Model of Subgrain Structure Formation in HTS Cuprates and Ferropnictides

MRS Proceedings ◽

10.1557/opl.2012.1407 ◽

2012 ◽

Vol 1434 ◽

Author(s):

Constantin G. Tretiatchenko ◽

Vassily L. Svetchnikov ◽

Harold Wiesmann

Keyword(s):

Film Growth ◽

Lattice Mismatch ◽

Subgrain Size ◽

Finite Size ◽

Interface Energy ◽

Rotational Relaxation ◽

Subgrain Structure ◽

Relaxation Of Stresses ◽

Validity Range ◽

Edge Dislocations

ABSTRACTWe have modified the model of rotational relaxation of stresses at mismatched interface by taking into account elastic strains of the growing film. This extended the model validity range to a wider class of compounds including pnictides. The model describes formation of low angle boundaries consisting of threading edge dislocations. Calculated interface energy shows that rotational relaxation occurs due to finite size of clusters and to non-equilibrium effect of the film growth. Subgrain size and expected angle of domain rotation depending on the lattice mismatch have been estimated. Unusual effect of increasing angle between the film subgrains at reduction of the deposition rate is predicted. The computed parameters of subgrains are consistent with the observed film nanostructure.

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Peculiarities of REBCO Films Growth on Single Crystalline Substrates

MRS Proceedings ◽

10.1557/opl.2011.1486 ◽

2011 ◽

Vol 1367 ◽

Cited By ~ 1

Author(s):

Constantin G. Tretiatchenko ◽

Victor S. Flis ◽

Vassily L. Svetchnikov ◽

Volodymyr M. Pan

Keyword(s):

Film Growth ◽

Lattice Mismatch ◽

Subgrain Size ◽

High Temperature Superconductors ◽

Finite Size ◽

Rotational Relaxation ◽

Layered Perovskite ◽

Layered Perovskite Structure ◽

Edge Dislocations ◽

Equilibrium Effect

ABSTRACTWe suggest a model of mismatched interface and calculate its energy in order to describe formation of threading edge dislocations by the mechanism of rotational relaxation of interface stresses. The model takes into account strongly layered perovskite structure of high-temperature superconductors. We have shown that rotational relaxation occurs due to finite size of clusters and to non-equilibrium effect of the film growth. We have predicted the subgrain size and the expected rotation of domains depending on the lattice mismatch. The computed values are consistent with the observed YBCO film nanostructure.

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Simulation of the Organization of Heteroepitaxial Monolayer Islands Under Anisotropic Conditions

MRS Proceedings ◽

10.1557/proc-854-u3.7 ◽

2004 ◽

Vol 854 ◽

Author(s):

Gajendra Pandey ◽

Robert V. Kukta

Keyword(s):

Point Defects ◽

Surface Stress ◽

Lattice Mismatch ◽

Finite Size ◽

Source Model ◽

Crystalline Material ◽

Elastic Fields ◽

High Anisotropy ◽

Degree Of Anisotropy ◽

Hexagonal Arrays

ABSTRACTThis paper addresses the effect of anisotropy on the organization of epitaxial islands deposited on a substrate. Focus is on in-plane anisotropies in surface stress and lattice mismatch between the film and substrate materials. Starting from a configuration where island sizes and position are random, evolution towards equilibrium through mass transport via condensation/evaporation is simulated. The effect of the degree of anisotropy is investigated. An efficient numerical method is obtained by reducing a model of square monolayer islands of finite size to point defects that interact through their elastic fields. Models for both the kinetics and energetics of the system are obtained by this reduction. It is found that the point source model is accurate for island separations larger than about 3 times the width of an island. Under isotropic conditions islands tend to form into hexagonal arrays, and as there is no preferred orientation of these arrays, defects analogous to grain boundaries in a crystalline material tend to arise. With anisotropy islands tend to align in particular directions. This is found to enhance organization in cases of modest anisotropy and cause islands to form into zigzagged lines in cases of high anisotropy.

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The mechanism of sputter-induced epitaxy modification in YBCO (001) films grown on MgO (001) substrates

Journal of Materials Research ◽

10.1557/jmr.1998.0460 ◽

1998 ◽

Vol 13 (12) ◽

pp. 3378-3388

Author(s):

Y. Huang ◽

B. V. Vuchic ◽

M. Carmody ◽

P. M. Baldo ◽

K. L. Merkle ◽

...

Keyword(s):

Buffer Layer ◽

Film Growth ◽

Ybco Film ◽

Lattice Mismatch ◽

Substrate Surface ◽

Oriented Growth ◽

Orientation Change ◽

Large Lattice Mismatch ◽

Major Factors ◽

Hot Filament

The sputter-induced epitaxy change of in-plane orientation occurring in YBa2Cu3O7-x (001) thin films grown on MgO (001) substrates by pulsed organo-metallic beam epitaxy (POMBE) is investigated by a series of film growth and characterization experiments, including RBS and TEM. The factors influencing the orientation change are systematically studied. The experimental results suggest that the substrate surface morphology change caused by the ion sputtering and the Ar ion implantation in the substrate surface layer are not the major factors that affect the orientation change. Instead, the implantation of W ions, which come from the hot filament of the ion gun, and the initial Ba deposition layer in the YBCO film growth play the most important roles in controlling the epitaxy orientation change. Microstructure studies show that a BaxMg1-xO buffer layer is formed on top of the sputtered substrate surface due to Ba diffusion into the W implanted layer. It is believed that the formation of this buffer layer relieves the large lattice mismatch and changes the YBCO film from the 45° oriented growth to the 0° oriented growth.

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Void and Dislocation Microstructure Development in Heteroepitaxial Film Growth

MRS Proceedings ◽

10.1557/proc-399-371 ◽

1995 ◽

Vol 399 ◽

Author(s):

Richard W. Smith ◽

David J. Srolovitz

Keyword(s):

Thin Films ◽

Molecular Dynamics ◽

Film Growth ◽

Lattice Misfit ◽

Two Dimensional ◽

Microstructure Development ◽

Non Equilibrium Molecular Dynamics ◽

Dynamics Simulations ◽

Film Substrate ◽

Edge Dislocations

ABSTRACTTwo dimensional, non-equilibrium molecular dynamics simulations have been performed to examine the microstructures of both homoepitaxial and heteroepitaxial thin films grown on single crystal substrates. The principal microstructural features to develop within these films are small voids and edge dislocations. Voids form near the surface of the growing film as surface depressions between microcolumns pinch off to become closed volumes. These voids often form in such a way as to introduce dislocations into the crystal with their cores positioned within the voids. Dislocations are also formed during heteroepitaxy at the interface between the substrate and film. These dislocations tend to be mobile. When voids are present in the film and when the lattice misfit is low, dislocations tend to be trapped in the voids or pulled toward them due to dislocation image interactions. Once attached to voids, dislocations are effectively pinned there. When voids are absent or when the misfit is high, dislocations are restricted to the film-substrate interface. In the case of heteroepitaxy, dislocations are found to relieve either tensile or compressive misfit stresses. Misfit stresses may also be accommodated, to some extent, merely by the free volume of the voids themselves.

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Sn-based Group-IV Semiconductors on Si: New Infrared Materials and New Templates for Mismatched Epitaxy

MRS Proceedings ◽

10.1557/proc-0891-ee12-08 ◽

2005 ◽

Vol 891 ◽

Author(s):

John Tolle ◽

Radek Roucka ◽

Vijay D'Costa ◽

Jose Menendez ◽

Andrew Chizmeshya ◽

...

Keyword(s):

Band Gap ◽

Buffer Layer ◽

Lattice Mismatch ◽

Group Iv ◽

Buffer Layers ◽

Direct Band Gap ◽

Group Iv Semiconductors ◽

Direct Band ◽

Infrared Materials ◽

Edge Dislocations

ABSTRACTWe report growth and properties of GeSn and SiGeSn alloys on Si (100). These materials are prepared using a novel CVD approach based on reactions of Si-Ge hydrides and SnD4. High quality GeSn films with Sn contents up to 20%, and strain free microstructures have been obtained. The lattice mismatch between the films and Si is relieved by Lomer edge dislocations located at the interface. This material is of interest due to the predicted cross-over to a direct gap semiconductor for moderate Sn concentrations. We find that the direct band gap, and, consequently, the main absorption edge, shifts monotonically to lower energies as the Sn concentration is increased. The compositional dependence of the direct band gap shows a strong bowing, such that the direct band gap is reduced to 0.4 eV (from 0.8 eV for pure Ge) for a concentration of 14% Sn. The ternary SiGeSn alloy has been grown for the first time on GeSn buffer layers. This material opens up entirely new opportunities for strain and band gap engineering using group-IV materials via decoupling of strain and composition. Our SiGeSn layers have lattice constants above and below that of pure Ge, and depending on the thickness and composition of the underlying buffer layer they can be grown relaxed, with compressive, or with tensile strain. In addition to acting as a buffer layer for the growth of SiGeSn, we have found that GeSn can act as a template for the subsequent growth of a variety of materials, including III-V semiconductors.

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Structural Defects and Their Relationship to Nucleation of Gan Thin Films

MRS Proceedings ◽

10.1557/proc-423-475 ◽

1996 ◽

Vol 423 ◽

Cited By ~ 36

Author(s):

Weida Gian ◽

Marek Skowronski ◽

Greg S. Rohrer

Keyword(s):

Film Growth ◽

Three Dimensional ◽

Scanning Force Microscopy ◽

Columnar Structure ◽

Layer Growth ◽

Buffer Layers ◽

Structural Defects ◽

Layer By Layer ◽

Extended Defects ◽

Edge Dislocations

AbstractMicrostructure and extended defects in α-GaN films grown by organometallic vapor phase epitaxy on sapphire substrates using low temperature AIN (or GaN) buffer layers have been studied using transmission electron microscopy. The types and distribution of extended defects were correlated with the film growth mode and the layer nucleation mechanism which was characterized by scanning force microscopy. The nature of the extended defects was directly related to the initial three-dimensional growth. It was found that inhomogeneous nucleation leads to a grain-like structure in the buffer; the GaN films then have a columnar structure with a high density of straight edge dislocations at grain boundaries which are less likely to be suppressed by common annihilation mechanisms. Layer-by-layer growth proceeds in many individual islands which is evidenced by the observation of hexagonal growth hillocks. Each growth hillock has an open-core screw dislocation at its center which emits monolayer-height spiral steps.

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Substructure of Ultrafine Grained Metals after Intensive External Influences at Study of Field Ion Microscopy Method

Materials Science Forum ◽

10.4028/www.scientific.net/msf.503-504.995 ◽

2006 ◽

Vol 503-504 ◽

pp. 995-1000

Author(s):

Viktor Varyukhin ◽

B. Efros ◽

V. Ivchenko ◽

N. Efros ◽

E. Popova

Keyword(s):

Plastic Deformation ◽

Grain Size ◽

Severe Plastic Deformation ◽

Subgrain Size ◽

Boundary Region ◽

Subgrain Structure ◽

Field Ion Microscopy ◽

Ultrafine Grained ◽

Microscopy Method ◽

Ion Microscopy

It has been revealed that in Iridium influenced be severe plastic deformation (SPD) a ultrafine grained (UFG) structure is formed (the grain size of 20-30 nm), but in the bodies of grains there are practically no defects of structure, however, after irradiation a subgrain structure, (subgrain size of 3-5 nm) is formed, and in the bodies of subgrains there are defects. The subgrain structure was also revealed in UFG Nickel and Copper after SPD (subgrain size of 3-15 nm), but in the latter case the observed boundary region is broader and subgrain are highly disoriented.

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Microstructural and Electrical Characterization of Misfit Dislocations at the InAs/GaP Heterointerface

MRS Proceedings ◽

10.1557/proc-500-63 ◽

1997 ◽

Vol 500 ◽

Author(s):

V. Gopal ◽

T. P. Chin ◽

A. L. Vasiliev ◽

J. M. Woodall ◽

E. P. Kvam

Keyword(s):

Misfit Dislocation ◽

Lattice Mismatch ◽

Electrical Characterization ◽

Growth Conditions ◽

Misfit Dislocations ◽

Ir Detectors ◽

Mbe Growth ◽

Transmission Electron ◽

Hall Effect Measurements ◽

Edge Dislocations

ABSTRACTInAs is a narrow band gap semiconductor with potential for such applications as IR detectors, low temperature transistors, etc‥ However, the lack of suitable substrates has hampered progress in the development of InAs based devices. In the present study, InAs was grown by Molecular Beam Epitaxy on (001) GaP substrates. Though this system has a high lattice mismatch, (∼11%), certain MBE growth conditions result in 80% relaxed InAs layers on GaP with the mismatch accommodated predominantly by 90° pure edge dislocations. Misfit dislocation microstructures were studied using Transmission Electron Microscopy. Electrical characterization using lateral conductance and Hall effect measurements were also performed. Preliminary results indicate the possibility of misfit dislocation related conductivity. The possible correlation between interface structure and electrical properties is discussed.

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High-resolution transmission electron microscopy (HRTEM) observation of dislocation structures in AlN thin films

Journal of Materials Research ◽

10.1557/jmr.2008.0265 ◽

2008 ◽

Vol 23 (8) ◽

pp. 2188-2194 ◽

Cited By ~ 11

Author(s):

Yuki Tokumoto ◽

Naoya Shibata ◽

Teruyasu Mizoguchi ◽

Masakazu Sugiyama ◽

Yukihiro Shimogaki ◽

...

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

High Resolution ◽

Film Growth ◽

Threading Dislocations ◽

Organic Vapor ◽

Transmission Electron ◽

Hrtem Observation ◽

Metal Organic ◽

Edge Dislocations

The structure and configuration of threading dislocations (TDs) in AlN films grown on (0001) sapphire by metal–organic vapor phase epitaxy (MOVPE) were characterized by high-resolution transmission electron microscopy (HRTEM). It was found that the TDs formed in the films were mainly the perfect edge dislocations with the Burgers vector of b = ⅓〈11¯20〉. The majority of the edge TDs were not randomly formed but densely arranged in lines. The arrays of the edge TDs were mainly observed on the {11¯20} and {10¯10} planes. These two planes showed different configurations of TDs. TD arrays on both of these planes constituted low-angle boundaries. We suggest that these TDs are introduced to compensate for slight misorientations between the subgrains during the film growth.

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