Observation of Hexagonal AiGaAs Grown by OMCVD

1990 ◽  
Vol 209 ◽  
Author(s):  
D. M. Hwang ◽  
T. S. Ravi ◽  
R. Bhat ◽  
S. Simhony ◽  
C. Y. Chen ◽  
...  
Keyword(s):  
High Resolution ◽  
Quantum Wire ◽  
Gaas Substrate ◽  
Hexagonal Phase ◽  
Stacking Faults ◽  
Hexagonal Structure ◽  
Cubic Phase ◽  
Lattice Images ◽  
Diffraction Patterns ◽  
Cladding Layers

ABSTRACTExtended regions of hexagonal zinc sulfide (wurtzite) structure are found to exist in AlGaAs grown by low-pressure OMCVD at 750°C. The specimen was prepared on a (001) GaAs substrate patterned with [110]-orientedV-grooves, intended for a quantum wire laser structure. A high density of planar faults was observed to originate in theAl0.66Ga0.34As cladding layers near the inner corners of the V-grooves and propagate towards the surface along the {111} planes. Many of these faults are stacking faults and microtwins. However, there also exhibit extended regions of hexagonal structure, revealed in electron diffraction patterns and high resolution lattice images. The hexagonal phase shares the same close-packed layers with the cubic phase, i.e., (0001)hexagonal // {111}cubic. The mechanism for the formation of hexagonal structure in this specimen is not yet fully understood.

The ultrastructure of coccoliths from the marine alga Emiliania huxleyi (Lohmann) Hay and Mohler: an ultra-high resolution electron microscope study

1983 ◽  
Vol 219 (1215) ◽  
pp. 111-117 ◽  
Keyword(s):  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Emiliania Huxleyi ◽  
Growth Patterns ◽  
Lattice Image ◽  
Nucleation Sites ◽  
Resolution Electron ◽  
Lattice Images ◽  
High Resolution Electron Microscope ◽  
Diffraction Patterns

The calcite coccoliths from the alga Emiliania huxleyi (Lohmann) Hay and Mohler have been studied by ultra-high resolution electron microscopy. This paper describes the two different types of structure observed, one in the upper elements, the other in the basal plate, or lower element. The former consisted of small, microdomain structures of 300-500 Å (1 Å = 10 -10 m) in length with no strong orientation. At places along these elements, and particularly in the junction between stem and head pieces, triangular patterns of lattice fringes were observed indicating multiple nucleation sites in the structure. In contrast, the lower element consisted of a very thin single crystalline sheet of calcite which could be resolved into a two dimensional lattice image, shown by a computer program that is capable of simulating electron diffraction patterns and lattice images to be a [421] zone of calcite. A possible mechanism for these growth patterns in the formation of coccoliths is discussed, together with the relevance of such mechanisms to biomineralization generally.

Thermo-elastic and optical properties of molybdenum nitride

2016 ◽  
Vol 94 (9) ◽  
pp. 902-912 ◽  
Author(s):  
Zainab N. Jaf ◽  
Zhong-Tao Jiang ◽  
Hussein A. Miran ◽  
Mohammednoor Altarawneh
Keyword(s):  
Mechanical Properties ◽  
Bulk Modulus ◽  
Hexagonal Phase ◽  
Harmonic Approximation ◽  
Elastic Stiffness ◽  
Hexagonal Structure ◽  
Cubic Phase ◽  
Slight Variation ◽  
Molybdenum Nitride ◽  
Thermal And Mechanical Properties

This contribution aims to investigate volume-dependent thermal and mechanical properties of the two most studied phases of molybdenum nitride (c-MoN and h-MoN) by means of the quasi-harmonic approximation approach (QHA) via first-principles calculations up to their melting point and a pressure of 12 GPa. Lattice constants, band gaps, and bulk modulus at 0 K match corresponding experimental measurements well. Calculated Bader’s charges indicate that Mo–N bonds exhibit a more ionic nature in the cubic MoN phase. Based on estimated Gibbs free energies, the cubic phase presents thermodynamic stability higher than that detected for hexagonl, with no phase transition observed in the selected T–P conditions as detected experimentally. The elastic stiffness coefficients of MoN in hexagonal structure revealed that it is stable elastically; in contrast to the cubic structure. The temperature dependence on the bulk modulus is more profound on the dense cubic phase than on the hexagonal phase. Overall, the two considered structures of molybdenum nitride display very minimal harmonic effects, evidenced by the slight variation of thermal and mechanical properties with the increase of pressure and temperature. The optical conductivity of both phases near a zero photon energy coincides well with their metallic character inferred by their corresponding DOS curves. It is expected that the thermo-elastic properties of saturated molybdenum nitrides reported in this study will aid in the continuous pursuit to enhance their catalytic and mechanical utilizations.

High-resolution TEM of C60 thin films

1992 ◽  
Vol 50 (1) ◽  
pp. 108-109
Author(s):  
W. Krakow ◽  
N.M. Rivera ◽  
R.A. Roy ◽  
J.J. Cuomo
Keyword(s):  
Thin Films ◽  
High Resolution ◽  
Room Temperature ◽  
Bulk Material ◽  
Hexagonal Phase ◽  
Hexagonal Structure ◽  
Scanning Tunneling ◽  
Bravais Lattice ◽  
Face Centered Cubic ◽  
Tunneling Microscopy

The ability to fabricate buckminsterfullerenes, C60 molecules, in reasonably large quantities has made possible studies of the structural properties of this form of carbon when it is in a crystalline state. At room temperature, x-ray diffraction from three-dimensional bulk C60 crystals shows that the molecules are centered on sites of a face-centered-cubic Bravais lattice, A∘ = 14.2Å. Somewhat earlier in time, a study of C60/C70 bulk material using electron diffraction and high resolution electron microscopy has revealed a hexagonal phase. It is now believed that this phase is a simple cubic structure rather than a hexagonal structure. Since it is reasonable to expect that highly ordered C60 thin films will have superior properties to bulk material, several studies have been undertaken to understand the early stages of C60 thin film growth. Monolayer growth on GaAs has been studied by scanning tunneling microscopy., and on mica at room temperature using helium scattering. Along similar lines we have grown thin films of C60 molecules on mica and NaCl and characterized the crystallinity and local structural arrangements. Here we present some of our results of the electron microscope examination of these materials.

Transmission electron microscopy studies of boron nitride thin films produced by pulsed laser deposition

1993 ◽  
Vol 51 ◽  
pp. 732-733
Author(s):  
D.L. Medlin ◽  
T.A. Friedmann ◽  
P. B. Mirkarimi ◽  
K.F. McCarty ◽  
M.J. Mills
Keyword(s):  
Boron Nitride ◽  
Phase Distribution ◽  
Hexagonal Phase ◽  
Pulsed Laser ◽  
Hexagonal Structure ◽  
Film Deposition ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Energy Beam ◽  
Deposition Conditions

We are synthesizing boron nitride films by pulsed laser ablation in order to study the deposition conditions necessary to produce the cubic phase (cBN) which has a number of useful applications as a hard coating, semiconductor, and optical material. The yield of cubic material is controlled in part by the simultaneous irradiation of the growing film with a low energy beam of N2 and Arions. In order to understand how this transformation process occurs, we are using TEM to investigate how the microstructure and phase distribution varies with film deposition conditions.In many ways analogous to carbon, boron nitride forms both sp3- and sp2-bonded phases. The cubic phase (cBN), which is sp3 bonded, has the zinc blende structure, and in addition, BN can also form an sp3 bonded hexagonal phase with the wurtzite structure (wBN). An sp2-bonded hexagonal structure (hBN) is the stable room temperature phase, but like its analog, graphite, the sp2-bonded material can also exist in a highly disordered state, often referred to as turbostratic (tBN).

Ordering In Zn0.5Fe0.5Se Epilayers Grown on InP Substrates by Molecular Beam Epitaxy

1991 ◽  
Vol 231 ◽  
Author(s):  
L. Salamanca Riba ◽  
K. Park ◽  
B. T. Jonker
Keyword(s):  
High Resolution ◽  
Ordered Structure ◽  
Cross Sectional ◽  
Zinc Blende ◽  
Transmission Electron ◽  
Lattice Images ◽  
High Resolution Images ◽  
Diffraction Patterns ◽  
Inp Substrates ◽  
Image Simulations

AbstractWe have observed an ordered structure in Zn0.5Fe0.5Se epilayers grown on (001) InP substrates using transmission electron microscopy. The ordered structure of Zn0.5Fe0.5Se has Fe atoms occupying the (0,0,0) and (½, ½, 0) sites and Zn atoms occupying the (0, ½, ½) and (½, 0, ½) sites in the zinc-blende unit cell. Ordering is observed in both electron diffraction patterns and cross-sectional high-resolution lattice images along the < 100 > and < 110 > directions. This ordered structure consists of alternating ZnSe and FeSe monolayers along the < 100 > and < 110 > directions. Computer image simulations of the high-resolution images under various thicknesses, and defocusing conditions have been obtained and are compared with those obtained experimentally.

Atomic structural images of crystalline cholesterol monohydrate in human atheroma

1990 ◽  
Vol 48 (3) ◽  
pp. 206-207
Author(s):  
Ying-Shiung Lee
Keyword(s):  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Crystal Lattices ◽  
Resolution Electron ◽  
Lattice Images ◽  
High Resolution Electron Microscope ◽  
Diffraction Patterns ◽  
Cholesterol Monohydrate ◽  
Human Atheroma

To gain further insight regarding the micromechanisms of progression and regression of human atherosclerotic plaques the present study was designed for characterization of crystal lattices of cholesterol monohydrate, demonstration of cholesterol crystallization processes, and identification of crystal disorders of cholesterol monohydrate by means of high resolution electron microscopy (HREM).Clusters of cholesterol clefts containing crystalline cholesterol monohydrate were obtained from atherosclerotic human aortas under a dissecting microscope at autopsy. Cholesterol clefts were milled to a powder with a porcelain pestle. The powdered samples without staining dispersed in distilled water were spread on the copper-grid and dried at room temperature. The air-dried specimens were directly examined by a Hitachi H-9000 high resolution electron microscope operated at 300 KV. High resolution lattice images were taken under an optimal defocus condition. Selected area images and electron diffraction patterns were simultaneously taken for the analysis of crystalline characteristics.

Comparative Raman and HRTEM Study of Nanostructured GaN Nucleation Layers and Device Layers on Sapphire (0001)

2008 ◽  
Vol 8 (11) ◽  
pp. 5985-5992
Author(s):  
P. Pant ◽  
J. Narayan ◽  
A. Wushuer ◽  
M. H. Manghnani
Keyword(s):  
Thermal Expansion ◽  
High Temperature ◽  
Compressive Stress ◽  
Hexagonal Phase ◽  
Stacking Faults ◽  
Growth Time ◽  
Cubic Phase ◽  
Device Layer ◽  
Temperature Growth ◽  
Gan Film

Raman spectroscopy in conjunction with high-resolution transmission electron microscopy (HRTEM) has been used to study structural characteristics and strain distribution of the nanostructured GaN nucleation layer (NL) and the GaN device layer on (0001) sapphire substrates used for light-emitting diodes and lasers. Raman peaks corresponding to the cubic and the hexagonal phase of GaN are observed in the Raman spectrum from 15 nm and 45 nm NLs. A comparison of the peak intensities for the cubic and hexagonal phases of GaN in the NLs suggests that the cubic phase is dominant in the 15 nm NL and the hexagonal phase in the 45 nm NL. An increase in the density of stacking faults in the metastable cubic GaN (c-GaN) phase with increasing growth time lowers the system energy as well as locally converts c-GaN phase into hexagonal GaN (h-GaN). It also explains the observation of the more intense peaks of h-GaN in the 45 nm NL compared to c-GaN peaks. For the sample wherein an h-GaN device layer was grown at higher temperatures on the NL, narrow Raman peaks corresponding to only h-GaN were observed, confirming the high-quality of the films. The peak shift of the E2H(LO) mode of h-GaN in the NLs and the h-GaN film suggests the presence of a tensile stress in the NL which is attributed to defects such as stacking faults and twins, and a compressive stress in high-temperature grown h-GaN film which is attributed to the thermal-expansion mismatch between the film and the substrate. The peak shifts of the substrate also reveal that during the low temperature growth of the NL the substrate is under a compressive stress which is attributed to defects in the NL and during the high temperature growth of the device layer, there is a tensile strain in the substrate as expected from differences in coefficients of thermal expansion of the film and the substrate during the cooling cycle.

Planar defects in β-iron disilicide (β-FeSi2) analyzed by transmission electron microscopy and modeling

1992 ◽  
Vol 25 (2) ◽  
pp. 122-128 ◽  
Author(s):  
Y. Zheng ◽  
A. Taccoen ◽  
J. F. Petroff
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Structural Model ◽  
Stacking Faults ◽  
Planar Defects ◽  
Iron Disilicide ◽  
Defect Position ◽  
Transmission Electron ◽  
Lattice Images ◽  
Diffraction Patterns

Microplanar defects were observed in β-iron disilicide by transmission electron microscopy. They were identified as (100)[011]/2 intrinsic stacking faults by means of electron diffraction patterns and observed in high-resolution lattice images. A structural model of the faults is proposed here in setting the defect position at x = ¼ within the cell.

Characterization of Dislocations and Interfaces in Semiconductors by High Resolution Electron Microscopy

1980 ◽  
Vol 2 ◽  
Author(s):  
J.C.H. Spence ◽  
A. Olsen
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Local Symmetry ◽  
Partial Dislocations ◽  
Resolution Electron ◽  
Lattice Images ◽  
Diffraction Patterns ◽  
The Individual

ABSTRACTIt is not presently possible to resolve the individual atoms in any semiconductor by high resolution electron microscopy (HREM). However symmetry arguments may be used to allow near-atomic resolution lattice images to be interpreted in rare favorable cases. This method is applied to the problem of distinguishing shuffle and glide set partial dislocations in silicon. It is also proposed that two dimensional characteristic loss energy selected diffraction patterns be used to reveal the local symmetry about selected substitutional species implanted in semiconductor lattices.

Amorphous Alloys Atomic Structure Investigation by Means of Electron Microscopy and Diffraction

2021 ◽  
Vol 887 ◽  
pp. 254-261
Author(s):  
Evgenii V. Pustovalov ◽  
Aleksandr N. Fedorets ◽  
Vladimir V. Tkachev
Keyword(s):  
Electron Microscopy ◽  
Atomic Structure ◽  
Hexagonal Phase ◽  
Hexagonal Structure ◽  
Electrolytic Deposition ◽  
Cubic Phase ◽  
Total System ◽  
Atomic Order ◽  
Coordination Spheres ◽  
Fourth Coordination

In the paper, the atomic structure of amorphous and nanocrystalline alloys of the electrolytically obtained CoP, NiP, CoNiP, CoW, and CoNiW systems has been studied. The structure was investigated by electron microscopy and diffraction using a Libra 200 HR FE transmission electron microscope at an accelerating voltage of 200 kV within a temperature range of 50-35 °C. The obtained radial atom distribution function and the coordination sphere radii are in good agreement with the data for the cobalt structure in the cubic and hexagonal modifications. The high coordination numbers of the third and fourth coordination spheres allow suggesting a predominantly cubic structure of the local atom environment in CoP samples but somewhat lower, which is explained by the presence of free volume and phosphorus atoms distorting the local structure. When heating, the near atomic order also corresponds to the cubic phase of cobalt, and the ordering occurs in the second, third, and fourth coordination spheres. The data obtained for CoNiP alloys indicate that by configuration, the local atomic environment is closer to the hexagonal structure of nickel. In general, the structure of the CoP-CoNiP system alloy films obtained by electrolytic deposition is already in one of the local minima of the total system energy, which is confirmed by the near atomic order similar to the cubic phase of cobalt or hexagonal phase of nickel. This determines the good stability of the structure and properties during thermal exposure.

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