Micro-Raman measurements of xBa(Mg1/3Ta2/3)O3–(1−x)Ba(Mg1/3Nb2/3)O3 perovskite ceramics, with x=0, 0.25, 0.50, 0.75, and 1.0, were taken at room temperature. Raman results clearly show the 1:2 ordered structures of these compounds. Four A1g and five Eg Raman modes were unambiguously assigned. The A1g(O) phonon of the oxygen-octahedron stretch mode, which possesses the largest energy and width of all the observed Raman phonons, significantly influences the microwave dielectric properties of the materials. A higher vibration frequency of A1g(O) mode results in a lower dielectric constant, and a wider width of the mode corresponds to a lower Q×f value.

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Nanorings with an average height and diameter of 1.2 and 65 nm, respectively, were observed to form in Si-capped Ge quantum dots grown at 600 °C by ultrahigh-vacuum chemical vapor deposition. The nanorings were captured with the rapid cooling of the samples with appropriate amount of Si capping. Based on the results of transmission electron microscopy and Raman spectroscopy, the formation of nanorings is attributed to alloying and strain relief in the Si/Ge/ ͑001͒Si system. The self-assembly of nanorings provides a useful scheme to form ultrasmall ring-like structure and facilitates the characterization of the physical properties of unconventional quantum structures.

Micro-Raman spectra were measured on a single freestanding GaN nanorod, which was grown by molecular beam epitaxy. A sharp linewidth of E 2 ͑high͒ mode of 2.1 cm −1 measured in the x͑y , y͒x configuration indicates the high crystalline quality of the nanorod. The angle-dependent Raman spectroscopy shows that the integrated intensities of these first-order Raman modes follow the theoretical sinusoidal functions. The forbidden E 1 ͑LO͒ mode that appeared in the x͑z , z͒x scattering configurations is assigned to the quasi-LO phonon mode. Power-dependent Raman spectroscopy shows redshift with increasing laser power density due to sample heating which is confirmed by Stokes and anti-Stokes measurements. The broadband centered at 708.5 cm −1 is ascribed to the surface mode of the nanostructure.

The relationship between the microwave dielectric properties and the IR active phonons of xBa(Mg1/3Ta2/3)O3–(1−x)Ba(Mg1/3Nb2/3)O3 ceramics was investigated. The IR modes were assigned, and the origin of dielectric response was determined. Among the 15 prominent IR modes, we found that the normal vibrations of the O layers and that of the Ta/Nb layers are strongly correlated to the measured dispersion parameters, such as the resonant strength (4πρ) and the damping coefficient (γ). The frequency shifts of the normal modes of the O layers and that of the Ta/Nb layers explain the linear decrease of microwave dielectric constant (K) as x increases, while the width of these modes correlate with the Q×f value.

Electrical impedance measurements on a congruent LiNbO 3 single crystal were performed as a function of both temperature and frequency. The measurements were carried out in the directions along the cand a-axes of the crystal. The temperature and frequency dependence of various dielectric properties have been studied. The result has revealed two remarkable dynamic relaxations: dielectric dipolar relaxation and ionic conductivity relaxation. The dipolar relaxation peaks were found at frequencies around 4 × 10 6 and 2 × 10 6 Hz for the c-axis and a-axis, respectively, and they were only slightly temperature dependent. The ionic conductivity relaxation was found at the lower-frequency end but it was temperature dependent. The temperature dependence of the dc electrical conductivity follows the Arrhenius law. It corresponds to the longrange ionic motion of Li + ions which are thermally activated with activation energy of 0.90 and 0.87 eV along the cand a-axis directions, respectively. The dc conductivities measured along the cand a-axes are very close to each other, and the value increases from 1.7 × 10 −6 to 1.9 × 10 −3 −1 cm −1 as the temperature is raised from 300 to 700 • C. The sample crystal becomes an ionic conductor as the temperature is raised.

Epitaxial needlelike ZnO nanowires were grown vertically over an entire epi-GaN/sapphire substrate at 550°C by low-pressure vapor phase deposition without employing any metal catalysts. A two-step oxygen injection process is the key of successful synthesis. The length of ZnO wires was up to 3.0 m. The diameters of the roots and tips of the ZnO nanowires were around 80-100 and 15-30 nm, respectively. X-ray diffraction showed the epitaxial orientation relationship between ZnO and GaN as ͓001͔ ZnO //͓001͔ GaN along the normal to the plane, and ͓100͔ ZnO //͓100͔ GaN along the in-plane direction, consistent with the selective area electron diffraction pattern taken at the ZnO/GaN heterointerface. High-resolution transmission electron microscopy confirmed that nanowire was a single crystal. A room-temperature photoluminescence spectrum of the wires revealed a low concentration of oxygen vacancy in the ZnO nanowires and showed high optical quality.