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Full-Text Articles in Engineering
Mechanical Behavior Of Ultra-Low-Dielectric-Constant Mesoporous Amorphous Silica, Dimitrios Maroudas, M. R. Gungor, J. J. Watkins
Mechanical Behavior Of Ultra-Low-Dielectric-Constant Mesoporous Amorphous Silica, Dimitrios Maroudas, M. R. Gungor, J. J. Watkins
Dimitrios Maroudas
We report results for the dependence of the mechanical properties of ordered mesoporous silica structures on the pore diameter based on molecular-dynamics simulations. We examine structures with spherical pores arranged in a simple cubic lattice and cylindrical pores arranged in a square lattice subjected to uniaxial tension and compression; for the structures with cylindrical pores, both radial and axial loading is studied with respect to the pore orientation. Our analysis provides a unifying explanation to the observed mechanical response based on the mechanical loading effects on the pore wall thickness.
Electromechanically Driven Chaotic Dynamics Of Voids In Metallic Thin Films, Dimitrios Maroudas, M. R. Gungor, V. Tomar
Electromechanically Driven Chaotic Dynamics Of Voids In Metallic Thin Films, Dimitrios Maroudas, M. R. Gungor, V. Tomar
Dimitrios Maroudas
We report a systematic investigation of complex asymptotic states reached in the electromigration-driven morphological evolution of void surfaces in thin films of face-centered cubic metals with ⟨110⟩- and ⟨100⟩-oriented film planes under the simultaneous action of biaxial tension. The analysis is based on self-consistent dynamical simulations according to a realistic, well-validated, and fully nonlinear model. For ⟨110⟩-oriented film planes, we show that upon increasing the applied mechanical stress level, morphologically stable steady states transition to time-periodic states through a subcritical Hopf bifurcation. Further increase in the stress level triggers a sequence of period-doubling bifurcations that sets the driven nonlinear system …
Rippling Instability On Surfaces Of Stressed Crystalline Conductors, Dimitrios Maroudas, M. R. Gungor, V. Tomar
Rippling Instability On Surfaces Of Stressed Crystalline Conductors, Dimitrios Maroudas, M. R. Gungor, V. Tomar
Dimitrios Maroudas
We report a surface morphological stability analysis for stressed, conducting crystalline solids without and with the simultaneous application of an electric field based on self-consistent dynamical simulations according to a fully nonlinear model. The analysis reveals that in addition to a cracklike surface instability, a very-long-wavelength instability may be triggered that leads to the formation of secondary ripples on the surface morphology. We demonstrate that the number of ripples formed scales linearly with the wavelength of the initial perturbation from the planar surface morphology and that a sufficiently strong electric field inhibits both the cracklike and the rippling instability.
Analysis Of Diamond Nanocrystal Formation From Multiwalled Carbon Nanotubes, Dimitrios Maroudas, E. S. Aydil, T. Singh, A. R. Muniz
Analysis Of Diamond Nanocrystal Formation From Multiwalled Carbon Nanotubes, Dimitrios Maroudas, E. S. Aydil, T. Singh, A. R. Muniz
Dimitrios Maroudas
A systematic analysis is presented of the nanocrystalline structures generated due to the intershell C-C bonding between adjacent concentric graphene walls of multiwalled carbon nanotubes (MWCNTs). The analysis combines a comprehensive exploration of the entire parameter space determined by the geometrical characteristics of the individual graphene walls comprising the MWCNT with first-principles density-functional theory calculations of intershell C-C bonding and structural relaxation by molecular-dynamics simulation of the resulting nanocrystalline structures. We find that these structures can provide seeds for the nucleation of the cubic-diamond and hexagonal-diamond phase in the form of nanocrystals embedded in the MWCNTs. The resulting lattice structure …
Comparative Study Of The Mechanical Behavior Under Biaxial Strain Of Prestrained Face-Centered Cubic Metallic Ultrathin Films, Dimitrios Maroudas, M. R. Gungor, K. Kolluri
Comparative Study Of The Mechanical Behavior Under Biaxial Strain Of Prestrained Face-Centered Cubic Metallic Ultrathin Films, Dimitrios Maroudas, M. R. Gungor, K. Kolluri
Dimitrios Maroudas
We report a molecular-dynamics study of the mechanical response to dynamic biaxial tensile straining of nanometer-scale-thick Al, Cu, and Ni films. We find that the mechanical behavior of such films of face-centered cubic metals with moderate-to-high propensity for stacking-fault formation (Cu and Ni) is significantly different from those where such propensity is low (Al). The plastic strain rate in Cu and Ni films is greater than that in Al ones, leading to an extended easy-glide stage in Cu and Ni but not in Al films. These differences arise due to the different dislocation annihilation mechanisms in the two film categories.
Molecular-Dynamics Simulations Of Stacking-Fault-Induced Dislocation Annihilation In Prestrained Ultrathin Single-Crystalline Copper Films, Dimitrios Maroudas, K. Kolluri, M. R. Gungor
Molecular-Dynamics Simulations Of Stacking-Fault-Induced Dislocation Annihilation In Prestrained Ultrathin Single-Crystalline Copper Films, Dimitrios Maroudas, K. Kolluri, M. R. Gungor
Dimitrios Maroudas
We report results of large-scale molecular-dynamics simulations of dynamic deformation under biaxial tensile strain of prestrained single-crystalline nanometer-scale-thick face-centered cubic (fcc) copper films. Our results show that stacking faults, which are abundantly present in fcc metals, may play a significant role in the dissociation, cross slip, and eventual annihilation of dislocations in small-volume structures of fcc metals. The underlying mechanisms are mediated by interactions within and between extended dislocations that lead to annihilation of Shockley partial dislocations or formation of perfect dislocations. Our findings demonstrate dislocation starvation in small-volume structures with ultrathin film geometry, governed by a mechanism other than …
Kinetic Monte Carlo Simulations Of Surface Growth During Plasma Deposition Of Silicon Thin Films, Dimitrios Maroudas, T. Singh, S. Pandey
Kinetic Monte Carlo Simulations Of Surface Growth During Plasma Deposition Of Silicon Thin Films, Dimitrios Maroudas, T. Singh, S. Pandey
Dimitrios Maroudas
Based on an atomically detailed surface growth model, we have performed kinetic Monte Carlo (KMC) simulations to determine the surface chemical composition of plasma deposited hydrogenated amorphous silicon (a-Si:H) thin films as a function of substrate temperature. Our surface growth kinetic model consists of a combination of various surface rate processes, including silyl (SiH3) radical chemisorption onto surface dangling bonds or insertion into Si–Si surface bonds, SiH3 physisorption, SiH3 surface diffusion, abstraction of surface H by SiH3 radicals, surface hydride dissociation reactions, as well as desorption of SiH3, SiH4, and Si2H6 species into the gas phase. Transition rates for the …
On The Hydrogen Storage Capacity Of Carbon Nanotube Bundles, Dimitrios Maroudas, A. R. Muniz, M. Meyyappan
On The Hydrogen Storage Capacity Of Carbon Nanotube Bundles, Dimitrios Maroudas, A. R. Muniz, M. Meyyappan
Dimitrios Maroudas
An analytical model is presented to describe the effect of carbon nanotube (CNT) swelling upon hydrogenation on the hydrogen storage capacity of single-walled CNT bundles; the model is properly parameterized using atomistic calculations for the relationship between CNT swelling and the degree of hydrogenation as measured by the coverage of the CNTs by chemisorbed atomic H. The model generates experimentally testable hypotheses, which can be used to explain the lower H storage capacities reported for CNT bundles and the experimentally observed nonuniformity of hydrogenation of CNT bundles.
Current-Induced Stabilization Of Surface Morphology In Stressed Solids, Dimitrios Maroudas, M. R. Gungor, V. Tomar
Current-Induced Stabilization Of Surface Morphology In Stressed Solids, Dimitrios Maroudas, M. R. Gungor, V. Tomar
Dimitrios Maroudas
We examine the surface morphological evolution of a conducting crystalline solid under the simultaneous action of an electric field and mechanical stress based on a fully nonlinear model and combining linear stability theory with self-consistent dynamical simulations. We demonstrate that electric current, through surface electromigration, can stabilize the surface morphology of the stressed solid against cracklike surface instabilities. The results also have more general implications for the morphological response of solid surfaces under the simultaneous action of multiple external forces.
Coarse Molecular-Dynamics Analysis Of An Order-To-Disorder Transformation Of A Krypton Monolayer On Graphite, Dimitrios Maroudas, I. G. Kevrekidis, V. A. Fonoberov, M. Arienti, M. A. Amat
Coarse Molecular-Dynamics Analysis Of An Order-To-Disorder Transformation Of A Krypton Monolayer On Graphite, Dimitrios Maroudas, I. G. Kevrekidis, V. A. Fonoberov, M. Arienti, M. A. Amat
Dimitrios Maroudas
The thermally induced order-to-disorder transition of a monolayer of krypton (Kr) atoms adsorbed on a graphite surface is studied based on a coarse molecular-dynamics (CMD) approach for the bracketing and location of the transition onset. A planar order parameter is identified as a coarse variable, ψ, that can describe the macroscopic state of the system. Implementation of the CMD method enables the construction of the underlying effective free-energy landscapes from which the transition temperature, Tt, is predicted. The CMD prediction of Tt is validated by comparison with predictions based on conventional molecular-dynamics (MD) techniques. The conventional MD computations include the …
Surface Smoothening Mechanism Of Amorphous Silicon Thin Films, Dimitrios Maroudas, E. S. Aydil, T Bakos, M. S. Valipa
Surface Smoothening Mechanism Of Amorphous Silicon Thin Films, Dimitrios Maroudas, E. S. Aydil, T Bakos, M. S. Valipa
Dimitrios Maroudas
An important concern in the deposition of thin hydrogenated amorphous silicon (a-Si∶H) films is to obtain smooth surfaces. Herein, we combine molecular-dynamics simulations with first-principles density functional theory calculations to elucidate the smoothening mechanism of plasma deposited a-Si∶H thin films. We show that the deposition precursor may diffuse rapidly on the a-Si∶H film surface via overcoordinated surface Si atoms and incorporate into the film preferentially in surface valleys, with activation barriers for incorporation dependent on the local surface morphology. Experimental data on smoothening and precursor diffusion are accounted for.