We characterize the atomic processes that underlie forming, reset, and set in HfO 2 -based resistive random access memory (RRAM) cells through molecular dynamics (MD) simulations, using an extended charge equilibration method to describe external electric fields. By tracking the migration of oxygen ions and the change in coordination of Hf atoms in the dielectric, we characterize the formation and dissolution of conductive filaments (CFs) during the operation of the device with atomic detail. Simulations of the forming process show that the CFs form through an oxygen exchange mechanism, induced by a cascade of oxygen displacements from the oxide to the active electrode, as opposed to aggregation of pre-existing oxygen vacancies. However, the filament breakup is dominated by lateral, rather than vertical (along the filament), motion of vacancies. In addition, depending on the temperature of the system, the reset can be achieved through a redox effect (bipolar switch), where oxygen diffusion is governed by the applied bias, or by a thermochemical process (unipolar switch), where the diffusion is driven by temperature. Unlike forming and similar to reset, the set process involves lateral oxygen atoms as well. This is driven by field localization associated with conductive paths.

We have studied the finite bias transport properties of a 2H-1T' MoS 2 lateral metal-semiconductor (M-S) junction by non-equilibrium Green's functions calculations, aimed at contacting the 2D channel in a field effect transistor. Our results indicate that (a) despite the fundamentally different electrostatics of line and planar dipoles, the Schottky barrier heights respond similarly to changes in doping and applied bias in 2D and 3D M-S junctions, (b) 2H-1T' MoS 2 lateral junctions are free from Fermi level pinning, (c) armchair interfaces have superior contacting properties vs. zigzag interfaces, (d) 1T' contacts to p channels will present a reduced contact resistance by a factor of 4-10 with respect to n channels and (e) contacts to intermediately doped n (p) channels operate in the field (thermionic) emission regime. We also provide an improved procedure to experimentally determine the emission regime in 2D material junctions.

First-principles calculations are undertaken to analyze the properties of carbon-silicon hybrid materials consisting of silicon modified graphene and defective graphene to evaluate the stability of the structure and their interactions with lithium. Underpotential shifts are determined for the different structures on defective surfaces, showing that decoration of graphene defects with a small number of silicon atoms should occur at underpotentials. Nucleation overpotentials are also determined using a thermodynamic formalism, showing that the formation of nuclei should be hindered with respect to free standing Si clusters. These results analyzes the possibility of using underpotential deposition of silicon on graphene to obtain high capacity and cycling stable material for anodes of lithium batteries.

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