167,380 research outputs found
Sequential pulsed laser deposition of homoepitaxial SrTiO thin films
Control of thin film stoichiometry is of primary relevance to achieve desired
functionality. Pulsed laser deposition ablating from binary-oxide targets
(sequential deposition) can be applied to precisely control the film
composition, offsetting the importance of growth conditions on the film
stoichiometry. In this work, we demonstrate that the cation stoichiometry of
SrTiO thin films can be finely tuned by sequential deposition from SrO and
TiO targets. Homoepitaxial SrTiO films were deposited at different
substrate temperatures and Ti/Sr pulse ratios, allowing the establishment of a
growth window for stoichiometric SrTiO. The growth kinetics and nucleation
processes were studied by reflection high-energy electron diffraction and
atomic force microscopy, providing information about the growth mode and the
degree of off-stoichiometry. At the optimal (stoichiometric) growth conditions,
films exhibit atomically flat surfaces, whereas off-stoichiometry is
accommodated by crystal defects, 3D islands and/or surface precipitates
depending on the substrate temperature and the excess cation. This technique
opens the way to precisely control stoichiometry and doping of oxide thin
films.Comment: 6 pages, 5 figure
Subunit Stoichiometry of a Heteromultimeric G protein-coupled Inward-rectifier K^+ Channel
We investigated the stoichiometry of the heteromultimeric G protein-coupled inward-recitfier K^+ channel (GIRK) formed from GIRK1 and GIRK4 subunits. Multimeric GIRK constructs with several concatenated channel subunits were expressed in Xenopus oocytes. Coexpression of various trimeric constructs with different monomers clearly showed that the functional channel has stoichiometry (GIRK1)_2(GIRK4)_2. Efforts to establish a preferred arrangement of subunits around the channel pore suggest that more than one arrangement may be viable
Synthesis and Stoichiometry of MgB2
The system MgxB2 has been investigated to investigate possible
nonstoichiometry in MgB2. When synthesized at 850oC, MgB2 is a line compound
with a possible Mg vacancy content of about 1%. Small changes in lattice
constants as a function of starting composition result from grain interaction
stresses, whose character is different in the Mg-rich, near-stoichiometric, and
Mg-deficient regimes. A small linear decrease of the superconducting transition
temperature, Tc, in the Mg-rich regime results from accidental impurity doping.Comment: Accepted for publication in Physica C. 24 pages, 7 figure
Live-Cell Imaging of Single Receptor Composition Using Zero-Mode Waveguide Nanostructures
We exploit the optical and spatial features of subwavelength nanostructures to examine individual receptors on the plasma membrane of living cells. Receptors were sequestered in portions of the membrane projected into zero-mode waveguides. Using single-step photobleaching of green fluorescent protein incorporated into individual subunits, the resulting spatial isolation was used to measure subunit stoichiometry in α4β4 and α4β2 nicotinic acetylcholine and P2X2 ATP receptors. We also show that nicotine and cytisine have differential effects on α4β2 stoichiometry
Effect of oxygen stoichiometry on T(sub c) of Bi-based superconductors
The role of oxygen stoichiometry on T(sub c) is relatively well established on La2CuO(4+x) and the YBa2Cu3O(7-x) (123) superconductors, as compared to the Bi-based superconductors. Results are presented of investigations on the effects of oxygen stoichiometry on the transition temperature T(sub c) of Bi2Sr2CaCu2O(8+x) (2212 phase), and Pb-doped Bi2Sr2Ca2Cu3O(10+X) (2223 phase). It is shown that the effects of oxygen stoichiometry on T(sub c) of these two phases are very different. These results may be helpful in understanding the mechanism of superconductivity in the Bi-based superconductors
Stoichiometry determination of chalcogenide superlattices by means of X-ray diffraction and its limits
In this paper we explore the potential of stoichiometry determination for
chalcogenide superlattices, promising candidates for next-generation
phase-change memory, via X-ray diffraction. To this end, a set of epitaxial
GeTe/Sb2Te3 superlattice samples with varying layer thicknesses is
sputter-deposited. Kinematical scattering theory is employed to link the
average composition with the diffraction features. The observed lattice
constants of the superlattice reference unit cell follow Vegard's law, enabling
a straight-forward and non-destructive stoichiometry determination.Comment: physica status solidi (RRL) - Rapid Research Letters (2019
Continuous Transition between Antiferromagnetic Insulator and Paramagnetic Metal in the Pyrochlore Iridate Eu2Ir2O7
Our single crystal study of the magneto-thermal and transport properties of
the pyrochlore iridate Eu2Ir2O7 reveals a continuous phase transition from a
paramagnetic metal to an antiferromagnetic insulator for a sample with
stoichiometry within ~1% resolution. The insulating phase has strong proximity
to an antiferromagnetic semimetal, which is stabilized by several % level of
the off-stoichiometry. Our observations suggest that in addition to electronic
correlation and spin-orbit coupling the magnetic order is essential for opening
the charge gap.Comment: 6 pages, 6 figure
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