645 research outputs found
Monte-Carlo simulation of localization dynamics of excitons in ZnO and CdZnO quantum well structures
Localization dynamics of excitons was studied for ZnO/MgZnO and CdZnO/MgZnO
quantum wells (QW). The experimental photoluminescence (PL) and absorption data
were compared with the results of Monte Carlo simulation in which the excitonic
hopping was modeled. The temperature-dependent PL linewidth and Stokes shift
were found to be in a qualitatively reasonable agreement with the hopping
model, with accounting for an additional inhomogeneous broadening for the case
of linewidth. The density of localized states used in the simulation for the
CdZnO QW was consistent with the absorption spectrum taken at 5 K.Comment: 4 figures, to appear in J. Appl. Phy
Why Some Interfaces Cannot be Sharp
A central goal of modern materials physics and nanoscience is control of
materials and their interfaces to atomic dimensions. For interfaces between
polar and non-polar layers, this goal is thwarted by a polar catastrophe that
forces an interfacial reconstruction. In traditional semiconductors this
reconstruction is achieved by an atomic disordering and stoichiometry change at
the interface, but in multivalent oxides a new option is available: if the
electrons can move, the atoms don`t have to. Using atomic-scale electron energy
loss spectroscopy we find that there is a fundamental asymmetry between
ionically and electronically compensated interfaces, both in interfacial
sharpness and carrier density. This suggests a general strategy to design sharp
interfaces, remove interfacial screening charges, control the band offset, and
hence dramatically improving the performance of oxide devices.Comment: 12 pages of text, 6 figure
Large capacitance enhancement and negative compressibility of two-dimensional electronic systems at LaAlO/SrTiO interfaces
Novel electronic systems forming at oxide interfaces comprise a class of new
materials with a wide array of potential applications. A high mobility electron
system forms at the LaAlO/SrTiO interface and, strikingly, both
superconducts and displays indications of hysteretic magnetoresistance. An
essential step for device applications is establishing the ability to vary the
electronic conductivity of the electron system by means of a gate. We have
fabricated metallic top gates above a conductive interface to vary the electron
density at the interface. By monitoring capacitance and electric field
penetration, we are able to tune the charge carrier density and establish that
we can completely deplete the metallic interface with small voltages. Moreover,
at low carrier densities, the capacitance is significantly enhanced beyond the
geometric capacitance for the structure. In the same low density region, the
metallic interface overscreens an external electric field. We attribute these
observations to a negative compressibility of the electronic system at the
interface. Similar phenomena have been observed previously in semiconducting
two-dimensional electronic systems. The observed compressibility result is
consistent with the interface containing a system of mobile electrons in two
dimensions.Comment: 4 figures in main text; 4 figures in the supplemen
Photoemission study of TiO2/VO2 interfaces
We have measured photoemission spectra of two kinds of TiO-capped VO
thin films, namely, that with rutile-type TiO (r-TiO/VO) and that
with amorphous TiO (a-TiO/VO) capping layers. Below the
Metal-insulator transition temperature of the VO thin films, K,
metallic states were not observed for the interfaces with TiO, in contrast
with the interfaces between the band insulator SrTiO and the Mott insulator
LaTiO in spite of the fact that both TiO and SrTiO are band
insulators with electronic configurations and both VO and LaTiO
are Mott insulators with electronic configurations. We discuss possible
origins of this difference and suggest the importance of the polarity
discontinuity of the interfaces. Stronger incoherent part was observed in
r-TiO/VO than in a-TiO/VO, suggesting Ti-V atomic diffusion due
to the higher deposition temperature for r-TiO/VO.Comment: 5 pages, 6 figure
The Effect of Pentoxifylline and Propentofylline(HWA-285) on Post-Ischemic Rat Brain
開始ページ、終了ページ: 冊子体のページ付
Experience in Use of Multi-Labeled Autoradiography by Means of 18F-Fluorodeoxyglucose and 14C-Iodoantipyrine
開始ページ、終了ページ: 冊子体のページ付
Estimation of Drug-effect in Use of Multi-tracer Autoradioqraphy - Effect of S-Adenosyl-L-Methionoie on Postischemic Brain Injury in Rat -
開始ページ、終了ページ: 冊子体のページ付
Tuning of metal-insulator transition of two-dimensional electrons at parylene/SrTiO interface by electric field
Electrostatic carrier doping using a field-effect-transistor structure is an
intriguing approach to explore electronic phases by critical control of carrier
concentration. We demonstrate the reversible control of the insulator-metal
transition (IMT) in a two dimensional (2D) electron gas at the interface of
insulating SrTiO single crystals. Superconductivity was observed in a
limited number of devices doped far beyond the IMT, which may imply the
presence of 2D metal-superconductor transition. This realization of a
two-dimensional metallic state on the most widely-used perovskite oxide is the
best manifestation of the potential of oxide electronics
Coexistence of Magnetic Order and Two-dimensional Superconductivity at LaAlO/SrTiO Interfaces
A two dimensional electronic system with novel electronic properties forms at
the interface between the insulators LaAlO and SrTiO. Samples
fabricated until now have been found to be either magnetic or superconducting,
depending on growth conditions. We combine transport measurements with
high-resolution magnetic torque magnetometry and report here evidence of
magnetic ordering of the two-dimensional electron liquid at the interface. The
magnetic ordering exists from well below the superconducting transition to up
to 200 K, and is characterized by an in-plane magnetic moment. Our results
suggest that there is either phase separation or coexistence between magnetic
and superconducting states. The coexistence scenario would point to an
unconventional superconducting phase in the ground state.Comment: 10 pages, 4 figure
Magnetic effects at the interface between nonmagnetic oxides
The electronic reconstruction at the interface between two insulating oxides
can give rise to a highly-conductive interface. In analogy to this remarkable
interface-induced conductivity we show how, additionally, magnetism can be
induced at the interface between the otherwise nonmagnetic insulating
perovskites SrTiO3 and LaAlO3. A large negative magnetoresistance of the
interface is found, together with a logarithmic temperature dependence of the
sheet resistance. At low temperatures, the sheet resistance reveals magnetic
hysteresis. Magnetic ordering is a key issue in solid-state science and its
underlying mechanisms are still the subject of intense research. In particular,
the interplay between localized magnetic moments and the spin of itinerant
conduction electrons in a solid gives rise to intriguing many-body effects such
as Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions, the Kondo effect, and
carrier-induced ferromagnetism in diluted magnetic semiconductors. The
conducting oxide interface now provides a versatile system to induce and
manipulate magnetic moments in otherwise nonmagnetic materials.Comment: Nature Materials, July issu
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