Giovanni Miano

An Integral Formulation for the Electrodynamics of Metallic Carbon Nanotubes Based on a Fluid Model

An integral formulation to model, in the frequency domain, the electromagnetic response of three-dimensional (3-D) structures formed by metallic carbon nanotubes and conductors, within the framework of the classical electrodynamics, is described. The conduction electrons of the metallic nanotube are modeled as an infinitesimally thin cylindrical layer of compressible fluid, whose dynamics are described by means of the linearized hydrodynamic equations. The resulting integral equations are solved numerically by the finite element method using the facet elements and the null-pinv decomposition. The proposed formulation is applied to study carbon nanotube interconnects and dipole antennas and some related results are outlined. The solutions highlight the high-frequency effects due to the electron inertia and the fluid pressure. In particular, since the kinetic inductance matrix dominates over the magnetic one, proximity effects are negligible

A transmission line model for metallic carbon nanotube interconnects

A transmission line (TL) model describing the propagation of electric signals along metallic single wall carbon nanotube (CNT) interconnects is derived in a simple and self-consistent way within the framework of the classical electrodynamics. The conduction electrons of metallic CNTs are modelled as an infinitesimally thin cylindrical layer of a compressible charged fluid with friction, moving in a uniform neutralizing background. The dynamic of the electron fluid is studied by means of the linearized hydrodynamic equations with the pressure assumed to be that of a degenerate spin-½ ideal Fermi gas. Transport effects due to the electron inertia, quantum fluid pressure and electron scattering with the ion lattice significantly influence the propagation features of the TL. The simplicity and robustness of the fluid model make the derivation of the TL equations more straightforward than other derivations recently proposed in the literature and provide simple and clear definitions of the per unit length (p.u.l.) TL parameters. In particular, this approach has provided a new circuit model that can be used effectively in the analysis of networks composed of CNT transmission lines and lumped elements. The differences and similarities between the proposed model and those given in the literature are highlighted. Copyright

Signal Propagation in Carbon Nanotubes of Arbitrary Chirality

In carbon nanotubes (CNTs) with large radii, either metallic or semiconducting, several subbands contribute to the electrical conduction, while in metallic nonarmchair nanotubes with small radii the wall curvature induces a large energy gap. In this paper, we propose a model for the signal propagation along single wall CNTs (SWCNTs) of arbitrary chirality, at microwave through terahertz frequencies, which takes into account both these characteristics in a self-consistent way. We first study an SWCNT, disregarding the wall curvature, in the frame of a semiclassical treatment based on the Boltzmann equation in the momentum-independent relaxation time approximation. It allows expressing the longitudinal dynamic conductivity in terms of the number of effective conducting channels. Next, we study the behavior of this number as the nanotube radius varies and its relation with the kinetic inductance and quantum capacitance. Furthermore, we show that the effects of the spatial dispersion are negligible in the collision dominated regimes, whereas they may be important in the collisionless regimes, giving rise to sound waves propagating with the Fermi velocity. Then, we study the effects on the electron transport of the terahertz quantum transition induced by the wall curvature by using a quantum kinetic approach. The nanotube curvature modifies the kinetic inductance and gives arise to an additional RLC branch in the equivalent circuit, related to the terahertz quantum transition. The proposed model can be used effectively for analyzing the signal propagation in complex structures composed of SWCNTs with different chirality, such as bundles of SWCNTs and multiwall CNTs, providing that the tunneling between adjacent shells may be disregarded.

The role of nanoparticle shapes and deterministic aperiodicity for the design of nanoplasmonic arrays

In this paper, we study the role of nanoparticle shape and aperiodic arrangement in the scattering and spatial localization properties of plasmonic modes in deterministic-aperiodic (DA) arrays of metal nanoparticles. By using an efficient coupled-dipole model for the study of the electromagnetic response of large arrays excited by an external field, we demonstrate that DA structures provide enhanced spatial localization of plasmonic modes and a higher density of enhanced field states with respect to their periodic counterparts. Finally, we introduce and discuss specific design rules for the engineering and optimization of field enhancement and localization in DA arrays. Our results, which we fully validated by rigorous Generalized Mie Theory (GMT) and transition matrix (T-matrix) theory, demonstrate that DA arrays provide a robust platform for the design of a variety of novel optical devices with enhanced and controllable plasmonic fields.

Performance Comparison Between Metallic Carbon Nanotube and Copper Nano-Interconnects

This paper addresses the problem of scaling interconnects to nanometric dimensions in future very-large-scale integration applications. Traditional copper interconnects are compared to innovative interconnects made by bundles of metallic carbon nanotubes. A new model is presented to describe the propagation of electric signals along carbon nanotube (CNT) bundles, in the framework of the classical transmission line theory. A possible implementation of a future scaled microstrip based on CNT bundle is analyzed and compared to a conventional microstrip.

Genetically engineered plasmonic nanoarrays

In the present Letter, we demonstrate how the design of metallic nanoparticle arrays with large electric field enhancement can be performed using the basic paradigm of engineering, namely the optimization of a well-defined objective function. Such optimization is carried out by coupling a genetic algorithm with the analytical multiparticle Mie theory. General design criteria for best enhancement of electric fields are obtained, unveiling the fundamental interplay between the near-field plasmonic and radiative photonic coupling. Our optimization approach is experimentally validated by surface-enhanced Raman scattering measurements, which demonstrate how genetically optimized arrays, fabricated using electron beam lithography, lead to order of ten improvement of Raman enhancement over nanoparticle dimer antennas, and order of one hundred improvement over optimal nanoparticle gratings. A rigorous design of nanoparticle arrays with optimal field enhancement is essential to the engineering of numerous nanoscale optical devices such as plasmon-enhanced biosensors, photodetectors, light sources and more efficient nonlinear optical elements for on chip integration.

Particle-swarm optimization of broadband nanoplasmonic arrays

We used the particle swarm optimization algorithm, an evolutionary computational technique, to design metal nanoparticle arrays that produce broadband plasmonic field enhancement over the entire visible spectral range. The resulting structures turn out to be aperiodic and feature dense Fourier spectra with many closely packed particle clusters. We conclude that broadband field-enhancement effects in nanoplasmonics can be achieved by engineering aperiodic arrays with a large number of spatial frequencies that provide the necessary interplay between long-range diffractive interactions at multiple length scales and near-field quasi-static coupling within small nanoparticle clusters.

A New Circuit Model for Carbon Nanotube Interconnects With Diameter-Dependent Parameters

In this paper, a new circuit model for the propagation of electric signals along carbon nanotube interconnects is derived from a fluid model description of the nanotube electrodynamics. The conduction electrons are regarded as a 2-D charged fluid, interacting with the electromagnetic field produced by the ion lattice, the conduction electron themselves, and the external sources. This interaction may be assumed to be governed by a linearized Eulers equation, which provides the nanotube constitutive equation to be coupled to Maxwell equations. A derivation of a circuit model is then possible within the frame of the classical multiconductor transmission-line (TL) theory. The elementary cell of this TL model differs from those proposed in literature, due to the definition of the circuit variable corresponding to the voltage. When considering small nanotube radius, we obtain values for the kinetic inductance and quantum capacitance that are consistent with literature. These values are corrected here to take into account the influence of larger values of radius properly. Conversely, the value of the per unit length resistance is roughly half of the value usually adopted in literature. The multiconductor TL model is used to study the scaling law of the parameters with the number of carbon nanotubes in a bundle.

Multipolar second harmonic generation from planar arrays of Au nanoparticles.

We demonstrate optical Second Harmonic Generation (SHG) in planar arrays of cylindrical Au nanoparticles arranged in periodic and deterministic aperiodic geometries. In order to understand the respective roles of near-field plasmonic coupling and long-range photonic interactions on the SHG signal, we systematically vary the interparticle separation from 60 nm to distances comparable to the incident pump wavelength. Using polarization-resolved measurements under femtosecond pumping, we demonstrate multipolar SHG signal largely tunable by the array geometry. Moreover, we show that the SHG signal intensity is maximized by arranging Au nanoparticles in aperiodic spiral arrays. The possibility to engineer multipolar SHG in planar arrays of metallic nanoparticles paves the way to the development of novel optical elements for nanophotonics, such as nonlinear optical sensors, compact frequency converters, optical mixers, and broadband harmonic generators on a chip.

Eddy current losses in ferromagnetic laminations

It is demonstrated through the comparison of analytical, numerical, and experimental results that the existence of excess eddy current losses can be explained by the peculiar nature of the nonlinear diffusion of electromagnetic fields in magnetically nonlinear laminations. The essence of this peculiar nature is that nonlinear diffusion occurs as inward progress of almost rectangular profiles of magnetic flux density of variable height. Approximating actual profiles of magnetic flux density by rectangular ones, the problem of nonlinear diffusion can be treated analytically by using a simple model. The accuracy and the limit of applicability of the rectangular profile model are discussed by comparing its predictions with finite elements numerical solutions of nonlinear diffusion equation as well as with experimental results.