Preparation and characterization of graphene paper for electromagnetic interference shielding
Introduction
The proliferation of electronic devices in recent decades has greatly increased the potential for EMI. Electromagnetic radiation at high frequencies can easily interfere with electronic devices and is also harmful to human health. Consequently, there is a significant interest in the development of materials for EMI shielding. Generally, materials with good electrical conductivity show good shielding performance in reducing the energy of penetrating electromagnetic radiations. For example, metals with good electrical conductivity (e.g., copper, nickel, aluminum) show good performance for EMI shielding [1]. However, in many applications (such as aerospace electronics), the material for EMI shielding besides of being effective, needs to be lightweight and flexible, especially in applications of flexible electronics, aircrafts and automobiles. Thus the density and flexibility of shielding materials are usually evaluated in EMI shielding applications, making carbon materials [2], [3], [4], [5] competitive with metals.
For example, research suggests that graphene has the potential to be an excellent EMI shielding material with up to 500 dB cm3 g−1 specific EMI shielding effectiveness when incorporated in a PMDS matrix [2]. Flexible graphite with an EMI shielding effectiveness of 130 dB was also reported [6]. However, the thickness is a major factor that needs to be considered when comparing the SE of different shielding materials. According to the plane-wave theory [7], larger thickness of shielding materials will yield higher shielding effectiveness in dB. This dependence is not linear, since both reflection and absorption are involved. Thus it is worth to mention that the thicknesses of the reported carbon shielding materials [2], [3], [4], [5], [6] are three orders higher compared to shield of copper film [1] which limit their applications as thin, protective layers for EMI shielding of sensitive instruments. The relative large thickness of these carbon based shielding materials is due to the poor mechanical properties that call for polymer coating, which enlarges the thickness and adds additional processing steps. This polymer coating reduces the carbon filler fraction in the carbon/polymer shield resulting in a low electrical conductivity of the composite material. This explains the absolute shielding effectiveness of these carbon/polymer composite materials [2], [3], [4], [5], [8], [9], [10], [11], [12], [13], [14], [15] is usually low compared to copper or nickel.
One approach to increase the electrical conductivity of carbon/polymer EMI shielding materials is to increase the carbon filler content, thus making paper-like pristine graphene materials [16], [17], [18], [19] promising for new shielding applications especially in the aerospace industry where the weight matters. This EMI shielding application of graphene paper is related to its low density, excellent flexibility and extraordinary electrical properties of graphene materials [20], [21], [22], [23]. Graphene paper [16] prepared by using graphene oxide (GO) as a template for synthesis and processing showed good mechanical properties with a breaking stress at 120 MPa. However, the poor conductivity of GO – resulting from the introduction of oxygen and surface defects during preparation – limits its applications [19]. Recently, highly electrical and thermal conductive GO paper prepared by direct evaporation demonstrated a EMI shielding effectiveness of 20 dB was reported [24], but GO paper prepared by similar method usually shows relatively high density [16], which limits its application as a light EMI shielding materials. Graphene made through CVD has an overall high quality. By using this method, graphene paper [18] with good electrical conductivity has been achieved by filtration of the CVD graphene foams [25], but the poor mechanical strength of this material requires supporting substrate and expensive catalyst template – nickel foam – which may be a barrier for industrial scale up.
Here, we report a novel, freestanding graphene paper prepared by CVD synthesis of 3D graphene pellets, extracting the Ni catalyst and pressing the remaining structure to form a paper-like material [26].
Section snippets
Fabrication of graphene pellet
Nickel powder (Alfa Aesar) of 2–3 μm average particle size and 0.68 m2 g−1 in specific surface area was pelletized into 6.4 cm diameter pellets using a compression machine (Carver, 973214A). The applied force was ∼10 MPa, and varied for different pellet thicknesses. The nickel pellet was placed on a quartz platform inside a quartz tube for growing of graphene by CVD. The nickel pellet was heated up to 1000 °C in a tube furnace (FirstNano, ET1000) under Ar (1000 sccm). Hydrogen (325 sccm) was then
Results and discussion
Fig. 1a illustrates the processing of graphene paper, in which nickel powder catalyst was pelletized by applying ∼10 MPa pressure to a known mass of the metal confined in a piston-cylinder mold. The metal catalyst powder was sintered into an interconnected foam-like structure under the applied high temperature inside the CVD reactor (Fig. S1a and b). Graphene was then synthesized from this pellet by introducing methane which resulted in forming of a monolith 3D graphene network of interconnected
Conclusion
We have developed a polymer free process for synthesis of three dimensional graphene structures and graphene paper, consisted of 100% graphene, using nickel pellet as a catalyst template during the CVD synthesis, followed by acid extraction the catalyst and pressing the remaining structure. The 3D graphene and the related graphene paper are mechanically robust. The paper shows high electrical conductivity, attributed to the good quality of the individual graphene flakes and their connectivity
Acknowledgments
This work was funded by the National Science Foundation through the following grants: CMMI-0727250; SNM-1120382; ERC-0812348; and by a DURIP-ONR grant. The support of the listed Government agencies is gratefully acknowledged.
References (28)
- et al.
Elastomer foam nanocomposites for electromagnetic dissipation and shielding applications
Compos Sci Technol
(2010) Electromagnetic shielding effectiveness of galvanostatically synthesized conducting polypyrrole films in the 300–2000 MHz frequency range
Mater Res Bull
(1996)Electromagnetic interference shielding effectiveness of carbon materials
Carbon
(2001)- et al.
Electromagnetic interference shielding of graphene/epoxy composites
Carbon
(2009) - et al.
Reflection and absorption contributions to the electromagnetic interference shielding of single-walled carbon nanotube/polyurethane composites
Carbon
(2007) - et al.
Electromagnetic interference shielding effectiveness of carbon-based materials prepared by screen printing
Carbon
(2009) - et al.
Synthesis of graphene-based nanosheets via chemical reduction of exfoliated graphite oxide
Carbon
(2007) - et al.
Nickel filament polymer-matrix composites with low surface impedance and high electromagnetic interference shielding effectiveness
J Electron Mater
(1997) - et al.
Lightweight and flexible graphene foam composites for high-performance electromagnetic interference shielding
Adv Mater
(2013) - et al.
Tough graphene−polymer microcellular foams for electromagnetic interference shielding
ACS Appl Mater Interfaces
(2011)
Novel carbon nanotube−polystyrene foam composites for electromagnetic interference shielding
Nano Lett
EMI shielding: methods and materials – A review
J App Poly Sci
Functionalized graphene–PVDF foam composites for EMI shielding
Macromol Mater Eng
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