Defect and Island Nucleation in Materials: Kinetic Monte Carlo, Rate Equation Theory and Temperature Accelerated Dynamics (TAD) Simulations
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| Language: | English |
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University of Toledo / OhioLINK
2018
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| Online Access: | http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544443201322287 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-toledo1544443201322287 |
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NDLTD |
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English |
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Physics |
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Physics Sabbar, Ehsan H. Defect and Island Nucleation in Materials: Kinetic Monte Carlo, Rate Equation Theory and Temperature Accelerated Dynamics (TAD) Simulations |
| author |
Sabbar, Ehsan H. |
| author_facet |
Sabbar, Ehsan H. |
| author_sort |
Sabbar, Ehsan H. |
| title |
Defect and Island Nucleation in Materials: Kinetic Monte Carlo, Rate Equation Theory and Temperature Accelerated Dynamics (TAD) Simulations |
| title_short |
Defect and Island Nucleation in Materials: Kinetic Monte Carlo, Rate Equation Theory and Temperature Accelerated Dynamics (TAD) Simulations |
| title_full |
Defect and Island Nucleation in Materials: Kinetic Monte Carlo, Rate Equation Theory and Temperature Accelerated Dynamics (TAD) Simulations |
| title_fullStr |
Defect and Island Nucleation in Materials: Kinetic Monte Carlo, Rate Equation Theory and Temperature Accelerated Dynamics (TAD) Simulations |
| title_full_unstemmed |
Defect and Island Nucleation in Materials: Kinetic Monte Carlo, Rate Equation Theory and Temperature Accelerated Dynamics (TAD) Simulations |
| title_sort |
defect and island nucleation in materials: kinetic monte carlo, rate equation theory and temperature accelerated dynamics (tad) simulations |
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University of Toledo / OhioLINK |
| publishDate |
2018 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544443201322287 |
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AT sabbarehsanh defectandislandnucleationinmaterialskineticmontecarlorateequationtheoryandtemperatureaccelerateddynamicstadsimulations |
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1719455002025525248 |
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ndltd-OhioLink-oai-etd.ohiolink.edu-toledo15444432013222872021-08-03T07:08:53Z Defect and Island Nucleation in Materials: Kinetic Monte Carlo, Rate Equation Theory and Temperature Accelerated Dynamics (TAD) Simulations Sabbar, Ehsan H. Physics Recently a general rate-equation (RE) theory of submonolayer island nucleation and growth was developed [J.G. Amar and M. Semaan, Phys. Rev. E 93}, 062805 (2016)] which takes into account the critical island-size i, island fractal dimension df, substrate dimension d, and diffusion exponent , and good agreement with simulations was found for the case of irreversible growth corresponding to a critical island-size i = 1 with d = 2. Here we present the results of simulations carried out in 1D (corresponding to d = 1) of island nucleation and growth with anomalous diffusion which were carried out for both the case of superdiffusion (μ > 1) and subdiffusion (μ < 1). Excellent agreement is found with the general RE theory for both irreversible growth (i = 1) as well as reversible growth with i = 2 for all 0 ≤ μ ≤ 2. Motivated by recent experiments on submonolayer organic film growth with anomalous diffusion, a general rate-equation (RE) theory of submonolayer island nucleation and growth was developed [J.G. Amar and M. Semaan, Phys. Rev. E {93}, 062805 (2016)] which takes into account the critical island-size i, island fractal dimension df, substrate dimension d, and diffusion exponent μ, and good agreement with simulations was found for the case of irreversible growth corresponding to a critical island-size i = 1 with d = 2. However, since many experiments correspond to reversible growth, it is of interest to determine if these results also hold for i > 1. Here we present the results of simulations of reversible island growth with i = d = 2 which were carried out for both the case of superdiffusion (μ > 1) and subdiffusion (μ < 1) as well as for both ramified islands (df \σ2) and point-islands (df = ∞). In the case of superdiffusion, corresponding to `hot' freshly deposited monomers, excellent agreement is obtained with the predictions of the generalized RE theory for the exponents χ (μ) and χ 1(μ) which describe the scaling of the island and monomer densities with deposition rate $F$. In addition, the exponents do not depend on whether or not monomers remain superdiffusive or are thermalized (e.g. undergo regular diffusion) after detaching from a dimer. However, we also find that, as was previously found in the case of irreversible growth, the exponent χ only approaches its asymptotic value logarithmically with increasing 1/F. This result has important implications for the interpretation of experiments. In contrast to these results for the case of superdiffusion, in the more complex case of subdiffusion we find only partial agreement with the RE theory for the case i = d = 2. In particular, while there is good agreement for the case of point-islands, in the case of ramified islands the exponents χ and χ1 are significantly higher than predicted. Recently, there has been significant interest in the effects of anomalous diffusion on island nucleation and growth. Of particular interest are the exponents χ and χ 1 which describe the dependence of the island and monomer density on deposition rate as well as the dependence of these exponents on the anomalous diffusion exponent μ and critical island size. While most simulations have been focused on growth on a 2D and/or quasi-1D substrate, here we present simulation results for the irreversible growth of ramified islands in three-dimensions (d = 3) for both cases of subdiffusion (μ< 1) and superdiffusion (1 <μ ≤ 2). Good agreement is found in both cases with a recently developed theory [J.G. Amar and M. Semaan, Phys. Rev. E { 93}, 062805 (2016)] which takes into account the critical island-size i, island fractal dimension df, substrate dimension d, and diffusion exponent μ . In addition, we confirm that in this case the critical value of μ is given by the general prediction μc = 2/d = 2/3. We also present results for the irreversible growth of point-islands in d = 3 and d = 4 for both monomer subdiffusion and superdiffusion, and good agreement with RE predictions is also obtained. In addition, our results confirm that for point-islands with d ≥ 3 one has μc =1 rather than 2/d. Results for the scaling of the capture-number distribution (CND), island-size distribution (ISD), and average capture number for the case of irreversible growth with monomer superdiffusion in d = 2 are also presented. Surprisingly, we find that both the scaled ISD and CND depend very weakly on the monomer diffusion exponent μ. These results indicate that - in contrast to the scaling of the average capture number which depends on the monomer diffusion exponent μ- both the scaled ISD and CND are primarily determined by the capture-zone distribution, which depends primarily on the ``history" of the nucleation process rather than the detailed mechanisms for monomer diffusion. We study the effect of the strain on the islands morphology of Cu/Cu(100) growth. The morphology of Cu growth depends on the applied strain and the island size. At 2% compressive strain the shape of Cu islands changes from semi square to blobby shape due to unexpected pop-out events. At 4% compressive strain, the bond between some atoms start breaking and the barrier energy for pop out event along <001> direction decreases due to the pop out events along <001> direction creating the vacancy. The presence of vacancy helps to form the dislocation. Also, at 4% compressive strain the average compressive strain is constant but increases rapidly right before the formation of dislocation. This strain surprisingly goes down after the formation of dislocation due to the increases in average bond length. At 8% tensile case there is no dislocation formed and the stress through out this process remains constant and the shape of the Cu island is elongated when the tensile strain is applied.Stacking faults are important type of crystal defects commonly observed in crystal structures . Understanding the formation mechanisms of stacking faults are crucial. We discovered a new mechanism, describing stacking fault dislocation discovered during accelerated molecular dynamics simulations of Cu/Cu(100). The presence of island on 4\% compressive substrate promotes the pop-out events of the atoms creating the vacancies on the substrate. The vacancies diffuse around the island. As soon as they come close to each other near the island, the stacking fault dislocation is formed. The kinetics of this mechanism is characterized by an extremely large rate prefactor which is tens of orders of magnitude larger than is typical of atomic processes in fcc metals. 2018 English text University of Toledo / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544443201322287 http://rave.ohiolink.edu/etdc/view?acc_num=toledo1544443201322287 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |