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THE IMPORTANCE OF IN SITU MONITORS IN THE PREPARATION OF LAYERED OXIDE HETROSTRUCTURES BY REACTIVE MBE
Structural and dielectric properties of SrTiO from first principles
We have investigated the structural and dielectric properties of
SrTiO,the first member of the SrTiO
Ruddlesden-Popper series, within density functional theory. Motivated by recent
work in which thin films of SrTiO were grown by molecular beam
epitaxy (MBE) on SrTiO substrates, the in-plane lattice parameter was
fixed to the theoretically optimized lattice constant of cubic SrTiO
(n=), while the out-of-plane lattice parameter and the internal
structural parameters were relaxed. The fully relaxed structure was also
investigated. Density functional perturbation theory was used to calculate the
zone-center phonon frequencies, Born effective charges, and the electronic
dielectric permittivity tensor. A detailed study of the contribution of
individual infrared-active modes to the static dielectric permittivity tensor
was performed. The calculated Raman and infrared phonon frequencies were found
to be in agreement with experiment where available. Comparisons of the
calculated static dielectric permittivity with experiments on both ceramic
powders and epitaxial thin films are discussed.Comment: 11 pages, 1 figure, 8 tables, submitted to Phys. Rev.
Polar phonons in some compressively stressed epitaxial and polycrystalline SrTiO3 thin films
Several SrTiO3 (STO) thin films without electrodes processed by pulsed laser
deposition, of thicknesses down to 40 nm, were studied using infrared
transmission and reflection spectroscopy. The complex dielectric responses of
polar phonon modes, particularly ferroelectric soft mode, in the films were
determined quantitatively. The compressed epitaxial STO films on (100)
La0.18Sr0.82Al0.59-Ta0.41O3 substrates (strain 0.9%) show strongly stiffened
phonon responses, whereas the soft mode in polycrystalline film on (0001)
sapphire substrate shows a strong broadening due to grain boundaries and/or
other inhomogeneities and defects. The stiffened soft mode is responsible for a
much lower static permittivity in the plane of the compressed film than in the
bulk samples.Comment: 11 page
Activator protein-1 (AP-1) signalling in human atherosclerosis: results of a systematic evaluation and intervention study
Vascular Surger
Growth of nanoscale BaTiO3/SMO3 superlattices by molecular-beam epitaxy
Commensurate BaTiO3/SrTiO3 superlattices were grown by reactive molecular-beam epitaxy on four different substrates: TiO2-terminated (001) SrTiO3, (101) DyScO3, (101) GdScO3, and (101) SmScO3. With the aid of reflection high-energy electron diffraction (RHEED), precise single-monolayer doses of BaO, SrO, and TiO2 were deposited sequentially to create commensurate BaTiO3/ SrTiO3 superlattices with a variety of periodicities. X-ray diffraction (XRD) measurements exhibit clear superlattice peaks at the expected positions. The rocking curve full width half-maximum of the soperlattices was as narrow as 7 arc s (0.002??). High-resolution transmission electron microscopy reveals nearly atomically abrupt interfaces. Temperature-dependent ultraviolet Raman and XRD were used to reveal the paraelectric-to-ferroeleotric transition temperature (TC). Our results demonstrate the importance of finite size and strain effects on the TC of BaTiO3/ SrTiO3 superlattices. In addition to probing finite size and strain effects, these heterostructures may be relevant: for novel phooon devices, including mirrors, filters, and cavities for coherent phonon generation and control.close171
Effect of misfit strain on the electrocaloric effect in epitaxial SrTiO 3 thin films
77.22.Ej Polarization and depolarization, 77.70.+a Pyroelectric and electrocaloric effects, 77.80.-e Ferroelectricity and antiferroelectricity,