A. Tamburrano

Sapienza University of Rome, Roma, Latium, Italy

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Publications (66)62.45 Total impact

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    ABSTRACT: A graphene-based porous paper made of multilayer graphene (MLG) microsheets is developed for application as a flexible electrically conducting shielding material at radio frequency. The production process is based on the thermal expansion of a graphite intercalated compound, the successive liquid-phase exfoliation of the resulting expanded graphite in a proper solvent, and finally the vacuum filtration of the MLG-suspension using a nanoporous alumina membrane. Enhancement of the electrical conductivity and electromagnetic shielding properties of the MLG paper is achieved by gentle annealing at 250 °C overnight, and by mechanical compression at 5 MPa. The obtained results show that the developed MLG papers are characterized by an electrical conductivity up to 1443.2 S/cm, porosity around 43%, high flexibility, shielding effectiveness up to 55 dB at 18 GHz with a thickness of 18 μm. Numerical simulations are performed in order to understand the main factors contributing to the shielding performance of the new material.
    Carbon 08/2015; 89. DOI:10.1016/j.carbon.2015.03.043 · 6.16 Impact Factor
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    ABSTRACT: The issue concerning the measurement of the shielding effectiveness (SE) of planar materials over a wide frequency range is of crucial relevance in several electromagnetic compatibility applications. This paper describes three different coaxial specimen holders for the measurement of the SE of thin metallic films over a nonconducting substrate or sandwiched between two insulating layers from a few kHz up to 18 GHz. Besides the well-known ASTM D4935 flanged coaxial cell, two novel versions of coaxial fixtures with an interrupted and continuous inner conductor are presented and compared. Their limits of applicability, advantages, and drawbacks are discussed with respect to frequency, sample characteristics, and test procedure. The analysis is performed by the use of simple equivalent circuit models, experimentally validated measuring thin copper films of different thicknesses which are deposited on kapton substrates by magnetron sputtering. It is demonstrated that the use of the three methods, properly combined, provides reliable SE results in the overall considered frequency range. It is also shown that the measurement of conducting films between two dielectric layers is critical at frequencies lower than some tens of MHz.
    IEEE Transactions on Electromagnetic Compatibility 12/2014; 56(6):1386-1395. DOI:10.1109/TEMC.2014.2329238 · 1.35 Impact Factor
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    ABSTRACT: Flexible composite foils made up of multilayer graphene (MLG) and ZnO nanowires (ZnO-NW) are produced via vacuum filtration of acetone-based suspension. The sheet resistance and effective dc electrical conductivity of the foils, with increasing content of ZnO-NW over a fixed amount of MLG, is measured in order to investigate the effect of ZnO inclusion in MLG papers. An enhancement in the dc conductivity of the composite foils with respect to a plain MLG-foil is noticed only for very low amounts of ZnO loading. The peak conductivity of 16.8 kS/m, representing an increase of 31% with respect to the conductivity of a plain MLG-foil, is observed at the optimum concentration of 10%wt ZnO over the MLG content. This confirms the physical and electronic interaction at the interface between MLG and ZnO-NW. At higher concentration of ZnO-NW, a linear decay in the effective conductivity of the foils is observed.
    IEEE-Nanotechnology Materials and Devices Conference 2014, Aci Castello, Italy; 10/2014
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    ABSTRACT: The transfer of chemical vapor deposited graphene is a crucial process, which can affect the quality of the transferred films and compromise their application in devices. Finding a robust and intrinsically clean material capable of easing the transfer of graphene without interfering with its properties remains a challenge. We here propose the use of an organic compound, cyclododecane, as a transfer material. This material can be easily spin coated on graphene and assist the transfer, leaving no residues and requiring no further removal processes. The effectiveness of this transfer method for few-layer graphene on a large area was evaluated and confirmed by microscopy, Raman spectroscopy, x-ray photoemission spectroscopy, and four-point probe measurements. Schottky-barrier solar cells with few-layer graphene were fabricated on silicon wafers by using the cyclododecane transfer method and outperformed reference cells made by standard methods.
    Applied Physics Letters 09/2014; 105(113101). DOI:10.1063/1.4895733] · 3.52 Impact Factor
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    ABSTRACT: The transfer of chemical vapor deposited graphene is a crucial process, which can affect the quality of the transferred films and compromise their application in devices. Finding a robust and intrinsically clean material capable of easing the transfer of graphene without interfering with its properties remains a challenge. We here propose the use of an organic compound, cyclododecane, as a transfer material. This material can be easily spin coated on graphene and assist the transfer, leaving no residues and requiring no further removal processes. The effectiveness of this transfer method for few-layer graphene on a large area was evaluated and confirmed by microscopy, Raman spectroscopy, x-ray photoemission spectroscopy, and four-point probe measurements. Schottky-barrier solar cells with few-layer graphene were fabricated on silicon wafers by using the cyclododecane transfer method and outperformed reference cells made by standard methods.
    Applied Physics Letters 09/2014; 105(11):113101. DOI:10.1063/1.4895733 · 3.52 Impact Factor
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    ABSTRACT: A graphene-based composite, consisting of a thermosetting polymeric matrix filled with multilayer graphene microsheets (MLGs), is developed for application in thin radar absorbing materials. An innovative simulation model is proposed for the calculation of the effective permittivity and electrical conductivity of the composite, and used for the electromagnetic design of thin radar absorbing screens. The model takes into account the effects of the MLG morphology and of the fabrication process on the effective electromagnetic properties of the composite. Experimental tests demonstrate the validity of the proposed approach and the accuracy of the developed simulation models, which allow to understand the interaction mechanism between the incident electromagnetic field radiation and the MLG-based composite. Two dielectric Salisbury screen prototypes with resonant frequency at 12 GHz or 12.5 GHz and total thickness of 1.8 mm and 1.7 mm, respectively, are fabricated and tested. The results and technique proposed represent a simple and effective approach to produce thin absorbing screens for application in stealth technology or electromagnetic interference suppression.
    Carbon 07/2014; 73:175–184. DOI:10.1016/j.carbon.2014.02.053 · 6.16 Impact Factor
  • M.S. Sarto, Sandra Greco, Alessio Tamburrano
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    ABSTRACT: An effective-layer model is proposed to predict the EM shielding performances of metallic wire grids typically used as protective layers in carbon fiber-reinforced composite laminates for aeronautical applications. The model is valid over a wide frequency range and it takes into account the field penetration through the grating. The shielding performance of the wire grid is estimated by means of the average shielding effectiveness, which represents the response of the material to an incident plane wave having both transverse-magnetic and transverse-electric polarizations. The proposed model is validated by comparison with experimental data, which demonstrates its validity over a wide frequency range, up to 18 GHz.
    IEEE Transactions on Electromagnetic Compatibility 06/2014; 56(3):615-621. DOI:10.1109/TEMC.2013.2292715 · 1.35 Impact Factor
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    ABSTRACT: This paper presents a morphological and functional characterization of nanostructured thin films featuring high radio frequency shielding effectiveness and high optical transparency in the wavelength range 400–1500 nm. The film morphology is analyzed at the micro- and nanoscales by processing the images acquired by a scanning electron microscope. A software tool developed for this purpose analyzes the statistical distributions of the film surface grains. Fitting models and experimental evidences are presented in order to describe and predict the correlations between the film morphological and functional properties. The adopted approach and measurement methods are developed to model and optimize a particular transparent conducting oxide but can be easily extended to similar materials, deposition processes, and applications.
    IEEE Transactions on Electromagnetic Compatibility 04/2014; 56(2):352-359. DOI:10.1109/TEMC.2013.2282085 · 1.35 Impact Factor
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    ABSTRACT: The strain-dependent electrical resistance of polyvinyl ester-based composites filled with different weight fractions of graphene nanoplatelets (GNPs) has been experimentally investigated. The GNP synthesis and nanocomposite fabrication process have been optimized in order to obtain highly homogeneous filler dispersion and outstanding electrical properties. The produced nanocomposites showed a low percolation threshold of 0.226 wt% and electrical conductivity of nearly 10 S m(-1) at only 4 wt% of GNPs. The piezoresistive response of thin nanocomposite laminae has been assessed by measuring the variation of the electrical resistance as a function of the flexural strain in three-point bending tests under both quasi-static monotonic and dynamic cyclic loading conditions. The obtained results showed higher strain sensitivity than traditional metal foil strain gauges or recently investigated carbon-based nanocomposite films.
    Nanotechnology 10/2013; 24(46):465702. DOI:10.1088/0957-4484/24/46/465702 · 3.67 Impact Factor
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    ABSTRACT: Graphene and its derivatives are nowadays gaining an ever increasing attention for diverse applications, such as supercapacitors, flexible screens and nanocomposites. One of the main challenges still limiting the wide spreading use of graphene-based nanomaterials in electrical and electromagnetic applications consists in the capability of controlling their morphological properties and electrical conductivity through the proper setting of the synthesis route and production process. In this paper graphene nanoplatelets (GNPs) are produced via thermochemical exfoliation of graphite intercalated compound (GIC). The crucial phase of the exfoliation process consists in the tip sonication of the solution containing thermally reduced GIC. The study presented here aims at evaluating the effect of several synthesis parameters, such as the sonication duty cycle and suspension temperature, on the DC conductivity of GNP thick films and on the morphological properties of GNPs.
    2013 IEEE 13th International Conference on Nanotechnology (IEEE-NANO); 08/2013
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    ABSTRACT: Well-aligned, open-ended carbon nanotubes (CNTs), free of catalyst and other carbon products, were synthesized inside the pores of an anodic aluminium oxide (AO) template without using any metallic catalyst. The CNTs and the CNT/AO composites were characterized by scanning and transmission electron microscopy, thermogravimetric analysis, Raman spectroscopy and X-ray diffraction. Particular care was devoted to the reactor design, synthesis conditions, the catalytic role of the templating alumina surface and the preservation of the alumina structure. The transport properties (sorption, diffusion and permeability) to water vapor were evaluated for both the alumina template and the CNT/AO composite membrane. The measured effective electrical volume conductivity of the CNT/AO composite was found ranging from a few up to 10 kS/m, in line with the recent literature. The estimated averaged values of the CNTs-wall conductivity was around 50 kS/m.
    Carbon 04/2013; 55:10 - 22. DOI:10.1016/j.carbon.2012.10.063 · 6.16 Impact Factor
  • S. Greco, A. Tamburrano, M.S. Sarto
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    ABSTRACT: The electromagnetic shielding properties of several conducting textiles are investigated by means of measurement techniques and numerical calculations. The features and performances of a computational Material Modeling Tool (MMT) are introduced and applied to the calculation of the shielding effectiveness of metallized woven fabrics, commonly used to reduce the effects of electromagnetic interferences aboard air-vehicles. Measured and computed data are compared and validated by means of both direct comparisons and automated tools.
    Electromagnetic Compatibility (EMC EUROPE), 2013 International Symposium on; 01/2013
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    ABSTRACT: Novel graphene-based nanocomposites, consisting of a polymeric-based system filled with graphenenanoplatelets (GNP), are developed for application as low-cost lightweight electromagnetic shielding materials. High concentration and good dispersion of the GNPs inside a thermosetting polymeric matrix is achieved in order to enhance the shielding properties of the nanocomposite through the control of the fabrication process. The good shielding performance of the new material is demonstrated by means of shielding effectiveness (SE) measurements on the fabricated samples. Moreover, numerical simulations are performed in order to validate the SE measurements and to design a nanocomposite panel providing a minimum shielding of 30 dB in the frequency range up to 18 GHz.
    Electromagnetic Compatibility (EMC EUROPE), 2013 International Symposium on; 01/2013
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    ABSTRACT: 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.
    Electromagnetic Compatibility (EMC), 2013 IEEE International Symposium on; 01/2013
  • Marcello D'Amore, A.G. D'Aloia, M.S. Sarto, Alessio Tamburrano
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    ABSTRACT: 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.
    IEEE Transactions on Electromagnetic Compatibility 10/2012; 54(5):998-1005. DOI:10.1109/TEMC.2012.2196045 · 1.35 Impact Factor
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    ABSTRACT: A robust design of the propagation characteristics of interconnect structures based on multiwall carbon nanotubes (MWCNTs) is carried out. The study allows us to identify the minimum number of shells N of the MWCNT able to guarantee that the time delay at 50% outperforms the Cu-based solution for the upcoming technology nodes, taking into account the uncertainties affecting other geometrical and physical parameters of the device. Such an investigation is carried out in the most severe conditions for the MWCNTs-based device, i.e., for short and thin wire structures, starting from the minimum interconnect length for which the MWCNT outperforms the Cu-based solution. A worst case polynomial expression of the time delay as a function of the number of the shells of the MWCNT, obtained on the basis of the equivalent single conductor model of the nano-interconnect, is adopted for the optimization procedure. The minimum number of shells that lead to outperform the Cu-based solution is determined by the use of an approach relying on a particular application of the interval analysis to find the upper bound of the performance function. The quality of the results is checked by a Monte Carlo analysis.
    IEEE Transactions on Nanotechnology 07/2012; 11(4):799-807. DOI:10.1109/TNANO.2012.2198922 · 1.62 Impact Factor
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    ABSTRACT: Multiwall carbon nanotubes represent a low-dimensional material that could serve as building blocks for future carbon-based nanoelectronics. The understanding of the electromagnetic performances at radio frequency of these materi-als for use in nanointerconnects is strictly related to the analysis of their transport properties as function of the working conditions. In this paper, we present an explicit expression of the conducting channels as function of diameter, temperature, doping, and supply voltage for both metallic and semiconducting carbon nanotubes. The proposed formula is based on the Dirac cone approximation of the conducting band energy of graphene nearby the Fermi points, combined with the Landauer–Buttiker formalism. Simplified ex-pressions are also obtained in case of large diameter nanotubes. We show that the conductance, kinetic inductance, and quantum capacitance of each carbon shell are strongly affected by those pa-rameters, and, consequently, that the current distribution among the shells of a multiwall carbon nanotube at radio frequency could be optimized with the proper definition of the nanotube configura-tion versus the working conditions. Index Terms—Carbon nanotube (CNT), conducting channel, current distribution, quantum transport, radio frequency (RF).
    IEEE Transactions on Nanotechnology 05/2012; 11(3):492. DOI:10.1109/TNANO.2011.2178610 · 1.62 Impact Factor
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    ABSTRACT: 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.
    IEEE Transactions on Electromagnetic Compatibility 02/2012; 54(1):17-27. DOI:10.1109/TEMC.2011.2178853 · 1.35 Impact Factor
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    ABSTRACT: A study concerning the characterization of a multiphase nanocomposite systems based on epoxy matrix, loaded with a 1% of hydrotalcite clay and a range of MWCNT is presented. The electromagnetic properties are measured over a very ample range of frequency (from dc to 12GHz). The use of the clay may determine a low aggregation of the MWCNT in the resin thus improving the EM performances of the nanocomposites.
    Electromagnetic Compatibility (EMC EUROPE), 2012 International Symposium on; 01/2012
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    ABSTRACT: This paper investigates the shielding effectiveness properties of different types of carbon fiber reinforced composites (CFRC), typically used aboard air-vehicles, in the frequency range from 100 kHz up to 18 GHz. Both single-layer and multilayer, unidirectional or woven, CFRCs are analyzed, and the critical issue concerning sample preparation is addressed. The study is aimed at defining an effective single layer model of the CFRC laminate, characterized by an effective frequency-dependent electrical conductivity, which is extracted from the measured shielding effectiveness.
    Electromagnetic Compatibility (EMC EUROPE), 2012 International Symposium on; 01/2012