569 research outputs found
Optical Properties of TiN Thin Films close to the Superconductor-Insulator Transition
We present the intrinsic optical properties over a broad spectral range of
TiN thin films deposited on a Si/SiO substrate. We analyze the measured
reflectivity spectra of the film-substrate multilayer structure within a
well-establish procedure based on the Fresnel equation and extract the real
part of the optical conductivity of TiN. We identify the metallic contribution
as well as the finite energy excitations and disentangle the spectral weight
distribution among them. The absorption spectrum of TiN bears some similarities
with the electrodynamic response observed in the normal state of the
high-temperature superconductors. Particularly, a mid-infrared feature in the
optical conductivity is quite reminiscent of a pseudogap-like excitation
Early light curves for Type Ia supernova explosion models
Upcoming high-cadence transient survey programmes will produce a wealth of
observational data for Type Ia supernovae. These data sets will contain
numerous events detected very early in their evolution, shortly after
explosion. Here, we present synthetic light curves, calculated with the
radiation hydrodynamical approach Stella for a number of different explosion
models, specifically focusing on these first few days after explosion. We show
that overall the early light curve evolution is similar for most of the
investigated models. Characteristic imprints are induced by radioactive
material located close to the surface. However, these are very similar to the
signatures expected from ejecta-CSM or ejecta-companion interaction. Apart from
the pure deflagration explosion models, none of our synthetic light curves
exhibit the commonly assumed power-law rise. We demonstrate that this can lead
to substantial errors in the determination of the time of explosion. In
summary, we illustrate with our calculations that even with very early data an
identification of specific explosion scenarios is challenging, if only
photometric observations are available.Comment: 15 pages, 14 figures, 3 tables, accepted for publication in MNRA
Impact of UV wavelength and curing time on the properties of spin-coated low-k films
Advanced spin-on k 2.3 films with similar to 40% porosity were enabled by liquid phase self-assembly (LPSA) mechanism on Si substrates. UV-assisted thermal template removal is investigated as a faster alternative to the conventional thermal process. The as-deposited films were exposed to narrow-band UV light of 172 nm, 222 nm, 254 nm or 185/254 nm at 400 degrees C for different time. The optical, mechanical, chemical and electrical properties of the resulting films are discussed in this work. Photons with wavelength of about 172 nm from one side are detrimental to the electrical and chemical properties of the low-k films hut from the other side notably improve the porous low-k mechanical properties. Exposure to 222 nm light as short as 3 min, is more efficient in terms of template removal when compared to 2h thermal cure, while in both cases similar mechanical and electrical properties are reported. UV-cure using 254 nm or dual band 254/185 nm photons seem to have a minor contribution to the template removal efficiency for the applied doses. Higher doses are necessary in order to better understand the effective contribution of these photon energies. Finally, the HF etching mechanism is discussed
Quantum Metallicity on the High-Field Side of the Superconductor-Insulator Transition
We investigate ultrathin superconducting TiN films, which are very close to
the localization threshold. Perpendicular magnetic field drives the films from
the superconducting to an insulating state, with very high resistance. Further
increase of the magnetic field leads to an exponential decay of the resistance
towards a finite value. In the limit of low temperatures, the saturation value
can be very accurately extrapolated to the universal quantum resistance h/e^2.
Our analysis suggests that at high magnetic fields a new ground state, distinct
from the normal metallic state occurring above the superconducting transition
temperature, is formed. A comparison with other studies on different materials
indicates that the quantum metallic phase following the magnetic-field-induced
insulating phase is a generic property of systems close to the disorder-driven
superconductor-insulator transition.Comment: 4 pages, 4 figures, published versio
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