Microwave dielectric ceramics such as Ba(Mg 1/3 Ta 2/3 )O 3 and Ba 2 Ti 9 O 20 possess high dielectric constant and low dielectric loss in microwave frequency regime and have tremendous potential for device applications. In these materials, the presence of extrinsic defects, such as secondary phases, usually altered the microwave dielectric properties of the materials markedly, but the correlation of the microwave dielectric response of the materials with their microstructure has not been fully understood due to the lack of dielectric response in the local area. In this article, microwave near-field microscopy and Raman spectroscopy were used to investigate the microwave dielectric mechanism, viz. we measured the microwave dielectric properties of the materials in micron region by using a evanescent microwave probe (EMP) and, at the same time, examined the lattice vibration characteristics of the region by using a micro-Raman spectrum. How the presence of the secondary phase affects the microwave dielectric properties of the materials is thus systematically investigated. The causes of intrinsic or extrinsic dielectric loss were explored by comparing the dielectric images in SEMP at microwave frequencies and the corresponding Raman Spectra.
Perovskite thin film materials possess good dielectric properties, which vary with applied voltage, and have thus been thoroughly investigated for applications as thin film tunable microwave devices. However, the tunability of the thin film materials derived from the frequency response of the thin film devices suffers from ambiguity in extracting the true dielectric response of the thin film materials in microwave frequency regime. To circumvent such a difficulty, we investigated the dielectric properties of perovskite thin films by using a novel scanning evanescent microwave microscopy (SEMM). To extract the dielectric parameters from original microwave frequency response signal of SEMM probe, we perform a 3-dimensional (3D) finite element simulation to model the frequency behavior of the SEMM microwave probe. Dielectric images of the thin films with submicron resolution can be obtained by using such a near-field technique, which correlates very well with the morphology of the films examined by atomic force microscopy. Moreover, the dielectric images of dielectric thin films were compared to those of ferroelectric thin films in order to discuss the related dielectric mechanism of the materials.
Phase transformation of carbonaceous species under the action of high intensity plasma was studied by using a specially designed setup in which a Fe-needle was used as an antenna to absorb microwave and to induce local plasma in the vicinity of needle-tip. Using such a setup, carbon nanotubes have been successfully synthesized on the needle using diamond powder as carbon source and organic iron as catalyst. Variety of nano-structure carbonaceous materials were observed besides carbon nanotubes, e.g., diamond recrystallized as starfruit shaped geometry. Moreover, there exist other kinds of unknown nanostructures on the needle substrate. Some are long, thin, smooth, and some are planar. The characteristics of these unique nanostructured materials will be systematically investigated and the possible growth mechanism will be discussed.
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