First-Principles Structural and Electronic Characterization of Ordered SiO₂Nanowires

Abstract

Density functional theory and molecular dynamics simulations have been used to optimize the structure of nanowires of SiO 2 . The starting structures were based on β -cristobalite, orthotridymite, β -tridymite, and rutile crystals. The analysis of the electronic structure has been validated by many-body perturbation calculations using the G 0 W 0 and GW + Bethe-Salpeter equation approximations, in order to account for quasi-particle and excitonic effects. The calculations indicate that many of these nanowires have semiconducting character, while the corresponding bulk solids are insulators. In the case of thick rutile-like nanowires we found the gap congested with surface states. Electronic charge is transferred from silicon atoms to oxygen atoms, and the bonding in the nanowires is partly ionic and partly covalent. The magnitude of the band gap can be engineered by changing the structure and the thickness of the nanowires.

Evaluation of the differential capacitance for ferroelectric materials using either charge-based or energy-based expressions

“…1 demonstrates Eqs. (16), (37) and (44) for, respectively, the energy, current and charge viewpoints, showing the negative differential capacitance condition for ferroelectric material. It is seen that the line separating the negative from positive differential capacitance changes when going from the current or charge viewpoints (blue line, n ¼ 1) to an energy viewpoint (dotted pink line, n ¼ 2).…”

“…The investigation here takes place in the larger context of finding ever smaller devices and material patterns to shrink active and control devices, partly determined and affected by charge storage and capacitance issues, occurring presently in elemental and binary, ternary and quaternary hetrostructure devices, carbon nanotube and graphene devices, and other nanowire and nanostructure devices. [34][35][36][37][38] For completeness, differential capacitance is related to the static capacitance in Appendix A, and conditions when the differential capacitance may go negative in relation to the static capacitance are shown.…”

Disorder Modifications of the Critical Temperature for Superconductivity: A Perspective from the Point of View of Nanoscience

“…Superconductivity may be able to play a new or improved role in advancing technologies such as wireless communications, satellites, and other electronic and electromagnetically technologies which require the use of microscopic or nanoscopic materials, structures and devices. These all enlist small superconductors in 3D, 2D, 1D, and 0D, which includes bulk like systems, layered or thin film or atomic sheet systems [Osofsky et al, 2016a], [Osofsky et al 2016b], nanowires/nanotubes/nanocables [Krowne, 2011], [Martinez et al, 2012], [Martinez et al, 2013], and quantum dots. Obtaining superconductors in such small systems necessitates relaxed requirements on critical values of temperature T c , current J c and magnetic field H c1 and H c2 .…”

Metallicity enhancement in core–shell SiO2@RuO2nanowires

“…Most low diameter SiO 2 nanowires have semiconducting character. 16 The constraints imposed on the surrounding RuO 2 shell by the underlying core may somehow affect its structure and electronic properties (as compared to the properties of empty RuO 2 nanotubes 10 ). Indeed, we nd that the electronic structure of the RuO 2 shell suffers changes in the region near the Fermi energy, which lead to a substantial enhancement of the conductance.…”

“…The nanowires have been constructed from RuO 2 nanotubes and SiO 2 nanowires investigated in previous works. 10,16 The thin composite wire was formed from a SiO 2 nanowire with four SiO 2 units per cell conned inside a RuO 2 nanotube of twelve RuO 2 units per cell, and the thick wire was formed from a SiO 2 nanowire with twelve SiO 2 units per cell conned inside a RuO 2 nanotube of sixteen RuO 2 units per cell. In the following, these two composite nanowires will be called (4/12) and (12/16) nanowires, respectively.…”