Patterning is a familiar approach for imparting novel functionalities to free surfaces. We extend the patterning paradigm to interfaces between crystalline solids. Many interfaces have non-uniform internal structures comprised of misfit dislocations, which in turn govern interface properties. We develop and validate a computational strategy for designing interfaces with controlled misfit dislocation patterns by tailoring interface crystallography and composition. Our approach relies on a novel method for predicting the internal structure of interfaces: rather than obtaining it from resource-intensive atomistic simulations, we compute it using an efficient reduced order model based on anisotropic elasticity theory. Moreover, our strategy incorporates interface synthesis as a constraint on the design process. As an illustration, we apply our approach to the design of interfaces with rapid, 1-D point defect diffusion. Patterned interfaces may be integrated into the microstructure of composite materials, markedly improving performance.
Silicon nanomembranes are thin nanoporous films that are frequently used as separation tools for nanoparticles and biological materials. In such applications, increased differential pressure across the nanomembranes directly increases process throughput. Therefore, a predictive tool governing the macroscale failure of the porous thin films is fundamentally important in application areas where high differential pressures are desired. Although the deflections and stresses of the nanomembranes can be reliably predicted, a straightforward and prognostic failure model has yet to be outlined. In this publication, a brittle macroscale failure model is established and validated with experimental results. Theoretical agreement with experiments within 10% accuracy offers reliable failure predictions for square membrane dimensions from 60 µm to 1.5 mm through over 100 trials. The methodology relies on an effective fracture toughness from previously published work that is incorporated through Griffith's law. These developments will be useful in the selection of nanomembranes for particular applications and will help guide the design of materials with improved strength. The model should also prove useful for high-volume, in-line processing and inspection of nanomembranes as their role becomes more prominent in industry.
The deformation mechanisms in Cu-Ni-Cu composite nanowires subjected to uniaxial tensile loading are investigated using molecular-dynamics simulations. We particularly explore the coupled effects of geometry and coherent interface on the tendency of nanowires to deform via twins and show pseudoelastic behavior. It is found that the critical size to exhibit pseudoelasticity in composite nanowires is 5.6ϫ 5.6 nm 2 , which is 6.5 times greater than single-crystalline Cu nanowires. Our results also show that the composite nanowires offer stiffness enhancement compared to the corresponding single-crystal Cu nanowires.
We present a new method for determining the unique reference state in which the Burgers vectors of misfit dislocations in semicoherent interfaces are defined. Similar to previous work, our method requires cancellation of coherency and dislocation stresses far from the interface as well as consistency of far-field rotations with a prescribed interface crystallographic character. We compute misfit dislocation elastic fields using Stroh's formalism and the Sextic theory, accounting fully for elastic anisotropy. The method is applicable to all types of interfaces, including ones with three sets of dislocations, and does not require the definition of a transformation path between adjacent crystals. We examine the accuracy of our method by comparing it with previous results on interfaces with one or two sets of dislocations. We then use it to carry out the first calculations of the coherent reference state of an interface with three sets of dislocations.
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