407 research outputs found
Parent and Child--Effect of Payment by Bank of Child\u27s Deposit to Parent Not a Legal Guardian
X-ray photoelectron spectroscopy studies of non-stoichiometric superconducting NbB2+x
Polycrystalline samples of NbB2+x with nominal composition (B/Nb) = 2.0, 2.1,
2.2, 2.3, 2.4 and 2.5 were studied by X-ray photoelectron spectroscopy (XPS).
The spectra revealed Nb and B oxides on the surface of the samples, mainly B2O3
and Nb2O5. After Ar ion etching the intensity of Nb and B oxides decreased. The
Nb 3d5/2 and B 1s core levels associated with the chemical states (B/Nb) were
identified and they do not change with etching time. The Binding Energy of the
Nb 3d5/2 and B 1s core levels increase as boron content increases, suggesting a
positive chemical shift in the core levels. On the other hand, analysis of
Valence Band spectra showed that the contribution of the Nb 4d states slightly
decreased while the contribution of the B 2p(pi) states increased as the boron
content increased. As a consequence, the electronic and superconducting
properties were substantially modified, in good agreement with band-structure
calculations.Comment: 10 pages, 7 figures, 1 tabl
Unusual features in the nonlinear microwave surface impedance of Y-Ba-Cu-O thin films
Striking features have been found in the nonlinear microwave (8 GHz) surface
impedance of high-quality YBaCuO thin films with comparable
low power characteristics [ and ]. The surface resistance is found to increase,
decrease, or remain independent of the microwave field (up to 60 mT)
at different temperatures and for different samples. However, the surface
reactance always follows the same functional form. Mechanisms which may
be responsible for the observed variations in and are briefly
discussed.Comment: 4 pages, 4 figure
Direct observation of non-local effects in a superconductor
We have used the technique of low energy muon spin rotation to measure the
local magnetic field profile B(z) beneath the surface of a lead film maintained
in the Meissner state (z depth from the surface, z <= 200 nm). The data
unambiguously show that B(z) clearly deviates from an exponential law and
represent the first direct, model independent proof for a non-local response in
a superconductor.Comment: 5 pages, 3 figure
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Electron Conditioning of Technical Aluminium Surfaces: Effect on the Secondary Electron Yield
The effect of electron conditioning on commercially aluminium alloys 1100 and
6063 were investigated. Contrary to the assumption that electron conditioning,
if performed long enough, can reduce and stabilize the SEY to low values (, value of many pure elements), the SEY of aluminium did not go lower than
1.8. In fact, it reincreases with continued electron exposure dose.Comment: 36 pages, 25 figures, submitted to JVST
Study of the microwave electrodynamic response of MgB2 thin films
We present a study on the power dependence of the microwave surface impedance
in thin films of the novel superconductor MgB2. 500 nm thick samples exhibiting
critical temperatures ranging between 26 and 38 K are synthesized by an ex-situ
post-anneal of e-beam evaporated boron in the presence of an Mg vapor at 900 C.
Preliminary results on films grown in situ by a high rate magnetron sputtering
technique from stoichiometric MgB2 and Mg targets are also reported. Microwave
measurements have been carried out employing a dielectrically loaded niobium
superconducting cavity operating at 19.8 GHz and 4 K. The study shows that the
electrodynamic response of MgB2 films is presently dominated by extrinsic
sources of dissipation, appearing already at low microwave power, likely to be
ascribed to the presence of grain boundaries and normal inclusions in the
samples.Comment: 10 pages, 3 figures, proceedings of the conference EUCAS 2001,
submitted to Physica
Esrrb extinction triggers dismantling of naïve pluripotency and marks commitment to differentiation
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