Electronic Properties of High-Performance Capacitor Materials and Nanoscale Multiterminal Devices

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 ferroelectric oxide-polymer composites for ultrahigh power density capacitors, necessary for pulsed power applications, such as electric discharges, power conditioning, and dense electronic circuitry, and (ii) electron transport properties of ballistic, multi-terminal molecular devices, which could form the basis for ultra-speed electronics and spintronics. For capacitor materials, we investigate the dielectric properties of PbTiO₃ slabs and polypropylene/PbTiO₃ nanocomposites. We evaluate both the optical and static local dielectric permittivity profiles for isolated PbTiO₃ slabs and across the polypropylene/PbTiO₃ interface. For thin ferroelectric slabs, we find that in order to maintain the ferroelectric structure, it is necessary to introduce compensating surface charges. Our results show that: (i) the surface- and interface-induced modifications to dielectric permittivity in polymer/metal-oxide composites are localized to only a few atomic layers; (ii) the interface effects are mainly confined to the metal-oxide side; and (iii) metal-oxide particles larger than a few nanometers retain the average macroscopic value of bulk dielectric permittivity. Turning to nanoelectronic devices, we investigate ballistic electron transport through a paradigmatic four-terminal molecular electronic device. In contrast to a conventional two-terminal setup, the same organic molecule placed between four electrodes exhibits new properties, such as a pronounced negative differential resistance.