139 research outputs found
A new technique for the determination of the critical current density in superconducting films and flat samples
The determination of their critical current density in the whole range of the
temperature below Tc is of first importance to understand the physical
processes occurring in superconducting films. We describe here a technique
suitable for square films based on the measurement of the magnetic moment due
to the currents persisting in the superconductor after the application of a
perpendicular high magnetic field. Typically, with a SQUID magnetometer, the
measurement time in the whole range of temperature with a 1K interval is of 2
hours only by this technique. An intriguing aspect of the obtained results is
that they are much more accurate if the current lines are supposed to be
circular than if we suppose, as suggested by theoretical considerations and
magneto-optical observations that they have the sample symmetry
Role of the oxygen plasma during in situ growth of YBa2Cu3O6+x thin films by pulsed laser deposition
The incorporation of oxygen into YBa2Cu3O6+x (YBaCuO) thin films during in situ growth by pulsed laser deposition (PLD) has been investigated as a function of the ablation conditions. A quenching technique has been used immediately after termination of growth to avoid any oxygen in or out-diffusion during the cooling down step. It is shown that superconducting YBaCuO thin films can be formed without any post-oxygenation procedure, contrary to what is expected from the (Image, T) thermodynamic diagram. Moreover, it is found that there is an optimal target-substrate distance, D, for each O2 deposition pressure, Image, that leads to the higher critical temperature (i.e., higher oxygenation) as well as to the best structural and morphological properties of quenched films. The results are discussed considering the formation of reactive oxygen in the laser-induced plasma during film growth
Radio-frequency discharges in Oxygen. Part 1: Modeling
In this series of three papers we present results from a combined
experimental and theoretical effort to quantitatively describe capacitively
coupled radio-frequency discharges in oxygen. The particle-in-cell Monte-Carlo
model on which the theoretical description is based will be described in the
present paper. It treats space charge fields and transport processes on an
equal footing with the most important plasma-chemical reactions. For given
external voltage and pressure, the model determines the electric potential
within the discharge and the distribution functions for electrons, negatively
charged atomic oxygen, and positively charged molecular oxygen. Previously used
scattering and reaction cross section data are critically assessed and in some
cases modified. To validate our model, we compare the densities in the bulk of
the discharge with experimental data and find good agreement, indicating that
essential aspects of an oxygen discharge are captured.Comment: 11 pages, 10 figure
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