One-Dimensional Metal–Halogen Junctions inside Extended Si₆O₆ Nanotubes Performing as Quasi-Single-Electron Diodes

Abstract

We propose and simulate one-dimensional (1D) diode devices exhibiting an ionic single metal–halogen interaction inside a semiconducting SiO-based nanotube (SiONT). After theoretically demonstrating the structural and dynamical stability of this tubular archetype, that is, Si6O6, we investigate the quantum transport of doped devices under applied bias voltages. The self-consistent density matrices of the diodes are calculated using the Keldysh nonequilibrium Green’s function technique, coupled to the electrodes via their exact self-energies. We examine devices containing 1D quantum wires of Li, Na, and Al, as cathodes, and of halogen atoms (F and Cl), as anodes, with a 50:50 atomic composition inside a SiONT. These devices give rise to ionic diatomic molecular junctions, ultimately allowing a single-electron transport. We show that the resulting alkali–halogen 1D diodes exhibit a region of current suppression, such as in Si-based p–n devices, with a fair rectifying behavior at [−2.0, +2.0 V]. For Si6O6 doped with ···Li···Li–F···F···, after the cut-in voltage, we observe a tunneling effect, with a significant negative differential resistance region. In the case of ···Al···Al–F···F··· doping, a Schottky-type contact emerges in the junction. These devices exhibit adjustable threshold voltages (0.5–1.0 V) and rectification ratios (51–2619) by the electrodes’ atomic composition. Our results suggest that these actually 1D diodes, based on a single metal–halogen bond inside a SiONT, are functional and may be used as prototypes for the development of quantum logic gates. Indeed, the proposed diatomic molecular tunnel junctions may exhibit quantum interference phenomenon, entangling bonding and antibonding states, spatially protected from the environment by an insulating nanotube.