Giorgos Fagas

Silicon nanowire band gap modification.

Band gap modification for small-diameter (approximately 1 nm) silicon nanowires resulting from the use of different species for surface termination is investigated by density functional theory calculations. Because of quantum confinement, small-diameter wires exhibit a direct band gap that increases as the wire diameter narrows, irrespective of surface termination. This effect has been observed in previous experimental and theoretical studies for hydrogenated wires. For a fixed cross-section, the functional group used to saturate the silicon surface significantly modifies the band gap, resulting in relative energy shifts of up to an electronvolt. The band gap shifts are traced to details of the hybridization between the silicon valence band and the frontier orbitals of the terminating group, which is in competition with quantum confinement.

Simulation of junctionless Si nanowire transistors with 3 nm gate length

Inspired by recent experimental realizations and theoretical simulations of thin silicon nanowire-based devices, we perform proof-of-concept simulations of junctionless gated Si nanowire transistors. Based on first-principles, our primary predictions are that Si-based transistors are physically possible without major changes in design philosophy at scales of ∼1 nm wire diameter and ∼3 nm gate length, and that the junctionless transistor avoids potentially serious difficulties affecting junctioned channels at these length scales. We also present investigations into atomic-level design factors such as dopant positioning and concentration.Inspired by recent experimental realizations and theoretical simulations of thin silicon nanowirebased devices, we perform predictive first-principles simulations of junctionless gated Si nanowire transistors. Our primary predictions are that Si-based transistors are physically possible without major changes in design philosophy at scales of ∼1 nm wire diameter and ∼3 nm gate length, and that the junctionless transistor [1, 2] may be the only physically sensible design at these length scales. We also present investigations into atomic-level design factors such as dopant positioning and concentration.

Theory of an all-carbon molecular switch

We have performed parameter-free calculations of electron transport across a carbon molecular junction consisting of a C

Introducing Molecular Electronics: A Brief Overview

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Fingerprints of mesoscopic leads in the conductance of a molecular wire

molecule sandwiched between two semi-infinite metallic carbon nanotubes. It is shown that the Landauer conductance of this carbon hybrid system can be tuned within orders of magnitude not only by varying the tube-C

Ballistic conductance in oxidized Si nanowires.

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Lattice dynamics of a disordered solid-solid interface

distance, but more importantly at fixed distances by i) changing the orientation of the Buckminsterfullerene or ii) rotating one of the tubes around its cylinder axis. Furthermore, it is explicitely shown that structural relaxation determines qualitatively the transmission spectrum of such devices.

A proposed confinement modulated gap nanowire transistor based on a metal (tin).

We give a brief account of the foundations, state-of-the-art, major topics, and challenges of charge transport at the molecular scale. This summary is not aiming at completeness, but rather gives an overview of what follows in the different chapters of this volume.

Tunnelling in alkanes anchored to gold electrodes via amine end groups.

The influence of contacts on linear transport through a molecular wire attached to mesoscopic tubule leads is studied. It is shown that low dimensional leads, such as carbon nanotubes, in contrast to bulky electrodes, strongly affect transport properties. By focusing on the specificity of the lead-wire contact, we show, in a fully analytical treatment, that the geometry of this hybrid system supports a mechanism of channel selection and a sum rule, which is a distinctive hallmark of the mesoscopic nature of the electrodes.

Electron transport in nanotube-molecular wire hybrids

The influence of local oxidation in silicon nanowires on hole transport, and hence the effect of varying the oxidation state of silicon atoms at the wire surface, is studied using density functional theory in conjunction with a Greens function scattering method. For silicon nanowires with growth direction along [110] and diameters of a few nanometers, it is found that the introduction of oxygen bridging and back bonds does not significantly degrade hole transport for voltages up to several hundred millivolts relative to the valence band edge. As a result, the mean free paths are comparable to or longer than the wire lengths envisioned for transistor and other nanoelectronics applications. Transport along [100]-oriented nanowires is less favorable, thus providing an advantage in terms of hole mobilities for [110] nanowire orientations, as preferentially produced in some growth methods.