B.D. Weaver

Microwave devices using YBa/sub 2/Cu/sub 3/O/sub 7- delta / films made by pulsed laser deposition

High-quality oriented thin films of YBa/sub 2/Cu/sub 3/O/sub 7- delta / with transition temperatures >88 K and critical current densities (at 77 K, zero magnetic field) >10/sup 6/ A/cm/sup 2/ have been produced by pulsed laser deposition on

Ion irradiation of electronic-type-separated single wall carbon nanotubes: A model for radiation effects in nanostructured carbon

The structural and electrical properties of electronic-type-separated (metallic and semiconducting) single wall carbon nanotube (SWCNT) thin-films have been investigated after irradiation with 150 keV 11B+ and 150 keV 31P+ with fluences ranging from 1012 to 1015 ions/cm2. Raman spectroscopy results indicate that the ratio of the Raman D to G′ band peak intensities (D/G′) is a more sensitive indicator of SWCNT structural modification induced by ion irradiation by one order of magnitude compared to the ratio of the Raman D to G band peak intensities (D/G). The increase in sheet resistance (Rs) of the thin-films follows a similar trend as the D/G′ ratio, suggesting that the radiation induced variation in bulk electrical transport for both electronic-types is equal and related to localized defect generation. The characterization results for the various samples are compared based on the displacement damage dose (DDD) imparted to the sample, which is material and damage source independent. Therefore, it is poss...

Proton-induced reduction of R sub s , J sub c and Tc in YBa sub 2 Cu sub 3 O sub 7 minus. delta. thin films

The authors explored the effect of 2-MeV H{sup +} irradiation on the superconducting transport properties of thin films of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} ({Tc}, J{sub c} (B = 0; 77 K, 4.2 K), and R{sub s} (36 GHz; T)). The inductively measured critical temperature {Tc} changed slowly and uniformly ({approximately}2 K per 10{sup 16}/cm{sup 2}) for fluences less than {approximately}3 {times} 10{sup 16}/cm{sup 2}. Beginning at {approximately}3-4 {times} 10{sup 16}/cm{sup 2}, the superconducting transition broadened and dropped more quickly with fluence. The critical current density measured at 77 and 4.2 K changed roughly linearly with fluence. The microwave {Tc} (as defined by the sharp transition in R{sub s} as a function of temperature) resembled the low-frequency inductive {Tc} measurement at low fluences but was depressed more strongly for large fluences. The residual surface resistance ({approximately}6-10 m{Omega}) was not affected for fluences up to 5 {times} 10{sup 16}cm{sup 2}. The sudden and reproducible reduction in the microwave {Tc} transition was interpreted as a sensitive indicator of disruption in the copper-oxygen chain sublattice, and the proton-induced change was compared to that observed in oxygen gettering studies of bulk materials.We have explored the effect of 2-MeVH+ irradiation on the superconducting transport properties of thin films of YBa2Cu3O7−δ [Tc, Jc(B=0; 77 K, 4.2 K), andRs(36 GHz;T)]. The inductively measured critical temperatureTc changed slowly and uniformly (∼2 K per 1016/cm2) for fluences less than ∼3×1016/cm2. Beginning at ∼3–4×1016/cm2, the superconducting transition broadened and dropped more quickly with fluence. The critical current density measured at 77 and 4.2 K changed roughly linearly with fluence. The microwaveTc (as defined by the sharp transition inRs as a function of temperature) resembled the low-frequency inductiveTc measurement at low fluences but was depressed more strongly for large fluences. The residual surface resistance (∼6–10 mΩ) was not affected for fluences up to 5×1016/cm2. We have interpreted the sudden and reproducible reduction in the microwaveTc transition as a sensitive indicator of disruption in the copper-oxygen chain sublattice and compared the proton-induced change to that observed in oxygen gettering studies of bulk materials.

Critical current enhancement in proton‐irradiated Tl2CaBa2Cu2O8 films

We have measured changes in the superconducting transition temperature Tc and critical current density Jc of epitaxial Tl2CaBa2Cu2O8 films upon exposure to 2 MeV protons. Jc was measured inductively at 4.2 and 77 K and in fields of H=0 and 0.2 T. At 77 K and H=0, Jc decreases monotonically with increasing fluence Φ. The rate of decrease is about 1.8 times greater than for YBa2Cu3O7 films, even though the rate of change of Tc with Φ is comparable. At 4.2 K, Jc is initially enhanced, even at H=0. The maximum observed increase is 34% (to 8 MA/cm2) at Φ≊1016 protons/cm2 and H=0.2 T. This enhancement is attributed to pinning of magnetic flux lines by proton‐induced defects.

Radiation effects in high temperature superconducting films and devices for the NRL high temperature superconductivity space experiment

The effects of proton irradiation on the performance of films and microwave devices made from the high temperature superconductors YBa/sub 2/Cu/sub 3/O/sub 7- delta / and Tl/sub 2/Ca/sub 2/BaCu/sub 2/O/sub 8/ have been measured and can be explained in terms of radiation-induced changes in material parameters such as surface impedance, critical current and transition temperature. Changes in material parameters can in turn be linked to atomic displacement effects. >

Particle-induced modification of thin film YBa/sub 2/Cu/sub 3/O/sub 7- delta / transport properties and microwave device performance

The authors examine the modification of the microwave surface resistance (R/sub s/), the critical current (J/sub c/), and the critical temperature (T/sub c/) resulting from 2-MeV H/sup +/ and 12-MeV Si/sup 4+/ irradiation of high-quality thin films of YBa/sub 2/Cu/sub 3/O/sub 7- delta / on LaAlO/sub 3/ substrates. For both ions, the change in T/sub c/ (R=0) and J/sub c/ (77 K and 4.2 K) was roughly linear with fluence. The change in these properties with fluence was quantitatively similar once corrected for differences in the rate of energy loss to atomic displacements. R/sub s/ was also measured as a function of temperature for the same films at 36 GHz using the cylindrical cavity end-wall replacement technique. High quality c-axis oriented films exhibited sharp transitions in R/sub s/ near T/sub c/, followed by a relatively temperature-independent R/sub s/ with a value of approximately 6 m Omega at 20 K. For irradiation with H/sup +/ and Si/sup 4+/ ions, the sharp transition in R/sub s/ was shifted to lower temperatures, although below the transition temperature R/sub s/(T) was unchanged. The loaded quality factor, or Q, of a 5.3-GHz ring resonator, patterned from a 500-nm film on MgO substrate, was measured as a function of temperature for 2-MeV H/sup +/ irradiation. While Q(T) was observed to decrease as a function of fluence, Q(T/T/sub c/) was invariant, as expected from the insensitivity of R/sub s/ to particle fluence below approximately 0.9 T/sub c/.