Electrolyte Diffusion in Gyroidal Nanoporous Carbon

The structural properties of gyroidal nanoporous carbon (GNC) materials and their diffusion properties are investigated using a combination of molecular dynamics methods. We consider nine different GNC materials with variable pore geometry and pore size to establish that the local curvature induced by the presence of specific carbon ring size imposes highly specific behavior on electrolyte diffusion inside the GNC channels. We also find that GNC materials containing carbon square and heptagon motifs are globally more rigid and locally more flexible than GNC materials containing octagonal rings. The most rigid GNC’s present a faster water diffusion, indicating that the diffusion properties can be controlled by a proper choice of gyroid size and density. The analysis emphasizes that a fine balance between water permeation and ionic conduction can lead to GNC materials with attractive properties for nanofluidic applications. The impact of these findings are discussed in terms of their ionic transport, water filtration, and energy storage properties

Electronic Transport of Recrystallized Freestanding Graphene Nanoribbons

The use of graphene and other two-dimensional materials in next-generation electronics is hampered by the significant damage caused by conventional lithographic processing techniques employed in device fabrication. To reduce the density of defects and increase mobility, Joule heating is often used since it facilitates lattice reconstruction and promotes self-repair. Despite its importance, an atomistic understanding of the structural and electronic enhancements in graphene devices enabled by current annealing is still lacking. To provide a deeper understanding of these mechanisms, atomic recrystallization and electronic transport in graphene nanoribbon (GNR) devices are investigated using a combination of experimental and theoretical methods. GNR devices with widths below 10 nm are defined and electrically measured <i>in situ</i> within the sample chamber of an aberration-corrected transmission electron microscope. Immediately after patterning, we observe few-layer polycrystalline GNRs with irregular sp²-bonded edges. Continued structural recrystallization toward a sharp, faceted edge is promoted by increasing application of Joule heat. Monte Carlo-based annealing simulations reveal that this is a result of concentrated local currents at lattice defects, which in turn promotes restructuring of unfavorable edge structures toward an atomically sharp state. We establish that intrinsic conductance doubles to 2.7 <i>e</i>²/<i>h</i> during the recrystallization process following an almost 3-fold reduction in device width, which is attributed to improved device crystallinity. In addition to the observation of consistent edge bonding in patterned GNRs, we further motivate the use of bonded bilayer GNRs for future nanoelectronic components by demonstrating how electronic structure can be tailored by an appropriate modification of the relative twist angle of the bonded bilayer