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Control of the oxygen octahedral coupling (OOC) provides a large degree of freedom to manipulate physical phenomena in complex oxide heterostructures. Recently, local tuning of the tilt angle has been found to control the magnetic anisotropy in ultrathin films of manganites and ruthenates, while symmetry control can manipulate the metal insulator transition in nickelate thin films. The required connectivity of the octahedra across the heterostructure interface enforces a geometric constraint to the 3-dimensional octahedral network in epitaxial films. Such geometric constraint will either change the tilt angle to retain the connectivity of the corner shared oxygen octahedral network or guide the formation of a specific symmetry throughout the epitaxial film. Here, we will discuss the control of OOC in manganite heterostructures by interface-engineering. OOC driven magnetic and transport anisotropies have been realized in LSMO/NGO heterostructures. Competition between the interfacial OOC and the strain further away from the interface leads to a thickness driven sharp transition of the anisotropic properties. Furthermore, octahedral relaxation leading to a change of p-d hybridization driven by interfacial OOC appears to be the strongest factor in thickness related variations of magnetic and transport properties in epitaxial LSMO films on NGO substrates. The results unequivocally link the atomic structure near the interfaces to the macroscopic properties. The strong correlation between a controllable oxygen network and the functionalities will have significant impact on both fundamental research and technological application of correlated perovskite heterostructures. By controlling the interfacial OOC, it is possible to pattern in 3 dimensions the magnetization to achieve non-collinear magnetization in both in-plane and out of plane directions, thus making the heterostructures promising for application in orthogonal spin transfer devices, spin oscillators, and low field sensors. [ABSTRACT FROM AUTHOR]

We report on the fabrication and mechanical properties of all-oxide, free-standing, heteroepitaxial, piezoelectric, microelectromechanical systems (MEMS) on silicon, using PbZr0.52Ti0.48O3 as the key functional material. The fabrication was enabled by the development of an epitaxial lift-off strategy for the patterning of multilayer oxide heterostructures grown on Si(001), employing a high temperature stable, sacrificial oxide template mask to obtain freestanding cantilever MEMS devices after substrate etching. All cantilevers, with lengths in the range 25-325 μm, width 50 μm, and total thickness of 300 nm, can be actuated by an external AC-bias. For lengths 50-125 μm, the second order bending mode formed the dominant resonance, whereas for the other lengths different or multiple modes were present. [ABSTRACT FROM AUTHOR]

We have performed high field magnetotransport measurements to investigate the interface electron gas in a high mobility SrTiO3/SrCuO2/LaAlO3/SrTiO3 heterostructure. Shubnikov-de Haas oscillations reveal several 2D conduction subbands with carrier effective masses of 0.9me and 2me, quantum mobilities of order 2000 cm²/V s, and band edges only a few millielectronvolts below the Fermi energy. Measurements in tilted magnetic fields confirm the 2D character of the electron gas, and show evidence of inter-subband scattering. [ABSTRACT FROM AUTHOR]

Epitaxial PbZr0.52Ti0.48O3 (PZT 52/48) heterostructures incorporating SrRuO3 electrodes were patterned through a single step epitaxial lift-off technique without using any acidic etching. This procedure enables patterning of high temperature grown perovskite multilayers through the use of a pre-patterned AlOx mask which acts as a high temperature sacrificial template. Ferroelectric properties of structured PZT grown on (001) SrTiO3 substrates as well as on commercially important platinized Si were investigated in capacitor configuration analogous to structures previously prepared through wet etching. In addition, the patterning technique is shown to be compatible with e-beam lithography for preparation of sub-micron device structures consisting of ferroelectric perovskite materials. [ABSTRACT FROM AUTHOR]

We report on the direct patterning of high-quality structures incorporating the LaAlO3-SrTiO3 interface by an epitaxial-liftoff technique avoiding any reactive ion beam etching. Detailed studies of temperature dependent magnetotransport properties were performed on the patterned heterostructures with variable thickness of the LaAlO3 layer and compared to their unstructured thin film analogues. The results demonstrate the conservation of the high-quality interface properties in the patterned structures enabling future studies of low-dimensional confinement on high mobility interface conductivity as well as interface magnetism. [ABSTRACT FROM AUTHOR]

The integration of ferroelectric layers on gallium nitride (GaN) offers a great potential for various applications. Lead zirconate titanate (PZT), in particular Pb(Zr 0.52 Ti 0.48 )O 3 , is an interesting candidate. For that a suitable buffer layer should be grown on GaN in order to prevent the reaction between PZT and GaN, and to obtain PZT with a preferred orientation and phase. Here, we study pulsed laser deposited (100) rutile titanium oxide (R-TiO 2 ) as a potential buffer layer candidate for ferroelectric PZT. For this purpose, the growth, morphology and the surface chemical composition of R-TiO 2 films were analyzed by reflection high-energy electron diffraction, atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. We find optimally (100) oriented R-TiO 2 growth on GaN (0002) using a 675 °C growth temperature and 2 Pa O 2 deposition pressure as process conditions. More importantly, the R-TiO 2 buffer layer grown on GaN/Si substrates prevents the unwanted formation of the PZT pyrochlore phase. Finally, the remnant polarization and coercive voltage of the PZT film on TiO 2 /GaN/Si with an interdigitated-electrode structure were found to be 25.6 μC/cm 2 and 8.1 V, respectively. [ABSTRACT FROM AUTHOR]

We report the formation of a nonmagnetic band insulator at the isopolar interface between the antiferromagnetic Mott-Hubbard insulator LaTiO3 and the antiferromagnetic charge transfer insulator LaFeO3. By density-functional theory calculations, we find that the formation of this interface state is driven by the combination of O band alignment and crystal field splitting energy of the t2g and eg bands. As a result of these two driving forces, the Fe 3d bands rearrange and electrons are transferred from Ti to Fe. This picture is supported by x-ray photoelectron spectroscopy, which confirms the rearrangement of the Fe 3d bands and reveals an unprecedented charge transfer up to 1.2 ± 0.2 e-/interface unit cell in our LaTiO3/LaFeO3 heterostructures. [ABSTRACT FROM AUTHOR]

The electronic structure of an epitaxial oxide heterostructure containing two spatially separated twodimensional conducting sheets, one electronlike (2DEG) and the other holelike (2DHG), has been investigated using variable temperature scanning tunneling spectroscopy. Heterostructures of LaAlO3/SrTiO3 bilayers on (OOl)-oriented SrTiO3 (STO) substrates provide the unique possibility to study the coupling between subnanometer spaced conducting interfaces. The band gap increases dramatically at low temperatures due to a blocking of the transition from the conduction band of the STO substrate to the top of the valence band of the STO capping layer This prevents the replenishment of the depleted electrons in the capping layer from the underlying 2DEG and enables charging of the 2DHG by applying a negative sample bias voltage within the band gap region. At low temperatures the 2DHG can be probed separately with the proposed experimental geometry, although the 2DEG is located less than 1 nm below. [ABSTRACT FROM AUTHOR]

Control of spin relaxation is an important prerequisite for the successful implementation of spintronic devices in a materials system. We realized two directly coupled two-dimensional (2D) electron gases (2DEG-2DEG) in a LaAlO3- SrTiO3 heterostructure system and observed a modification of the spin relaxation mechanism by varying the coupling strength. A strong enhancement of the carrier density for separation distances below a critical thickness of 6 unit cells was revealed. Electric-field-dependent analysis demonstrated tuning from positive to negative magnetoresistance for large separation distances of 10 unit cells indicating Rashba-type spin-orbit coupling, while for small separation distances of only 1 unit cell the magnetoresistance always remained positive. Analysis of the spin-orbit relaxation time and elastic scattering time revealed a modification of the spin relaxation mechanism between Elliott-Yafet and D'yakonov-Perel' for separation distances of 1 and 10 unit cells, respectively. The tunable spin relaxation fits very well with the presence (or absence) of structural inversion symmetry in our coupled 2DEGs system for different separation distances. [ABSTRACT FROM AUTHOR]