Showing papers by "Zhifeng Ren published in 2000"
TL;DR: A two-layer process to deposit biaxially textured Tl-oxide films by electrodeposition (ED) on Ag-coated, single-crystal substrates is described in this article.
Abstract: We report on developing a two-layer process to deposit biaxially textured Tl-oxide films by electrodeposition (ED) on Ag-coated, single-crystal substrates. Pole-figure measurements of two-layer, electrodeposited (Tl,Bi)–(Sr,Ba)–Ca–Cu–O (TBSBCCO) films on 300 A Ag/LaAlO 3 (LAO), with thickness between 1 and 5 μm, clearly show strong biaxial texturing. The omega scan and phi scan of 1.6 μm (TlBi) 0.9 Sr 1.6 Ba 0.4 Ca 2 Cu 3 Ag 0.2 O x films indicate the full width at half maximum (FWHM) of only 0.92° and 0.6°, respectively, indicating a very high-quality film prepared by the ED process. Transport measurements for the electrodeposited, thallium-oxide-based superconductor films show values above 10 6 A/cm 2 at 77 K in zero field.
20 citations
TL;DR: In this paper, the growth of epitaxial Cr-doped (Tl,Bi)-1212 films on LaAlO3 substrates by pulsed laser deposition (PLD) and post-deposition annealing in static air has been achieved.
Abstract: Growth of epitaxial Cr-doped (Tl,Bi)-1212 films on LaAlO3 substrates by pulsed laser deposition (PLD) and post-deposition annealing in static air has been achieved. The films exhibit a high transport Jc of over 1.5 × 106 A cm-2 at 77 K and self-field. Tc values measured by the four-probe method are in the range 94-100 K. ICP emission spectroscopy measurement shows a thallium deficiency, with about 0.15 atom bismuth per formula in the film. XRD -2 , and scans show that the dominant phase is 1212, with excellent epitaxy. The film surface has typical PLD morphology as analysed by SEM. TEM analysis found some inclusions in the film, and HREM found that three 1201 layers exist between the interface of 1212 phase and substrate.
16 citations
TL;DR: In this paper, superconducting Tl-based, 1212-structured films were grown on both LaAlO 3 and CeO 2 /YSZ substrates by post-deposition annealing in flowing argon gas.
Abstract: Epitaxial (Tl,Bi)Sr 2 Cr 0.15 Ca 0.85 Cu 2 O y [(Tl,Bi)-1212] films have been successfully grown on both LaAlO 3 and CeO 2 /YSZ substrates by post-deposition annealing in flowing argon gas. These superconducting Tl-based, 1212-structured films on LaAlO 3 substrates have T c values in the range of 94–100 K, and J c values over 1.0×10 6 A/cm 2 at 77 K. The films are predominately 1212 phase, with excellent epitaxy as determined by XRD θ –2 θ , ω and φ scans. The films on CeO 2 /YSZ substrates have T c values in the range of 94–96 K, J c (77 K) values close to 6×10 5 A/cm 2 and excellent epitaxy on the CeO 2 buffer layers.
11 citations
TL;DR: In this paper, the superconducting state response is interpreted in terms of pair formation from non-equilibrium quasiparticles in the nodes of a d-wave superconding gap.
Abstract: We present measurements of the ultrafast time-resolved reflectance of optimally doped Tl2Ba2CuO6+δ. The superconducting state response is interpreted in terms of pair formation from non-equilibrium quasiparticles in the nodes of a d-wave superconducting gap. For T ⪆ T c the response shows evidence for dynamic superconducting fluctuations.
7 citations
TL;DR: In this article, the authors present measurements of the ultrafast optical response of BSCCO-2212 in the weak perturbation limit (photoexcitation density ≤ 10μJcm−2), where the superconducting condensate is destroyed.
Abstract: We present measurements of the ultrafast optical response of BSCCO-2212 in the weak perturbation limit (photoexcitation density ≤ 10μJcm−2), where we focus attention on the dynamics of electronic correlations associated with the pseudogap, and also in the strong perturbation limit (≥ 1JJcm−2), where the superconducting condensate is destroyed.
5 citations
TL;DR: In this article, the size of the carbon nanotubes was found to be closely related to the diameter of the dot, and it was found that the nanotube height was controlled by the growth time and the uniformity has been greatly improved by introducing a two-phase process of nucleation and growth.
Abstract: We have successfully fabricated many freestanding carbon nanotube arrays on silicon substrates. Two sizes of nickel dot arrays have been made by E-beam lithography. It has been found that the size of the carbon nanotubes is closely related to the size of the dot. Compared with our previous report on diameters of about 300 –400 nm, much thinner carbon nanotubes of 100 –150 nm have been made. With even smaller dots, it is expected that even thinner nanotubes of a few tens of nanometers could be made. The nanotube height is controlled by the growth time and nanotube uniformity has been greatly improved by introduction of a two-phase process of nucleation and growth.
3 citations
TL;DR: In this paper, a two-layer electrodeposition process was used to prepare Tl-Ba-Ca-Cu-O films with Tl 1212 and Tl 2212 stoichiometry.
Abstract: This paper reports on a study to convert electrodeposited Tl-oxide films to Hg-1212 using the cation-exchange process. A two-layer electrodeposition process was used to prepare Tl–Ba–Ca–Cu–O films with Tl-1212 and Tl-2212 stoichiometry. Electrodeposited Tl-films were also deposited with Bi and Sr substituted for the Tl and Ba, respectively and also reacted using cation exchange to attempt formation of Hg-1212. The superconducting transition temperature for the ‘‘non-substituted’’ films improved from 97 to 120 K after the cation-exchange process with a critical current density exceeding 2 � 10 6 at 5 K in zero field. The cation-exchange process for the Bi, Sr substituted films appears to be more difficult with no marked improvement in superconducting properties. 2001 Elsevier Science B.V. All rights reserved.
1 citations