4,294 research outputs found
Pauli susceptibility of nonadiabatic Fermi liquids
The nonadiabatic regime of the electron-phonon interaction leads to behaviors
of some physical measurable quantities qualitatively different from those
expected from the Migdal-Eliashberg theory. Here we identify in the Pauli
paramagnetic susceptibility one of such quantities and show that the
nonadiabatic corrections reduce with respect to its adiabatic limit. We
show also that the nonadiabatic regime induces an isotope dependence of ,
which in principle could be measured.Comment: 7 pages, 3 figures, euromacr.tex, europhys.sty. Replaced with
accepted version (Europhysics Letters
Compensating impurity effect on epitaxial regrowth rate of amorphized Si
The epitaxial regrowth of ion-implanted amorphous layers on Si with partly compensated doping profiles of 11B, 75As, and 31P was studied. Single implants of these impurities are found to increase the regrowth rate at 475 and 500°C. The compensated layers with equal concentrations of 11B and 31P or 11B and 75As show a strong decrease of the regrowth whereas for the layers with overlapping 75As and 31P profiles no compensation has been found
Ion implantation and low-temperature epitaxial regrowth of GaAs
Channeling and transmission electron microscopy have been used to investigate the parameters that govern the extent of damage in ion‐implanted GaAs and the crystal quality following capless furnace annealing at low temperature (∼400 °C). The implantation‐induced disorder showed a strong dependence on the implanted ion mass and on the substrate temperature during implantation. When the implantation produced a fully amorphous surface layer the main parameter governing the regrowth was the amorphous thickness. Formation of microtwins after annealing was observed when the initial amorphous layer was thicker than 400 Å. Also, the number of extended residual defects after annealing increased linearly with the initial amorphous thickness and extrapolation of that curve predicts good regrowth of very thin (<400 Å) GaAs amorphous layers produced by ion implantation. A model is presented to explain the observed features of the low‐temperature annealing of GaAs
Anomalous impurity effects in nonadiabatic superconductors
We show that, in contrast with the usual electron-phonon Migdal-Eliashberg
theory, the critical temperature Tc of an isotropic s-wave nonadiabatic
superconductor is strongly reduced by the presence of diluted non-magnetic
impurities. Our results suggest that the recently observed Tc-suppression
driven by disorder in K3C60 [Phys. Rev. B vol.55, 3866 (1997)] and in
Nd(2-x)CexCuO(4-delta) [Phys. Rev. B vol.58, 8800 (1998)] could be explained in
terms of a nonadiabatic electron-phonon coupling. Moreover, we predict that the
isotope effect on Tc has an impurity dependence qualitatively different from
the one expected for anisotropic superconductors.Comment: 10 pages, euromacr.tex, europhys.sty, 6 figures. Replaced with
accepted version (Europhysics Letters
Epitaxial regrowth of thin amorphous GaAs layers
Channeling and transmission electron microscopy have been used to investigate the parameters that govern the crystal quality following capless funace annealing at low temperature (~ 400 °C) in ion-implanted GaAs. From the results obtained, we concluded that the crystal quality after annealing depends strongly on the thickness of the amorphous layer generated by ion implantation and the number of residual defects increases linearly with the thickness of the implanted layer. Single-crystal regrowth free of defects detectable by megaelectron volt He + channeling was achieved for a very thin amorphous layer (<~ 400 Å)
Nano-shaping of gold particles on silicon carbide substrate from solid-state to liquid-state dewetting
Abstract This work reports on the effect of annealing temperature on the size, shape and wetting of particles obtained on 4H-SiC substrate by the dewetting process of a deposited nanoscale-thick Au film, with focus on the difference between solid-state dewetting (below Au melting temperature) and liquid-state dewetting (above Au melting temperature). After depositing nanoscale-thick Au film on the SiC substrate, annealings are perfomed so to induce the solid-state or liquid-state dewetting process of the film with the consequent formation of particles. Plan-view and cross-view scanning electron microscopy analyses are carried out to quantify the evolution of the average planar size and vertical size of the particles and of the average contact angle of the particles to the SiC surface versus the annealing temperature. These analyses allow us to extract quantitative information on the wetting behaviour of the particles on the SiC surface by calculating the adhesion work versus the annealing temperature. Energy dispersive x-ray analyses are, also, performed on the dewetted particles to analyze their composition in the various annealing conditions. Overall, we set a general framework connecting process parameters to the nano-shape of the dewetted particles towards specific shape design for selected applications
Nonadiabatic Pauli susceptibility in fullerene compounds
Pauli paramagnetic susceptibility is unaffected by the electron-phonon
interaction in the Migdal-Eliashberg context. Fullerene compounds however do
not fulfill the adiabatic assumption of Migdal's theorem and nonadiabatic
effects are expected to be relevant in these materials. In this paper we
investigate the Pauli spin susceptibility in nonadiabatic regime by following a
conserving approach based on Ward's identity. We find that a sizable
renormalization of due to electron-phonon coupling appears when
nonadiabatic effects are taken into account. The intrinsic dependence of
on the electron-phonon interaction gives rise to a finite and negative isotope
effect which could be experimentally detected in fullerides. In addition, we
find an enhancement of the spin susceptibility with temperature increasing, in
agreement with the temperature dependence of observed in fullerene
compounds. The role of electronic correlation is also discussed.Comment: Revtex, 10 pages, 8 figures include
Simulations of the Light Scattering Properties of Metal/Oxide Core/Shell Nanospheres
Given the importance of the optical properties of metal/dielectric core/shell nanoparticles, in this work we focus our attention on the light scattering properties, within the Mie framework, of some specific categories of these noteworthy nanostructures. In particular, we report theoretical results of angle-dependent light scattering intensity and scattering efficiency for Ag/Ag2O, Al/Al2O2, Cu/Cu2O, Pd/PdO, and Ti/TiO2 core/shell nanoparticles as a function of the core radius/shell thickness ratio and on a relative comparison. The results highlight the light scattering characteristics of these systems as a function of the radius/shell thickness ratio, helping in the choice of the more suitable materials and sizes for specific applications (i.e., dynamic light scattering for biological and molecular recognition, increasing light trapping in thin-film silicon, organic solar cells for achieving a higher photocurrent)
Tunneling and Non-Universality in Continuum Percolation Systems
The values obtained experimentally for the conductivity critical exponent in
numerous percolation systems, in which the interparticle conduction is by
tunnelling, were found to be in the range of and about , where
is the universal conductivity exponent. These latter values are however
considerably smaller than those predicted by the available ``one
dimensional"-like theory of tunneling-percolation. In this letter we show that
this long-standing discrepancy can be resolved by considering the more
realistic "three dimensional" model and the limited proximity to the
percolation threshold in all the many available experimental studiesComment: 4 pages, 2 figure
“Exit Italy”? social and spatial (im)mobilities as conditions of protracted displacement
This article examines how the experience of protracted displacement interacts with mobility desires and practices of a diverse population of asylum-seekers, refugees and undocumented migrants in Italy. Drawing from ethnographic data collected in different Italian localities and among different nationalities, we focus on participants’ translocal connections, both as ways ‘out of limbo’ and as factors in protracted legal and socio-economic precariousness. We propose an interpretation of complex spatial mobilities to understand under what conditions spatial mobility translates into an improvement in the living conditions of migrants, producing upward socio-economic
mobility, and under what conditions spatial mobility perpetuates marginality and isolation. Although translocal connections provide space for action, migrants risk being trapped in a loop of movements between different countries and different localities within Italy, without the possibility to achieve legal protection in any of these
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