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Presentation

Background

The study of the interaction of electromagnetic fields with a nanostructure constitutes a new field of research called nanoelectromagnetics. In particular, nanostructures can amplify locally the amplitude of the incident field, giving rise to spectacular effects such as enhanced Raman scattering or subwavelength concentration of electromagnetic energy density. Much more is under investigation: nanophotonics, nanoantenna, nanoresonnator ... belong to the terminology used nowadays.

In parallel with the developement of nanotechnlogy, the race for more and more compact and fast electronic processors and memories raises many technological as well as fundamental problems. Today, integrated transistors incorporate channels with dimension as small as 20 nm, only a factor of four times the electron de Broglie wavelength at room temperature. At this scale, quantum mechanics imposes its laws and limitations. It is not at all sure that the future electronic chips will remain all-silicon made. Due to their remarkable properties, carbon nanostructures, such as nanotubes and graphene nanoribbons, may become part of future nanocircuits. It is therefore important to understand their electronic structure and to investigate how they behave in an electromagnetic field.

Together with the increase of wireless telecommunication, our environment is more and more polluted with electromagnetic radiations, especially in the GHz part of the spectrum. Electromagnetic interferences may disturb sensitive electronic devices. As a consequence, stringent safety measures imposed by electromagnetic compatibility tend to maintain unwanted effects as small as possible, not forgetting those possibly acting on living organisms. It often occurs that shielding, either the electromagnetic source or the sensitive device, provides the only valuable protection. In most cases, the shielding overlayer should be light, thin and cheap. Polymer composites loaded with various types of carbon nanostructures are well-suited candidates for this purpose.

Highlights from published papers

This page displays clips extracted from scientific results published recently under the FP7 Marie Curie IRSES project FAEmCar. More highlights follow in a next page.

Image of a composite obtained by impulse microscopy

A special tool, developed by the Emanuel Institute of Biochemical Physics (the Russian partner of Faemcar), named impulse acoustic microscopy, has been used to characterize the microstructure of nanocomposites [M. Levin et al, Physics Procedia 70 (2015) 703]. This is a high-resolution ultrasonic technique whose ability to reveal micrometer-scale agglomerates of nanofillers embedded in an epoxy matrix has been demonstrated for different kinds of nanocarbons, including nanotubes and graphene nanoplatelets. Nanocarbon agglomerates generate scattered waves, like point sources that can be visualized by a numerical treatment of the ultrasound signals. The acoustic image displayed above was generated by a sample of epoxy containing 1 wt.% graphene nanoplatelets. The image corresponds to a 60-μm thick slice located 380 μm below the free surface. The many bright spots are believed to originate from porous agglomerates of nanoplatelets with air inside, which is responsible for the observed efficient scattering [V. Levin et al, Phys. Status Solidi b 253 (2016) 1952].

Temperature dependence of IR spectra of SWNT

The temperature dependence of the absorbance spectra of thin free-standing films of single-walled carbon nanotubes (SWCNT) were studied in the infrared range as a function of the ambient temperature. The observed variation with temperature of the spectra, such as illustrated here above, has been explained by two mechanisms: (i) a strong variation of the conductivity of p-type doped semiconducting SWCNTs and (ii) the variation of the electron relaxation time for intra-band electron transitions in metallic SWCNTs [M.V. Shuba et al, J. Appl. Phys. 119 (2016) 104303].

IS-parameters of BLM-PLA sandwiches

Artificial structures, in which layers made of nanocarbon-doped PLA polymer ("3D Black Magic") alternate with layers of the same undoped polymer, were produced by 3D printing. The electromagnetic properties of these stratified composites were analyzed in both GHz and THz domains using waveguide measurements and open air time-domain spectroscopy, respectively. As shown by the scattering parameters plotted in the above figure, these materials have a great potential for electromagnetic compatibility applications in the microwave range. The samples denoted BMLx-PLA (x = 1 ... 4) are composed of x repetitions of a 3D Black Magic layer on top of a PLA layer, each layer being 0.1 mm thick. The sample denoted REF is a pure PLA film. Sandwich structures containing only two nano-carbon layers already become nontransparent to microwaves with a significant contribution of absorption [A. Paddubskaya et al, Appl. Phys. Lett. 119 (2016) 135102].

Electric field simulation

The fabrication of an electromagnetic shield based on a pyrolytic carbon (PyC) layer has been analyzed in the context of the so-called robust design. The figure represents the spatial variations of the parallel component of the electric field versus the normal coordinate for a PyC film of 110 nm thickness on silica substrate (0.5 mm). Each curve corresponds to a specific frequency between 20 and 40 GHz. Such electromagnetic simualtions combined with a Monte Carlo method have demonstrated that even a deviation of 15-20% around the nominal values of the most important parameters for a PyC film on silica, i.e. its thickness and sheet resistance, still leads to the desired level of shielding effectiveness. Therefore, a reliable and robust design of the shielding performances can be achieved [P. Lamberti, P. Kuzhir, and V. Tucci, AIP Advances 6 (2016) 075301]. PyC layers, being scalable, chemically inert, relatively transparent in the visible range and offering the possibility to be deposited onto both metals and dielectric substrates, including flexible polymers, meet the high technological needs of graphene revolution and can be exploited from laboratory to mass production applications.

More highlights in the next page ...