68 research outputs found
Field-Induced Resistive Switching in Metal-Oxide Interfaces
We investigate the polarity-dependent field-induced resistive switching
phenomenon driven by electric pulses in perovskite oxides. Our data show that
the switching is a common occurrence restricted to an interfacial layer between
a deposited metal electrode and the oxide. We determine through impedance
spectroscopy that the interfacial layer is no thicker than 10 nm and that the
switch is accompanied by a small capacitance increase associated with charge
accumulation. Based on interfacial I-V characterization and measurement of the
temperature dependence of the resistance, we propose that a field-created
crystalline defect mechanism, which is controllable for devices, drives the
switch.Comment: 4 pages, 3 figure
Imaging Oxygen Defects and their Motion at a Manganite Surface
Manganites are technologically important materials, used widely as solid
oxide fuel cell cathodes: they have also been shown to exhibit
electroresistance. Oxygen bulk diffusion and surface exchange processes are
critical for catalytic action, and numerous studies of manganites have linked
electroresistance to electrochemical oxygen migration. Direct imaging of
individual oxygen defects is needed to underpin understanding of these
important processes. It is not currently possible to collect the required
images in the bulk, but scanning tunnelling microscopy could provide such data
for surfaces. Here we show the first atomic resolution images of oxygen defects
at a manganite surface. Our experiments also reveal defect dynamics, including
oxygen adatom migration, vacancy-adatom recombination and adatom bistability.
Beyond providing an experimental basis for testing models describing the
microscopics of oxygen migration at transition metal oxide interfaces, our work
resolves the long-standing puzzle of why scanning tunnelling microscopy is more
challenging for layered manganites than for cuprates.Comment: 7 figure
Field-Driven Hysteretic and Reversible Resistive Switch at the Ag-Pr0.7Ca0.3MnO3 Interface
The hysteretic and reversible polarity-dependent resistive switch driven by
electric pulses is studied in both Ag/Pr0.7Ca0.3MnO3/YBa2Cu3O7 sandwiches and
single-layer Pr0.7Ca0.3MnO3 strips. The data demonstrate that the switch takes
place at the Ag-Pr0.7Ca0.3MnO3 interface. A model, which describes the data
well, is proposed. We further suggest that electrochemical diffusion is the
cause for the switch.Comment: 4 pages, 3 figures; submitted to Appl. Phys. Lett. (December 17,
2002
The Superconductivity, Intragrain Penetration Depth and Meissner Effect of RuSr2(Gd,Ce)2Cu2O10+delta
The hole concentration (p)(delta), the transition temperature Tc, the
intragrain penetration depth lambda, and the Meissner effect were measured for
annealed RuSr2(Gd,Ce)2Cu2O10+delta samples. The intragrain superconducting
transition temperature Tc} varied from 17 to 40 K while the p changed by only
0.03 holes/CuO2. The intragrain superfluid-density 1/lambda^2 and the
diamagnetic drop of the field-cooled magnetization across Tc (the Meissner
effect), however, increased more than 10 times. All of these findings are in
disagreement with both the Tc vs. p and the Tc vs. 1/lambda^2 correlations
proposed for homogeneous cuprates, but are in line with a possible
phase-separation and the granularity associated with it.Comment: 7 pages, 6 figures, accepted for publication in Phys. Rev. B (May 2,
2002
Structure-Function Studies of DNA Binding Domain of Response Regulator KdpE Reveals Equal Affinity Interactions at DNA Half-Sites
Expression of KdpFABC, a K+ pump that restores osmotic balance, is controlled by binding of the response regulator KdpE to a specific DNA sequence (kdpFABCBS) via the winged helix-turn-helix type DNA binding domain (KdpEDBD). Exploration of E. coli KdpEDBD and kdpFABCBS interaction resulted in the identification of two conserved, AT-rich 6 bp direct repeats that form half-sites. Despite binding to these half-sites, KdpEDBD was incapable of promoting gene expression in vivo. Structure-function studies guided by our 2.5 Å X-ray structure of KdpEDBD revealed the importance of residues R193 and R200 in the α-8 DNA recognition helix and T215 in the wing region for DNA binding. Mutation of these residues renders KdpE incapable of inducing expression of the kdpFABC operon. Detailed biophysical analysis of interactions using analytical ultracentrifugation revealed a 2∶1 stoichiometry of protein to DNA with dissociation constants of 200±100 and 350±100 nM at half-sites. Inactivation of one half-site does not influence binding at the other, indicating that KdpEDBD binds independently to the half-sites with approximately equal affinity and no discernable cooperativity. To our knowledge, these data are the first to describe in quantitative terms the binding at half-sites under equilibrium conditions for a member of the ubiquitous OmpR/PhoB family of proteins
The Escherichia coli NarL receiver domain regulates transcription through promoter specific functions
BACKGROUND: The Escherichia coli response regulator NarL controls transcription of genes involved in nitrate respiration during anaerobiosis. NarL consists of two domains joined by a linker that wraps around the interdomain interface. Phosphorylation of the NarL N-terminal receiver domain (RD) releases the, otherwise sequestered, C-terminal output domain (OD) that subsequently binds specific DNA promoter sites to repress or activate gene expression. The aim of this study is to investigate the extent to which the NarL OD and RD function independently to regulate transcription, and the affect of the linker on OD function. RESULTS: NarL OD constructs containing different linker segments were examined for their ability to repress frdA-lacZ or activate narG-lacZ reporter fusion genes. These in vivo expression assays revealed that the NarL OD, in the absence or presence of linker helix α6, constitutively repressed frdA-lacZ expression regardless of nitrate availability. However, the presence of the linker loop α5-α6 reversed this repression and also showed impaired DNA binding in vitro. The OD alone could not activate narG-lacZ expression; this activity required the presence of the NarL RD. A footprint assay demonstrated that the NarL OD only partially bound recognition sites at the narG promoter, and the binding affinity was increased by the presence of the phosphorylated RD. Analytical ultracentrifugation used to examine domain oligomerization showed that the NarL RD forms dimers in solution while the OD is monomeric. CONCLUSIONS: The NarL RD operates as an on-off switch to occlude or release the OD in a nitrate-responsive manner, but has additional roles to directly stimulate transcription at promoters for which the OD lacks independent function. One such role of the RD is to enhance the DNA binding affinity of the OD to target promoter sites. The data also imply that NarL phosphorylation results in RD dimerization and in the separation of the entire linker region from the OD. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s12866-015-0502-9) contains supplementary material, which is available to authorized users
Thin film deposition of metal oxides in resistance switching devices: electrode material dependence of resistance switching in manganite films
YBCO/YCBCO multi-layer healing technique for YBCO coated conductors
The influence of (Y0.8Ca0.2)Ba2Cu3Oy (YCBCO) over-layers on YBCO film properties has been studied on multi-layer YBCO/YCBCO films. The films were deposited on (001) MgO single-crystal substrates by pulsed-laser deposition. The results unambiguously demonstrate that a YCBCO over-layer can greatly improve the overall crystallinity of the YBCO films and thus their J(c). An optimal layer-number (n) of the multi-layer YBCO (n layers)/YCBCO (n-1 layers) has been identified to produce a maximum J(c) enhancement. The observations suggest that the YBCO/YCBCO multi-layer healing technique (MLHT) mentioned above may be used for the fabrication of low cost, high performance YBCO coated conductors by relaxing the stringent and costly requirements for precise atomic alignment employed in previous fabrication methods
- …