Enhancement of ferroelectric polarization stability by interface engineering.

By using theoretical predictions based on first-principle calculations, we explore an interface engineering approach to stabilize polarization states in ferroelectric heterostructures with a thickness of just several nanometers.

Giant piezoelectricity on Si for hyperactive MEMS.

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.

Metallic and insulating oxide interfaces controlled by electronic correlations.

The formation of two-dimensional electron gases (2DEGs) at complex oxide interfaces is directly influenced by the oxide electronic properties. We investigated how local electron correlations control the 2DEG by inserting a single atomic layer of a rare-earth oxide (RO) [(R is lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), or yttrium (Y)] into an epitaxial strontium titanate oxide (SrTiO(3)) matrix using pulsed-laser deposition with atomic layer control. We find that structures with La, Pr, and Nd ions result in conducting 2DEGs at the inserted layer, whereas the structures with Sm or Y ions are insulating. Our local spectroscopic and theoretical results indicate that the interfacial conductivity is dependent on electronic correlations that decay spatially into the SrTiO(3) matrix. Such correlation effects can lead to new functionalities in designed heterostructures.

Creation of a two-dimensional electron gas at an oxide interface on silicon.

In recent years, reversible control over metal-insulator transition has been shown, at the nanoscale, in a two-dimensional electron gas (2DEG) formed at the interface between two complex oxides. These materials have thus been suggested as possible platforms for developing ultrahigh-density oxide nanoelectronics. A prerequisite for the development of these new technologies is the integration with existing semiconductor electronics platforms. Here, we demonstrate room-temperature conductivity switching of 2DEG nanowires formed at atomically sharp LaAlO(3)/SrTiO(3) (LAO/STO) heterointerfaces grown directly on (001) Silicon (Si) substrates. The room-temperature electrical transport properties of LAO/STO heterointerfaces on Si are comparable with those formed from a SrTiO(3) bulk single crystal. The ability to form reversible conducting nanostructures directly on Si wafers opens new opportunities to incorporate ultrahigh-density oxide nanoelectronic memory and logic elements into well-established Si-based platforms.

Tunneling electroresistance effect in ferroelectric tunnel junctions at the nanoscale.

Using a set of scanning probe microscopy techniques, we demonstrate the reproducible tunneling electroresistance effect on nanometer-thick epitaxial BaTiO(3) single-crystalline thin films on SrRuO(3) bottom electrodes. Correlation between ferroelectric and electronic transport properties is established by direct nanoscale visualization and control of polarization and tunneling current. The obtained results show a change in resistance by about 2 orders of magnitude upon polarization reversal on a lateral scale of 20 nm at room temperature. These results are promising for employing ferroelectric tunnel junctions in nonvolatile memory and logic devices.

Strain-induced polarization rotation in epitaxial (001) BiFeO3 thin films.

Direct measurement of the remanent polarization of high quality (001)-oriented epitaxial BiFeO3 thin films shows a strong strain dependence, even larger than conventional (001)-oriented PbTiO3 films. Thermodynamic analysis reveals that a strain-induced polarization rotation mechanism is responsible for the large change in the out-of-plane polarization of (001) BiFeO3 with biaxial strain while the spontaneous polarization itself remains almost constant.

High-dose methylprednisolone therapy for acute graft-versus-host disease associated with matched unrelated donor bone marrow transplantation.

Acute graft-versus-host disease (aGVHD) is a major barrier to successful bone marrow transplantation (BMT) with matched unrelated donors. Eight of eight recipients of matched unrelated donor BMT developed aGVHD. We used a regimen of high-dose methylprednisolone (5 mg/kg/day for 4 days with responders continuing on treatment, and dose escalation to 10 mg/kg/day for non-responders) as initial therapy of aGVHD. One patient died on the second day of steroid administration. Each of the seven remaining patients responded to methylprednisolone, five at the 5 mg/kg/day dose and two at the 10 mg/kg/day dose. Three of five patients developed flare of aGVHD during reduction of the corticosteroid dosage and died with aGVHD and infection. Two patients have undergone reduction of methylprednisolone at a modified rate without a flare. Infectious complications during methylprednisolone treatment were very common and contributed to the death of the three patients with flare of aGVHD. Four patients in whom aGVHD was in remission survived serious systemic infections. High-dose methylprednisolone is effective initial therapy for aGVHD associated with matched unrelated BMT, but is associated with a high risk of serious infections.