Scattering matrix approach to multichannel transport in many lead graphene nanoribbons.

Multichannel analysis of graphene nanoribbons (GNR), often required for describing applications to practical devices, constitutes a heavy computational task, even in a simplified framework like that provided by discrete or nearest neighbour models. Scattering (S) matrix techniques, widely used for quantum transport in low dimensional systems and for the computation of electromagnetic fields, is shown here to provide a powerful formal platform for the analysis, and, in principle, the synthesis, of GNR multiport circuits. Periodic modes, solutions of GNR waveguides, are demonstrated to obey charge conservation and reciprocity constraints corresponding to unitary and symmetry properties of the S-matrix, under proper normalization conditions. We propose a systematic use of this approach to deal with problems such as scattering by lattice defects, the presence of external applied fields, crossing GNRs and T-junctions.

Modelling of multi-wall CNT devices by self-consistent analysis of multichannel transport.

We present a generalization of the self-consistent analysis of carbon nanotube (CNT) field effect transistors (FETs) to the case of multi-wall/multi-band coherent carrier transport. The contribution to charge diffusion, due to different walls and sub-bands of a multi-wall (mw) CNT is shown to be non-negligible, especially for high applied external voltages and 'large' diameters. The transmission line formalism is used in order to solve the Schrödinger equation for carrier propagation, coupled to the Poisson equation describing the spatial voltage distribution throughout the device. We provide detailed numerical results for semiconducting mw-nanotubes of different diameters and lengths, such as current-voltage characteristics and frequency responses.

Optical and mechanical shrinkage effects in dye-doped photonic bandgap structures based on organic materials.

In this work we study the effects of the optical shrinkage in polymer and liquid crystal (LC) mixtures optimized for their use as active media in compact plastic laser devices. These mixtures are characterized by the presence of the rhodamine 6G as an active dye. Modifications in the reflection properties of the gratings as a function of the active dye concentration have been determined experimentally and a detailed theoretical simulation of the optical transmittance properties of these devices is provided. Moreover, the comparison between two different experimental approaches clarifies the contribution to the optical shrinkage due to the presence of the active dye. In principle this approach allows determining the linear mechanical shrinkage by separating the contribution to optical shrinkage due to photochemical transformations from that due to mechanical effects.

Rigorous time-domain analysis of dielectric optical waveguides using Hertzian potentials formulation.

This work analyzes a new simulation approach to the evaluation of the time-domain electromagnetic (EM) field by reducing the number of equations to solve. Scalar Helmholtz-equations are utilized in order to determine the electric and magnetic Hertzian-potentials that yield the EM field. The method is applied to the example of optical waveguide arrays by considering the field-perturbation effect due to high dielectric contrast and dielectric discontinuities. The rigorous Hertzian potentials formulation is extended to bi-dimensional structures.