Shielding effect of graphene/polymer multilayer materials

The shielding efficiency of heterostructures composed of polymer/graphene multilayers against electromagnetic radiations is studied.

The first study demonstrates that graphene can be an interesting material to screen the electromagnetic radiations. This is an important technological issue, because we all are immersed in a bath of gsm, wifi ... radiations. All the nano-devices of the future nanotechnology will have to be protected against these radiations, which behave like a strong perturbation at the nanoscale. The paper proves, both experimentally and theoretically, that a few (five to seven) graphene atomic planes may absorb microwave radiations in the most efficient possible way. The most efficient absorbing layer must have a conductivity that matches the sum of admittances of the two media located on both sides. In free air, the corresponding conductivity is 5.31 mS square, which corresponds to a resistance of 188 Ohm/sq. A few atomic planes of graphene, parallel to each other, can achieve that value. The system used to study the shielding effect was a pile of 1, 2, 3 ... thin polymer films, each covered by an individual graphene plane (see figure). It was then easy to determine how many graphene atomic planes were present in the sample. The absorption of microwave radiations reaches its maximum when 6 polymer/graphene units are stacked on each other. The same effect could be obtained by deposition of a metallic layer of 3-5 nm thickness, which would however be very fragile against bending, corrosion ... . Graphene, being almost inert and very flexible, is much well suited [1].

graphenePMMA

Fig. 1. Artificial heterostructures composed of graphene planes (one-atom thick) separated by PMMA thin films (~ 700 nm thick) stacked onto a silica substrate.


Another work theoretically confirms the good shielding efficiency of polymer/graphene heterostructures against GHZ electromagnetic perturbations that was pointed out in the previous study described above. An optimum number of graphene planes, separated by thin polymer spacers, leads to maximum absorption for millimeter waves.

 

Heterostructure

Fig. 2. Electromagnetic radiation impinging on a graphene-PMMA heterostructure composed of N PMMA/ graphene units, lying on SiO2 substrate. Adsorption (blue), reflection (red) and transmission (black) at normal incidence of the PMMA/ graphene multilayer with the optimum number of layers N = 7, containing perfect graphene (dotted lines) or non-covering graphene (dotted line circles) with variable defect surface fraction. The absorbance is not affected by small inclusions of circular air holes.

Here, electrodynamics of ideal polymer/graphene multilayered material is first approached with a well-adapted continued fraction formalism. In a second stage, rigorous coupled wave analysis is used to account for the presence of defects in graphene that are typical of samples produced by chemical vapor deposition, namely microscopic holes, microscopic dots (embryos of a second layer) and grain boundaries. It is shown that the optimum absorbance of graphene/polymer multilayers does not weaken to the first order in defect concentration. This finding testifies to the robustness of the shielding efficiency of the proposed absorption device [2].



[1]  K. Batrakov, P. Kuzhir, S. Maksimenko, A. Paddubskaya, S. Voronovich, Ph. Lambin, T. Kaplas, and Yu. Svirko, Scientific Reports, 2014, 4, 7191.1-5.

[2] M. Lobet, N. Reckinger, L. Henrard, Ph. Lambin, Nanotechnology, 2015, 26, 285702.