A. G. D'Aloia

Synthesis, Modeling, and Experimental Characterization of Graphite Nanoplatelet-Based Composites for EMC Applications

Graphite nanoplatelets (GNPs) are bidimensional carbon nanostructures consisting of stacks of graphene sheets, having thickness in the range from one up to a few tens of nanometers, and lateral linear dimension in the micrometer range. These nanostructures represent a good candidate to replace carbon nanotubes in composites for electromagnetic applications. This paper proposes a new model based on the Maxwell-Garnett approach to compute the effective complex permittivity of GNP-filled nanocomposites. The effect of the dimensional probabilistic distribution of the nanofiller is investigated. To this purpose, an extensive experimental characterization of the morphological and physical properties of the GNPs after synthesis is performed. The proposed model is validated by comparison with the measured effective permittivity of GNP-composites with different concentrations, and it is used for the design of radar-absorbing materials in the frequency range 1-18 GHz.

Skin-effect modeling of carbon nanotube bundles: The high-frequency effective impedance

A bundle of single wall carbon nanotubes (SWCNTs) with circular cross-section is treated as a homogeneous material with a.c. effective conductivity σ(ω), which is evaluated by using the Drudes complex expression. The effective d.c. conductivity of the homogeneous bundle is obtained from the total d.c. resistance. The frequency-domain distribution of current density along radial direction of the bundle is utilized to obtain the expressions of the skin depth and the effective impedance. Applications of the proposed formulation to SWCNT bundles of different configurations are carried out. The obtained results show the saturation behaviour of the effective resistance and inductance above a critical frequency, which depends on the momentum relaxation time of the CNTs.

Terahertz Shielding Effectiveness of Graphene-Based Multilayer Screens Controlled by Electric Field Bias in a Reverberating Environment

Innovative multilayered screens made of laminated graphene sheets, with SiO2 as interlayer, over a glass substrate are proposed as electrically-tunable electromagnetic shields at terahertz. The shielding effectiveness (SE) modeling is developed applying the transmission line method in a reverberating environment (i.e., with the screen surface illuminated by an infinite set of plane waves impinging with all possible propagation directions), which is of particular relevance in electromagnetic compatibility (EMC) studies. A new equivalent single layer (ESL) model of the graphene/SiO2 laminate (GL) is also proposed in order to provide a simple computationally-efficient method for the EMC design of GL shielding configuration via numerical EM tools. The approximate model is validated by comparison with the results obtained applying the exact one. The sensitivity analysis of the SE in reverberating environment is performed in the frequency range up to several tens of terahertz with respect to: the electric field bias of the graphene sheets, affecting their chemical potential level through an electrostatic carrier doping; the relaxation time characterizing the electron transport in graphene; the thickness of the SiO2 interlayers. Finally, the SE computed for different shielding configurations against a plane wave with normal or oblique incidence is compared with the one obtained in a reverberating environment in order to highlight the most significant differences at terahertz frequencies.

Antimicrobial activity of graphene nanoplatelets against Streptococcus mutans

In recent years, several studies have demonstrated the strong cytotoxicity toward bacteria of graphene-based materials, suggesting their use as antimicrobial agents. The objective of this study was to evaluate the antibacterial activity against Streptococcus mutans, the principal microbiological agent in the etiology of dental caries, of two types of graphene nanoplatelets (GNPs), characterized by different thickness and lateral dimensions of the flakes. The antimicrobial properties of GNPs were valued on some plaque and saliva samples extracted from children with dental caries. Our results show that the killing effect of GNPs on S. mutans cells is both lateral size and thickness dependent. In fact, lower thickness and smaller size GNPs exhibit stronger antibacterial activity than larger and thicker ones. Scanning electron microscopy analysis revealed that GNPs interact strongly with cells. This study suggests that GNPs may be highly effective against S. mutans and therefore caries.

Optimal terahertz shielding performances of flexible multilayer screens based on chemically doped graphene on polymer substrate

The shielding performances of multilayer screens made of laminated graphene sheets with flexible polymeric interlayer depend on several factors such as thickness of the polymer interlayers, number of laminated graphene sheets, electron transport properties of graphene, and frequency range. Previous studies have highlighted that the frequency dependent graphene conductivity is a function of the charge carrier density, mobility and quantum scattering time, and it is strongly affected by doping and fabrication route. This paper is aimed at the analysis of the shielding performances of laminated graphene/polymer multilayers at terahertz, in order to provide insights on the optimum shield design as a function of frequency. The proposed simulation model accounts for the frequency dispersive properties of the graphene monolayer and of the polyethylene terephthalate (PET), which is considered as flexible polymeric interlayer material. The optimal choice of the substrate thickness is discussed in order to achieve the maximum value of the shielding effectiveness (SE) in the terahertz frequency range. The proposed design procedure is applied to three multilayer shield configurations, which are made of different types of chemically doped graphene. The computed frequency spectra of the shielding effectiveness up to 10 THz highlight the shielding performances of the considered samples.

Electromechanical modeling of GNP nanocomposites for stress sensors applications

Graphite nanoplatelets (GNPs) can be included in very low weight percentages in a polymer matrix to create new lightweight nanocomposites with desired electromechanical properties, for application in strain sensors. The development of simulation models for the prediction of the electromechanical characteristics of such composites is very important for design and performance optimization purposes. In this study we propose an electromechanical model for the prediction of the response of a strain sensor made of GNP-filled composite. The developed simulation approach is based on the tunneling-percolation model of the electrical transport in the composite, and on the experimental characterization of the dc conductivity of GNPs and GNP-filled composites at different concentrations, produced in the CNIS Labs of Sapienza University.

High frequency performance limits of nanointerconnects based on CVD-grown graphene films transferred on SiO 2 -substrate

Graphene films are grown by chemical vapour deposition on copper layer and then transferred onto a silicon substrate, coated with silicon dioxide. The topological characterization of the produced film is performed by atomic force microscopy, and the sheet resistance is measured by applying the four-probe test method. The equivalent single conductor model is then used in order to analyze the signal propagation along a nanointerconnect made with multilayer graphene over silicon dioxide, in a wide frequency range, up to 100 GHz. The comparison of the radio-frequency performances of the nanointerconnect, modeled by using either the measured value of effective resistivity or a theoretical estimation of the p.u.l. resistance, suggests that graphene films grown by chemical vapor deposition are more suitable for application as low frequency electrical interconnections in flexible electronics, than in high-speed integrated circuits.

Bundles of multiwall carbon nanotube interconnects: RF crosstalk analysis by equivalent circuits

The crosstalk analysis among MWCNTs in a complex bundle is performed in the frequency domain in the range up to 100 GHz. Numerical simulations are performed by using both the multiconductor transmission line (MTL) method and reduced-order equivalent models based on the equivalent single conductor (ESC) approach in order to reduce the complexity of the system. Each MWCNT of the bundle is firstly modeled as an ESC; next, the parallel connected ESCs of the bundle are further represented by only one equivalent conductor. The accuracy of the proposed approximation is assessed and discussed.

Electromagnetic field radiation from MWCNTs and SWCNT bundles: A comparative analysis

The electromagnetic field radiated by a multiwall carbon nanotube is predicted in the frequency domain using the equivalent single conductor (ESC) formulation, and it is compared with the field radiated by a single wall carbon nanotube bundle having circular cross section and the same external diameter. The effect of the frequency and of the configuration on the near field level is investigated, in order to predict the risk of electromagnetic interference against nearby components and devices, and to define the most critical conditions.

Near Field Radiated From Carbon Nanotube Bundles

The near field radiated in the common-mode excitation from single-walled carbon nanotube (SWCNT) bundles with rectangular or hexagonal cross section above a perfect conductive plane is predicted in the gigahertz frequency range using the equivalent single conductor (ESC) method. The risk of electromagnetic interference against nearby components and devices can be estimated. The computed frequency spectra and spatial distributions of the electric and magnetic fields are validated by comparison with the ones radiated from all the conductive SWCNTs in the bundle represented by the multiconductor transmission line (MTL) model. The obtained results highlight the noticeable accuracy and simplicity of the ESC approach with respect to the very time consuming MTL formulation.