sublimation “sandwich method” on the SiC substrates. Two types of containers were used: (i) Ta container with a surface layer of TaC created by the special annealing in contact with carbon, (ii) TaC container created by pressing of TaC powder. Cryptocrystalline AlN wafers grown by oversublimation of the original industrial high purity AlN powder were used as a vapor source. So a considerable decrease of oxygen concentration in the source (10 – 30 times) was achieved. 4H and 6H SiC bulk crystals grown by Nitride Crystals, Ltd., which were used as wafers, were crack-free, micropipe-free and have a low dislocation density (1- 4.103cm-2). The method allowed to grow thick AlN bulk crystals up to 5mm height and up to two inches in diameter with smooth mirror-like surface. X-ray diffractometry and topography of the grown AlN layers show that FWHMs of the rocking curves in ω-scan lie in the range of 60-120 arcsec.

Structure and electrical properties of tetragonal tungsten bronze Ba2CeFeNb4O15

RSC Advances ◽  
2015 ◽  
Vol 5 (94) ◽  
pp. 76957-76962 ◽  
Author(s):  
Hongqiang Ma ◽  
Kun Lin ◽  
Laijun Liu ◽  
Baoling Yang ◽  
Yangchun Rong ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Electrical Property ◽  
Electrical Properties ◽  
Impedance Spectroscopy ◽  
Electron Diffraction ◽  
Tungsten Bronze ◽  
Ac Impedance Spectroscopy ◽  
Tetragonal Tungsten Bronze ◽  
X Ray ◽  
Selected Area Electron Diffraction

The crystal structure and electrical property of a tetragonal tungsten bronze ceramic, BaCeFeNb4O15, were investigated by synchrotron X-ray powder diffraction, selected area electron diffraction, and AC impedance spectroscopy.

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