Polina Kuzhir, Alesia Paddubskaya, Nadzeya Volynets, Konstantin Batrakov, Sergey Maksimenko, Elena Golubeva, Gintaras Valusis, Tommi Kaplas, Nicolas Reckinger, Michaël Lobet, Philippe Lambin
The influence of chemical vapor deposition (CVD) graphene grain size on the electromagnetic (EM) shielding performance of graphene/polymethyl methacrylate (PMMA) multilayers in Ka-band was studied both experimentally and theoretically. We found that increasing the average graphene grain size from 20 to 400 μm does not change the EM properties of heterostructures consisting of graphene layers sandwiched between submicron thick PMMA spacers. The independence of EM interference shielding effectiveness on the graphene grain size between 20 and 400 μm allows one to use cheaper (or more convenient regimes of CVD) graphene samples with low crystallinity and small grain size in the development of new graphene-based passive EM devices operated at high frequencies.
The ability of thin conductive films, including graphene, pyrolytic carbon (PyC), graphitic PyC (GrPyC), graphene with graphitic islands (GrI), glassy carbon (GC), and sandwich structures made of all these materials separated by polymer slabs to absorb electromagnetic radiation in microwave-THz frequency range, is discussed. The main physical principles making a basis for high absorption ability of these heterostructures are explained both in the language of electromagnetic theory and using representation of equivalent electrical circuits. The idea of using carbonaceous thin films as the main working elements of passive radiofrequency (RF) devices, such as shields, filters, polarizers, collimators, is proposed theoretically and proved experimentally. The important advantage of PyC, GrI, GrPyC, and GC is that, in contrast to graphene, they either can be easily deposited onto a dielectric substrate or are strong enough to allow their transfer from the catalytic substrate without a shuttle polymer layer. This opens a new avenue toward the development of a scalable protocol for cost-efficient production of ultralight electromagnetic shields that can be transferred to commercial applications. A robust design via finite-element method and design of experiment for RF devices based on carbon/graphene films and sandwiches is also discussed in the context of virtual prototyping.
If graphene is a promising material in many respects, its remarkable properties may be impaired by unavoidable defects. Chemical vapor deposition-grown graphene samples are polycrystalline in nature, with many grain boundaries. Those extended defects influence the global electronic structure and the transport properties of graphene in a way that remains to be clarified. As a step forward in this direction, we have undertaken quantum mechanical calculations of electron wave-packet dynamics in a multigrain self-supported graphene layer. Our computer simulations show that a grain boundary may act as a reflector at some energies and for some incidences of the Bloch waves. In addition, our calculations reveal that when two grain boundaries run parallel to each other, the graphene ribbon confined between them may behave like a channel for the charge carriers. We emphasize therefore the possibility of creating nanoscale electronic waveguides and nanowires on the graphene surface by a controlled engineering of its grain boundaries.
A short review of electron-energy-loss spectroscopy (EELS) experiments of carbon nanotubes and onions is presented. The dielectric response function of these nanostructures is derived from electrodynamics. Loss spectra computed with the dielectric theory are compared with spatially-resolved experimental spectra. The main features of the loss spectra obtained with non-penetrating electrons can be attributed to surface plasmon excitations (π plasmon at 6 eV and π + σ plasmon at 15 and 17-18 eV).
Spontaneous decay process of an excited two-level atom placed
inside or outside a single-wall carbon nanotube is analyzed for
both weak and strong atom-radiation-field coupling regime. In the
weak coupling regime, the effect of the nanotube surface has been
demonstrated to dramatically increase the spontaneous decay rate
-- by 4 to 5 orders of magnitude compared with that of the same
atom in vacuum. Such an increase is associated with the
nonradiative decay via surface quasiparticle excitations in the
nanotube. In the strong coupling regime, the decay of the upper
atomic state proceeds via damped Rabi oscillations with the
frequency assigned by the density of final photonic states of the
system. Possible applications of the effect predicted are
discussed.
One of the most versatile formalism for the study of the electrodynamic response of solids, surfaces and interfaces or nanoparticles is the continuum dielectric model. In this contribution, we develop an application of this dielectric approach to nanocylinders and more particularly to the simulation of near-field electron energy loss (EEL)spectra of nanotube bundles. On the experimental side, EELS in a Scanning Transmission Electron Microscope (STEM) combines both spatial and energy resolutions in the plasmonic energy range and then permits the spectroscopic analysis of the surface and volume excitations of nanoparticles.
Amongst the challenges brought about by the discovery of carbon nanotubes, one can cite the understanding of their optical properties. In this contribution, pursuing this goal within a dielectric continuum model, we focus on the dispersion and coupling of surface plasmon excitations of hollow nanocylinders and on the near-field EELS of nanotube nanocrystals (bundles). Experimental EELS in a STEM have also been obtained on bundles of carbon nanotubes. The interpretation in terms of effectif medium theory is successfuly performed both for surface and bulk losses associated with the σ plasmon.
Regularly coiled carbon nanotubes, their structure and formation mechanism are puzzling questions since many years. The first models were based on the very regular incorporation of a small fraction (of the order of 10%) of non-hexagonal (n-Hx) rings: (pentagons and heptagons) in a perfect hexagonal (Hx) lattice. It is difficult to understand by which mechanism takes place such a regular incorporation of isolated n-Hx rings. In the present work a new family of Haeckelite nanotubes is generated in a systematic way by rolling up a two-dimensional three-fold coordinated carbon network composed of pentagon-heptagon pairs and hexagons in proportion 2:3. In this model the n-Hx rings are treated like regular building blocks of the structure. Cohesion energy calculation shows that the stability of the generated 3D Haeckelite structures falls between that of straight carbon nanotubes and that of C60. Electronic density of states of the Haeckelite computed with a tight-binding Hamiltonian that includes the C-μ orbitals only shows that the structures are semiconductor. The relation of the structures with experimental observations is discussed.
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