Many potential applications of graphene require either the possibility of tuning its electronic structure or the addition of reactive sites on its chemically inert basal plane. Among the various strategies proposed to reach these objectives, nitrogen doping, i.e., the incorporation of nitrogen atoms in the carbon lattice, leads in most cases to a globally n-doped material and to the presence of various types of point defects. In this context, the interactions between chemical dopants in graphene have important consequences on the electronic properties of the systems and cannot be neglected when interpreting spectroscopic data or setting up devices. In this report, the structural and electronic properties of complex doping sites in nitrogen-doped graphene have been investigated by means of scanning tunneling microscopy and spectroscopy, supported by density functional theory and tight-binding calculations. In particular, based on combined experimental and simulation works, we have systematically studied the electronic fingerprints of complex doping configurations made of pairs of substitutional nitrogen atoms. Localized bonding states are observed between the Dirac point and the Fermi level in contrast with the unoccupied state associated with single substitutional N atoms. For pyridinic nitrogen sites (i.e., the combination of N atoms with vacancies), a resonant state is observed close to the Dirac energy. This insight into the modifications of electronic structure induced by nitrogen doping in graphene provides us with a fair understanding of complex doping configurations in graphene, as it appears in real samples.

Nanoelectronics requires the development of a priori technology evaluation for materials and device design that takes into account quantum physical effects and the explicit chemical nature at the atomic scale. Here, we present a cross-platform quantum transport computation tool. Using first-principles electronic structure, it allows for flexible and efficient calculations of materials transport properties and realistic device simulations to extract current-voltage and transfer characteristics. We apply this computational method to the calculation of the mean free path in silicon nanowires with dopant and surface oxygen impurities. The dependence of transport on basis set is established, with the optimized double zeta polarized basis giving a reasonable compromise between converged results and efficiency. The current-voltage characteristics of ultrascaled (3 nm length) nanowire-based transistors with p-i-p and p-n-p doping profiles are also investigated. It is found that charge self-consistency affects the device characteristics more significantly than the choice of the basis set. These devices yield sourced-drain tunneling currents in the range of 0.5 nA (p-n-p junction) to 2 nA (p-i-p junction), implying that junctioned transistor designs at these length scales would likely fail to keep carriers out of the channel in the off-state. (C) 2013 AIP Publishing LLC

No abstract

We performed first-principle calculations by the Density Functional Theory in order to study the scattering properties of silicon nanowires with two different crystalline orientations, [100] and [110], and different types of dopants. The nanowire axis orientation is found to have a strong influence on transmission, which can alter the normal behavior of dopants. Boron, a p-type dopant, can act indeed as a strong scatterer in the conduction band of [100]-oriented silicon nanowires. Using Boltzmann transport theory, we calculated the charge mobility of boron-doped silicon nanowires with different diameters. Although the scattering strength is shown to be strongly dependent on dopant locations and wire cross-sectional size, the hole mobilities are rather insensitive. It was found that the doping density and the nanowire width strongly influence the hole mobility. It was also found that in small diameter nanowires scattering by neutral impurities can be quite significant and act as a limiting factor to the mobility. At low doping densities, the hole mobility increases monotonically with the width of the nanowire.

No abstract