The Effect of Growth Stoichiometry on the GaN Dislocation Core Structure

2002 ◽  
Vol 743 ◽  
Author(s):  
Marcus Q. Baines ◽  
David Cherns ◽  
Julia W. P. Hsu ◽  
Michael J. Manfra
Keyword(s):  
Molecular Beam ◽  
Dislocation Core ◽  
Sample Surface ◽  
Plan View ◽  
The Core ◽  
Transmission Electron ◽  
Dislocation Core Structure ◽  
Edge Dislocations ◽  
Open Core ◽  
Lean Conditions

ABSTRACTPlan-view transmission electron microscopy was used to study the core structures of different dislocations in (0001) GaN layers grown under Ga-rich and Ga-lean conditions by molecular beam epitaxy. In Ga-rich samples at least one third of mixed type dislocations were open-core, and edge dislocations were observed to be closed-core. In contrast, under Ga-lean conditions, all dislocations were observed to be closed-core, and many were associated with pits at the sample surface. High resolution studies of the open core dislocations revealed that many were decorated with a disordered deposit, the origin of which is discussed.

scholarly journals Screw Dislocations in GaN Grown by Different Methods

2004 ◽  
Vol 10 (1) ◽  
pp. 47-54 ◽  
Author(s):  
Z. Liliental-Weber ◽  
D. Zakharov ◽  
J. Jasinski ◽  
M.A. O'Keefe ◽  
H. Morkoc
Keyword(s):  
Dislocation Core ◽  
Hydride Vapor Phase Epitaxy ◽  
Scattered Electron ◽  
Atomic Column ◽  
Plan View ◽  
Screw Dislocations ◽  
The Core ◽  
Transmission Electron ◽  
The Matrix ◽  
High Resolution Images

A study of screw dislocations in hydride-vapor-phase-epitaxy (HVPE) template and molecular-beam-epitaxy (MBE) overlayers was performed using transmission electron microscopy (TEM) in plan view and in cross section. It was observed that screw dislocations in the HVPE layers were decorated by small voids arranged along the screw axis. However, no voids were observed along screw dislocations in MBE overlayers. This was true both for MBE samples grown under Ga-lean and Ga-rich conditions. Dislocation core structures have been studied in these samples in the plan-view configuration. These experiments were supported by image simulation using the most recent models. A direct reconstruction of the phase and amplitude of the scattered electron wave from a focal series of high-resolution images was applied. It was shown that the core structures of screw dislocations in the studied materials were filled. The filed dislocation cores in an MBE samples were stoichiometric. However, in HVPE materials, single atomic columns show substantial differences in intensities and might indicate the possibility of higher Ga concentration in the core than in the matrix. A much lower intensity of the atomic column at the tip of the void was observed. This might suggest presence of lighter elements, such as oxygen, responsible for their formation.

Dislocations in GaAs/Si Interfaces

1988 ◽  
Vol 144 ◽  
Author(s):  
Jane G. Zhu ◽  
S. McKernan ◽  
C. B. Carter ◽  
W. J. Schaff ◽  
L. F. Eastman
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Molecular Beam Epitaxy ◽  
Molecular Beam ◽  
Dislocation Network ◽  
Plan View ◽  
Transmission Electron ◽  
Edge Dislocations

ABSTRACTDislocations present at GaAs/Si interfaces have been characterized using transmission electron microscopy in plan-view. The GaAs was grown by molecular-beam epitaxy on Si (001) substrate tilted* towards the [110] direction. The dislocation network at the interface consists primarily of orthogonal edge dislocations with Burgers vectors of a/2[110] and a/2[110]. However, displacements of these dislocation lines at the interface are observed. These displacements can be attributed to the interaction of 60* dislocations with the network of orthogonal edge dislocations. The density of these 60* dislocations along [110] direction is different from that along [110] direction.

Structural properties of molecular beam epitaxy grown Ni/Pt superlattices

1997 ◽  
Vol 12 (1) ◽  
pp. 161-174 ◽  
Author(s):  
W. Staiger ◽  
A. Michel ◽  
V. Pierron-Bohnes ◽  
N. Hermann ◽  
M. C. Cadeville
Keyword(s):  
Molecular Beam ◽  
Growth Direction ◽  
Misfit Dislocations ◽  
X Ray Diffraction ◽  
Plan View ◽  
X Ray ◽  
Transmission Electron ◽  
Superlattice Peak ◽  
Diffraction Peaks ◽  
Diffraction Patterns

We find that the [Ni3.2nmPt1.6nm] × 15 and [Ni3.2nmPt0.8nm] × 15 multilayers are semicoherent and display a columnar morphology. From both the period of the moir’e fringes and the positions of the diffraction peaks in electronic (plan-view and crosssection geometries) and x-ray diffraction patterns, one deduces that the nickel is relaxed (at least in the error bars of all our measurements), whereas the platinum remains slightly strained (≈−1%). The interfaces are sharp; no intermixing takes place giving rise to neat contrasts in transmission electron microscopy (TEM) and to high intensities of the superlattice peaks in the growth direction in both diffraction techniques. The relaxation of the interfacial misfit occurs partially through misfit dislocations, partially through the strain of platinum. A quasiperiodic twinning occurs at the interfaces, the stacking fault which forms the twin being the most often located at the interface Pt/Ni, i.e., when a Pt layer begins to grow on the Ni layer. The simulation of the θ/2θ superlattice peak intensities takes into account the columnar microstructure. It shows that the roughness is predominantly at medium scale with a fluctuation of about 12.5% for Ni layers and negligible for Pt layers.

The Structure of Dislocations in GaN Grown by MBE as a Function of the Gallium to Nitrogen Ratio

2003 ◽  
Vol 798 ◽  
Author(s):  
Marcus Q. Baines ◽  
David Cherns ◽  
Sergei V. Novikov ◽  
Michael J. Manfra ◽  
C. Thomas Foxon
Keyword(s):  
Electron Microscopy ◽  
Molecular Beam ◽  
Fundamental Property ◽  
Growth Surface ◽  
Force Microscopy ◽  
The Core ◽  
Weak Beam ◽  
Atomic Force ◽  
Transmission Electron ◽  
Nitrogen Ratio

ABSTRACTTransmission electron microscopy (TEM) and atomic force microscopy (AFM) have been used to analyse the core structure of dislocations in GaN grown by molecular beam epitaxy (MBE) as a function of the gallium to nitrogen ratio. Ga-rich samples had a much smoother morphology; TEM observations showed that amorphous deposits decorated some dislocations and occasional surface pits, but weak beam and end-on imaging suggested that, away from the growth surface, dislocations of all types had closed core structures, in contrast to previous observations (Hsu et al, Appl. Phys. Lett. 78, 3980 (2001), Baines et al, Mat. Res. Soc. Symp. Proc. 743, L2.5 (2003)). Ga-poor samples were found to have much rougher surfaces; dislocations were often at the centers of deep surface pits but were observed to be undecorated and to have closed core structures. It is concluded that in growth under Ga-rich conditions, decoration of dislocation cores depends on the accumulation of Ga at surface pits, rather than being a fundamental property of dislocation formation.

scholarly journals Revealing and Controlling the Core of Screw Dislocations in BCC Metals

2021 ◽  
Author(s):  
Zhaoxuan Wu ◽  
Rui Wang ◽  
Lingyu Zhu ◽  
Subrahmanyam Pattamatta ◽  
David Srolov
Keyword(s):  
Dft Calculations ◽  
Density Functional ◽  
Dislocation Core ◽  
Core Structure ◽  
Valence Electron Concentration ◽  
Interatomic Potentials ◽  
Structure Transition ◽  
The Core ◽  
Bcc Metals ◽  
Dislocation Core Structure

Abstract Body-centred-cubic (BCC) transition metals (TMs) tend to be brittle at low temperatures, posing significant challenges in their processing and major concerns for damage tolerance in critical load-carrying applications. The brittleness is largely dictated by the screw dislocation core structure; the nature and control of which has remained a puzzle for nearly a century. Here, we introduce a universal model and a physics-based material index χ that guides the manipulation of dislocation core structure in all pure BCC metals and alloys. We show that the core structure, commonly classified as degenerate (D) or non-degenerate (ND), is governed by the energy difference between BCC and face-centred cubic (FCC) structures and χ robustly captures this key quantity. For BCC TMs alloys, the core structure transition from ND to D occurs when χ drops below a threshold, as seen in atomistic simulations based on nearly all extant interatomic potentials and density functional theory (DFT) calculations of W-Re/Ta alloys. In binary W-TMs alloys, DFT calculations show that χ is related to the valence electron concentration at low to moderate solute concentrations, and can be controlled via alloying. χ can be quantitatively and efficiently predicted via rapid, low-cost DFT calculations for any BCC metal alloys, providing a robust, easily applied tool for the design of ductile and tough BCC alloys.

Screw Dislocations in MBE GaN Layers Grown on Top of HVPE Layers: Are They Different?

2002 ◽  
Vol 743 ◽  
Author(s):  
Z. Liliental-Weber ◽  
D. Zakharov ◽  
J. Jasinski ◽  
J. Washburn ◽  
M. A. O'Keefe ◽  
...  
Keyword(s):  
Cross Section ◽  
Electron Wave ◽  
Scattered Electron ◽  
Screw Axis ◽  
Plan View ◽  
Screw Dislocations ◽  
The Core ◽  
Transmission Electron ◽  
The Matrix ◽  
High Resolution Images

ABSTRACTTransmission Electron Microscopy was applied to study HVPE template and MBE over-layers in plan-view and cross-section. It was observed that screw dislocations in the HVPE layers are decorated by small voids arranged along the screw axis. However, no voids were observed along screw dislocations in MBE overlayers grown with excess Ga, despite the fact that Ga droplets were observed on the layer surface as well as imbedded in the layer. By applying a direct reconstruction of the phase and amplitude of the scattered electron wave from a focal series of high-resolution images, the core structures of screw dislocations in both materials have been studied and show that all screw dislocations have filled cores. Dislocation cores in MBE samples grown Ga-rich and N-rich show no substantial differences and no stoichiometric change compared to the matrix. However, in HVPE materials, single atomic columns show substantial differences in intensities and indicate the possibility of Ga presence. These Ga-rich cores might be responsible for the attraction impurities forming voids in their close vicinity.

Thin Film Superconducting MgB2 Grown by MBE without Post-Anneal

2001 ◽  
Vol 689 ◽  
Author(s):  
William Jo ◽  
Jeong-Uk Huh ◽  
Tsuyoshi Ohnishi ◽  
Ann F. Marshall ◽  
Malcolm R. Beasley ◽  
...  
Keyword(s):  
Deposition Temperature ◽  
Molecular Beam ◽  
Electron Beam Evaporation ◽  
Superconducting Transition ◽  
Full Width ◽  
Half Maximum ◽  
Plan View ◽  
Sapphire Substrates ◽  
Transmission Electron

ABSTRACTWe report the synthesis of superconducting MgB2 thin films grown in-situ by molecular beam epitaxy (MBE). Mg-rich fluxes are deposited with B-flux by electron beam evaporation onto c- and r-plane sapphire substrates. Deposition temperature is varied between 260 ∼ 320 °C. Base pressure of the MBE chamber is at low 10-10 Torr, rising to 10-8 Torr during deposition due mostly to the presence of hydrogen and nitrogen. Asgrown MgB2 films show superconducting transition at ∼ 34 K with ΔTc < 1 K. The films on c-plane sapphire substrates exhibit c-axis oriented peaks of MgB2, and full-width at half maximum of 3 degree in their rocking curves. Azimuthal phi-scan of the MgB2(101) peak shows 12-fold symmetric peaks, which is confirmed by selected area diffraction pattern in transmission electron microscopy (TEM). Plan-view TEM shows hexagonal-shaped grain growth with grain size of about 400 Å.

Dislocation Core Structure Evolution During Dislocation Glide in FCC Lattices

2003 ◽  
Vol 779 ◽  
Author(s):  
M.A. Soare ◽  
R.C. Picu
Keyword(s):  
Shear Stress ◽  
Elastic Field ◽  
Dislocation Core ◽  
Peierls Stress ◽  
Atomistic Simulations ◽  
Structure Evolution ◽  
Dislocation Glide ◽  
The Core ◽  
Fcc Lattice ◽  
Dislocation Core Structure

AbstractA dislocation core model is developed in terms of a singular decomposition of the elastic field surrounding the defect in a power series of 1/rn. The decomposition is a Laurent expansion beginning with the term corresponding to the Volterra dislocation and continuing with a series of dipoles and multipoles. The analysis is performed for an edge dislocation in an fcc lattice. The field surrounding the dislocation is derived by means of atomistic simulations. The coefficients of the series expansion are determined from the elastic field using path independent integrals. When loaded by a shear stress smaller than the Peierls stress, the core distorts. The distortion up to the instability (Peierls stress) is monitored based on the variation of these coefficients. The stacking fault separating the two partials is characterized, by using a similar procedure, as a source of elastic field.

The effect of shear stress on the screw dislocation core structure in body-centred cubic lattices

1973 ◽  
Vol 332 (1588) ◽  
pp. 85-111 ◽  
Keyword(s):  
Shear Stress ◽  
Screw Dislocation ◽  
Plastic Flow ◽  
Stacking Faults ◽  
Dislocation Core ◽  
Stacking Fault ◽  
Core Structure ◽  
Cubic Lattices ◽  
The Core ◽  
Dislocation Core Structure

The behaviour of the ½ a <111> screw dislocation core in the presence of an external shear stress on {110} planes has been studied for a variety of effective interionic potentials, each representing a stable b. c. c. lattice. The distortion and motion of the core are described using the concept of fractional dislocations, which are imperfect dislocations bounding a ribbon of generalized (unstable) stacking fault. Three essentially distinct types of movement are found, and the relation of these to plastic flow and twinning in real b. c. c. metals is discussed. It is found that the movement of the dislocation core can be rationalized in terms of the relative stresses needed to create generalized stacking faults on {110} and {112} planes.

In situ observations of electromigration induced void behavior

1995 ◽  
Vol 53 ◽  
pp. 244-245
Author(s):  
T. Marieb ◽  
J. C. Bravman ◽  
P. Flinn ◽  
D. Gardner ◽  
M. Madden
Keyword(s):  
Electron Microscopy ◽  
Void Nucleation ◽  
Plan View ◽  
Transmission Electron ◽  
Nucleation Sites ◽  
Microelectronics Industry ◽  
In Situ Observations ◽  
Backscatter Electron Detector ◽  
Voltage Scanning

Electromigration and stress voiding have been active areas of research in the microelectronics industry for many years. While accelerated testing of these phenomena has been performed for the last 25 years[1-2], only recently has the introduction of high voltage scanning electron microscopy (HVSEM) made possible in situ testing of realistic, passivated, full thickness samples at high resolution.With a combination of in situ HVSEM and post-testing transmission electron microscopy (TEM) , electromigration void nucleation sites in both normal polycrystalline and near-bamboo pure Al were investigated. The effect of the microstructure of the lines on the void motion was also studied.The HVSEM used was a slightly modified JEOL 1200 EX II scanning TEM with a backscatter electron detector placed above the sample[3]. To observe electromigration in situ the sample was heated and the line had current supplied to it to accelerate the voiding process. After testing lines were prepared for TEM by employing the plan-view wedge technique [6].

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