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Supercritical antisolvent precipitation of submicronic particles of superconductor precursors.
No full textIND. ENG. CHEM. RES
dc transport properties and resistance fluctuation processes in Sr2FeMoO6 polycrystalline thin films
No full textWe performed transport measurements and voltage noise analysis on Sr2FeMoO6 thin films, in zero applied magnetic field as a function of temperature T, down to 10 K. The samples, grown by pulsed laser deposition on SrTiO3 substrates, showed a negative resistivity thermal coefficient and, at T<50 K, the observed temperature dependence of resistivity and the I-V curves were correctly described by the fluctuation-induced tunneling model which assumes the presence of intergranular tunneling of charge carriers. Moreover, the analysis of the low temperature resistance fluctuation processes, pointed out the presence of a voltage noise component independent of the frequency within the whole investigated bandwidth with a spectral density directly proportional to the square of the bias current. We interpreted this unusual behavior as a possible consequence of tunneling intergranular processes
Local magneto-optical response of H+ irradiated Zn1−xCoxO thin films
No full textThe local distribution of magneto-optical properties of hydrogen irradiated Zn1−xCoxO thin films has been investigated by means of magneto-optical Kerr microscope magnetometer, capable of simultaneously measuring the magnetic properties with a micrometer spatial resolution. The experimental results indicate that the magneto-optical response is quite homogenous on the micrometer scale, indicating that the film grain size is crucial in determining the local coercivity distribution
Supercritical Antisolvent Precipitation:A New Technique for Preparing Submicronic Yttrium Powders to Improve YBCO Superconductors
No full textEffects of cobalt substitution on ZnO surface reactivity and electronic structure
No full textWe have performed scanning probe microscopy investigations of ZnO and Co-substituted ZnO under dark/UV conditions as well as in air and an ultra-high vacuum environment to shine a light on the change in electronic structure and surface reactivity as a consequence of Zn substitution with Co. We have achieved two major results: first, Co substituting Zn atoms significantly downward shifts by about 400 meV the Fermi level, which is close to the conduction band in the as-grown n-type ZnO. Second, a thoroughly novel result, Co substitution strongly reduces the absorption of negative oxygen species (NOS) at the ZnO surface. These two experimental findings are fully explained by a phenomenological model assuming the formation of Co-defect (Co-D) complexes that induce the appearance of an unoccupied impurity band in the ZnO energy gap. NOS play a central role in both the operating principles of UV photodetectors and applications in nanomedicine. Thus, the inhibiting effect of Co-D complexes on NOS formation has many applicative implications since it suggests that defect-engineering procedures might be devised for realizing nano-patterned Co-doped ZnO surfaces with regions showing different surface properties
Transport mechanisms in Co-doped ZnO (ZCO) and H-irradiated ZCO polycrystalline thin films
No full textIn the present study, the electrical resistivity (ρ) as a function of the temperature (T) has been measured in polycrystalline ZnO, Co-doped ZnO (ZCO) and H irradiated ZCO (HZCO) samples, in the 300-20 K range. The achieved results show impressive effects of Co doping and H irradiation on the ZnO transport properties. The Co dopant increases the ZnO resistivity at highT(HT), whereas it has an opposite effect at lowT(LT). H balances the Co effects by neutralizing theρincrease at HT and strengthening its decrease at LT. A careful analysis of theρdata permits to identify two different thermally activated processes as those governing the charge transport in the three materials at HT and LT, respectively. The occurrence of such processes has been fully explained in terms of a previously proposed model based on an acceptor impurity band, induced by the formation of Co-oxygen vacancy complexes, as well as known effects produced by H on the ZnO properties. The same analysis shows that both Co and H reduce the effects of grain boundaries on the transport processes. The high conductivity of HZCO in the wholeT-range and its low noise level resulting from electric noise spectroscopy make this material a very interesting one for technological applications
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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