Showing papers by "Jonathan A. Fan published in 2015"

Materials and Fractal Designs for 3D Multifunctional Integumentary Membranes with Capabilities in Cardiac Electrotherapy

Abstract: Advanced materials and fractal design concepts form the basis of a 3D conformal electronic platform with unique capabilities in cardiac electrotherapies. Fractal geometries, advanced electrode materials, and thin, elastomeric membranes yield a class of device capable of integration with the entire 3D surface of the heart, with unique operational capabilities in low power defibrillation. Co-integrated collections of sensors allow simultaneous monitoring of physiological responses. Animal experiments on Langendorff-perfused rabbit hearts demonstrate the key features of these systems.

Optics and Nonlinear Buckling Mechanics in Large-Area, Highly Stretchable Arrays of Plasmonic Nanostructures.

Abstract: Large-scale, dense arrays of plasmonic nanodisks on low-modulus, high-elongation elastomeric substrates represent a class of tunable optical systems, with reversible ability to shift key optical resonances over a range of nearly 600 nm at near-infrared wavelengths. At the most extreme levels of mechanical deformation (strains >100%), nonlinear buckling processes transform initially planar arrays into three-dimensional configurations, in which the nanodisks rotate out of the plane to form linear arrays with "wavy" geometries. Analytical, finite-element, and finite-difference time-domain models capture not only the physics of these buckling processes, including all of the observed modes, but also the quantitative effects of these deformations on the plasmonic responses. The results have relevance to mechanically tunable optical systems, particularly to soft optical sensors that integrate on or in the human body.

Elasticity of fractal inspired interconnects

Abstract: The use of fractal-inspired geometric designs in electrical interconnects represents an important approach to simultaneously achieve large stretchability and high aerial coverage of active devices for stretchable electronics. The elastic stiffness of fractal interconnects is determined analytically in this paper. Specifically, the elastic energy and the tensile stiffness for an order n fractal interconnect of arbitrary shape are obtained, and are verified by the finite element analysis and experiments.

Nanostructure formation mechanism and ion diffusion in iron–titanium composite materials with chemical looping redox reactions

Abstract: Iron oxide composites are enabling materials in energy conversion systems including chemical looping and photocatalysis. Extensive earlier experimental findings indicate that inert oxides such as titanium oxide can greatly improve the reactivity of iron oxide over multiple redox cycles. Knowledge on the evolution of the nanoscale morphology of the Fe–Ti materials during the oxidation and reduction is thus of considerable importance. It is also of interest to the fundamental understanding of the ion diffusion mechanism in the reaction processes. In this study, Fe–Ti composite microparticles undergoing cycles of oxidation and reduction are examined at the nano-scale, and the interfacial characteristics of the iron titanium oxides within the composites are probed. Nanobelts are observed to simultaneously form on the microparticle surface during the oxidation at 700 °C, while microblades are found at 900 °C. Additionally, unlike pure iron microparticles that become dense on surface due to sintering effect, Fe–Ti microparticles are transformed into porous particles after redox cycles. The atomistic thermodynamics methods and density functional theory calculations are carried out to investigate the ionic diffusion and vacancy formation during the oxidation and reduction process. A number of surface configurations are considered, and the Ti–Ti–O– terminated surface is computed to the most stable surface structure at experimental conditions. It was found that in oxidation processes, surface Ti atoms are more favorable for oxygen adsorption and dissociation than Fe atoms. The energy barrier of Fe ion diffusion towards the surface, on the other hand, is lower than Ti ion diffusion, which contributes to the Fe2O3-dominant nanobelt formation. The volume change due to high temperature associated with the solid state transformation at the Fe2O3/FeTiO3 interface produces compressive stresses, which stimulate Fe2O3 nanobelt growth to accompany the interface reaction. Also, as the vacancy formation energy of FeTiO3 is lower than Fe2O3 in the reduction process, it indicates that it is easier for a FeTiO3 surface to form vacancy defects, thereby enhancing the porous surface structure formation and O2 diffusivity. The good agreements between experiments and DFT calculations further substantiate nanostructure formation mechanism in redox reactions of iron titanium composite materials.