Multiscale Simulations of High Performance Capacitors and Nanoelectronic Devices

Abstract

Recent advances in theoretical methods combined with the advent of massively-parallel supercomputers allow one to reliably simulate the properties of complex materials and device structures from .first principles. We describe applications in two general areas: (i) novel polymer composites for ultrahigh density capacitors, necessary for pulsed power applications, such as electric discharges, power conditioning, and dense electronic circuitry, and (ii) electronic properties of graphene nanoribbons, which are candidate materials for ultraspeed electronics and spintronics. Polypropylene is an excellent capacitor dielectric that, however, has already reached its energy density limit. We investigate polypropylene-alumina nanocomposites and show that the dielectric permittivity of the composite can be significantly enhanced. For sufficiently dispersed alumina, the composite should still exhibit the excellent stability and high breakdown .field of pure polypropylene. We have also investigated Poly-Vinylidene Fluoride (PVDF)-based copolymers and show that in addition to co-polymer of VDF-chlorotrifluoroethylene [P(VDFCTFE)], P(VDF-TeFE) can also be a high energy density material, provided an appropriate TeFE concentration and dispersion is achieved. We present a composition range where its energy density would be similar to that of P(VDF-CTFE). For graphene nanoribbons, we report the results of extensive ab initio investigations of the properties of edge states, .nding that the edge-related peaks in the local density of states depend on spin polarization, and that defects at zigzag edges and/or higher-index edges can switch o. The polarization, leading to a non-magnetic ribbon. Our results explain differences between disparate scanning tunneling spectroscopy experiments as due to spin-polarized and unpolarized edges, respectively.