Atomistic Simulations: The Driving Force Behind Modern Thermodynamic Research

Author(s):  
René Spencer Chatwell ◽  
Robin Fingerhut ◽  
Gabriela Guevara-Carrion ◽  
Matthias Heinen ◽  
Timon Hitz ◽  
...  
2001 ◽  
Vol 696 ◽  
Author(s):  
A.G. Cullis ◽  
D.J. Norris ◽  
T. Walther ◽  
M.A. Migliorato ◽  
M. Hopkinson

AbstractThe way in which the Stranski-Krastanow epitaxial islanding transition can be controlled by strain due to elemental segregation within the initially-formed flat ‘wetting’ layer is examined in detail. Experimentally measured critical ‘wetting’ layer thicknesses for the InxGa1−xAs/GaAs system (x = 0.25 - 1) are demonstrated to show good agreement with values calculated using a segregation model. The strain energy associated with the segregated surface layer is determined for the complete range of deposited In concentrations using atomistic simulations. The segregation-mediated driving force for the Stranski-Krastanow transition is considered to be important also for all other epitaxial systems exhibiting the transition.


2003 ◽  
Vol 795 ◽  
Author(s):  
H. H. Yu ◽  
P. Shrotriya ◽  
J. Wang ◽  
K.-S. Kim

ABSTRACTA myriad of engineering applications involve contact between two surfaces, which induces localized plastic deformation near the surface asperities. As a generic problem in studying nanometer scale plastic deformation of solid surfaces, a unit process model of dislocation formation near a surface step under contact loading of a flat rigid surface is considered. The driving force on the dislocation is calculated using conservation integrals. The effect of surface adhesion, step size and lattice resistance on the dislocation driving force are analyzed in a continuum dislocation model, while the nucleation process is simulated atomistically. The driving force formula is used for a dislocation nucleation criterion and to get the equilibrium distance traveled by the dislocation away from the surface step. Results of the unit process model show that under a normal contact load dislocations nucleated in certain slip planes can only stay in a thin layer near the surface, while dislocations nucleated along other slip planes easily move away from the surface into the bulk material. The former dislocation is named anti-load dislocation and the latter dislocation is called pro-load dislocation. Embedded atom method (EAM) is utilized to perform the atomistic simulation of the unit-process model. As predicted by the continuum dislocation model, the atomistic simulations also indicate that surface adhesion plays significant role in dislocation nucleation process. Varying the surface adhesion leads to three different regimes of load-deflection instabilities, namely, just dislocation nucleation instability for no adhesive interaction, two distinct surface adhesion and dislocation nucleation instabilities for weak adhesive interaction and a simultaneous surface adhesion and dislocation nucleation instability for strong adhesive interaction. The atomistic simulations provide additional information on dislocation nucleation and growth near the surface steps. The results of dislocation segregation predict existence of a thin tensile-stress layer near the deformed surface and the results on the adhesion effect provides a cold-welding criterion.


Author(s):  
Tai D. Nguyen ◽  
Ronald Gronsky ◽  
Jeffrey B. Kortright

Nanometer period Ru/C multilayers are one of the prime candidates for normal incident reflecting mirrors at wavelengths < 10 nm. Superior performance, which requires uniform layers and smooth interfaces, and high stability of the layered structure under thermal loadings are some of the demands in practical applications. Previous studies however show that the Ru layers in the 2 nm period Ru/C multilayer agglomerate upon moderate annealing, and the layered structure is no longer retained. This agglomeration and crystallization of the Ru layers upon annealing to form almost spherical crystallites is a result of the reduction of surface or interfacial energy from die amorphous high energy non-equilibrium state of the as-prepared sample dirough diffusive arrangements of the atoms. Proposed models for mechanism of thin film agglomeration include one analogous to Rayleigh instability, and grain boundary grooving in polycrystalline films. These models however are not necessarily appropriate to explain for the agglomeration in the sub-nanometer amorphous Ru layers in Ru/C multilayers. The Ru-C phase diagram shows a wide miscible gap, which indicates the preference of phase separation between these two materials and provides an additional driving force for agglomeration. In this paper, we study the evolution of the microstructures and layered structure via in-situ Transmission Electron Microscopy (TEM), and attempt to determine the order of occurence of agglomeration and crystallization in the Ru layers by observing the diffraction patterns.


Author(s):  
P. J. Goodhew

Cavity nucleation and growth at grain and phase boundaries is of concern because it can lead to failure during creep and can lead to embrittlement as a result of radiation damage. Two major types of cavity are usually distinguished: The term bubble is applied to a cavity which contains gas at a pressure which is at least sufficient to support the surface tension (2g/r for a spherical bubble of radius r and surface energy g). The term void is generally applied to any cavity which contains less gas than this, but is not necessarily empty of gas. A void would therefore tend to shrink in the absence of any imposed driving force for growth, whereas a bubble would be stable or would tend to grow. It is widely considered that cavity nucleation always requires the presence of one or more gas atoms. However since it is extremely difficult to prepare experimental materials with a gas impurity concentration lower than their eventual cavity concentration there is little to be gained by debating this point.


2014 ◽  
Vol 122 (03) ◽  
Author(s):  
C Stache ◽  
A Hölsken ◽  
SM Schlaffer ◽  
A Hess ◽  
M Metzler ◽  
...  
Keyword(s):  

2018 ◽  
Author(s):  
H Jodeleit ◽  
P Palamides ◽  
O Al-amodi ◽  
G Beikircher ◽  
S Schönthaler ◽  
...  

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