86 research outputs found
Atomically Resolved Surface Structure of SrTiO3(001) Thin Films Grown in Step-Flow Mode by Pulsed Laser Deposition
The surface structure of SrTiO3(001) thin films homoepitaxially grown by PLD
in step-flow mode was characterized using low temperature STM. It was found
that one-dimensional (1D) TiOx-based nanostructures were formed on the thin
film surface and their density increased with increasing thin film thickness.
Most of the 1D nanostructures disappeared after a post-deposition annealing,
indicating that this structure is metastable due to the nonequilibrium growth
mode. The resulting surface after annealing exhibited similar features to that
of a thinner film, having a domain structure with (2x1) and (1x2)
reconstructions, but with fewer oxygen-vacancy-type defects. These results
imply that the step-flow growth is likely to produce TiOx-rich surface and Ti
deficiencies in the film. By the post-deposition annealing, the rich TiOx would
diffuse from the surface into the film to compensate defects associated with Ti
vacancies and oxygen vacancies, resulting in the stable surface structure with
fewer oxygen vacancies. Thus, STM measurements can provide us with a
microscopic picture of surface stoichiometry of thin films originating in the
dynamics of the growth process, and can present a new approach for designing
functional oxide films.Comment: 12 pages, 4 figure
Stripe charge ordering in SrO-terminated SrTiO3(001) surfaces
The local electronic structure of the SrO-terminated SrTiO3(001) surface was
explored using scanning tunneling microscopy. At low bias voltages in the empty
states, a unidirectional structure with a periodicity of 3 unit cells,
superimposed on a c(2 x 2) reconstructed structure, was found to develop along
the crystallographic a axis. This structure indicates a charge-ordered stripe
induced by carrier doping from oxygen vacancies in the SrO and the subsurface
TiO2 planes. In the filled states, localized deep in-gap states were observed
in addition to large energy gaps in the tunneling spectra. This result
represents inelastic tunneling due to significant electron-lattice interaction
associated with unidirectional lattice distortion in the SrO-terminated
surface.Comment: 6 pages, 5 figures, accepted for publication in PR
Gunning-Narasimhan's theorem with a growth condition
Given a compact Riemann surface X and a point x_0 in X, we construct a
holomorphic function without critical points on the punctured Riemann surface R
= X - x_0 which is of finite order at the point x_0. This complements the
result of Gunning and Narasimhan from 1967 who constructed a noncritical
holomorphic function on every open Riemann surface, but without imposing any
growth condition. On the other hand, if the genus of X is at least one, then we
show that every algebraic function on R admits a critical point. Our proof also
shows that every cohomology class in H^1(X;C) is represented as a de Rham class
by a nowhere vanishing holomorphic one-form of finite order on the punctured
surface X-x_0.Comment: J. Geom. Anal., in pres
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