Material Properties in Codimension > 0: Graphene Edge Properties

2010 ◽  
Vol 1258 ◽  
Author(s):  
Paulo Sergio Branicio ◽  
David J Srolovitz
Keyword(s):  
Graphene Sheet ◽  
Material Properties ◽  
Electrostatic Interactions ◽  
Interatomic Potential ◽  
Equilibrium Shape ◽  
Elastic Strain Energy ◽  
Orientation Dependence ◽  
Three Dimensions ◽  
Order Of Magnitude ◽  
Equilibrium Shapes

AbstractWhen materials are very thin in one or more dimensions, their equilibrium shapes are often curved/bent. Such shapes commonly represent a compromise between elastic strain energy and other thermodynamic forces (e.g. related to surface stresses, electrostatic interactions, or adsorption). Examples include ZnO and SnO2 nanobelts, silica/carbonate helicoids, and graphene sheets and nanoribbons. Here, we demonstrate that when the equilibrium shape of a nanomaterial is not flat/straight, important fundamental material properties may be orders of magnitude different from their bulk counterparts. We focus here primarily on the graphene edges. Graphene in three dimensions is a codimension c = 1 material; the codimension is c = D – d = 3 – 2 = 1, where D is the dimensionality of the space in which the material is embedded and d is the dimensionality of the object. By contrast, a flat graphene sheet has c = 2 – 2 = 0. We use the REBO-II interatomic potential to calculate the edge orientation dependence of the edge energy and edge stresses of graphene with c = 0 and c = 1. The edge stress for all edge orientations is compressive with c = 0. Both edge energy and stresses are in reasonable agreement with DFT calculations. The compressive edge stresses in c = 0 lead to edge buckling (out-of-the-plane of the graphene sheet) for all edge orientations (c = 1). The edge buckling in c = 1 reduces all edge energies and dramatically reduces all edge stresses to near zero (more than an order of magnitude drop). We also report the effect of codimension on the free energy and entropy of a graphene sheet and the elastic properties of ZnO nanohelices.

Shape Evolution and Splitting of a Single Coherent Particle

1997 ◽  
Vol 481 ◽  
Author(s):  
J. D. Zhang ◽  
D. Y. Li ◽  
L. Q. Chen
Keyword(s):  
Lattice Mismatch ◽  
Elastic Anisotropy ◽  
Equilibrium Shape ◽  
Elastic Strain Energy ◽  
Two Dimensions ◽  
Three Dimensions ◽  
Energy Contribution ◽  
Hilliard Equation ◽  
The Matrix ◽  
Cahn Hilliard Equation

ABSTRACTThe morphology and its evolution of a single coherent precipitate was investigated using the Cahn-Hilliard equation and Khachaturyan's continuum elasticity theory for solid solutions. A cubic solid solution with negative elastic anisotropy and isotropic interfacial energy was considered. The lattice mismatch between the precipitate and the matrix was assumed to be purely dilatational and its compositional dependence obeys the Vegard's law. Both two- and three-dimensional systems were studied. The Cahn-Hilliard equation was numerically solved using a semi-implicit Fourier-spectral method. It was demonstrated that, with increasing elastic energy contribution, the equilibrium shape of a coherent particle gradually changes from a circle to a square in two dimensions, and from a sphere to a cube in three dimensions, and the composition profile becomes increasingly inhomogeneous within the precipitate with the minimum at the center of the particle, consistent with previous theoretical studies and experimental observations. It was also shown that, with sufficiently large elastic strain energy contribution, a coherent particle may split to four particles from a square, or eight particles from a sphere, during its evolution to equilibrium. For both two and three dimensions, the splitting starts by nucleating the matrix phase at the center of the particle.

Rational Design of Organic Electro-Optic Materials

2001 ◽  
Vol 708 ◽  
Author(s):  
Alex Jen ◽  
Robert Neilsen ◽  
Bruce Robinson ◽  
William H. Steier ◽  
Larry Dalton
Keyword(s):  
Wavelength Division Multiplexing ◽  
Material Properties ◽  
Electrostatic Interactions ◽  
Rational Design ◽  
Elevated Temperatures ◽  
Optical Loss ◽  
Quality Factors ◽  
Electro Optic ◽  
Lattice Hardening

ABSTRACTA number of material properties must be optimized before organic electro-optic materials can be used for practical device applications. These include electro-optic activity, optical transparency, and stability including both thermal and photochemical stability. Exploiting an improved understanding of the structure/function relationships, we have recently prepared materials exhibiting electro-optic coefficients of greater than 50 pm/V and optical loss values of less than 0.7 dB/cm at the telecommunication wavelengths of 1.3 and 1.55 microns. When oxygen is excluded to a reasonable extent, long-term photostability to optical power levels of 20 mW has been observed. Photostability is further improved by addition of scavengers and by lattice hardening. Long-term (greater than 1000 hours) thermal stability of poling-induced electro-optic activity is also observed at elevated temperatures (greater than 80°C) when appropriate lattice hardening is used. The successful improvement of organic electro-optic materials rests upon (1) attention to the design of chromophore structure including design to inhibit unwanted intermolecular electrostatic interactions and to improve chromophore instability and (2) attention to processing conditions including those involved in spin casting, electric field poling, and lattice hardening. A particularly attractive new direction has been the exploitation of dendrimer structures and particularly of multi-chromophore containing dendrimer structures. This approach has permitted the simultaneous improvement of all material properties. Development of new materials has facilitated the fabrication of a number of prototype devices and most recently has permitted investigation of the incorporation of electro-optic materials into photonic bandgap and microresonator structures. The latter are relevant to active wavelength division multiplexing (WDM). Significant quality factors (greater than 10,000) have been realized for such devices permitting wavelength discrimination at telecommunication wavelengths of 0.01 nm.

scholarly journals Simulation study towards quantitative X-ray and neutron tensor tomography regarding the validity of linear approximations of dark-field anisotropy

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jonas Graetz
Keyword(s):  
Simulation Study ◽  
Full Range ◽  
Dark Field ◽  
Orientation Dependence ◽  
Field Tensor ◽  
Axis Orientation ◽  
X Ray ◽  
Tensor Tomography ◽  
Order Of Magnitude ◽  
Linear Contrast

AbstractTensor tomography is fundamentally based on the assumption of a both anisotropic and linear contrast mechanism. While the X-ray or neutron dark-field contrast obtained with Talbot(-Lau) interferometers features the required anisotropy, a preceding detailed study of dark-field signal origination however found its specific orientation dependence to be a non-linear function of the underlying anisotropic mass distribution and its orientation, especially challenging the common assumption that dark-field signals are describable by a function over the unit sphere. Here, two approximative linear tensor models with reduced orientation dependence are investigated in a simulation study with regard to their applicability to grating based X-ray or neutron dark-field tensor tomography. By systematically simulating and reconstructing a large sample of isolated volume elements covering the full range of feasible anisotropies and orientations, direct correspondences are drawn between the respective tensors characterizing the physically based dark-field model used for signal synthesization and the mathematically motivated simplified models used for reconstruction. The anisotropy of freely rotating volume elements is thereby confirmed to be, for practical reconstruction purposes, approximable both as a function of the optical axis’ orientation or as a function of the interferometer’s grating orientation. The eigenvalues of the surrogate models’ tensors are found to exhibit fuzzy, yet almost linear relations to those of the synthesization model. Dominant orientations are found to be recoverable with a margin of error on the order of magnitude of 1$$^{\circ }$$ ∘ . Although the input data must adequately address the full orientation dependence of dark-field anisotropy, the present results clearly support the general feasibility of quantitative X-ray dark-field tensor tomography within an inherent yet acceptable statistical margin of uncertainty.

scholarly journals Development and assessment of CootVR, a virtual reality computer program for model building

2021 ◽  
Vol 77 (1) ◽  
pp. 19-27
Author(s):  
Hamish Todd ◽  
Paul Emsley
Keyword(s):  
Virtual Reality ◽  
Computer Program ◽  
Model Building ◽  
Three Dimensional ◽  
Specific Model ◽  
Three Dimensions ◽  
Biological Macromolecules ◽  
Data Set ◽  
X Ray Crystallography ◽  
Order Of Magnitude

Biological macromolecules have complex three-dimensional shapes that are experimentally examined using X-ray crystallography and electron cryo-microscopy. Interpreting the data that these methods yield involves building 3D atomic models. With almost every data set, some portion of the time put into creating these models must be spent manually modifying the model in order to make it consistent with the data; this is difficult and time-consuming, in part because the data are `blurry' in three dimensions. This paper describes the design and assessment of CootVR (available at http://hamishtodd1.github.io/cvr), a prototype computer program for performing this task in virtual reality, allowing structural biologists to build molecular models into cryo-EM and crystallographic data using their hands. CootVR was timed against Coot for a very specific model-building task, and was found to give an order-of-magnitude speedup for this task. A from-scratch model build using CootVR was also attempted; from this experience it is concluded that currently CootVR does not give a speedup over Coot overall.

scholarly journals Feeling the Force: Measurements of Platelet Contraction and Their Diagnostic Implications

2018 ◽  
Vol 45 (03) ◽  
pp. 285-296 ◽  
Author(s):  
Evelyn Williams ◽  
Oluwamayokun Oshinowo ◽  
Abhijit Ravindran ◽  
Wilbur Lam ◽  
David Myers
Keyword(s):  
Mechanical Properties ◽  
Heart Disease ◽  
Ischemic Heart Disease ◽  
Material Properties ◽  
Blood Cells ◽  
Ischemic Heart ◽  
Force Measurements ◽  
Blood Clots ◽  
Order Of Magnitude

AbstractIn addition to the classical biological and biochemical framework, blood clots can also be considered as active biomaterials composed of dynamically contracting platelets, nascent polymeric fibrin that functions as a matrix scaffold, and entrapped blood cells. As platelets sense, rearrange, and apply forces to the surrounding microenvironment, they dramatically change the material properties of the nascent clot, increasing its stiffness by an order of magnitude. Hence, the mechanical properties of blood clots are intricately tied to the forces applied by individual platelets. Research has also shown that the pathophysiological changes in clot mechanical properties are associated with bleeding and clotting disorders, cancer, stroke, ischemic heart disease, and more. By approaching the study of hemostasis and thrombosis from a biophysical and mechanical perspective, important insights have been made into how the mechanics of clotting and the forces applied by platelets are linked to various diseases. This review will familiarize the reader with a mechanics framework that is contextualized with relevant biology. The review also includes a discussion of relevant tools used to study platelet forces either directly or indirectly, and finally, concludes with a summary of potential links between clotting forces and disease.

Effect of Fe Segregation on the Migration of a Non-Symmetric Σ5 Tilt Grain Boundary in Al

2005 ◽  
Vol 20 (1) ◽  
pp. 208-218 ◽  
Author(s):  
M.I. Mendelev ◽  
D.J. Srolovitz ◽  
G.J. Ackland ◽  
S. Han
Keyword(s):  
Grain Boundary ◽  
Interatomic Potential ◽  
Boundary Migration ◽  
Physical Parameters ◽  
Boundary Mobility ◽  
Grain Boundary Mobility ◽  
Bulk Diffusivity ◽  
Order Of Magnitude ◽  
Effect Of Impurities ◽  
Fe Impurities

We present an analysis, based upon atomistic simulation data, of the effect of Fe impurities on grain boundary migration in Al. The first step is the development of a new interatomic potential for Fe in Al. This potential provides an accurate description of Al–Fe liquid diffraction data and the bulk diffusivity of Fe in Al. We use this potential to determine the physical parameters in the Cahn–Lücke–Stüwe (CLS) model for the effect of impurities on grain boundary mobility. These include the heat of segregation of Fe to grain boundaries in Al and the diffusivity of Fe in Al. Using the simulation-parameterized CLS model, we predict the grain boundary mobility in Al in the presence of Fe as a function of temperature and Fe concentration. The order of magnitude and the trends in the mobility from the simulations are in agreement with existing experimental results.

scholarly journals Numerical Studies on the Design of Self-Resetting Active Bistable Cross-Shaped Structure for Morphing Applications

Proceedings ◽  
2020 ◽  
Vol 64 (1) ◽  
pp. 16
Author(s):  
P. M. Anilkumar ◽  
A. Haldar ◽  
S. Scheffler ◽  
B. N. Rao ◽  
R. Rolfes
Keyword(s):  
Stable Equilibrium ◽  
Fibre Composite ◽  
Equilibrium Shape ◽  
Middle Portion ◽  
Stable Equilibrium State ◽  
Control Effort ◽  
Unsymmetric Laminates ◽  
Numerical Studies ◽  
Finite Element Package ◽  
Equilibrium Shapes

Multistable structures that possess more than one elastically stable equilibrium state are highly attractive for advanced shape-changing (morphing) applications due to the nominal control effort required to maintain the structure in any of its specific stable shapes. The aim of the paper is to develop a bistable cross-shaped structure consisting of symmetric and unsymmetric laminate actuated using Macro Fibre Composite (MFC) actuators. The critical snap-through voltages required to change the shapes are investigated in a commercially available finite element package. The use of MFC actuators to snap the bistable laminate from one equilibrium shape to another and back again (self-resetting) is demonstrated. A new cross-shaped design of active bistable laminate with MFC actuators is proposed where the cross-shape consist of four rectangles on the four legs and a square on the middle portion. All the rectangles are made up of unsymmetric laminates, and the central portion is designed with a symmetric laminate. MFC actuators are bonded on both sides of the four legs to trigger snap-through and snap-back actions. An attempt is made to address the possible design difficulties arising from the additional stiffness contribution by MFC layers on the naturally cured equilibrium shapes of cross-shaped bistable laminates.

Size-Dependent Equilibrium Shapes of Solid Pb Inclusions in Al

1997 ◽  
Vol 3 (S2) ◽  
pp. 629-630
Author(s):  
U. Dahmen ◽  
E. Johnson ◽  
S.Q. Xiao ◽  
S. Paciornik ◽  
A. Johansen
Keyword(s):  
Size Dependence ◽  
Equilibrium Shape ◽  
Alloy System ◽  
Lattice Parameter ◽  
Al Alloys ◽  
Size Dependent ◽  
Interfacial Energies ◽  
Relative Extent ◽  
Equilibrium Shapes ◽  
Melting And Solidification

Small Pb inclusions in Al have been studied by a number of investigators because the alloy system offers the possibility of observing the processes of melting and solidification directly. Both solids are fee, and the mutual solubility of solid Pb and Al is negligible. Despite a large difference in lattice parameter, it has been found that inclusions follow a parallel-cube orientation relationship and their equilibrium shape is a cuboctahedron, bounded by ﹛111﹜ and ﹛100﹜ facets [1]. Following Herring, the relative extent of the two types of facet directly indicates a ratio of interfacial energies γl00/γ111- However, recent investigations have shown that for inclusions in the range of a few to a few tens of nanometers the equilibrium shape becomes a function of size [2].In the present work, this size dependence of the equilibrium shape has been investigated further. Al alloys with about lat.% Pb were prepared by rapid solidification or by ion implantation, and equilibrated by annealing at about 300°C.

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