134 research outputs found
Aluminum Oxide Layers as Possible Components for Layered Tunnel Barriers
We have studied transport properties of Nb/Al/AlOx/Nb tunnel junctions with
ultrathin aluminum oxide layers formed by (i) thermal oxidation and (ii) plasma
oxidation, before and after rapid thermal post-annealing of the completed
structures at temperatures up to 550 deg C. Post-annealing at temperatures
above 300 deg C results in a significant decrease of the tunneling conductance
of thermally-grown barriers, while plasma-grown barriers start to change only
at annealing temperatures above 450 deg C. Fitting the experimental I-V curves
of the junctions using the results of the microscopic theory of direct
tunneling shows that the annealing of thermally-grown oxides at temperatures
above 300 deg C results in a substantial increase of their average tunnel
barriers height, from ~1.8 eV to ~2.45 eV, versus the practically unchanged
height of ~2.0 eV for plasma-grown layers. This difference, together with high
endurance of annealed barriers under electric stress (breakdown field above 10
MV/cm) may enable all-AlOx and SiO2/AlOx layered "crested" barriers for
advanced floating-gate memory applications.Comment: 7 pages, 6 figure
Aluminum Hard Mask Technique for the Fabrication of High-Quality Submicron Nb/Al-AlOx/Nb Josephson Junctions
We have developed a combined photolithography and electron-beam lithography
fabrication process for sub-\mum to \mum-size Nb/Al-AlOx/Nb Josephson
junctions. In order to define the junction size and protect its top electrode
during anodic oxidation, we developed and used the new concept of an aluminum
hard mask. Josephson junctions of sizes down to 0.5 \mum2 have been fabricated
and thoroughly characterized. We found that they have a very high quality,
which is witnessed by the IV curves with quality parameters Vm > 50 mV and Vgap
= 2.8 mV at 4.2 K, as well as IcRN products of 1.75-1.93 mV obtained at lower
temperatures. In order to test the usability of our fabrication process for
superconducting quantum bits, we have also designed, fabricated and
experimentally investigated phase qubits made of these junctions. We found a
relaxation time of T1 = 26 ns and a dephasing time of T2 = 21 ns
Disorder and transport in cuprates: weak localization and magnetic contributions
We report resistivity measurements in underdoped YBaCuOand overdoped TlBaCuO single crystals in which the
concentration of defects in the CuO planes is controlled by electron
irradiation. Low upturns of the resistivity are observed in both cases for
large defect content. In the Tl compound the decrease of conductivity scales as
expected from weak localization theory. On the contrary in
YBaCuO the much larger low T contribution to the
resistivity is proportional to the defect content and might then be associated
to a Kondo like spin flip scattering term. This would be consistent with the
results on the magnetic properties induced by spinless defects.Comment: latex rullier1.tex, 5 files, 4 pages [SPEC-S01/003], submitted to
Phys. Rev. Let
High-Throughput Method of Whole-Brain Sectioning, Using the Tape-Transfer Technique
Cryostat sectioning is a popular but labor-intensive method for preparing histological brain sections. We have developed a modification of the commercially available CryoJane tape collection method that significantly improves the ease of collection and the final quality of the tissue sections. The key modification involves an array of UVLEDs to achieve uniform polymerization of the glass slide and robust adhesion between the section and slide. This report presents system components and detailed procedural steps, and provides examples of end results; that is, 20mum mouse brain sections that have been successfully processed for routine Nissl, myelin staining, DAB histochemistry, and fluorescence. The method is also suitable for larger brains, such as rat and monkey
Combined potential and spin impurity scattering in cuprates
We present a theory of combined nonmagnetic and magnetic impurity scattering
in anisotropic superconductors accounting for the momentum-dependent impurity
potential. Applying the model to the d-wave superconducting state, we obtain a
quantitative agreement with the initial suppression of the critical temperature
due to Zn and Ni substitutions as well as electron irradiation defects in the
cuprates. We suggest, that the unequal pair-breaking effect of Zn and Ni may be
related to a different nature of the magnetic moments induced by these
impurities.Comment: 5 pages, 3 tables, RevTex, to be published in Phys. Rev.
Multi-layered Ruthenium-modified Bond Coats for Thermal Barrier Coatings
Diffusional approaches for fabrication of multi-layered Ru-modified bond coats for thermal
barrier coatings have been developed via low activity chemical vapor deposition and high activity
pack aluminization. Both processes yield bond coats comprising two distinct B2 layers, based on
NiAl and RuAl, however, the position of these layers relative to the bond coat surface is reversed
when switching processes. The structural evolution of each coating at various stages of the
fabrication process has been and subsequent cyclic oxidation is presented, and the relevant
interdiffusion and phase equilibria issues in are discussed. Evaluation of the oxidation behavior of
these Ru-modified bond coat structures reveals that each B2 interlayer arrangement leads to the
formation of α-Al 2 O 3 TGO at 1100°C, but the durability of the TGO is somewhat different and in
need of further improvement in both cases
Anisotropic impurities in anisotropic superconductors
Physical properties of anisotropic superconductors like the critical
temperature and others depend sensitively on the electron mean free path. The
sensitivity to impurity scattering and the resulting anomalies are considered a
characteristic feature of strongly anisotropic pairing. These anomalies are
usually analyzed in terms of s-wave impurity scattering which leads to
universal pair breaking effects depending on only two scattering parameters,
the mean free path and the impurity cross section. We investigate here
corrections coming from anisotropies in the scattering cross section, and find
not only quantitative but also qualitative deviations from universal s-wave
isotropic pairbreaking. The properties we study are the transition temperature,
the density of states, quasiparticle bound states at impurities, and pinning of
flux lines by impurities.Comment: 19 page
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