1.6 μm Emission from InAs Quantum Dots grown on a GaAs Substrate using an AlGaAsSb Metamorphic Buffer

2002 ◽  
Vol 737 ◽  
Author(s):  
G. Balakrishnan ◽  
S. Birudavolu ◽  
L. R. Dawson ◽  
D. L. Huffaker ◽  
Huifang Xu ◽  
...  
Keyword(s):  
Gaas Substrate ◽  
Lattice Mismatch ◽  
Defect Density ◽  
Matrix Material ◽  
Metamorphic Buffer ◽  
Transmission Electron ◽  
Digital Alloy ◽  
The Matrix ◽  
Matrix Lattice ◽  
Wavelength Emission

ABSTRACTWe report 1.6 μm emission from InAs QDs (QDs) grown on a GaAs substrate. The ensemble is grown on a graded digital alloy (DA), which increases the matrix lattice constant from 5.65 Å to 5.77 Å. The reduced lattice mismatch between the InAs and matrix material produces larger QDs and thereby allows longer wavelength emission compared to standard growth techniques. The resulting QD density ranges from 2×1010 to 8×1010/cm2 with QD dimensions of 5nm x 30nm measured using atomic force microscopy (AFM). According to x-ray diffraction (XRD) data and transmission electron microscopy (TEM), the metamorphic buffer is unstrained with low defect density.

Temporal Evolution of Bimodal Distribution of γ’ Precipitates in Ni-Al-Mo Alloys under the Influence of Coherency Strains

1995 ◽  
Vol 398 ◽  
Author(s):  
A.D. Sequeira ◽  
H.A. Calderon ◽  
G. Kostorz
Keyword(s):  
Lattice Mismatch ◽  
Bimodal Distribution ◽  
X Ray Diffraction ◽  
Double Step ◽  
Bimodal Size Distribution ◽  
Elastic Fields ◽  
Transmission Electron ◽  
The Matrix ◽  
Kinetics Of ◽  
Coherency Strains

ABSTRACTThe influence of coherency strains produced by the γ-γ’ lattice mismatch, δ, on the decomposition process of Ni-Al-Mo alloys with a bimodal size distribution is presented. Samples with δ ranging from positive to negative, were investigated in a double-step aging procedure. The evolution of the microstructure and the kinetics of coarsening were studied using transmission electron microscopy (TEM). The lattice mismatch between the matrix and the different classes of precipitates was determined by high-resolution high-temperature x-ray diffraction. It is shown that the strain fields produced by the lattice mismatch can influence dramatically the decomposition of metallic alloys. It is suggested that the reduction of the coarsening rate of the large precipitates, the fast coarsening rate of the small precipitates and the distortions detected in the matrix are all direct consequences of the elastic fields produced by the γ-γ’ lattice mismatch.

Growth of a-plane ZnO Thin Films on r-plane Sapphire by Plasma-assisted MBE

2005 ◽  
Vol 891 ◽  
Author(s):  
Junqing Q. Xie ◽  
J. W. Dong ◽  
A. Osinsky ◽  
P. P. Chow ◽  
Y. W. Heo ◽  
...  
Keyword(s):  
Thin Films ◽  
Lattice Mismatch ◽  
Defect Density ◽  
Zno Thin Films ◽  
Rf Plasma ◽  
Misfit Dislocations ◽  
Epitaxial Relationship ◽  
Cross Sectional ◽  
Transmission Electron ◽  
Small Lattice

ABSTRACTZnO thin films have been epitaxially grown on r-plane sapphire by RF-plasma-assisted molecular beam epitaxy. X-ray diffraction (XRD) and transmission electron microscopy (TEM) studies indicate that the epitaxial relationship between ZnO and r-plane sapphire is (1120)ZnO // (1102)sapphire and [0001]ZnO // [1101]sapphire. Atomic force microscopy measurements reveal islands extended along the sapphire [1101] direction. XRD omega rocking curves for the ZnO (1120) reflection measured either parallel or perpendicular to the island direction suggest the defect density anisotropy along these directions. Due to the small lattice mismatch along the ZnO [0001] direction, few misfit dislocations were observed at the ZnO/Al2O3 interface in the high-resolution cross-sectional TEM image with the zone axis along the ZnO [1100] direction.

Structural Defects and Critical Electric Field in 3C-SiC

2006 ◽  
Vol 527-529 ◽  
pp. 431-434 ◽  
Author(s):  
Michael A. Capano ◽  
A.R. Smith ◽  
Byeung C. Kim ◽  
E.P. Kvam ◽  
S. Tsoi ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Electric Field ◽  
Lattice Mismatch ◽  
Defect Density ◽  
Chemical Vapor ◽  
Structural Defects ◽  
X Ray ◽  
Transmission Electron ◽  
Current Voltage ◽  
P Type

3C-SiC p-type epilayers were grown to thicknesses of 1.5, 3, 6 and 10 μm on 2.5° off-axis Si(001) substrates by chemical vapor deposition (CVD). Silane and propane were used as precursors. Structural analysis of epilayers was performed using transmission electron microscopy (TEM), high-resolution x-ray diffractometry (HRXRD), and Raman spectroscopy. TEM showed defect densities (stacking faults, twins and dislocations) decreasing with increasing distance from the SiC/Si interface as the lattice mismatch stress is relaxed. This observation was corroborated by a monotonic decrease in HRXRD peak width (FWHM) from 780 arcsecs (1.5 μm thick epilayer) to 350 arcsecs (10 μm thick epilayer). Significant further reduction in x-ray FWHM is possible because the minimum FWHM detected is greater than the theoretical FWHM for SiC (about 12 arcsecs). Raman spectroscopy also indicates that the residual biaxial in-plane strain decreases with increasing epilayer thickness initially, but becomes essentially constant between 6 and 10 μm. Structural defect density shows the most significant reduction in the first 2 μm of growth. Phosphorus implantation was used to generate n+/p junctions for the measurement of the critical electric field in 3C-SiC. Based on current-voltage analyses, the critical electric field in p-type 3C-SiC with a doping of 2x1017 cm-3 is 1.3x106 V/cm.

Characterization of Chemically Vapor Deposited GaN on Sic on a Simox Substrate

1997 ◽  
Vol 3 (S2) ◽  
pp. 487-488
Author(s):  
W.L. Zhou ◽  
P. Pirouz
Keyword(s):  
Lattice Mismatch ◽  
Defect Density ◽  
Silicon Layer ◽  
Large Defect ◽  
Cross Sectional ◽  
Light Emitting ◽  
Light Emitting Devices ◽  
Transmission Electron ◽  
Potential Applications ◽  
Gan Film

GaN has been intensively studied because of its potential applications for the fabrication of blue- or ultraviolet-light emitting devices. Sapphire (α-Al2O3) is generally used as the substrate for growth of GaN film. However, the large lattice mismatch between GaN and Al2O3is a possible cause of the large defect density in the GaN films. Consequently, alternative substrates are being studied with the aim of growing films of lesser defect densities and improved opto-electronic properties. In this paper, we report a transmission electron microscopy (TEM) study of a GaN film grown on cubic SiC which has been obtained by carbonization of the top silicon layer of a SIMOX substrate, i.e. the system GaN/SiC/Si/SiO2/Si.Cross-sectional TEM specimens were prepared by the conventional sandwich technique with the foil surface normal to the Si[l10] direction. The composite sample was ground and dimpled to a thickness of ∼ 10μm, and subsequently ion thinned to electron transparency.

Phase Decomposition and Deformation of L12-Ordered Co-Rich Co3Ti

1994 ◽  
Vol 364 ◽  
Author(s):  
M. Nemoto ◽  
W. H. Tian ◽  
K. Hayashi
Keyword(s):  
Electron Microscope ◽  
High Temperature ◽  
Annealing Temperature ◽  
High Temperature Strength ◽  
Phase Decomposition ◽  
Solution Annealing ◽  
Rich Phase ◽  
Transmission Electron ◽  
The Matrix ◽  
Matrix Lattice

AbstractThe Co3Ti phase hardens appreciably by the fine precipitation of disordered fee Co-rich phase upon aging after quenching from solution annealing temperature. Transmission electron microscope(TEM) observations revealed that the precipitates are platelet in shape, lying nearly parallel to the {100} planes of the L12-ordered matrix, and perfectly coherent with the matrix lattice at the beginning of aging. The high temperature strength increases appreciably with the fine precipitation of disordered Co-rich phase over the whole temperature range investigated. TEM observations of the underaged and deformed alloys revealed that superdislocations are pinned by precipitates indicating an attractive interaction between dislocations and precipitates. At the overaged state, thin twins are introduced in the fee Co-rich precipitates during deformation.

Precipitation Hardening Analysis of an Al-8%Ag Alloy

2014 ◽  
Vol 976 ◽  
pp. 154-158
Author(s):  
Sergio Eliseo Hernández Martínez ◽  
Jorge García Rocha ◽  
José de Jesús Cruz Rivera ◽  
José Luis Hernandez Rivera
Keyword(s):  
Average Diameter ◽  
Specific Weight ◽  
Peak Hardness ◽  
Precipitation Process ◽  
Transmission Electron ◽  
The Matrix ◽  
Aa 2024 ◽  
Matrix Lattice ◽  
Dislocations Density ◽  
Size And Morphology

Aluminum alloys are important in aerospace industry, due to their mechanical properties, low specific weight and good corrosion resistance. Such properties are achieved due to a heat treatment of solubilization, quenching and aging, in order to precipitate metastables phases, which act as dislocation obstacles, increasing the strength of the alloy. In the present study, the precipitation sequence of Al-8%Ag alloy was analyzed via Vickers hardness and Transmission Electron Microscopy. The size and morphology of the precipitated particles, involved in the stages of precipitation process was characterized. It was determined the microstructure at the peak hardness, which is mainly composed of spherical GP zones with about 6 nm average diameter, which are responsible for the alloy achieve a value of 72 HVN. It was observed that this hardness value does not compete with others well known alloys, like AA 6061 and AA 2024, which can be precipitation hardened. The main reason for the low values of HVN, is because of there is no enough difference between the matrix and the precipitated particles lattice parameters, and dont cause a significant elastic strain by coherence in the matrix lattice, that could produce a substantial hardening. To ascertain this assumption, the aged material was severely plastic deformed, achieving 94 HVN, and the grain refinement and high dislocations density were the major hardening mechanisms, since the precipitates behavior was similar as the matrix, because particles were distorted instead of acting as impediment to material flow.

Effect of the Ge preamorphisation dose on the thermal evolution of End of Range defects

2001 ◽  
Vol 669 ◽  
Author(s):  
B. Colombeau ◽  
F. Cristiano ◽  
J-C. Marrot ◽  
G. Ben Assayag ◽  
A. Claverie
Keyword(s):  
Ostwald Ripening ◽  
Defect Density ◽  
Thermal Evolution ◽  
Plan View ◽  
Transmission Electron ◽  
The Matrix ◽  
Mean Size ◽  
Defect Size Distribution ◽  
Increasing Function ◽  
Imaging Conditions

ABSTRACTIn this paper, we study the effect of the Ge+ preamorphisation dose on the thermal evolution of End of Range (EOR) defects upon annealing. Amorphisations were carried out by implanting Ge+ at 150 keV to doses ranging from 1×1015 ions/cm2 to 8×1015ions/cm2. Rapid Thermal Annealing (RTA) was performed for various time/temperature combinations in nitrogen ambient. Plan view transmission electron microscopy under specific imaging conditions was used to measure the size distributions and densities of the EOR defects. We found that for a fixed thermal budget, the increase in the Ge ion dose results in an increase in the defect density but has no effect on the defect size distribution. This invariance of the mean size of defects with respect to the initial supersaturation introduced in the matrix is an expected characteristic of a conservative Ostwald ripening mechanism. Moreover, the total number (Nb) of Si interstitial atoms bound to the EOR defects is a monotonically increasing function of the Ge ion dose. Furthermore, we found that Nb is directly proportional to the number of Si atoms in excess of the vacancies found below the a/c interface as calculated by MonteCarlo simulations. This is consistent with the “excess interstitial” model which explains the origin of the EOR defects.

scholarly journals Characterization of γ′ Precipitates in Cast Ni-Based Superalloy and Their Behaviour at High-Homologous Temperatures Studied by TEM and in Situ XRD

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2397 ◽  
Author(s):  
Łukasz Rakoczy ◽  
Ondrej Milkovič ◽  
Bogdan Rutkowski ◽  
Rafał Cygan ◽  
Małgorzata Grudzień-Rakoczy ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Matrix Material ◽  
High Volume ◽  
Lattice Parameter ◽  
X Ray Diffraction ◽  
In Situ Xrd ◽  
Transmission Electron ◽  
The Matrix

In situ X-ray diffraction and transmission electron microscopy has been used to investigate René 108 Ni-based superalloy after short-term annealing at high-homologous temperatures. Current work is focused on characterisation of γ′ precipitates, their volume fraction, evolution of the lattice parameter of γ and γ′ phases and misfit parameter of γ′ in the matrix. Material in the initial condition is characterised by a high-volume fraction (over 63%) of γ′ precipitates. Irregular distribution of alloying elements was observed. Matrix channels were strongly enriched in Cr, Co, W and Mo, whereas precipitates contain large amount of Al, Ti, Ta and Hf. Exposure to high-homologous temperatures in the range 1100–1250 °C led to the dissolution of the precipitates, which influenced the change of lattice parameter of both γ and γ′ phases. The lattice parameter of the matrix continuously grew during holding at high temperatures, which had a dominant influence on the more negative misfit coefficient.

Modeling Misfit Dislocation Arrays for the Growth of Low-Defect Density AlSb on Si

2006 ◽  
Vol 934 ◽  
Author(s):  
Anitha Jallipalli ◽  
G. Balakrishnan ◽  
S.H. Huang ◽  
A. Khoshakhlagh ◽  
L.R. Dawson ◽  
...  
Keyword(s):  
Lattice Mismatch ◽  
Defect Density ◽  
Analytical Models ◽  
Misfit Dislocations ◽  
Growth Interface ◽  
Strain Relief ◽  
Transmission Electron ◽  
Dislocation Arrays ◽  
Two Systems ◽  
Extensive Growth

ABSTRACTWe present analytical models and experimental results to describe low-defect density growth (∼ 6 × 105/cm2) of highly mismatched antimonides on Si and GaAs substrates, with strain relief achieved at the growth interface through periodic, 90° interfacial misfit dislocations (IMF). We use molecular mechanics (MM) based modeling techniques to understand, at the atomic level, the spontaneous formation and energetics of these IMF. We have modeled, grown and characterized two systems extensively, these are - AlSb on Si with ∼ 13% mismatch and GaSb on GaAs with 7.83% lattice mismatch. Growth of these materials by molecular beam epitaxy (MBE) and subsequent High-Resolution Transmission Electron Microscopy (HR-TEM) has indicated that there is no tetragonal distortion in these two systems despite the high lattice mismatch. Instead, the mismatched epi-layers spontaneously form periodic IMF arrays that run along both [110] and [1-10] directions and relieve almost 100% of the strain in a few monolayers of deposition. To model this form of strain relief, we use existing theories of strain relief adapted for very high strain conditions and we also use bond energetics to model the strain-relieving interface. The IMFs in these systems are periodic and so is the deviation in bond lengths and bond angles, which restricts our calculation space to a finite number of elements. We shall also demonstrate extensive growth and characterization results of the materials grown with a particular emphasis on the strain-relieving interface to show excellent agreement of the experimental data with the proposed models. The high quality and low-defect density in AlSb grown on Si, has helped us demonstrate optically pumped IR VCSELs and edge emitters monolithically on Si (001) and this data will also be presented.

Constitutive Modeling of Near-Equiatomic NiTi Shape Memory Alloys Considering Composition and Heat Treatment

2016 ◽  
Vol 856 ◽  
pp. 78-84
Author(s):  
Austin Cox ◽  
Theocharis Baxevanis ◽  
Dimitris C. Lagoudas
Keyword(s):  
Heat Treatment ◽  
Shape Memory Alloys ◽  
Shape Memory ◽  
Volume Fraction ◽  
Lattice Mismatch ◽  
Memory Performance ◽  
Matrix Material ◽  
Precipitate Growth ◽  
The Matrix ◽  
Niti Shape Memory Alloys

A predictive microscale-informed model that takes into account the precipitate–shape memory performance relations and allows for the evaluation of the effective thermomechanical response of precipitated Ni-rich NiTi shape memory alloys on the basis of composition and heat treatment is presented. The model considers the structural effect of the precipitates (coherency stresses due to the lattice mismatch between the precipitates and the matrix material and precipitate volume fraction), as well as the effect of the Ni-concentration gradient in the matrix, resulting from Ni-depletion during precipitate growth. The predictive capability of the model is tested against experimental data obtained fromNi50.7Ti (at. %) that has been heat treated under different conditions and good agreement is shown.

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