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The miniaturization and integration of frequency-agile microwave circuits--relevant to electronically tunable filters, antennas, resonators and phase shifters--with microelectronics offers tantalizing device possibilities, yet requires thin films whose dielectric constant at gigahertz frequencies can be tuned by applying a quasi-static electric field (1). Appropriate systems such as [Ba.sub.x][Sr.sub.1-x]Ti[O.sub.3] have a paraelectric-ferroelectric transition just below ambient temperature, providing high tunability (1-3). Unfortunately, such films suffer significant losses arising from defects. Recognizing that progress is stymied by dielectric loss, we start with a system with exceptionally low loss--[Sr.sub.n+1][Ti.sub.n][O.sub.3n+1] phases (4,5)--in which [(SrO).sub.2] crystallographic shear (6,7) planes provide an alternative to the formation of point defects for accommodating non-stoichiometry (8,9). Here we report the experimental realization of a highly tunable ground state arising from the emergence of a local ferroelectric instability (10) in bi-axially strained [Sr.sub.n+1][Ti.sub.n][O.sub.3n+1] phases with n [greater than or equal to] 3 at frequencies up to 125 GHz. In contrast to traditional methods of modifying ferroelectrics--doping (1-3,11,12) or strain (13-16)--in this unique system an increase in the separation between the [(SrO).sub.2] planes, which can be achieved by changing n, bolsters the local ferroelectric instability. This new control parameter, n, can be exploited to achieve a figure of merit at room temperature that rivals all known tunable microwave dielectrics (3)., Ferroelectric thin films possessing a nonlinear dielectric response to a quasi-static electric field have been widely pursued for tunable dielectric devices (17-20) that work at gigahertz frequencies. [Ba.sub.x][Sr.sub.1-x]Ti[O.sub.3] is the [...]

Metal overlayers can be electrodeposited onto dissimilar metal substrates at potentials less negative than the Nernst value, otherwise called underpotential deposition (UPD). The evolution of UPD processes was studied using time-resolved surface X-ray scattering method on Cu UPD and Pt(111) in the presence of Cl anion. Findings show that the development of long-range periodic order in the CuCl overlayer requires significantly more time than that required for electrodeposition. This suggest that the latter is not the rate-limiting process.