B. Minetti

Politecnico di Torino, Torino, Piedmont, Italy

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Publications (232)162.49 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Radiation-hard sensors are at present time highly requested for applications in environments with potential radiation hazard such as space, accelerators and fusion machines. We developed device prototypes for magnetic field and THz photon detection, both based on YBa2Cu3O7−x (YBCO) superconducting films locally nanostructured by means of 0.25GeV Au-ion lithography. This micro-collimated implantation of high-density columnar defects in YBCO films allows localizing external electromagnetic excitations by means of dissipative signals only induced into the nanostructured regions. The radiation hardness of detector prototypes was checked under fast neutron radiation. It turns out that, up to a neutron fluence comparable with those expected for 10years long permanence in the space, no significant change was detected in superconductor characteristics such as zero-field resistance-temperature or magneto-resistance, whose variations could dramatically affect device figures of merit as responsivity or noise equivalent power. Fluences and energy spectrum of the neutrons impinging on the sensor prototypes were determined by a Monte-Carlo code implemented “ad hoc”.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 02/2012; · 1.19 Impact Factor
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    ABSTRACT: We report about the functional exploiting of the High-Energy Heavy-Ion (HEHI) lithography aimed at modulating in confined regions both structural and electrical properties of high temperature superconducting YBa2Cu3O7−x (YBCO) films. We discuss the physical behaviors related to the HEHI modification of such films by means of 3D columnar defects, exhibiting nanometric cross section. A major part of this paper is devoted to the viability of well-defined (B,T,J) phase-diagram zones, where electrical decoupling between as-grown and modified parts occurs and so guarantees external-signal localization.In order to stress out complementary behaviors into different phase-diagram regions of locally modified YBCO films, we present low-temperature magnetic imaging, accounting for the case where a spatially continuous Meissner state holds on throughout the whole sample. In this case, the continuity of the Meissner state hampers localization of dissipative signals in the nanostructured region. On the contrary, inside the (B,T,J) phase-diagram zones belonging to the temperature range where the Meissner state is spatially broken, the temperature range of dissipation confinement under external stimuli can be functionally exploited. Then the main target of a road map pointing towards position-sensitive infrared superconducting sensors is enlightened by means of crucial experimental results. With this respect, a device layout, consisting into HEHI modified YBCO film grown either on YSZ or MgO substrates, is chosen to test the functional behavior of infrared detectors working above liquid nitrogen temperature and, in the case of MgO substrate, displaying sub-millisecond response-time.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 02/2012; · 1.19 Impact Factor
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    ABSTRACT: The critical current Jc of superconducting films is about two order of magnitude larger than that of single crystals. The dependence of such Jc on field depends on the presence and distribution of defects. We speculate that High Temperature Superconducting (HTS) films can be modeled as an agglomeration of islands coupled via Josephson contacts and then considered as a network of Long Josephson Junctions (LJJ) between superconducting islands. In order to check this hypothesis we further developed a model firstly introduced by Fehrenbacher based on the modulation of critical current densities in LJJ by means of suitable distribution of defects. The defects act by modulating the coupling energy of the junction. Critical current densities are calculated in the case of periodic and random defect distributions.
    International Journal of Modern Physics B 01/2012; 13(09n10). · 0.46 Impact Factor
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    ABSTRACT: This paper studies the striking correlation between nanosized structural patterns in YBCO films and macroscopic transport current. A nanosized network of parallel Josephson junctions laced by insulating dislocations is almost mimicking the grain boundary structural network. It contributes to the macroscopic properties and accounts for the strong intergranular pinning across the film in the intermediate temperature range. The correlation between the two networks enables to find out an outstanding scaling law in the (Jc, B) plane and to determine meaningful parameters concerning the matching between the vortex lattice and the intergranular defect lattice. Two asymptotic behaviors of the pinning force below the flux flow regime are checked: the corresponding vortex phases are clearly individuated.
    International Journal of Modern Physics B 01/2012; 14(25n27). · 0.46 Impact Factor
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    ABSTRACT: An experimental set-up for magneto-optical analysis equipped with a new low- temperature controlling system is described. Magneto-optical investigations of the magnetic flux distribution are performed on as-grown as well as Au-on ion-irradiated Bi-2122 single crystals. The comparative analysis of as-grown and irradiated specimens shows that the magneto-optical technique provides information complementary to those provided by other techniques, such as, for example, susceptometric characterization.
    International Journal of Modern Physics B 01/2012; 14(25n27). · 0.46 Impact Factor
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    ABSTRACT: The possibility to enhance in a predictable way the superconducting properties behavior of a bulk material by introducing linearly correlated defects within a surface layer has been demonstrated. Ag/BSCCO-2223 tapes were irradiated by means of 0.25 GeV Au ions at different fluences, with a dose equivalent field Bϕ ranging from 1 T to 5 T. The implantation depth was about 15 μm corresponding to about 15% of the total sample thickness. Sample independent enhancements of different a.c and d.c properties show up, due to vortex confinement in the whole sample. The sample independence exhibited by all the experimental findings as well as, on the other side, the dose dependence of the enhancements, allow to design in advance the performances of a monofilamentary tape where defect trenches of nanometric size are scratched.
    International Journal of Modern Physics B 01/2012; 13(09n10). · 0.46 Impact Factor
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    ABSTRACT: In the framework of a research aimed to superconductor/semiconductor integrated electronics, we have grown a-axis oriented YBa2Cu3O7-δ (YBCO) thin films on silicon (100) substrates with (111) oriented insulating buffer layers of cerium dioxide (CeO2), using magnetron sputtering deposition techniques. The properties of the cerium dioxide layer have been preliminary optimized by means of several layout and by monitoring the growing procedures through X-ray diffraction, AFM and TEM techniques. The lattice matching between CeO2 and YBCO resulted to be worsened by an amorphous thin SiO2 layer at the Si/CeO2 interface, that decouples the buffer orientation from the seed orientation. However, it was possible to grow a relatively thick, optimally textured layer of CeO2 without spurious orientations. The YBCO films deposited on top of this layer result preferentially a-axis oriented. The transition widths are very large, jet well controllable and reproducible. Some technological applications can be already envisaged.
    International Journal of Modern Physics B 01/2012; 17(04n06). · 0.46 Impact Factor
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    ABSTRACT: By using ac susceptibility measurements at different frequencies and dc fields we investigated the creep properties of MgB2 bulk samples. Two independent analysis have been used in order to determine the behavior of the pinning energy in the whole investigated temperature and field ranges. The main result of the first analysis (χ′′-peak analysis) is that the attempt frequency v0 in the Arrhenius formula is about 104Hz, a value significantly lower than that usually reported for HTS's. By means of the second analysis a field dependent maximum of the pinning energy as a function of temperature has been found. It turns out that the phase points corresponding to the peak of the pinning energy are coincident with the irreversibility line, as determined by magnetization cycles. The results coming from different and independent analysis lead to the determination of a vortexphase diagram for bulk MgB2, which seems to be largely dominated by creep phenomena.
    International Journal of Modern Physics B 01/2012; 17(04n06). · 0.46 Impact Factor
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    ABSTRACT: Surface columnar defects, SCDs, are produced in high quality (Bi,Pb)2Sr2Ca2Cu3Oy/Ag tapes by irradiating them with 0.25 GeV gold ions only on a top layer up to ≈15% of the full volume. The ion beam is orthogonal to the tape plane. In this paper we report experimental results of the surface implantation of columnar defects both in the high-current and in the low-current regime with a particular emphasis on the influence of SCDs on the anisotropy dependent properties. Some characteristic labels of the SCD implantation are pointed out. A comparison between all the results in the two current regimes is made. A hint is given concerning analogous results obtained by means of transport electrical measurements. The experimental data can be interpreted by assuming that a new confined phase driven by SCDs sets up in both the current regimes. Acting on the dose, it is possible to obtain tunable control of the in-field performance in both regimes.
    International Journal of Modern Physics B 01/2012; 14(25n27). · 0.46 Impact Factor
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    ABSTRACT: The aim of the present work is the optimization of the Si/buffer-layer/YBCO multilayer deposition process so as to grow superconducting films of quality suitable for device applications. The structural properties of the Si/CeO2 system, obtained by RF magnetron sputtering of CeO2 targets in Ar atmosphere, have been studied. More than 50 films have been deposited and some of them submitted to post-deposition annealing treatments both in N2 and O2 atmospheres. The presence of an unwanted amorphous SiO2 layer at the Si/CeO2 interface compromises the YBCO c-axis orientation, and therefore the sharpness of the R versus T transition. A newly designed deposition system has been realized: it has been specially conceived for obtaining bi- and tri-layers, adopting two targets in YSZ and CeO2, respectively. Results on YSZ/Si and CeO2/YSZ/Si systems obtained with the new machine are presented and discussed: (100) oriented YSZ films with nominal thickness of 40 nm have been obtained. The CeO2 film subsequently deposited has the desired (100) orientation. The YBCO film, in the final YBCO/YSZ/CeO2/Si configuration, is c-axis oriented.
    International Journal of Modern Physics B 01/2012; 19(31). · 0.46 Impact Factor
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    ABSTRACT: A local magnetic characterization of disk-shaped MgB<sub>2</sub> bulk samples synthesized by the Spark-Plasma-Sintering technique was carried out aimed at studying the material magnetic shielding properties. This growth technique allows one to produce samples in different shapes and sizes as required for shielding applications. The analysis employed a linear array of Hall probes mounted on a custom-designed stage able to move perpendicular to the sample surface with micrometric resolution. Spatial distributions of the axial component of the shielding magnetic-induction field generated by the superconductor were evaluated in the temperature range 20-36 K and in applied magnetic field up to 1.5 T. By the analysis of these shielding field profiles in the framework of the critical state model, critical current densities, J<sub>c</sub>, higher than 10<sup>10</sup> A/m<sup>2</sup> were found at T=20 K. On the basis of the found J<sub>c</sub> values a preliminary estimation of the full penetration field inside a tube-shaped shield component was carried out. It indicates that the material under test is a good candidate for passive magnetic shields.
    IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
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    ABSTRACT: Broadband electromagnetic characterization of hot plasmas and electron beams requires real-time, direct detection of high flux of electromagnetic radiation. We report about a project aimed at creating robust THz detectors based on YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7-x</sub> (YBCO) films, working around liquid nitrogen temperature and in a regime of low dissipation. The sensor layout mainly consists in two contiguous meanders that are integrated on the same substrate. One of them is nanostructured by local high-energy heavy-ion irradiation; the other one (as-grown YBCO) is used for thermo-electric signal reference. By measuring the voltage response to THz excitation of YBCO film, at a given bias current and temperature, on selected substrates (Yttria Stabilized Zirconia (YSZ) and MgO), it turns out that only the nanostructured part is brought in the dissipative state when exposed to THz radiation. We present estimated noise equivalent power and relaxation times for YBCO grown on YSZ and on MgO substrates. On the latter, we experimentally checked out the device response to time-varying Far-Infrared (FIR) signals up to 800 Hz. The proposed device turns out to fit the necessary requirements for measurement of electron cyclotron emission of hot plasmas or of electron beams in the FIR spectrum.
    IEEE Transactions on Applied Superconductivity 07/2011; · 1.20 Impact Factor
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    ABSTRACT: Magnetic shielding properties of MgB2 bulk samples synthesized by the SPS (Spark–Plasma–Sintering) technique were characterized in low applied magnetic fields at temperatures ranging from 20 to 37 K. The used growth technique allows one to produce this compound in different shapes and sizes required for shielding applications. In this framework, shielding magnetic-induction field profiles generated by MgB2-based shield components, shaped as planar thick disks, were measured by means of a suitable Hall probe in-plane array. The magnetic field distribution at different vertical distances above the sample was also obtained by a micrometric motion of the probe ensemble. Magnetic field profiles were then analyzed in the framework of the critical state model and the critical current density, J c , was evaluated. The J c magnitude indicates that the material under test is a good candidate for passive magnetic shield manufacturing up to temperatures close to the transition one. KeywordsMgB2 bulk–Magnetic shielding–Critical current density–Scanning Hall probe technique
    Journal of Superconductivity and Novel Magnetism 01/2011; 24(1):307-312. · 0.93 Impact Factor
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    ABSTRACT: We investigate the nonlinear behavior of magnesium diboride coplanar waveguide resonators in order to iden- tify the basic mechanisms limiting the performance of polycrys- talline films in microwave applications. In particular, we focus on several kinds of switching response. Switching is observed due to increase of rf currents above a given threshold or to ap- plication of dc fields. In the former case a thermic model is able to account for the observed behaviors, including the presence of a thermal bistability regime. In the latter case, penetration of vor- tices at low fields is demonstrated and the effects of thermo-mag- netic instabilities at higher fields are described. Index Terms—Coplanar waveguide resonators, local Joule heating, magnesium diboride thin films, superconducting mi- crowave devices, vortex avalanches, vortex penetration in super- conductors.
    IEEE Transactions on Applied Superconductivity - IEEE TRANS APPL SUPERCONDUCT. 01/2011; 21(3):579-582.
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    ABSTRACT: Quantitative imaging of the local magnetic field and of current density distribution in superconductors (with microscopic resolution over macroscopic length scales) is achieved by means of the Magneto-Optical Imaging technique with an indicator film. We exploit this technique to study the vortex arrangement and the corresponding supercurrent distribution in high temperature superconducting YBa2Cu3O7−x films. Several patterned superconducting films were studied, either non-simply connected structures, which imply macroscopic flux quantization, and superconductors whose local properties were tailored by means of confined heavy-ion irradiation. Moreover, by means of electrical transport measurements coupled with the real-time imaging of the magnetic pattern, it is directly shown how the local current distribution in patterned superconductors is affected by the electrical transport both in the Meissner and in the vortex regimes. The relevance of a controlled and localized dissipation induced by the confined vortex motion in tailored superconducting films is demonstrated for direct applications of this phenomenology to superconducting devices, such as magnetic field and photon detectors. KeywordsSuperconducting films–Magneto-optics–Heavy ion irradiation–Controlled flux flow–Magnetic field detector–Photon detector
    Journal of Superconductivity and Novel Magnetism 01/2011; 24(1):75-80. · 0.93 Impact Factor
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    ABSTRACT: Broadband electromagnetic characterization of hot plasmas, such as in nuclear fusion reactors and related experiments, requires detecting systems that must withstand high flux of particles and electromagnetic radiations. We propose a rugged layout of a high temperature superconducting detector aimed at 3 THz collective Thomson scattering (CTS) spectroscopy in hot fusion plasma. The YBa2Cu3O7 − x superconducting film is patterned by standard photolithography and the sensing area of the device is created by means of high-energy heavy ion irradiation, in order to modify the crystal structure both of the superconducting film and of the substrate. This method diminishes process costs and resulting device fragility due to membrane or air-bridge structures that are commonly needed for MIR and FIR radiation detection. Moreover the sensing area of the device is wired by the same superconducting material and thus excellent mechanical strength is exhibited by the whole device, due to the oxide substrate. Continuous wave operation of prototype devices is demonstrated at liquid nitrogen temperature, for selected infrared spectra of broadband thermal energy sources. Several solutions, which exploit the advantages coming from the robustness of this layout in terms of intrinsic radiation hardness of the superconducting material and of the needed optical components, are analysed with reference to applications of infrared electromagnetic detectors in a tokamak machine environment.
    Superconductor Science and Technology 11/2010; 23(12):125008. · 2.76 Impact Factor
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    ABSTRACT: Superconducting and normal-state properties of MgB2 polycrystalline samples with non magnetic (SiC) and magnetic (Co) dopant addition were analysed in order to study the doping influence on the magnetic anisotropy of MgB2 polycrystalline samples and to correlate this influence with the doping-induced changes in band scattering processes. Both doping typologies result in a decrease of the MgB2 upper critical field anisotropy factor. For SiC-doped samples this result is joined to an upper critical field (Bc2) shift toward higher temperatures whereas Co doped samples exhibit a Bc2 decrease. To guide the application road map a theoretical approach to the analysis of the normal state resistivities (SiC doping) and of the upper critical field dependence on temperature (SiC and Co dopings) was performed. According to this scenario, band scattering rate as well as electron diffusivity values obtained by these analyses showed for both the investigated doping typologies an increase of intraband scattering processes in the more anisotropic σ band whereas the conductivity of π band remains almost unaffected.
    Journal of Physics Conference Series 07/2010; 234(1):012014.
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    ABSTRACT: Research and application of THz technology, pursued all over the last century, are currently focused either on high-performance sources and detectors or on low-cost and rugged devices that are suitable for widespread use. Besides semiconductors, high temperature superconductors are good candidates for next generation superconducting bolometers. We employ the high energy heavy ion (HEHI) lithography for modulating the local structural and electrical properties of high temperature superconducting YBa<sub>2</sub>Cu<sub>3</sub>O<sub>7</sub> (YBCO) films in a functional way. In this report, measurements of the photoresponse of a prototype device to electromagnetic radiation in the far infrared band (THz region) are presented. It is demonstrated that HEHI lithography is an effective tool to enhance the absorption band of the YBCO film in the infrared spectrum, enabling the THz detection of YBCO sensors, in the superconducting state and above the liquid nitrogen temperature.
    IEEE Sensors Journal 05/2010; · 1.48 Impact Factor
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    ABSTRACT: In this paper we report on the effects of “surface columnar defects” (blind holes) generated by heavy ion irradiation by performing Field Emission Scanning Electron Microscopy (FESEM) imaging of the columns created across a selected set of specimens, ranging from YBa2Cu3O7−x melt-textured bulks and Bi2Sr2Ca2Cu3Ox monofilamentary tapes to YBa2Cu3O7−x single crystals. Different ion fluences, resulting into modifying the superconducting properties, were sampled. A correlation between FESEM patterns and volume integrated measurements shows how surface columnar defects claim the leadership of the superconducting behaviors of the ion implanted samples.
    Physica C Superconductivity 02/2010; 470(19):914-917. · 0.72 Impact Factor
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    ABSTRACT: High energy heavy ion lithography was used for modulating through implanted nanostructures the local structural and electrical properties of high temperature superconducting YBa2Cu3O7 films. The controlled reduction of the critical temperature of irradiated films results in a localization into heavy ion patterned micro-regions of the electrical dissipation, viable in a given temperature range and driven by ion fluence, bias current and applied magnetic field. The measurement of the response of such nanostructured YBCO films to electromagnetic radiation in the infrared band (MIR–FIR region) is presented. It turns out that the ion induced structural modification of both superconducting film and substrate is actually enabling the infrared optical absorption of YBCO, so that the viability of low noise THz detection above the liquid nitrogen temperature is shown.
    Physica C Superconductivity 01/2010; · 0.72 Impact Factor

Publication Stats

439 Citations
162.49 Total Impact Points

Institutions

  • 1968–2012
    • Politecnico di Torino
      Torino, Piedmont, Italy
  • 2011
    • INRIM Istituto Nazionale di Ricerca Metrologica
      Torino, Piedmont, Italy
  • 1996–2007
    • INFN - Istituto Nazionale di Fisica Nucleare
      Frascati, Latium, Italy
  • 1965–2007
    • Università degli Studi di Torino
      • Department of Physics
      Torino, Piedmont, Italy
  • 1997
    • Università degli Studi di Trieste
      • Department of Physics
      Trieste, Friuli Venezia Giulia, Italy
  • 1985–1993
    • Università degli studi di Cagliari
      • Department of Physics
      Cagliari, Sardinia, Italy
    • CERN
      Genève, Geneva, Switzerland
  • 1988
    • Tel Aviv University
      • Department of Physics and Astronomy
      Tel Aviv, Tel Aviv, Israel