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High-quality epitaxial thin films of Co-doped anatase TiO[SUB2] (Co:TiO2[SUB2) were grown epitaxially on SrTiO[SUB3] (001) substrates by using pulsed laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, P[SUBO2], during the growth was systematically varied. As P[SUBO2] decreased, the growth behavior altered from a two-dimensional layer-by-layer-like growth to a three-dimensional island-like pattern. Electrical conductivity and saturation magnetization increased, seemingly consistent with the picture of carrier-induced ferromagnetism. However, we also found that the spatial distribution of Co ions became highly nonuniform and the chemical state of Co ions changed from ionic to metallic. All of these P[SUBO2] dependences, even including the transport and the magnetic properties, can be explained in terms of the formation of cobalt clusters, whose existence was clearly demonstrated by transmission-electron-microscope studies. Our work clearly indicates that the cobalt clustering will result in the room-temperature ferromagnetism observed in our Co:TiO[SUB2].films. To check the possible spin polarization of carriers in Co:TiO[SUB2] films, we also fabricated a heterojunction composed of a ferromagnetic Co:TiO[SUB2], an insulating SrTiO[SUB3], and a ferromagnetic half-metallic (La,Ba)MnO[SUB3] layer. When the magnetic field was varied, we could not observe any changes in its I-V characteristic curves, which suggests that there might be little spin-polarization effect in the anatase Co:TiO[SUB2] layer. [ABSTRACT FROM AUTHOR]

To investigate the critical thickness of ferroelectric BaTiO3 (BTO) films, we fabricated fully strained SrRuO3/BTO/SrRuO3 heterostructures on SrTiO3 substrates by pulsed laser deposition with in situ reflection high-energy electron diffraction. We varied the BTO layer thickness from 3 to 30 nm. By fabricating 10×10 μm2 capacitors, we could observe polarization versus electric-field hysteresis loops, which demonstrate the existence of ferroelectricity in BTO layers thicker than 5 nm. This observation provides an experimental upper bound of 5 nm for the critical thickness. The BTO thickness-dependent scaling of the remanent polarization agrees with the predictions of recent first-principle simulations [J. Junquera and P. Ghosez, Nature 422, 506 (2003)]. [ABSTRACT FROM AUTHOR]

The interfacial states of the HfO2 thin film grown on the Si(100) substrate by the pulsed laser deposition method is investigated in situ using x-ray photoelectron spectroscopy. They are found to depend on the HfO2 film thickness, oxygen pressure during the pulsed laser deposition growth, and the deposition process. The hafnium silicide is formed in an oxygen-deficient condition, and it can be most effectively controlled by the ambient oxygen pressure during film growth. The close relation between the silicide formation and abundance of the silicon suboxides at the interface is presented. [ABSTRACT FROM AUTHOR]

We observed superparamagnetism in Co-ion-implanted anatase TiO[sub 2] thin films on SrTiO[sub 3] (001) substrates. After postannealing under oxygen pressure of 1.0×10[sup -6] Torr, the blocking temperature increased with increasing annealing temperature. Eventually, the 600 °C-annealed sample became ferromagnetic at room temperature. These phenomena can be explained by the formation of Co (or ferromagnetic Co compound) particles and their growth during postannealing, as directly observed with transmission electron microscopy. High oxygen pressure during annealing reduced the size of the clusters and saturation magnetization moment, which indicates that cobalt clustering should be the main cause of the room-temperature ferromagnetism in the Co-ion-implanted films. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The surface structure of an anatase Ti[sub 0.94]Co[sub 0.06]O[sub 2] (001) film, grown epitaxially on a Nb-doped SrTiO[sub 3] (001) substrate, was investigated using in situ scanning tunneling microscopy. For the as-grown film, a (1 × n) (n = 3, 4, 5, and 6) reconstructed surface was observed that shows (n - 2) faint rows between adjacent bright rows. After annealing at 650 °C, nanoparticles appeared, mostly on the step edges. From the I - V curves measured by scanning tunneling spectroscopy, the tunneling gap of Co:TiO[sub 2] was estimated to be about 3.0 eV, consistent with the band gap (E[sub g] = 3.2 eV) of pure anatase TiO[sub 2]. However, on nanoparticles, the I - V curve showed a much smaller gap, suggesting that the particle must be different from TiO[sub 2]. [ABSTRACT FROM AUTHOR]

We have measured the transport spin polarization of epitaxial thin films of the conductive ferromagnetic oxide, SrRuO[SUB3], using point contact Andreev reflection spectroscopy. In spite of the fact that spin-up and spin-down electronic densities of states at the Fermi level for SrRuO[SUB3] calculated from band structure theory are practically the same, the experimental transport spin polarization for these films was found to be about 50%. This is a direct consequence of the Fermi velocity disparity between the majority and minority bands. The experimental results are compared with our theoretical estimates of the spin polarization in the ballistic and diffusive limits. [ABSTRACT FROM AUTHOR]

Anatase Ti[sub 0.96]Co[sub 0.04]O[sub 2] films were grown epitaxially on SrTiO[sub 3] (001) substrates by using pulsed laser deposition with in-situ reflection high-energy electron diffraction. The oxygen partial pressure, P[sub O[sub 2]], during the growth was systematically varied. As P[sub O[sub 2]] decreased, the growth behavior was changed from a two-dimensional layer-by-layer-like growth to a three-dimensional island-like one, which resulted in an increase in the saturation magnetization. These structural and magnetic changes were explained in terms of the formation of cobalt clusters whose existence was proved by transmission-electron-microscope studies. Our work clearly indicates that the cobalt clustering will cause room-temperature ferromagnetism in the Co-doped TiO[sub 2] films. [ABSTRACT FROM AUTHOR]

We report the growth and properties of epitaxial MgB[sub 2] thin films on (0001) Al[sub 2]O[sub 3] substrates. The MgB[sub 2] thin films were prepared by depositing boron films via radio-frequency (rf) magnetron sputtering, followed by a postdeposition anneal at 850 °C in magnesium vapor. X-ray diffraction and cross-sectional transmission electron microscopy reveal that the epitaxial MgB[sub 2] films are oriented with their c-axis normal to the (0001) Al[sub 2]O[sub 3] substrate with a 30° rotation in the (0001) plane with respect to the substrate. The critical temperature was found to be 35 K and the anisotropy ratio, H[sup ][sub c2]/H[sup ⊥][sub c2], was about 3 at 25 K. The critical current densities at 4.2 and 20 K (at 1 T perpendicular magnetic field) are 5 × 10[sup 6] and 1 × 10[sup 6] A/cm², respectively. The controlled growth of epitaxial MgB[sub 2] thin films opens a new avenue in both understanding superconductivity in MgB[sub 2] and technological applications. [ABSTRACT FROM AUTHOR]

The microstructure and interfacial atomic structure of MgB[sub 2] thin films fabricated on the (0001) Al[sub 2]O[sub 3] substrate were characterized by transmission electron microscopy. It was found that the MgB[sub 2] films grow epitaxially on the substrate with an orientation relationship with respect to the substrate as: (0001)MgB[sub 2](0001)Al[sub 2]O[sub 3] and [11&2macr;0]MgB[sub 2]II[10&1macr;0]Al[sub 2]O[sub 3]. At the film/substrate interface, both MgO and MgAl[sub 2]O[sub 4] phases were observed, which also grow epitaxially on the (0001) Al[sub 2]O[sub 3] substrate. The formation of these intermediate phases is ascribed to the existence of oxygen during the annealing. [ABSTRACT FROM AUTHOR]

(103) fiber-textured SrBi[sub 2]Nb[sub 2]O[sub 9] thin films have been grown on Pt-coated Si substrates using a SrRuO[sub 3] buffer layer. High-resolution transmission electron microscopy reveals that the fiber texture arises from the local epitaxial growth of (111) SrRuO[sub 3] grains on (111) Pt grains and in turn (103) SrBi[sub 2]Nb[sub 2]O[sub 9] grains on (111) SrRuO[sub 3] grains. The films exhibit remanent polarization values of 9 µC/cm². The uniform grain orientation (fiber texture) should minimize grain-to-grain variations in the remanent polarization, which is important to continued scaling of ferroelectric memory device structures. [ABSTRACT FROM AUTHOR]

We report the perovskite phase stabilization of 0.67Pb(Mg[sub 1/3]Nb[sub 2/3])O[sub 3]–0.33PbTiO[sub 3] (PMN-PT) epitaxial thin films by deposition onto miscut substrates. Films were grown on (001) SrTiO[sub 3] substrates with miscut angles from 0 to 8 degrees toward the [100] direction using 90° off-axis magnetron sputtering. Films on high miscut substrates (>4°) showed almost the pure perovskite phase in both x-ray diffraction and transmission electron microscopy image, and were nearly stoichiometric. In contrast, films on exact (001) SrTiO[sub 3] contained a high volume fraction of pyrochlore phases with Pb deficiency. Atomic force microscopy reveals that films on 8° miscut substrates have a much smoother surface morphology than those on exact (001) SrTiO[sub 3]. Cross-sectional transmission electron microscopy images reveal that the pyrochlore phases nucleate on top of the perovskite phase, and that the amount of the pyrochlore phases increase with film thickness. A film on an 8° miscut substrate exhibits a polarization hysteresis loop with a remnent polarization of 20 μC/cm[sup 2] at room temperature. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This article presents a correction of a previously published article regarding hafnium oxide interfaces.

Two kinds of epitaxial Sr–Bi–Ta oxides were grown on La[sub 0.5]Sr[sub 0.5]CoO[sub 3](001)/LaAlO[sub 3](001) substrates by pulsed laser deposition. At a temperature higher than 650 °C, c-axis oriented SrBi[sub 2]Ta[sub 2]O[sub 9] films could be deposited epitaxially. At 550 °C, an epitaxial film with a cubic fluorite-like phase could be grown. Although the film with the cubic phase does not show ferroelectric properties, it has good electrical properties which are suitable for high capacitance applications. © 1998 American Institute of Physics. [ABSTRACT FROM AUTHOR]