AlN–SWCNT Metacomposites Having Tunable Negative Permittivity in Radio and Microwave Frequencies

Abstract

Discovery of plasmon resonance and negative permittivity in carbon allotropes at much lower frequencies than those of metals has evoked interest to develop random metacomposites by suitable means of addition of these dispersoids in an overall dielectric matrix. Random metacomposites have always the advantage for their easy preparation techniques over those of their regular arrayed artificial counterpart. However, thermal management during the heat generation by electromagnetic attenuation in metamaterials is not yet studied well. The present communication discusses the dielectric permittivities and loss parameters of aluminum nitride−single-wall carbon nanotube (AlN−SWCNT) composites considering high thermal conductivities of both materials. The composites are dense and have been prepared by a standard powder technological method using hot pressing at 1850 °C under a nitrogen atmosphere. Increase in the negative permittivity value with SWCNT concentration (1, 3, and 6 vol %) in the composites had been observed at low frequencies. Characterization of the materials with Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and microstructure analysis by scanning and transmission electron microscopy (TEM) revealed the survivability of the SWCNTs and the nature of the matrix−filler interface. Plasmonic resonance following Drude's law could be observed at much lower plasma frequencies than that of pure SWCNT and for very little SWCNT addition. Exhibition of the negative permittivity has been explained with relation to the microstructure of the composites observed from field emission scanning electron micrographs (FESEM), TEM images, and the equivalent circuit model. High energy conversion efficiency is expected in these composites due to the possession of dual functionalities like high thermal conductivity as well as high negative permittivity, which should ensure the application of these materials in wave filter, cloaking device, supercapacitors, and wireless communication.

Epsilon-negative media from the viewpoint of materials science

“…The induced electric dipoles in isolated MWCNTs caused the dielectric resonance for composites with low filling content, and the formed conductive networks of MWCNTs within insulting Al 2 O 3 matrix resulted in the plasma-like negative permittivity behavior, similar phenomena have been also observed in some metal/ceramic composites [38]. Moreover, it's interesting to found that negative permittivity of CMCs with carbonaceous fillers hold smaller absolute values than that of metal/ceramic composites, which may be related to the moderate carrier concentration of the carbonaceous fillers [58,63]. In short, CMCs provide an alternative for the preparation of epsilon-negative materials, of which the negative permittivity can be tailored by the research methods of materials science.…”

The effect of boron nitride nanosheets on the mechanical and thermal properties of aluminum nitride ceramics

“…With the increasing requirements for the new applications, pure AlN ceramics often cannot match the actual requirements. Therefore, great attention has been paid on the composite ceramics with AlN as the main phase 10–14 . In order to effectively improve the mechanical properties of AlN ceramics, some reinforcement materials have also been tried to be added to AlN.…”

“…Moreover, when superabundant graphene is added to AlN, the relative density and hardness of the composites will be significantly reduced, 15 and its application will be affected. Therefore, although adding some carbon materials (e.g., SWCNT) into AlN can effectively improve the mechanical properties of composites, it is very meaningful to study other AlN matrix composites 13,14,16,17 …”

“…Therefore, great attention has been paid on the composite ceramics with AlN as the main phase. [10][11][12][13][14] In order to effectively improve the mechanical properties of AlN ceramics, some reinforcement materials have also been tried to be added to AlN. For example, adding some of graphene nanosheets to AlN can significantly improve the bending strength and fracture toughness of AlN.…”

“…Therefore, although adding some carbon materials (e.g., SWCNT) into AlN can effectively improve the mechanical properties of composites, it is very meaningful to study other AlN matrix composites. 13,14,16,17 Boron nitride nanosheets (BNNSs), stripped from h-BN, possess a good two-dimensional lamellar structure, similar to graphene nanosheets. 18,19 But unlike graphene, except for excellent thermal conductivity and mechanical properties, BNNSs also have brilliant electrical insulating property.…”