The silicon-based microelectronics industry is rapidly approaching a point where device fabrication can no longer be simply scaled to progressively smaller sizes. Technological decisions must now be made that will substantially alter the directions along which silicon devices continue to develop. One such challenge is the need for higher permittivity dielectrics to replace silicon dioxide, the properties of which have hitherto been instrumental to the industry's success. Considerable efforts have already been made to develop replacement dielectrics for dynamic random-access memories. These developments serve to illustrate the magnitude of the now urgent problem of identifying alternatives to silicon dioxide for the gate dielectric in logic devices, such as the ubiquitous field-effect transistor.

We report the observation of periodic 180 degrees stripe domains below the ferroelectric transition in thin films. Epitaxial PbTiO3 films of thickness d=1.6 to 42 nm on SrTiO3 substrates were studied using x-ray scattering. Upon cooling below T(C), satellites appeared around Bragg peaks indicating the presence of 180 degrees stripe domains of period Lambda=3.7 to 24 nm. The dependence of Lambda on d agrees well with theory including epitaxial strain effects, while the suppression of T(C) for thinner films is significantly larger than that expected solely from stripe domains.

Microelectromechanical systems (MEMS) incorporating active piezoelectric layers offer integrated actuation, sensing, and transduction. The broad implementation of such active MEMS has long been constrained by the inability to integrate materials with giant piezoelectric response, such as Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PMN-PT). We synthesized high-quality PMN-PT epitaxial thin films on vicinal (001) Si wafers with the use of an epitaxial (001) SrTiO(3) template layer with superior piezoelectric coefficients (e(31,f) = -27 ± 3 coulombs per square meter) and figures of merit for piezoelectric energy-harvesting systems. We have incorporated these heterostructures into microcantilevers that are actuated with extremely low drive voltage due to thin-film piezoelectric properties that rival bulk PMN-PT single crystals. These epitaxial heterostructures exhibit very large electromechanical coupling for ultrasound medical imaging, microfluidic control, mechanical sensing, and energy harvesting.

According to recent experiments and predictions, the orientation of the polarization at the surface of a ferroelectric material can affect its surface chemistry. Here we demonstrate the converse effect: the chemical environment can control the polarization orientation in a ferroelectric film. In situ synchrotron x-ray scattering measurements show that high or low oxygen partial pressure induces outward or inward polarization, respectively, in an ultrathin PbTiO3 film. Ab initio calculations provide insight into surface structure changes observed during chemical switching.

Using in situ high-resolution synchrotron x-ray scattering, the Curie temperature T C has been determined for ultrathin c-axis epitaxial PbTiO 3 films on conducting substrates (SrRuO 3 on SrTiO 3 ), with surfaces exposed to a controlled vapor environment. The suppression of T C was relatively small, even for the thinnest film (1.2 nm). We observe that 180 stripe domains do not form, indicating that the depolarizing field is compensated by free charge at both interfaces. This is confirmed by ab initio calculations that find polar ground states in the presence of ionic adsorbates.