The highly mobile electrons at the interface of SrTiO3 with other oxide insulators, such as LaAlO3 or AlOx, are of great current interest. A vertical gate voltage allows controlling a metal/superconductor-to-insulator transition, as well as electrical modulation of the spin-orbit Rashba coupling for spin-charge conversion. These findings raise important questions about the origin of the confined electrons as well as the mechanisms that govern the interfacial electric field. Here we use infrared ellipsometry and confocal Raman spectroscopy to show that an anomalous polar moment is induced at the interface that is non-collinear, highly asymmetric and hysteretic with respect to the vertical gate electric field. Our data indicate that an important role is played by the electromigration of oxygen vacancies and their clustering at the antiferrodistortive domain boundaries of SrTiO3, which generates local electric and possibly also flexoelectric fields and subsequent polar moments with a large lateral component. Our results open new perspectives for the defect engineering of lateral devices with strongly enhanced and hysteretic local electric fields that can be manipulated with various other parameters, like strain, temperature, or photons.

Iridates have attracted immense interest since their strong spin-orbit coupling (SOC) can lead to rich exotic phenomena such as a J(eff )= 1/2 Mott insulating state. Here we report a novel iridate discovered in our efforts which aimed to synthesize Ba2IrO4 thin films Through systematic transmission and scanning transmission electron microscopy studies, we have shown this new compound possesses a layered orthorhombic structure with the composition of Ba7Ir3O13+delta (BIO). This material is an insulator with an optical band gap of similar to 1.3 eV. Furthermore, we found that the thin films of this material can be grown on differently orientated perovskite substrates or MgO substrates. Although all these films maintain an identical crystallographic orientation, i.e. its c-axis perpendicular to the substrate surface, they form various domain structures dependent on the substrate. When (001)-oriented LaAlO3 and (111) oriented SrTiO3 perovskites are used as substrates, the domains show 12 fold and 6 fold symmetry respectively, and the domain orientations are highly coherent and the domain-walls are atomically sharp. However, the films on the (110) oriented MgO substrates feature much less coherent domain walls and thread dislocations occur at the domain boundaries. These findings not only reveal a new playground for the study of the novel SOC physics of iridates, but also provide a route to tailor the domain wall structure via epitaxial lattice mismatch in films.

Field effect transistors were fabricated using carbon nanotube (CNT) intra-connnects. The intra-connects — individual tube or a small bundle of tubes spanning across the planar electrodes — were grown by using chemical vapor deposition (CVD) precisely between very sharp metal tips on the pre-fabricated electrodes. Gate-controlled N-shaped negative differential resistance (NDR) has been demonstrated. Enhanced differential photoconductance, which was associated with NDR was observed, as well.

In this study, we investigated the structural and optical properties of Ge-doped SbTe (Ge-ST) thin films with three differing compositions: Ge0.06Sb0.77Te0.17 (Ge-STH), Ge0.05Sb0.70Te0.25 (Ge-STM), and Ge0.05Sb0.64Te0.31 (Ge-STL), grown on Si substrate by radio-frequency sputtering method. The films were annealed at 250 degrees C for crystallization and their crystal structures were examined by X-ray diffraction. Compared to the X-ray diffraction spectra of the undoped SbTe, the Ge-ST thin films had a hexagonal structure with large stacking periods. Using Raman spectroscopy, we investigated the shift of the phonon mode frequencies (A(1g) and E-g) of the films with varying Sb:Te ratios. We compared the dependence of the phonon frequencies of Ge-ST on the Sb content to those of the corresponding undoped SbTe. The composition dependence of the A(1g) phonon frequency could be explained in terms of the linear extrapolation of Sb and Sb2Te3 crystals. By using spectroscopic ellipsometry, we measured the dielectric function of the thin films in the near-IR, visible, and ultraviolet spectral regions. The optical energy gaps and bandgaps of the amorphous and crystalline phases, respectively, were determined using linear extrapolation of the absorption coefficient. The optical gap energies of the amorphous Ge-ST films were determined to be about 0.5-0.6 eV, whereas the indirect bandgap energies of the crystalline films shrank substantially to about 0.15-0.2 eV. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3532547] All rights reserved.

New testing for small size scales Professor Matthew Miller and his group from the Sibley School of Mechanical and Aerospace Engineering standing in front of the load frame / diffractometer system located in Rhodes Hall, Cornell University. Back row (left to right): Michael Ross, Kevin McNelis, and Jay Schuren. Front row (left to right): Jon Acquaviva, Zachary Peeples, Ben Oswald, and Professor Miller. The system was designed and built for their high energy diffraction work at CHESS Complete article on page 37.

Circular pillar structures of various diameters have been prepared by a focused ion beam (FIB) through a 4-μm-thick epitaxial gallium nitride (GaN) film grown on a sapphire substrate. Micro-Raman scattering is used to measure residual stresses based on the shift of an E2 phonon in the GaN film. Measurements of residual stress profiles are compared to Winkler's elastic formalism for a shear-supported film with proper boundary conditions. The model, optimized at a cleave edge, is compared to the experimental shape of stress variations inside and outside the pillar structures.

We study polarization rotations by a dispersion compensation module responding to quasi-periodic room temperature oscillations. The rotations seems to have a functional temperature dependence on short time scales interrupted by rather abrupt shifts occurring, on average, every month. (2 pages)