Planar defects in ordered (Ga,In)P

1988 ◽  
Vol 46 ◽  
pp. 902-903
Author(s):  
S. McKernan ◽  
C. B. Carter ◽  
D. Bour ◽  
J. R. Shealy
Keyword(s):  
Electron Diffraction ◽  
Vapor Phase ◽  
Growth Direction ◽  
High Density ◽  
Ordered Structure ◽  
Planar Defects ◽  
Diffraction Patterns ◽  
Ternary Semiconductors ◽  
Anion Species ◽  
Metallic Vapor

The growth of ternary III-V semiconductors by organo-metallic vapor phase epitaxy (OMVPE) is widely practiced. It has been generally assumed that the resulting structure is the same as that of the corresponding binary semiconductors, but with the two different cation or anion species randomly distributed on their appropriate sublattice sites. Recently several different ternary semiconductors including AlxGa1-xAs, Gaxln-1-xAs and Gaxln1-xP1-6 have been observed in ordered states. A common feature of these ordered compounds is that they contain a relatively high density of defects. This is evident in electron diffraction patterns from these materials where streaks, which are typically parallel to the growth direction, are associated with the extra reflections arising from the ordering. However, where the (Ga,ln)P epilayer is reasonably well ordered the streaking is extremely faint, and the intensity of the ordered spot at 1/2(111) is much greater than that at 1/2(111). In these cases it is possible to image relatively clearly many of the defects found in the ordered structure.

Ordered Structures of Zn1−xFexSe Epilayers Grown on InP and GaAs Substrates

1993 ◽  
Vol 312 ◽  
Author(s):  
K. Park ◽  
H.- Y. Wei ◽  
L. Salamanca-Riba ◽  
B. T. Jonker
Keyword(s):  
Lattice Mismatch ◽  
Misfit Strain ◽  
Growth Direction ◽  
Ordered Structure ◽  
Cross Sectional ◽  
Ordered Structures ◽  
Gaas Substrates ◽  
Lattice Images ◽  
Diffraction Patterns ◽  
Inp Substrates

AbstractWe present evidence for two types of ordered structures, CuAu-I and CuPt, in Zn1−xFexSe (x≈ 0.4) epilayers grown by molecular beam epitaxy. These ordered structures are observed in both electron diffraction patterns and cross-sectional high-resolution lattice images. The CuAu-I ordered structure occurs in Zn1−xFexSe epilayers grown on (001) InP substrates, while the CuPt-type occurs in epilayers grown on (001) GaAs substrates. The ordered structure of Zn1−xFexSe grown on InP substrates consists of alternating ZnSe and FeSe layers along the [001] growth direction and the [110] direction. In contrast, the ordered structure of Zn1−xFexSe grown on GaAs substrates consists of alternating ZnSe and FeSe layers along the < 111 > directions. We have also investigated the role of the misfit strain associated with the lattice mismatch between the epilayers and the substrates on the type of ordered structure.

scholarly journals Исследование структуры нитевидных нанокристаллов сульфида кадмия, синтезированных методом вакуумного испарения и конденсации в квазизамкнутом объеме

2018 ◽  
Vol 52 (1) ◽  
pp. 125
Author(s):  
А.П. Беляев ◽  
В.В. Антипов ◽  
В.П. Рубец
Keyword(s):  
Electron Diffraction ◽  
Cadmium Sulfide ◽  
Vapor Phase ◽  
Degree Of Crystallinity ◽  
Closed Volume ◽  
Diffraction Patterns ◽  
High Degree

AbstractThe results of crystallinity studies of an ensemble of cadmium-sulfide nanowire crystals synthesized from the vapor phase in a quasi-closed volume are reported. The nanowires are from 10 nm to several micrometers in diameter and tens of millimeters in length. Electron diffraction and luminescence are studied. The diffraction patterns and micrographs are presented. The results suggest a high degree of crystallinity of the nanowires.

Quasi-fivefold symmetric electron diffraction patterns due to multiple twinning in silicon thin films grown from hexamethyldisiloxane

2016 ◽  
Vol 49 (6) ◽  
pp. 2226-2234 ◽  
Author(s):  
Farah Haddad ◽  
Prabal Goyal ◽  
Erik V. Johnson ◽  
Junegie Hong ◽  
Pere Roca i Cabarrocas ◽  
...  
Keyword(s):  
Thin Films ◽  
Electron Diffraction ◽  
Chemical Vapour ◽  
Growth Conditions ◽  
Growth Direction ◽  
Fivefold Symmetry ◽  
Silicon Thin Films ◽  
Carbon Impurities ◽  
Diffraction Patterns ◽  
Multiple Twinning

Unusual quasi-fivefold symmetric electron diffraction patterns are observed for silicon thin films grown by plasma-enhanced chemical vapour deposition and containing oxygen and carbon impurities in the range of 0.3–5.5%. These films were grown on crystalline (100) silicon wafers using a liquid precursor, hexamethyldisiloxane (HMDSO), mixed with silane, hydrogen and diborane diluted in argon. The occurrence of this quasi-fivefold symmetry is explained by multiple twinning and imperfect epitaxy. A quantitative method performed on the diffraction patterns is developed to evaluate the number of twin operations. This method is also used to discriminate twin positions from random microcrystalline ones in the diffraction patterns and thus to estimate their respective ratios for different growth conditions. Quite remarkably, the random microcrystalline part remains in the range of a few per cent and the diffracted intensities are the sum of two main contributions: multiple (micro-) twinned and amorphous. Increasing the amount of HMDSO decreases the microtwinned part directly to the benefit of the amorphous part with no significant microcrystalline phase. The causes of twinning are presented and discussed by comparing the observations with the literature; dynamical considerations where the system tends to align {111} planes with the growth direction would explain multiple twinning and, in turn, the fivefold symmetry.

Observations on a fibrous form of silicon carbide

1990 ◽  
Vol 48 (4) ◽  
pp. 1040-1041
Author(s):  
L.C. Otero Diaz ◽  
A.R. Landa Canovas ◽  
S. Hansen ◽  
B.G. Hyde
Keyword(s):  
Silicon Carbide ◽  
Electron Microscope ◽  
Electron Diffraction ◽  
Structure Analysis ◽  
Phase Structure ◽  
Optical Microscope ◽  
Fibre Axis ◽  
Planar Defects ◽  
Diffraction Patterns ◽  
Fibre Morphology

During a phase and structure analysis of the ytterbium sulphide system we observed, in addition to various ytterbium sulphides , some fibrous crystals ≃10-100 μm long, ≃0.5 μm diameter, e.g. Fig.10. In the optical microscope they were seen to be crystalline, white and transparent. In the electron microscope planar defects were seen in parts of them; usually normal to the fibre axis, and often closely aggregated into groups, e.g. Figs. 1a and 2a, which were taken with JE0L 2000 FX and 4000 EX microscopes.The fibre morphology was unexpected, and ytterbium sulphides (with the exception of Yb2S3, which is yellow)are black and metallic in appearance. Futhermore the electron diffraction patterns from the fibres did not correspond to any knownor possible YbS phase/ structure.EDSxanalysis (with a LINK AN 10000, JE0L 2000 FX microscope) revealed the presence of Si in the fibres, but not heavier elements.

Ordered structure formation in the flux-grown Ba(Mg1/3Ta2/3)O3 single crystals

2001 ◽  
Vol 16 (6) ◽  
pp. 1593-1599 ◽  
Author(s):  
Yu-Chang Lee ◽  
Chen-Chia Chou ◽  
Dah-Shyang Tsai
Keyword(s):  
Electron Diffraction ◽  
Single Crystals ◽  
Annealing Time ◽  
High Resolution Electron Microscopy ◽  
Maximum Intensity ◽  
Ordered Structure ◽  
X Ray Diffraction ◽  
Resolution Electron ◽  
Higher Temperature ◽  
Diffraction Patterns

Formation of ordered structure in flux-grown Ba(Mg1/3Ta2/3)O3(BMT) single crystals was studied using x-ray diffraction, electron diffraction, and high-resolution electron microscopy. The low-temperature-grown crystals exhibited no sign of B-site ordering. Annealing at 1500 °C induced the 1:2 ordered phase, and its content increased with the annealing time. The superlattice diffraction peaks were broad initially; they sharpened rapidly with the annealing time. Diffuse superlattice reflections were found in electron diffraction patterns of 1500 °C annealed BMT; they turned into sharp reflections under long annealing time or higher temperature, 1600 °C. The intensity of diffuse reflections was sparsely distributed, but the maximum intensity location was determined in the digitized recording of image plate. The maximum intensity sites of two diffuse reflections in the 〈111〉 direction deviated from the presumed 1/3 and 2/3 positions and shifted towards the center. The diffuse reflection and the deviation from regular positions were interpreted as the composition modulation during B-site cation diffusion.

Atomic Ordering of III-V Alloy Semiconductors Grown on (110)InP and its Influence on Electron Mobility

1995 ◽  
Vol 417 ◽  
Author(s):  
O. Ueda
Keyword(s):  
Electron Diffraction ◽  
Growth Surface ◽  
Ordered Structure ◽  
Atomic Ordering ◽  
Ordered Structures ◽  
Limited Mobility ◽  
Alloy Scattering ◽  
Channel Layer ◽  
Diffraction Patterns ◽  
Dimensional Electron Gas

AbstractAtomic ordering in InGaAs, InAlAs, and GaAsSb crystals grown on (110) InP substrates by molecular beam epitaxy, has been studied by transmission electron microscopy. In the electron diffraction pattern from these crystals, superstructure spots associated with CuAu-I type ordered structure are found. When the tilting angle of the substrates increases, the ordering becomes stronger. The ordering is also stronger in crystals grown on substrates tilted toward the <001> or the <001> direction than those on substrates tilted toward the <110> direction. From these results, one can conclude that atomic steps on the growth surface play an important role in the formation of ordered structures. The ordering becomes stronger when the growth temperature increases. In high resolution images of the crystal, doubling in periodicity of 220 and 200 lattice fringes is found, which is associated with CuAu-I type ordered structure. Moreover, anti-phase boundaries are very often observed in the ordered regions. It is also found that ordering is not perfect, and that ordered regions are plate-like microdomains lying on planes slightly tilted from the (110) plane. On the basis of these results together with considerations of the atomic arrangement of the ordered structure and surface reconstruction on the (110) plane, we propose four possible models for the ordering. Through precise evaluation of these models, two models are selected as the most probable ones: these involve formation of the ordered structures on surfaces dominated by two monolayer steps. These models have been experimentally proven by the analyses of electron diffraction patterns from different InGaAs crystals grown on different growth surfaces. We have fabricated InGaAs/N-InAlAs heterostructures with a strongly ordered InGaAs channel layer. The measured two-dimensional electron gas mobilities from these structures are found to be 100,000 cm2/Vs in the <110> direction and 161,000 cm2/Vs in the <110> direction with a sheet electron concentration (Ns) of 9.5 × 1011 cm−2 at 6 K. The latter mobility is much higher than both calculated alloy scattering limited mobility and the best experimental results for lattice-matched InGaAs/N-InA]As systems. The mobility enhancement in the <110> direction is considered to be achieved by the suppression of alloy scattering due to the occurrence of ordering in the InGaAs channel layer.

Electron diffraction of copper perfluorophthalocyanine on the HVEM

1995 ◽  
Vol 53 ◽  
pp. 158-159
Author(s):  
W. F. Tivol ◽  
J. R. Fryer
Keyword(s):  
Electron Beam ◽  
Electron Diffraction ◽  
Ab Initio ◽  
Vapor Phase ◽  
High Energy ◽  
Illumination Level ◽  
Objective Lens ◽  
Crystal Face ◽  
Correct Orientation ◽  
Diffraction Patterns

The use of high-energy (1200 kV) electrons has been shown to be advantageous in the ab initio structure analysis from electron diffraction of organic compounds. Previous studies showed that ab initio analysis of copper perchlorophthalocyanine could be accomplished at accelerating voltages at or above 1000 kV, but not at 400 kV for crystals which are about 10 nm thick. Copper perbromophthalocyanine could also be analyzed ab initio at 1200 kV, but the presence of severe dynamical scattering precluded such analysis at lower voltages.Copper perfluorophthalocyanine (Cu FPC) was grown epitaxially from the vapor phase onto a clean KC1 crystal face. Electron diffraction patterns were obtained from crystals tilted at 20° and oriented so that the electron beam was parallel to the c-axis.Electron doses were kept to a minimum by the use of a 100 μm condenser aperture and a highly excited first condenser lens. A video system allows scanning the specimen to find a crystal suitable for the correct orientation of the grid by rotating it within its own plane and focusing the objective lens, all at an illumination level below that necessary to distinguish anything by eye on the HVEM's phosphor screen.

The defects and intergrowth of lead oxides revealed by HRTEM

1992 ◽  
Vol 25 (2) ◽  
pp. 199-204 ◽  
Author(s):  
Y. G. Wang ◽  
H. Q. Ye ◽  
K. H. Kuo ◽  
J. G. Guo
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Electron Diffraction ◽  
Structural Models ◽  
Planar Defects ◽  
Transmission Electron ◽  
Lead Oxides ◽  
Diffraction Patterns ◽  
Relationship Of

High-resolution transmission electron microscopy (HRTEM) and electron diffraction were used to investigate the microstructure of natural lead oxides found in Panzhihua Mountain, China. The electron diffraction patterns showed crossing of diffraction spots along 〈110〉 directions in litharge and along 〈100〉 directions in massicot and the structural images showed the domain-like texture, probably constructed by arrays of planar defects in the fundamental structures. Based upon the structure of these oxides the possible structural models of planar defects are discussed and the orientation relationship of litharge and massicot is determined.

Computer Indexing of Electron Diffraction Patterns Including the Effects of Lattice Symmetry

1977 ◽  
Vol 35 ◽  
pp. 22-23
Author(s):  
J. S. Lally ◽  
R. J. Lee
Keyword(s):  
Electron Diffraction ◽  
Zone Axis ◽  
Crystal Thickness ◽  
Double Diffraction ◽  
Automated Method ◽  
Lattice Symmetry ◽  
Intensity Calculations ◽  
Unknown Structure ◽  
Diffraction Patterns ◽  
Orientation Parameters

In the 50 year period since the discovery of electron diffraction from crystals there has been much theoretical effort devoted to the calculation of diffracted intensities as a function of crystal thickness, orientation, and structure. However, in many applications of electron diffraction what is required is a simple identification of an unknown structure when some of the shape and orientation parameters required for intensity calculations are not known. In these circumstances an automated method is needed to solve diffraction patterns obtained near crystal zone axis directions that includes the effects of systematic absences of reflections due to lattice symmetry effects and additional reflections due to double diffraction processes.Two programs have been developed to enable relatively inexperienced microscopists to identify unknown crystals from diffraction patterns. Before indexing any given electron diffraction pattern, a set of possible crystal structures must be selected for comparison against the unknown.

Electron-diffraction studies in synthetic polymer materials

1983 ◽  
Vol 41 ◽  
pp. 362-365
Author(s):  
D.T. Grubb
Keyword(s):  
Electron Diffraction ◽  
Synthetic Polymer ◽  
Polymer Materials ◽  
Crystallographic Structure ◽  
High Dose ◽  
Electron Dose ◽  
Dose Rates ◽  
First Case ◽  
Diffraction Patterns ◽  
The Many

Diffraction studies in polymeric and other beam sensitive materials may bring to mind the many experiments where diffracted intensity has been used as a measure of the electron dose required to destroy fine structure in the TEM. But this paper is concerned with a range of cases where the diffraction pattern itself contains the important information.In the first case, electron diffraction from paraffins, degraded polyethylene and polyethylene single crystals, all the samples are highly ordered, and their crystallographic structure is well known. The diffraction patterns fade on irradiation and may also change considerably in a-spacing, increasing the unit cell volume on irradiation. The effect is large and continuous far C94H190 paraffin and for PE, while for shorter chains to C 28H58 the change is less, levelling off at high dose, Fig.l. It is also found that the change in a-spacing increases at higher dose rates and at higher irradiation temperatures.

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