The research activity of the “electromagnetics (microwave/RF/photonics) group” at the “Dipartimento di Ingegneria dell’Informazione” of the “Università Politecnica delle Marche”, Ancona, Italy, brings unique experience in the frequency (energy)/time-domain full-wave multiphysics modeling of the combined electromagnetic-coherent transport problem in carbon-based (graphene, CNT) nano-structured materials and devices. It has been the first “em group”, in Italy, in dealing with carbon nano-structures. The core concept is that while the advancement of research in this area heavily depends on the progress of manufacturing technology, still, the global modeling of multi-physics phenomena at the nanoscale is crucial to its development. Modeling, in turn, provides the appropriate basis for design. The bridge between nanosciences and the realized circuits can be achieved by using the panoply of microwave/RF engineering at our disposal. From the theoretical models and techniques, we produced effecient software for the anlysis and design. Very many contributions have been published in high impacting journals (IEEE Transactions, Physical Review, etc.)

In our models, the quantum transport is described by the Schrödinger equation or its Dirac-like counterpart, for small energies. The electromagnetic field provides sources terms for the quantum transport equations, that, in turn, provide charges and currents for the electromagnetic field. In the frequency-domain, a rigorous Poissoncoherent transport equation system is provided, including electrostatic sources (bias potentials). Interesting results involve new concept-devices, such as GNR nano-transistors and multipath/multilayer GNR circuits, where charges are ballistically scattered among different ports under external electrostatic control. Further examples are given by the simulation of cold-cathodes for field emission based on graphene and by the analysis of optical emission/absorption by single or few layer GNR.

Recently, we began to work on i) the model of the graphene/CNT-metal transition and related equivalent circuits models, ii) the inclusion of thermal effects in graphene/CNT, e.g. as deriving from ballistic path reduction due to phonon scattering and as arising at the contact between graphene and silicon dioxide.

In the time-domain, we now avail a novel Schrödinger/Dirac-based transmission line matrix (TLM) solver for the self-consistent analysis of the electromagnetic-coherent transport dynamics in realistic environments. It is highlighted that the self-generated electromagnetic field may affect the dynamics (group velocity, kinetic energy

etc.) of the quantum transport. This is particularly important in the analysis of time transients and in the describing the behavior of high energy carrier bands, as well as the onset of non-linear phenomena due to impinging external electromagnetic fields. We are now capable of modelling THz carbon-based emitters/detectors, CNT-enabled traveling wave (TW-CNT) devices, and the carbon-metal transition; we are exploiting novel properties and devices based on frequency multiplication, graphene gyrotropic effects, photoconductive effects.
Regarding the laboratory activity, we recently introduced a broadband Scanning Microwave Microscopy (SMM).

The SMM performs local quantitative measurements of electromagnetic properties such as dielectric constant, conductivity and surface impedance. In addition, the broadband measurements of these parameters open the possibility to perform local microwave spectroscopy and a time-domain analysis of microwave images.

The SMM system includes a commercial scanning tunneling microscope (STM), whose conducting tip is also used as a microwave probe, connected to a VNA, featuring 70-GHz bandwidth. The STM probe is a platinumiridium sharp tip; the STM tip works as the microwave probe. The VNA and STM devices are controlled and synchronized by means of a software produced by us that allows at the same time the processing of the obtained measurements. The spectrum acquired can be analyzed in the frequency (by means of the correlation of images recorded at different frequencies) and time domain (Time-Domain Reflectometry). The system was applied in the study of carbon multiwalled nanotubes, biological samples and multi-layers graphene structures.

Laboratory Resources:

Microwave Laboratory: two vector network analyzers (VNA) Agilent, model E5071C, featuring 8.5 GHz bandwidth, model E8361A, 70 GHz maximum bandwidth.
Photonics Laboratory: active anti-vibration tables, laser sources, detectors, fiber optic somponents, optical spectrum analyser working in the Thz range, fiber-optic Fabry-Perot microscopy system for near/far field measurements of infrared reflectivity and absorption on micrometer scales.
Microscopy Laboratory
AFM Microscope, able to provide Electric Force Microscopy, Scanning Capacitance Microscopy and Kelvin Probe Microscopy, STM and broadband Scanning Microwave Microscope (SMM) for the characterization of electromagnetic and quantum-mechanical properties of materials.