We demonstrate a metamaterial device whose far-infrared resonance frequency can be dynamically tuned. Dynamic tuning should alleviate many bandwidth-related roadblocks to metamaterial application by granting a wide matrix of selectable electromagnetic properties. This tuning effect is achieved via a hybrid-metamaterial architecture; intertwining split ring resonator metamaterial elements with vanadium dioxide ͑VO 2 ͒-a material whose optical properties can be strongly and quickly changed via external stimulus. This hybrid structure concept opens a fresh dimension in both exploring and exploiting the intriguing electromagnetic behavior of metamaterials.

Highly oriented VO 2 thin films were grown on sapphire substrates by the sol-gel method that includes a low pressure annealing in an oxygen atmosphere. This reduction process effectively promotes the formation of the VO 2 phase over a relatively wide range of pressures below 100 mTorr and temperatures above 400 • C. X-ray diffraction analysis showed that as-deposited films

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VO 2 thin films were successfully grown on sapphire and SiO 2 /Si substrates by the sol-gel process. The VO 2 phase was well formed during simplified low pressure annealing in oxygen. The films prepared on sapphire directly crystallized to the VO 2 phase without passing through intermediate phases with increasing the annealing temperature, resulting in highly [010]oriented films on Al 2 O 3 (10 " 1 10) substrate. In contrast, the polycrystal films grown on SiO 2 /Si reached the final VO 2 phase with passing through several phases. Mixed phases existed at the interface between the film and substrate. For the films on sapphire, the phases with low-valent vanadium appeared drastically at the interface region along the depth, whereas the phase of the polycrystal film slowly changed into a low valence state at the initial stage of the interface and then returned to a high value. And both films showed an abrupt change in resistivity at the different transition temperature. The property of the interface may affect the crystallization and the metal-insulator transition of the films.

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This study systematically evaluates residential consumer responses to a utility conservation initiative based on an econometric analysis of a sample of 510 households served by Artesian Water Company, Inc. (New Castle County of Delaware). Using a panel study approach covering the period from 1992 to 1997, this study shows that Artesian's water conservation program has had statistically significant and persistent impacts on residential water consumption.

Optimization of hydrogenated amorphous silicon germanium thin films and solar cells deposited by hot wire chemical vapor deposition, Thin Solid Films (2015), ABSTRACTThis work studies hydrogenated amorphous silicon germanium films, deposited by hot wire chemical vapor deposition, to be used as low band gap absorber material in thin film solar cells. Material properties, such as the bonding configurations, the ambipolar diffusion length and the optical band gap, were examined as a function of the substrate temperature and germanium content. Our best materials were incorporated in single junction solar cells with high long-wavelength response and a tandem solar cell with an efficiency of 10.42%.

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