115 research outputs found
Strong electronic correlation and strain effects at the interfaces between polar and nonpolar complex oxides
The interface between the polar LaAlO and nonpolar SrTiO layers has
been shown to exhibit various electronic and magnetic phases such as two
dimensional electron gas, superconductivity, magnetism and electronic phase
separation. These rich phases are expected due to the strong interplay between
charge, spin and orbital degree of freedom at the interface between these
complex oxides, leading to the electronic reconstruction in this system.
However, until now all of these new properties have been studied extensively
based on the interfaces which involve a polar LaAlO layer. To investigate
the role of the A and B cationic sites of the ABO polar layer, here we
study various combinations of polar/nonpolar oxide (NdAlO/SrTiO,
PrAlO/SrTiO and NdGaO/SrTiO) interfaces which are similar in
nature to LaAlO/SrTiO interface. Our results show that all of these new
interfaces can also produce 2DEG at their interfaces, supporting the idea that
the electronic reconstruction is the driving mechanism for the creation of the
2DEG at these oxide interfaces. Furthermore, the electrical properties of these
interfaces are shown to be strongly governed by the interface strain and strong
correlation effects provided by the polar layers. Our observations may provide
a novel approach to further tune the properties of the 2DEG at the selected
polar/nonpolar oxide interfaces.Comment: 5 pages, 4 figure
Size effect in ion transport through angstrom-scale slits
It has been an ultimate but seemingly distant goal of nanofluidics to
controllably fabricate capillaries with dimensions approaching the size of
small ions and water molecules. We report ion transport through ultimately
narrow slits that are fabricated by effectively removing a single atomic plane
from a bulk crystal. The atomically flat angstrom-scale slits exhibit little
surface charge, allowing elucidation of the role of steric effects. We find
that ions with hydrated diameters larger than the slit size can still permeate
through, albeit with reduced mobility. The confinement also leads to a notable
asymmetry between anions and cations of the same diameter. Our results provide
a platform for studying effects of angstrom-scale confinement, which is
important for development of nanofluidics, molecular separation and other
nanoscale technologies
Carrier freeze-out induced metal-insulator transition in oxygen deficient SrTiO3 films
We report the optical, electrical transport, and magnetotransport properties
of high quality oxygen deficient SrTiO3 (STO) single crystal film fabricated by
pulsed laser deposition and reduced in the vacuum chamber. The oxygen vacancy
distribution in the thin film is expected to be uniform. By comparing the
electrical properties with oxygen deficient bulk STO, it was found that the
oxygen vacancies in bulk STO is far from uniform over the whole material. The
metal-insulator transition (MIT) observed in the oxygen deficient STO film was
found to be induced by the carrier freeze-out effect. The low temperature
frozen state can be re-excited by an electric field, Joule heating, and
surprisingly also a large magnetic field.Comment: 5 pages, 5 figure
Magnetoresistance of 2D and 3D Electron Gas in LaAlO3/SrTiO3 Heterostructures: Influence of Magnetic Ordering, Interface Scattering and Dimensionality
Magnetoresistance (MR) anisotropy in LaAlO3/SrTiO3 (LAO/STO) interfaces is
compared between samples prepared in high oxygen partial pressure (PO2) of 10-4
mbar exhibiting quasi-two-dimensional (quasi-2D) electron gas and low PO2 of
10-6 mbar exhibiting 3D conductivity. While MR of an order of magnitude larger
was observed in low PO2 samples compared to those of high PO2 samples, large MR
anisotropies were observed in both cases. The MR with the out-of-plane field is
always larger compared to the MR with in-plane field suggesting lower
dissipation of electrons from interface versus defect scattering. The quasi-2D
interfaces show a negative MR at low temperatures while the 3D interfaces show
positive MR for all temperatures. Furthermore, the angle relationship of MR
anisotropy for these two different cases and temperature dependence of in-plane
MR are also presented. Our study demonstrates that MR can be used to
distinguish the dimensionality of the charge transport and various (defect,
magnetic center, and interface boundary) scattering processes in this system.Comment: 14 pages, 5 figure
Sharp-1 regulates TGF-β signaling and skeletal muscle regeneration
10.1242/jcs.136648Journal of Cell Science1273599-608JNCS
Ambipolar bistable switching effect of graphene
Reproducible current hysteresis is observed in graphene with a back gate
structure in a two-terminal configuration. By applying a back gate bias to tune
the Fermi level, an opposite sequence of switching with the different charge
carriers, holes and electrons, is found. The charging and discharging effect is
proposed to explain this ambipolar bistable hysteretic switching. To confirm
this hypothesis, one-level transport model simulations including charging
effect are performed and the results are consistent with our experimental data.
Methods of improving the ON/OFF ratio of graphene resistive switching are
suggested
Tunneling characteristics of graphene
Negative differential conductance and tunneling characteristics of
two-terminal graphene devices are observed before and after electric breakdown,
respectively. The former is caused by the strong scattering under a high
E-field, and the latter is due to the appearance of a tunneling barrier in
graphene channel induced by a structural transformation from crystalline
graphene to disordered graphene because of the breakdown. Using Raman
spectroscopy and imaging, the presence of non-uniform disordered graphene is
confirmed. A memory switching effect of 100000% ON/OFF ratio is demonstrated in
the tunneling regime which can be employed in various applications
CCR2 and CXCR4 regulate peripheral blood monocyte pharmacodynamics and link to efficacy in experimental autoimmune encephalomyelitis
<p>Abstract</p> <p>Background</p> <p>CCR2 plays a key role in regulating monocyte trafficking to sites of inflammation and therefore has been the focus of much interest as a target for inflammatory disease.</p> <p>Methods</p> <p>Here we examined the effects of CCR2 blockade with a potent small molecule antagonist to determine the pharmacodynamic consequences on the peripheral blood monocyte compartment in the context of acute and chronic inflammatory processes.</p> <p>Results</p> <p>We demonstrate that CCR2 antagonism <it>in vivo </it>led to a rapid decrease in the number of circulating Ly6C<sup>hi </sup>monocytes and that this decrease was largely due to the CXCR4-dependent sequestration of these cells in the bone marrow, providing pharmacological evidence for a mechanism by which monocyte dynamics are regulated <it>in vivo</it>. CCR2 antagonism led to an accumulation of circulating CCL2 and CCL7 levels in the blood, indicating a role for CCR2 in regulating the levels of its ligands under homeostatic conditions. Finally, we show that the pharmacodynamic changes due to CCR2 antagonism were apparent after chronic dosing in mouse experimental autoimmune encephalomyelitis, a model in which CCR2 blockade demonstrated a dramatic reduction in disease severity, manifest in a reduced accumulation of monocytes and other cells in the CNS.</p> <p>Conclusion</p> <p>CCR2 antagonism <it>in vivo </it>has tractable pharmacodynamic effects that can be used to align target engagement with biologic effects on disease activity.</p
The effect of layer number and substrate on the stability of graphene under MeV proton beam irradiation
The use of graphene electronics in space will depend on the radiation
hardness of graphene. The damage threshold of graphene samples, subjected to 2
MeV proton irradiation, was found to increase with layer number and also when
the graphene layer was supported by a substrate. The thermal properties of
graphene as a function of the number of layers or as influenced by the
substrate argue against a thermal model for the production of damage by the ion
beam. We propose a model of intense electronically-stimulated surface
desorption of the atoms as the most likely process for this damage mechanism.Comment: 20 pages, 5 figure
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