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.
ABSTRACT
In GaAs-based pseudomorphic high-electron mobility transistor device structures, strain and composition of the In x Ga1-x As channel layer are very important as they influence the electronic properties of these devices. In this context, transmission electron microscopy techniques such as (002) dark-field imaging, high-resolution transmission electron microscopy (HRTEM) imaging, scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF) imaging and selected area diffraction, are useful. A quantitative comparative study using these techniques is relevant for assessing the merits and limitations of the respective techniques. In this article, we have investigated strain and composition of the In x Ga1-x As layer with the mentioned techniques and compared the results. The HRTEM images were investigated with strain state analysis. The indium content in this layer was quantified by HAADF imaging and correlated with STEM simulations. The studies showed that the In x Ga1-x As channel layer was pseudomorphically grown leading to tetragonal strain along the [001] growth direction and that the average indium content (x) in the epilayer is ~0.12. We found consistency in the results obtained using various methods of analysis.
