Barium strontium titanate thin films were deposited by sputtering on Pt/SiO 2 structures using five different host substrates: magnesium oxide, strontium titanate, sapphire, silicon, and vycor glass. These substrates were chosen to provide a systematic change in thermal strain while maintaining the same film microstructure. All films have a weakly textured microstructure. Temperature dependent dielectric measurements from 100-500 K determined that decreasing thermal expansion coefficient of the host substrate ͑i.e., larger tensile thermal strain͒ reduced the film dielectric permittivity. The experimentally determined Curie-Weiss temperature decreased with increasing tensile thermal strain and the Curie-Weiss constant increased with tensile strain as predicted by Pertsev et al. ͓J.

Large variations in the permittivity of rf magnetron sputtered thin-film barium strontium titanate have been obtained through optimization of growth conditions for maximum dielectric strength and zero-field permittivity in a parallel-plate capacitor structure. Using nominal target compositions of Ba 0.5 Sr 0.5 TiO 3 , and Pt electrodes on c-plane sapphire substrates, adjustment of the O 2 partial pressure during deposition was used to vary the excess Ti incorporation into the films, which influenced the low-field permittivity, loss tangent, and dielectric strength. By balancing the benefits of a high permittivity with dielectric strength and loss, we have produced films capable of sustaining short-duration fields greater than 4 MV/ cm with over 13:1 ͑Ͼ90% ͒ change in dielectric constant, and greater than 5:1 tunability in bias fields under 1 MV/ cm.

We demonstrate a compact spectrometer based on an array of high-quality-factor photonic crystal nanocavities, coupled via a planar two-dimensional waveguide. This architecture enables spectral analysis of incident light with resolution as high as the bandwidth of the cavity mode–0.3 nm at 840 nm for our device. The design is easily extended to the visible and deep-infrared spectral ranges. The two-dimensional cavity array can be mated to commercial two-dimensional optical detector arrays, creating a compact and high-resolution spectrometer suitable for a range of applications including materials and chemical analysis.

Abstract:We demonstrate a new kind of optical spectrometer employing photonic crystal patterns to outcouple waveguided light from a transparent substrate. This spectrometer consists of an array of photonic crystal patterns, nanofabricated in a polymer on a glass substrate, combined with a camera. The camera captures an image of the light outcoupled from the patterned substrate; the array of patterns produces a spatially resolved map of intensities for different wavelength bands. The intensity map of the image is converted into a spectrum using the photonic crystal pattern response functions. We present a proof of concept by characterizing a white LED with our photonic crystal spectrometer.

The dielectric permittivity, dielectric quality factor ͑inverse dielectric loss͒, and lattice parameter of 140 nm sputtered SrTiO 3 films were dependent on the oxygen partial pressure and total chamber pressure (O 2 ϩAr) during film growth. Films were grown at 25 and 75 mTorr ͑mT͒ in an oxygen rich and oxygen deficient sputtering gas environment concurrently on ͑100͒ SrTiO 3 and ͑111͒ Pt/͑0001͒ Al 2 O 3 substrates. Films were deposited on platinized sapphire for electrical characterization and the homoepitaxial films were used as a structural and chemical standard. High resolution triple axis x-ray diffraction results showed an increase in mismatch between the film and substrate ͑200͒ peak in homoepitaxial SrTiO 3 films with higher total growth and lower oxygen pressures. Dielectric quality factors of the SrTiO 3 films on platinized sapphire at 1 MHz for the 25 mT ͑50 sccm Ar/50 sccm O 2 ), 25 mT ͑90 sccm Ar/10 sccm O 2 ), 75 mT ͑50 sccm Ar/50 sccm O 2 ), and 75 mT ͑90 sccm Ar/10 sccm O 2 ) film growths were 320, 251, 209, and 102, respectively; likewise, the dielectric constants follow as 241, 230, 220, and 170, respectively. Improved film dielectric properties were observed for films closer to stoichiometric SrTiO 3 .