Zone Melting Recrystallization of GaAs Films on Oxidized Si

1985 ◽  
Vol 53 ◽  
Author(s):  
Weiwen Zhu ◽  
Weiyuan Wang
Keyword(s):  
Grain Size ◽  
Electron Diffraction ◽  
Single Crystal ◽  
Electron Mobility ◽  
Zone Melting ◽  
Hall Measurement ◽  
Signal Ratio ◽  
Before And After ◽  
Gaas Films ◽  
Diffraction Patterns

ABSTRACTIn this paper, GaAs SOI consisting of MBE deposited GaAs films on oxidized Si was recrystallized by narrow-zone melting in a RF induction graphite strip heater at a rate of 1–1.2 mm/s. The original grain size of MBE GaAs SOI films is smaller than 800 Å, and the electron diffraction patterns appear as typical polycrystalline rings as determined by SEM and ED, respectively. After zone melting recrystallization, the grain size of GaAs SOI films increases to 1 µm, the prefered ˂111˃ diffraction spots appear apparently, and the carrier concentrations and electron mobility amount to 3×1017cm−3 and 1.1×103cm2/v.s as determined by Hall measurement. The AES Ga/As signal ratio of the GaAs SO before and after recrystallization is the same as that of the GaAs single crystal. The possible application of GaAs SOI to devices is discussed.

An analysis of preferred orientation in YBa2Cu3O7–x superconducting films deposited by CVD on single-crystal and polycrystalline substrates

1994 ◽  
Vol 9 (4) ◽  
pp. 250-259 ◽  
Author(s):  
E. A. Judson ◽  
D. N. Hill ◽  
R. A. Young ◽  
J. R. Cagle ◽  
W. J. Lackey ◽  
...  
Keyword(s):  
Single Crystal ◽  
Chemical Vapor ◽  
Preferred Orientation ◽  
Superconducting Properties ◽  
High Temperature Anneal ◽  
Pole Figures ◽  
Before And After ◽  
Diffraction Patterns ◽  
A Minor ◽  
Orientation Phenomenon

YBa2Cu3O7–x films were deposited by chemical vapor deposition (CVD) onto single-crystal MgO, single-crystal Al2O3, and polycrystalline Al2O3 substrates, characterized before and after annealing, and tested for their superconducting properties. The preferred orientation in the films was analyzed (i) with pole figures and (ii) by comparison of experimental x-ray powder diffraction patterns with those calculated for the material using the March–Dollase function to model the degree of preferred orientation. Preferred orientation was significant in as-deposited films, with March coefficients ranging from 0.1–0.5 (random orientation would have a coefficient of 1.0). The (006) pole figures of the films on single crystal substrates exhibited uniquely symmetric patterns. On single-crystal MgO before annealing, a minor secondary orientation of (006) poles in the film was observed in a pattern consistent with the symmetry of major crystallographic directions of MgO. On single-crystal Al2O3 after annealing, a “dual orientation” phenomenon was observed. The high-temperature anneal destroyed the orientation and superconducting properties of the CVD films deposited at high temperatures.

A complex pseudo-decagonal quasicrystal approximant, Al37(Co,Ni)15.5, solved by rotation electron diffraction

2014 ◽  
Vol 47 (1) ◽  
pp. 215-221 ◽  
Author(s):  
Devinder Singh ◽  
Yifeng Yun ◽  
Wei Wan ◽  
Benjamin Grushko ◽  
Xiaodong Zou ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Diffraction Data ◽  
Three Dimensional ◽  
Basic Structure ◽  
Electron Diffraction Data ◽  
Dimensional Electron ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Patterns

Electron diffraction is a complementary technique to single-crystal X-ray diffraction and powder X-ray diffraction for structure solution of unknown crystals. Crystals too small to be studied by single-crystal X-ray diffraction or too complex to be solved by powder X-ray diffraction can be studied by electron diffraction. The main drawbacks of electron diffraction have been the difficulties in collecting complete three-dimensional electron diffraction data by conventional electron diffraction methods and the very time-consuming data collection. In addition, the intensities of electron diffraction suffer from dynamical scattering. Recently, a new electron diffraction method, rotation electron diffraction (RED), was developed, which can overcome the drawbacks and reduce dynamical effects. A complete three-dimensional electron diffraction data set can be collected from a sub-micrometre-sized single crystal in less than 2 h. Here the RED method is applied forab initiostructure determination of an unknown complex intermetallic phase, the pseudo-decagonal (PD) quasicrystal approximant Al37.0(Co,Ni)15.5, denoted as PD2. RED shows that the crystal is F-centered, witha= 46.4,b= 64.6,c= 8.2 Å. However, as with other approximants in the PD series, the reflections with oddlindices are much weaker than those withleven, so it was decided to first solve the PD2 structure in the smaller, primitive unit cell. The basic structure of PD2 with unit-cell parametersa= 23.2,b= 32.3,c= 4.1 Å and space groupPnmmhas been solved in the present study. The structure withc= 8.2 Å will be taken up in the near future. The basic structure contains 55 unique atoms (17 Co/Ni and 38 Al) and is one of the most complex structures solved by electron diffraction. PD2 is built of characteristic 2 nm wheel clusters with fivefold rotational symmetry, which agrees with results from high-resolution electron microscopy images. Simulated electron diffraction patterns for the structure model are in good agreement with the experimental electron diffraction patterns obtained by RED.

Compositional variation within some sedimentary chlorites and some comments on their origin

1985 ◽  
Vol 49 (352) ◽  
pp. 375-386 ◽  
Author(s):  
C. D. Curtis ◽  
C. R. Hughes ◽  
J. A. Whiteman ◽  
C. K. Whittle
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Diffraction ◽  
Single Crystal ◽  
Compositional Variation ◽  
Analytical Transmission Electron Microscopy ◽  
Decomposition Reactions ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
Crystal Electron

AbstractA range of authigenic sedimentary chlorites from sandstones has been studied by analytical transmission electron microscopy. Selected area (single crystal) electron diffraction patterns are of the Ib (β = 90°) polytype confirming the earlier observations of Hayes (1970).TEM analyses show all samples to be relatively rich in both Al and Fe. In the general formula (Mg,Fe,Al)n [Si8−xAlxO20](OH)16, x varies between 1.5 and 2.6; Fe/(Fe + Mg) between 0.47 and 0.83 and n between 10.80 and 11.54. Octahedral Al is close to 3 in this formulation and Fe2+ predominates over Fe3+. Swelling chlorites have significantly different compositions which are consistent with smectite/chlorite interstratifications.The Ib (β = 90°) polytype appears to be stable under conditions of moderate to deep burial. It replaces berthierine and swelling chlorites formed at lower temperatures. As commonly seen in grain coatings, however, it precipitates from porewater; solutes probably being contributed from several mineral decomposition reactions.

Electron-optical data for crystals of scarbroite

1960 ◽  
Vol 32 (248) ◽  
pp. 363-365 ◽  
Author(s):  
G. W. Brindley ◽  
J. J. Comer
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Electron Micrographs ◽  
Optical Data ◽  
Diffraction Patterns ◽  
Crystal Electron

SummaryElectron micrographs of scarbroite show thin platy crystals of about 1 μ size, having rhombic outlines with angles 66° ± 1° and 113° ± 1°. Single-crystal electron-diffraction patterns show rectangular net patterns, with d100 = 9·90 Å., d010 = 14·67 Å., γ* = 90° ± 0·05°. Strong hk0 reflections show a pseudohexagonal arrangement, but true symmetry is probably orthorhombic or monoclinic. Faces outlining rhombic forms are of type {11l}, .

scholarly journals Indexing of icosahedral quasiperiodic crystals

1986 ◽  
Vol 1 (1) ◽  
pp. 13-26 ◽  
Author(s):  
John W. Cahn ◽  
Dan Shechtman ◽  
Denis Gratias
Keyword(s):  
Fourier Transform ◽  
Electron Diffraction ◽  
Single Crystal ◽  
Coordinate System ◽  
Powder Diffraction ◽  
Simple Application ◽  
Coordinate Systems ◽  
Diffraction Patterns ◽  
Definition Of ◽  
Crystal Electron

Since the definition of quasiperiodicity is intimately connected to the indexing of a Fourier transform, for the case of an icosahedral solid, the step necessary to prove, using diffraction, that an object is quasiperiodic, is described. Various coordinate systems are discussed and reasons are given for choosing one aligned with a set of three orthogonal two-fold axes. Based on this coordinate system, the main crystallographic projections are presented and several analyzed single-crystal electron diffraction patterns are demonstrated. The extinction rules for three of the five icosahedral Bravais quasilattices are compared, and some simple relationships with the six-dimensional cut and projection crystallography are derived. This analysis leads to a simple application for indexing powder diffraction patterns.

Electron diffraction analysis of a metastable state in ion-irradiated MgAl2O4 spinel

1995 ◽  
Vol 53 ◽  
pp. 160-161
Author(s):  
Ram Devanathan ◽  
Ning Yu ◽  
Kurt E. Sickafus ◽  
Michael Nastasi
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Lattice Constant ◽  
Metastable State ◽  
Fast Neutrons ◽  
Bravais Lattice ◽  
Energetic Ions ◽  
Radiation Resistant ◽  
Diffraction Patterns ◽  
First Time

Magnesium aluminate spinel is considered to be a remarkably radiation resistant material. Single crystal spinel exhibits very little damage when irradiated with fast neutrons or energetic ions. Recently, amorphization of single-crystal MgAl204 was observed, for the first time, following irradiation with 400 keV Xe2+ at about 100 K to a peak dose of 25 dpa. Electron diffraction patterns from spinel subjected to different doses show the extinction of first-order fundamental reflections prior to the occurence of amorphization. This suggests that, enroute to becoming amorphous, ion-irradiated spinel transforms to a metastable crystalline state with a lattice constant that is half that of spinel. In an effort to understand this phase transformation, we have analyzed the structure of the metastable state using electron diffraction.Spinel belongs to the spacegroup Fd3m (fee Bravais lattice). The unit cell has a lattice constant of about 0.8 nm and is made of two sets of four octants.

Straczekite, a new calcium barium potassium vanadate mineral from Wilson Springs, Arkansas

1984 ◽  
Vol 48 (347) ◽  
pp. 289-293 ◽  
Author(s):  
Howard T. Evans ◽  
Gordon Nord ◽  
John Marinenko ◽  
Charles Milton
Keyword(s):  
Electron Diffraction ◽  
Chemical Analysis ◽  
Single Crystal ◽  
General Formula ◽  
Secondary Mineral ◽  
Calculated Density ◽  
X Ray ◽  
Cell Parameters ◽  
Diffraction Patterns ◽  
Ray Patterns

AbstractStraczekite, a new calcium barium potassium vanadate from Wilson Springs (formerly Potash Sulfur Springs), Arkansas, occurs as a rare secondary mineral in fibrous seams in gangue. The dark greenish-black crystals are very soft, thin laths up to 0.5 mm in length, forming thick masses. No single-crystal X-ray patterns could be obtained, but good electron diffraction patterns yielded a monoclinic unit cell in space group C2/m, C2, or Cm. The cell parameters were refined by least squares analysis of Guinier-Hägg X-ray powder data: a 11.679(2), b 3.6608(4), c 10.636(2)Å, β = 100.53(4)° (strongest lines are: 003, 3.486, 100; 001, 10.449, 50; 020 1.8306, 50; 6̄01/510, 1.9437, 15; 111/2̄03, 3.255, 10; 311/3̄12, 2.492, 10; 021, 1.8030, 10). Chemical analysis yields the formula: (Ca0.39Ba0.31K0.33Na0.11)(V1.594+V6.315+Fe0.103+)O20.02(H2O)2.9. The calculated density is 3.21 g/cm3. The mineral conforms to a series of synthetic vanadium bronzes, typified by Ag1-xV2O5 of known structure. It represents a new series of layer vanadate minerals of general formula MxV8O20·yH2O, similar in properties but distinct from the hewettite series (MxV6O16·yH2O).

STEM Electron Diffraction from Areas less than 30Å; Application to Amorphous Films

1975 ◽  
Vol 33 ◽  
pp. 218-219
Author(s):  
R. H. Geiss
Keyword(s):  
Electron Diffraction ◽  
Single Crystal ◽  
Thick Film ◽  
Amorphous Films ◽  
Single Crystal Diffraction ◽  
Gold Particles ◽  
Transmission Electron Diffraction ◽  
Transmission Electron ◽  
Diffraction Patterns

A technique of selective micro-area transmission electron diffraction has been developed using the Philips 301 TEM with a scanning (STEM) attachment. With this technique we are able to obtain electron diffraction patterns from selected areas less than 30 Å in diameter or about 103 atoms! This is to be compared with the best published results which show selected area diffraction (SAD) from areas at least 100 Å in diameter, approximately 105 atoms, or the conventional SAD techniques applicable to areas down to 2000 Å diameter, approximately 5 x 106 atoms. (The number of atoms was calculated assuming a 50 Å thick film of a f.c.c. structure with ao = 5 Å.) The selected micro-area capability was proven by experimentally obtaining discrete single crystal diffraction patterns from an array of evaporated gold particles some less than 30 Å diameter and separated by 30 Å or less, Fig. 1.

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