Cooperative dislocation generation under applied loads via Kosterlitz-Thouless mechanism : a Monte Carlo study / Mang-mang Ling.

Format:

Book

Manuscript

Microformat

Thesis/Dissertation

Author/Creator:

Ling, Mang-mang.

Contributor:

Vitek, V., advisor.

University of Pennsylvania.

Language:

English

Subjects (All):

Penn dissertations--Physics.

Physics--Penn dissertations.

Penn dissertations--Astronomy.

Astronomy--Penn dissertations.

Local Subjects:

Penn dissertations--Physics.

Physics--Penn dissertations.

Penn dissertations--Astronomy.

Astronomy--Penn dissertations.

Physical Description:

xxxv, 287 pages : illustrations ; 29 cm

Production:

1999.

Summary:

In this thesis Monte Carlo simulations have been performed to probe the KPV model of cooperative dissociation of dislocation dipoles. This model predicts that such a dissociation occurs at temperatures well below the K-T transition temperature in the presence of applied loads. The goal of this thesis is to examine whether the lowering of the transition temperature under applied loads can be demonstrated by Monte Carlo (MC) simulations. The Monte Carlo results show that the critical temperature is, indeed, progressively reduced from the zero-field Kosterlitz and Thouless (e.g. K-T) limit as the applied electric field and/or stress is increased. Good agreement between the numerical results and the theoretical predictions (i.e. the AHNS (Ambegaokar, Halperin et al. 1978; Ambegaokar, Halperin et al. 1980), MP (Minnhagen, Westman et al. 1995) and KPV predictions) has been found.

The goal of this thesis is also to test by MC simulations the basic hypothesis of the KPV model, namely, the enhanced rate of formation of dipoles and the increased feedback effect which leads to expansion of the dipoles in the presence of an applied field. The KPV model distinguishes this positive feedback effect from the thermally-activated field-driven dissociation of individual dipoles that can take place at any temperature. For this purpose we have investigated the charge current-voltage characteristics of the 2DCG model. Analogous MC studies have also been made for the plastic strain-stress characteristics of the 2D dislocation dipole system. The power-law exponent of the current-voltage characteristics of the 2DCG system obtained from MC simulations reveals nonlinear behavior (i.e. the nonlinear conductance of the 2DCG system) at temperatures below the K-T transition temperature, TKT . In contrast, it reveals a linear behavior (i.e. linear conductance of the 2DCG system) at temperatures well above TKT . This charge current-voltage characteristics of the 2DCG model clearly shows the enhanced formation and expansion of charge dipoles in the presence of the applied electric field. Similarly, a power-law relation has been found for the plastic strain-stress relationship in the 2D dislocation dipole system. Features analogous to the charge current-voltage characteristics of the 2DCG model have been revealed. It is shown by MC that the formation and expansion of dislocation dipoles, which directly affect the transition temperature, are both enhanced in the presence of the applied stress. Thus, the basic predictions of the KPV model have been confirmed by our MC simulations. (Abstract shortened by UMI.)

Notes:

Adviser: Vaclav Vitek.

Thesis (Ph.D. in Physics and Astronomy) -- University of Pennsylvania, 1999.

Includes bibliographical references.

Local Notes:

University Microfilms order no.: 99-26104.

OCLC:

244971065