Competition of Moiré Network Sites to Form Electronic Quantum Dots in Reconstructed MoX2/WX2 Heterostructures.

Twisted bilayers of two-dimensional semiconductors offer a versatile platform for engineering quantum states for charge carriers using moiré superlattice effects. Among the systems of recent interest are twistronic MoX2/WX2 heterostructures (X = Se or S), which undergo reconstruction into preferential stacking domains and highly strained domain wall networks, determining the electron/hole localization across moiré superlattices. Here, we present a catalogue of options for the formation of self-organized quantum dots and wires in lattice-reconstructed marginally twisted MoX2/WX2 bilayers with a relative lattice mismatch δ ≪ 1 for twist angles ranging from perfect alignment to θ ∼ 1°. On the basis of multiscale modeling taking into account twirling of domain wall networks, we analyze bilayers with both parallel and antiparallel orientations of their unit cells and describe crossovers between different positioning of band edges for electrons and holes across moiré superlattices when θ < δ and θ > δ.

Dataset for stacking-mediated diffusion of ruthenium nanoclusters in bilayer graphene and graphite.

The data in this article are related to the research article "Stacking-Mediated Diffusion of Ruthenium Nanoclusters in Bilayer Graphene and Graphite" (J G McHugh, 2022). The data consists of Ru atom cluster intercalation calculations on graphene surfaces, within AA/AB bilayer graphene and graphite. We tabulate data for cluster sizes of 3, 4, 5 and 7 Ru atoms, which includes adsorption energies and diffusion energy barriers between all the highly symmetric sites in graphene/graphite. These data were obtained from density functional theory calculations. We provide tabulated data of relaxed structures that are useful for future classical interatomic potential fittings.

Graphene Confers Ultralow Friction on Nanogear Cogs.

Friction-induced energy dissipation impedes the performance of nanomechanical devices. Nevertheless, the application of graphene is known to modulate frictional dissipation by inducing local strain. This work reports on the nanomechanics of graphene conformed on different textured silicon surfaces that mimic the cogs of a nanoscale gear. The variation in the pitch lengths regulates the strain induced in capped graphene revealed by scanning probe techniques, Raman spectroscopy, and molecular dynamics simulation. The atomistic visualization elucidates asymmetric straining of CC bonds over the corrugated architecture resulting in distinct friction dissipation with respect to the groove axis. Experimental results are reported for strain-dependent solid lubrication which can be regulated by the corrugation and leads to ultralow frictional forces. The results are applicable for graphene covered corrugated structures with movable components such as nanoelectromechanical systems, nanoscale gears, and robotics.

Structural Defects Modulate Electronic and Nanomechanical Properties of 2D Materials.

Two-dimensional materials such as graphene and molybdenum disulfide are often subject to out-of-plane deformation, but its influence on electronic and nanomechanical properties remains poorly understood. These physical distortions modulate important properties which can be studied by atomic force microscopy and Raman spectroscopic mapping. Herein, we have identified and investigated different geometries of line defects in graphene and molybdenum disulfide such as standing collapsed wrinkles, folded wrinkles, and grain boundaries that exhibit distinct strain and doping. In addition, we apply nanomechanical atomic force microscopy to determine the influence of these defects on local stiffness. For wrinkles of similar height, the stiffness of graphene was found to be higher than that of molybdenum disulfide by 10-15% due to stronger in-plane covalent bonding. Interestingly, deflated graphene nanobubbles exhibited entirely different characteristics from wrinkles and exhibit the lowest stiffness of all graphene defects. Density functional theory reveals alteration of the bandstructures of graphene and MoS2 due to the wrinkled structure; such modulation is higher in MoS2 compared to graphene. Using this approach, we can ascertain that wrinkles are subject to significant strain but minimal doping, while edges show significant doping and minimal strain. Furthermore, defects in graphene predominantly show compressive strain and increased carrier density. Defects in molybdenum disulfide predominantly show tensile strain and reduced carrier density, with increasing tensile strain minimizing doping across all defects in both materials. The present work provides critical fundamental insights into the electronic and nanomechanical influence of intrinsic structural defects at the nanoscale, which will be valuable in straintronic device engineering.