110 research outputs found
Investigation of interface properties of sputter deposited TiN/CrN superlattices by low-angle X-ray reflectivity
Approximately 1.8 m thick nanolayered multilayer coatings of TiN/CrN (also known as superlattices) were deposited on silicon (100) substrates at different modulation wavelengths (4.6–12.8 nm), substrate temperatures (50-400 °C) and substrate bias voltages (-50 to -200 V) using a reactive direct current magnetron sputtering system. X-ray reflectivity (XRR) technique was employed to determine various properties of the multilayers such as interface roughness, surface roughness, electron density, critical angle and individual layer thicknesses. The modulation wavelengths of the TiN/CrN superlattice coatings were calculated using modified Bragg’s law. Furthermore, the experimental X-ray reflectivity patterns were simulated using theoretically generated patterns and a good fit was obtained for a three layer model, i.e., (1) top surface roughness layer, (2) TiN/CrN multilayer coating (approximately 1.8 m) and (3) Ti interlayer (~ 0.5 m) at the film-substrate interface. For the superlattice coatings prepared at a modulation wavelength of 9.7 nm, a substrate bias of -200 V and a substrate temperature of 400 C the XRR patterns showed Bragg reflections up to 5th order, indicating well-defined periodicity of the constituent layers and relatively sharp interfaces. The simulation showed that the superlattice coatings prepared under the above conditions exhibited low surface and interface roughnesses. We also present the effect of substrate temperature and substrate bias, which are critical parameters for controlling the superlattice properties, onto the various interface properties of TiN/CrN superlattices
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
Atomically flat interface between a single-terminated LaAlO3 substrate and SrTiO3 thin film is insulating
The surface termination of (100)-oriented LaAlO3 (LAO) single crystals was
examined by atomic force microscopy and optimized to produce a
single-terminated atomically flat surface by annealing. Then the atomically
flat STO film was achieved on a single-terminated LAO substrate, which is
expected to be similar to the n-type interface of two-dimensional electron gas
(2DEG), i.e., (LaO)-(TiO2). Particularly, that can serve as a mirror structure
for the typical 2DEG heterostructure to further clarify the origin of 2DEG.
This newly developed interface was determined to be highly insulating.
Additionally, this study demonstrates an approach to achieve atomically flat
film growth based on LAO substrates.Comment: 4 pages, 3 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
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
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
Extremely large magnetoresistance in few-layer graphene/boron-nitride heterostructures
Understanding magnetoresistance, the change in electrical resistance upon an
external magnetic field, at the atomic level is of great interest both
fundamentally and technologically. Graphene and other two-dimensional layered
materials provide an unprecedented opportunity to explore magnetoresistance at
its nascent stage of structural formation. Here, we report an extremely large
local magnetoresistance of ~ 2,000% at 400 K and a non-local magnetoresistance
of > 90,000% in 9 T at 300 K in few-layer graphene/boron-nitride
heterostructures. The local magnetoresistance is understood to arise from large
differential transport parameters, such as the carrier mobility, across various
layers of few-layer graphene upon a normal magnetic field, whereas the
non-local magnetoresistance is due to the magnetic field induced
Ettingshausen-Nernst effect. Non-local magnetoresistance suggests the
possibility of a graphene based gate tunable thermal switch. In addition, our
results demonstrate that graphene heterostructures may be promising for
magnetic field sensing applications
Sharp-1 regulates TGF-β signaling and skeletal muscle regeneration
10.1242/jcs.136648Journal of Cell Science1273599-608JNCS
- …