Generic role of the anisotropic surface free energy on the morphological evolution in a strained-heteroepitaxial solid droplet on a rigid substrate

A systematic study based on the self-consistent dynamical simulations is presented for the spontaneous evolution of an isolated thin solid droplet on a rigid substrate, which is driven by the surface drift diffusion induced by the anisotropic capillary forces (surface stiffness) and mismatch stresses. In this work, we studied the affect of surface free energy anisotropies on the development kinetics of the 'Stranski-Krastanow' island type morphology. The anisotropic surface free energy and the surface stiffness were treated with well accepted trigonometric functions. Although, various tilt angles and anisotropy constants were considered during simulations, the main emphasis was given on the effect of rotational symmetries associated with the surface Helmholtz free energy topography in 2D space. Our computer simulations revealed the formation of an extremely thin wetting layer during the development of the bell-shaped Stranski-Krastanow island through the mass accumulation at the central region of the droplet via surface drift-diffusion. In the strong (anomalous) anisotropy constant domain, we demonstrated the existence of two distinct morphological modes: i) the complete stability of the initial Cosine-shaped droplet just above a certain anisotropy constant threshold level by spontaneous slight readjustments of the base and the height of the cluster; ii) the Frank-van der Merwe mode of thin film formation for very large values of the anisotropy constant by the spreading and coalescence of the droplets over the substrate surface. During the course of the simulations, we have continuously tracked both the morphology (i.e., the peak height, the extension of the wetting layer beyond the domain boundaries, and the triple junction contact angle) and energetic (the global Helmholtz free energy changes associated with the total strain and surface energy variations) of the system.Comment: anisotropic surface free energy, Quantum Dots, elastostatic load, morphological evolution, strained-heteroepitaxial soli

2nd International Workshop on Physics-Based Modelling of Material Properties and Experimental Observations with special focus on Fracture and Damage Mechanics: Book of Abstracts

This report covers the book of abstracts of the 2nd International Workshop on Physics Based Modelling of Material Properties and Experimental Observations, with special focus on Fracture and Damage Mechanics. The workshop is organized in the context of European Commission’s Enlargement and Integration Action, by the Joint Research Centre in collaboration with the TOBB University of Economics and Technology (TOBB ETU) on 15th-17th May 2013 in Antalya, Turkey. The abstracts of the keynote lectures and all the technical presentations are included in the book. This workshop will give an overview of different physics-based models for fracture and degradation of metallic materials and how they can be used for improved understanding and more reliable predictions. Models of interest include cohesive zones to simulate fracture processes, ductile-brittle transition for ferritic steels, ductile fracture mechanisms such as void growth or localized shear, fatigue crack initiation and short crack growth, environmental assisted cracking. Experimental studies that support such models and case studies that illustrate their use are also within the scope. The workshop is also an opportunity for scientists and engineers from EU Member States and target countries to discuss research activities that could be a basis for future collaborations.JRC.F.4-Nuclear Reactor Integrity Assessment and Knowledge Managemen

Peptide-directed co-assembly of nanoprobes on multimaterial patterned solid surfaces

This is the published version. Copyright 2012 Royal Society of ChemistryBiocombinatorially selected solid-binding peptides, through their unique material affinity and selectivity, are a promising platform for building up complex hierarchical assemblies of nanoscale materials and molecular probes, targeted to specific practical solid surfaces. Here, we demonstrate the material-specific characteristics of engineered gold-binding and silica-binding peptides through co-assembly onto micro- and nano-patterned gold surfaces on silica substrates. To build hierarchical nanostructures on patterned solid surfaces, we utilize peptides as molecular tools and monitor their behavior by either conjugating biotin to them for specific affinity to streptavidin-coated QDot nanoparticles or labelling them with small fluorescent labels. This biomimetic peptide-based approach could be used as an alternative to conventional chemical coupling and surface functionalization techniques with substantial advantages, allowing simultaneous assembly of two or more inorganic nano-entities and/or molecular probes onto patterned inorganic solid substrates. The results have significant implications in a wide range of potential applications, including controlled assembly of hybrid nanostructures in bionanophotonic and biosensing devices

Threshold voltage control in organic thin film transistors with dielectric layer modified by a genetically engineered polypeptide

This is the published version. Copyright 2010 American Institute of PhysicsPrecise control over the threshold voltage of pentacene-based organic thin film transistors was achieved by inserting a genetically engineered quartz-binding polypeptide at the semiconductor-dielectric interface. A 30 V range was accessed with the same peptide by adjusting the pH of the solution for peptide assembly while leaving other device properties unaffected. Mobility of 0.1–0.2 cm2 V−1 s−1 and on/off current ratio of >106 could be achieved for all devices regardless of the presence of the neutral peptide or the peptide assembled in acidic or basic conditions. This shift in threshold voltages is explained by the generation of charged species and dipoles due to variation in assembling conditions. Controlling device characteristics such as threshold voltage is essential for integration of transistors into electronic circuits

Mesoscopic irreversible thermodynamics of morphological evolution kinetics of helical conformation in bioproteins ‘DNA’ under the isothermal isobaric conditions

The morphological evolution kinetics and instabilities of alpha helical peptide 3.613, which involves large amount of stored torsional elastic deformation energy (3-40 eV/molecule), is formulated by the variational method based on the connection between the rates of internal entropy production and the changes in the global Gibbs free energy, assuming that one has isobaric irreversible processes under the isothermal conditions. The present mesoscopic nonequilibrium thermodynamic approach relies on the fact that the global Gibbs free energy of helical conformation involves not only the bulk Gibbs free energy of the amino-acid back bone structure but also the interfacial Gibbs free energy of the enclosing cylindrical shell or the cage associated with the side-wall molecular branches, and their interactions with the immediate surroundings. The proposed variational analysis applied directly on the proposed macro-model has furnished a nonlinear integral equation in terms of the normalized and scaled internal and external variables. This allows us to track down the motion of the total pitch height of the alpha polypeptide along the well-defined trajectories in the displacement-time space, dictated not only by the initial configuration of the helix but also through the gradients of the global Gibbs free energy of the strained helical conformation as the main driving force. In the negative manifold, there is a well-defined region below the dynamic instability regime, in which the helical conformation can evolve towards the nonequilibrium stationary states by expanding, or contracting, depending upon whether the interfacial free energy and/or the applied stress system are below or above the well-defined thresholds level dictated by the initial pitch height. The highest life time may be realized along that trajectory, which follows up the threshold level of the interfacial specific Gibbs free energy, which is gs = -315 erg/cm2. In the upper region of the negative manifold, the helical conformations are driven by the very large applied uniaxial tension or the negative pressure induced by the thermal expansion, in the range of p > 1GPa and/or the strong negative interfacial free energies [3-4 pH] or their combinations, they show strong kinematic instabilities, which can cause not only the accelerated unfolding phenomenon but also cause large extensions that end up with the catastrophic decimations by ruptures and fragmentations. In the positive manifold, the aging behavior of the polypeptide follows up a S-shape path having rather speedy aging behavior compared to the negative manifold, which is separated from by a well-defined boundary, which represents the isochoric path having longest relaxation times, which can be achieved with great stability. Finally, one could attempt to estimate the upper limit of the relaxation time of aging for the modern hominin, from samples of exceptional preservations, relying on the present nonequilibrium theory as well as on the very limited knowledge on the post-mortem DNA and the present pitch heights of the modern hominin, which is found to be about 25,840 yrs, with a life expectation of 451,800 yrs. These figures are very close to those calculated for Neanderthals (SH), which are found to be 31,820 yrs and 499,100 yrs, respectively

Morphological evolution of edge-hillocks on single-crystal films having anisotropic drift-diffusion under the capillary and electromigration forces

The morphological evolution of hillocks at the unpassivated sidewalls of single-crystal metallic thin film interconnects is investigated via computer simulations using the free-moving boundary value problem. The effect of drift-diffusion anisotropy on the development of surface topographical scenarios is fully explored under the action of electromigration and capillary forces, utilizing numerous combinations of the surface texture, the drift-diffusion anisotropy and the direction of the applied electric field. The simulation studies yield analytical relationships for the velocity of the surface solitary waves and the drift velocity of electromigration-induced internal voids as a function of the applied current densities, which contain intrinsic and structural properties of the single-crystal thin films. The threshold value of the applied current density, above which electromigration-induced internal voids can be formed and may cause the catastrophic failure of interconnects by breaching, also appears explicitly in this relationship. (c) 2006 Published by Elsevier B.V

Morphological evolution of tilted grain-boundary thermal grooving by surface diffusion in bicrystal thin solid films having strong anisotropic surface Gibbs free energies

The variational extremum method is further extended to give the full coverage for the inclined (tilted) grain-boundary (GB) configuration with respect to the sidewalls of a bicrystal thin solid film having strong anisotropic specific surface Gibbs free energy associated with the singular directions (faceting). A set of critical computer simulation experiments is performed on the asymmetrically disposed (inclination) bicrystal thin metallic films having four- and sixfold anisotropic specific surface Gibbs free energies to demonstrate the various GB-groove root topologies. Special computer runs are also designed using the realistic structural and physicochemical properties to simulate the thermal grooving profile of polycrystalline alumina (Lucalox (TM)), and tungsten, which undergone heat treatments for 90 and 120 min at 1650 and 1350 degrees C in air and vacuum (10(-4) Pa), respectively. The simulation profiles almost perfectly agree with the published experimental atomic force microscopy photographs after linewidth matching procedures, and the simulations produced very accurate mean surface (mass) diffusivities of alumina and tungsten given by D-Al2O3 congruent to 6.45x10(-12) m(2)/s and D-W congruent to 5.2x10(-13) m(2)/s, respectively. These findings are in good agreement with the diffusivities reported in the literature. (c) 2008 American Institute of Physics

Mapping DNA Conformations Using Single-Molecule Conductance Measurements

DNA is an attractive material for a range of applications in nanoscience and nanotechnology, and it has recently been demonstrated that the electronic properties of DNA are uniquely sensitive to its sequence and structure, opening new opportunities for the development of electronic DNA biosensors. In this report, we examine the origin of multiple conductance peaks that can occur during single-molecule break-junction (SMBJ)-based conductance measurements on DNA. We demonstrate that these peaks originate from the presence of multiple DNA conformations within the solutions, in particular, double-stranded B-form DNA (dsDNA) and G-quadruplex structures. Using a combination of circular dichroism (CD) spectroscopy, computational approaches, sequence and environmental controls, and single-molecule conductance measurements, we disentangle the conductance information and demonstrate that specific conductance values come from specific conformations of the DNA and that the occurrence of these peaks can be controlled by controlling the local environment. In addition, we demonstrate that conductance measurements are uniquely sensitive to identifying these conformations in solutions and that multiple configurations can be detected in solutions over an extremely large concentration range, opening new possibilities for examining low-probability DNA conformations in solutions