Mapping the spatial distribution of charge carriers in LaAlO3/SrTiO3 heterostructures.

At the interface between complex insulating oxides, novel phases with interesting properties may occur, such as the metallic state reported in the LaAlO(3)/SrTiO(3) system . Although this state has been predicted and reported to be confined at the interface, some studies indicate a much broader spatial extension, thereby questioning its origin. Here, we provide for the first time a direct determination of the carrier density profile of this system through resistance profile mappings collected in cross-section LaAlO(3)/SrTiO(3) samples with a conducting-tip atomic force microscope (CT-AFM). We find that, depending on specific growth protocols, the spatial extension of the high-mobility electron gas can be varied from hundreds of micrometres into SrTiO(3) to a few nanometres next to the LaAlO(3)/SrTiO(3) interface. Our results emphasize the potential of CT-AFM as a novel tool to characterize complex oxide interfaces and provide us with a definitive and conclusive way to reconcile the body of experimental data in this system.

Using half-metallic manganite interfaces to reveal insights into spintronics.

A half-metal has been defined as a material with propagating electron states at the Fermi energy only for one of the two possible spin projections, and as such has been promoted as an interesting research direction for spin electronics. This review details recent advances on manganite thin film research within the field of spintronics, before presenting the structural, electronic and spin-polarized solid-state tunnelling transport studies that we have performed on heterostructures involving La(2/3)Sr(1/3)MnO(3) thin films separated by SrTiO(3) barriers. These experiments demonstrate that, with a polarization of spin [Formula: see text] electrons at the Fermi level that can reach 99%, the La(2/3)Sr(1/3)MnO(3)/SrTiO(3) interface for all practical purposes exhibits half-metallic behaviour. We offer insight into the electronic structure of the interface, including the electronic symmetry of any remaining spin [Formula: see text] states at the Fermi level. Finally, we present experiments that use the experimental half-metallic property of manganites as tools to reveal novel features of spintronics.

Natural occurrence of the diamond hexagonal structure in silicon nanowires grown by a plasma-assisted vapour-liquid-solid method.

Silicon nanowires have been grown by a plasma-assisted vapour-liquid-solid method using tin as the catalyst. Transmission electron microscopy in the [12[combining macron]10] zone axis shows that the diamond hexagonal (P63/mmc) crystal structure is present in several nanowires. This is the first unambiguous proof of the natural occurrence of this metastable phase to our knowledge.

Towards two-dimensional metallic behavior at LaAlO3/SrTiO3 interfaces.

Using a low-temperature conductive-tip atomic force microscope in cross-section geometry we have characterized the local transport properties of the metallic electron gas that forms at the interface between LaAlO3 and SrTiO3. At low temperature, we find that the carriers do not spread away from the interface but are confined within approximately 10 nm, just like at room temperature. Simulations taking into account both the large temperature and electric-field dependence of the permittivity of SrTiO3 predict a confinement over a few nm for sheet carrier densities larger than approximately 6x10(13) cm(-2). We discuss the experimental and simulations results in terms of a multiband carrier system. Remarkably, the Fermi wavelength estimated from Hall measurements is approximately 16 nm, indicating that the electron gas in on the verge of two dimensionality.

Co-doped (La, Sr)TiO(3-delta) : a high Curie temperature diluted magnetic system with large spin polarization.

We report on tunneling magnetoresistance (TMR) experiments that demonstrate the existence of a significant spin polarization in Co-doped (La, Sr)TiO(3-delta) (Co-LSTO), a ferromagnetic diluted magnetic oxide system (DMOS) with high Curie temperature. These TMR experiments have been performed on magnetic tunnel junctions associating Co-LSTO and Co electrodes. Extensive structural analysis of Co-LSTO combining high-resolution transmission electron microscopy and Auger electron spectroscopy excluded the presence of Co clusters in the Co-LSTO layer and thus, the measured ferromagnetism and high spin polarization are intrinsic properties of this DMOS. Our results argue for the DMOS approach with complex oxide materials in spintronics.

Growth of Au clusters on amorphous Al2O3: evidence of cluster mobility above a critical size.

We study the 3D growth of clusters during the deposition of Au atoms on amorphous Al2O3. By comparing transmission electron microscopy images of the growth with Monte Carlo simulations, we show that nucleation takes place on substrate defects, but that further stages of growth imply that clusters leave the defects after they have reached a given critical size, and diffuse. An interesting consequence of this property is that, in contrast to intuition, and in a certain range of size, larger clusters are more mobile than smaller ones in this system.