Linear density of implanted ions as a function of the depth in a system irradiated with 0.25 GeV and 4.2 GeV Au-ions, respectively, as estimated by means of SRIM.EXE© simulations.
Line profile from the tapping mode AFM measurement included in the inset. The profile was taken perpendicular to the interface between the as-grown (left) and 250 MeV Au-ion irradiated (right) regions and was averaged along the vertical direction in order to reduce the effect of the YBCO film roughness.
(a) FESEM image of the interface between the as-grown (left) and the 250 MeV Au-ion irradiated (right) area, close to the edge of the device. The effect of HEHI bombardment is evident on the buffer layer (right up). (b) High-magnification FESEM measurement in correspondence to the boundary (indicated by black arrows) between irradiated (up)/as-grown (down) regions of the YBCO film. The image shows such interface crossing a single YBCO grain.
Optical image ( magnification) of a patterned YBCO sample with a linear array of microscale irradiated regions (indicated by white arrows). The superconducting pads were placed in order to pick up independent voltage contacts for each irradiated area. Sensitive areas were irradiated with different HEHI fluences. The highest fluence irradiations are visible also on the substrate as darker vertical stripes.
Normalized resistance vs temperature curves measured with constant bias current of two devices with different 250 MeV Au-ion fluences. The device with the irradiated region at was created on a strip wide with a sensitive element length (irradiated area length) of , the other device with has a strip width of and a sensitive element length (irradiated area length) of . The film thickness is 300 nm and the voltage contact distance along the strip is . The zero-dissipation temperatures, , for the irradiated and as-grown area, are marked by arrows. The unirradiated curve was measured simultaneously on other two voltage contacts on the strip with the irradiated area at (very similar unirradiated resistance vs. temperature characteristics were obtained on the other samples).
Normalized resistance vs temperature curves in applied magnetic field (perpendicular to the film plane). The after-irradiation zero-field curve is also depicted. It is remarkable to note that above the functional decoupling is lost because dissipation starts in the whole YBCO strip (at this temperature), as shown in the inset, where the magnetoresistance measurement is reported for both irradiated and unirradiated parts.
Voltage vs current curves in zero applied magnetic field at 81.2 K (strip width: , film thickness: 300 nm, irradiated area length: , voltage contact distance along the strip: ). The sensitive element displays a linear behavior while the unirradiated part is completely dissipationless for all the applied currents (voltage noise below 50 nV). Inset: voltage vs current curves in zero applied magnetic field at . At this temperature, outside the useful working phase diagram region for the functional decoupling, the irradiated part shows a nonlinear response and the and values, evaluated with the criterion, are and , respectively.
High-frequency noise spectrum of the device during the magnetoresistance measurement (, , , strip width , film thickness 300 nm, irradiated area length ). The high-frequency cutoff is associated to the fast movement of vortices whose speed is also limiting the maximum bandwidth of the device (operating in the flux-flow state).
Real-time resistance measurements of HEHI nanostructured and as-grown zones during uniform irradiation with 3.5 MeV proton beam pulses (flux about ). The thermoelectric origin of the voltage signal in the as-grown area was checked out by measuring with inverse bias current (inset).
Offline measurements of the device performances after radiation annealing with a 3.5 MeV proton fluence of . The device critical temperature was not degraded, as demonstrated by the resistance vs temperature plot (the curves collapse). The magnetic sensitivity was also unaffected by this proton fluence, as shown in the inset by the magnetoresistance measurements.
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