Preparation and properties of precursor Ba–Ca–Cu–(O, F) thin films deposited from fluorides for superconducting Tl- and Hg-based films

The long-term stability of superconducting properties of Hg-based cuprate thin films is presented. The mercury-based films were synthesized from an air-stable Ba-Ca-Cu-(O, F) precursor prepared by thermal evaporation from fluorides BaF 2 , CaF 2 and metallic Cu. The stability of the films prepared was studied using x-ray diffraction patterns and their electrical properties. The main features of superconducting transition (the onset and the midpoint temperature, as well as the width of transition) remained unchanged during 18 months, but the zero-resistivity critical temperature decreased from 117.5 K to 112 K (about 4%) due to an elongated low-resistivity tail. The good stability of the Hg-based cuprate thin films can be attributed to the dense character of our films that did not show any evident grain boundary morphology. Therefore, we assume that the main reason for the film degradation (as a rule localized at the grain boundaries) was eliminated.

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Long-term stability of Hg-based cuprate superconducting thin films prepared from a fluoride precursor

Štrbı́k

Plesch

Chromík

et al. 2002

“…As a precursor, a 200 nm thick Ba-Ca-Cu-(O, F) film was deposited by sequential evaporation of BaF 2 , Cu and CaF 2 with an approximate stoichiometric ratio of Ba:Ca:Cu = 2:2:3. Then the deposition was followed by an ex situ vacuum annealing process at 700 • C at an oxygen partial pressure of 10 −5 Pa, gradually increased to atmospheric pressure in order to decrease the content of fluorine in the precursor film [9].…”

Section: Methodsmentioning

confidence: 99%

“…In this paper we report on the properties of Hg-based cuprate thin films grown on R-plane sapphire with a CeO 2 buffer layer. The air stable precursor Ba-Ca-Cu-(O, F) thin films [9] prepared on the base of fluorides (BaF 2 and CaF 2 ) were used. The films were mercurated with a source of mercury, which was an unreacted pellet of Re-doped Hg-Re-Ba-Ca-Cu.…”

Section: Introductionmentioning

confidence: 99%

Hg-based cuprate superconducting thin films prepared on CeO₂buffered R-plane sapphire substrate

Chromík

Sin²,

Štrbı́k

et al. 2001

Hg-Ba-Ca-Cu-O films have been grown on CeO 2 /R-plane sapphire substrates using a two-step process. First, a 200 nm thick Ba-Ca-Cu-(O, F) precursor film was prepared by sequential evaporation, then Hg-Re-Ba-Ca-Cu-O pellets as a source of Hg-vapour were applied using heat treatment. The prepared films were continuous with sufficient adhesion to the substrate and a maximum zero-resistance critical temperature of T C0 = 118 K. The x-ray diffraction measurements of all the prepared films confirmed the Hg-1212 phase as well as the minor Hg-1223 phase in some cases. We found that the best results were obtained at the mercuration temperature of 775 • C and an optimal annealing time within the range 0.5-5 h. The superconducting properties of the films prepared under unsuitable conditions were mostly improved after annealing in oxygen atmosphere. Darker parts of the film exhibited a different surface morphology and the presence of the Hg-1223 phase in plate-like grains.

“…High-quality MgB 2 thin films are not only especially required for microelectronics applications, but also for various basic studies of material properties. Several methods were so far applied to synthesize MgB 2 films: e-beam evaporation [2,3], thermal deposition [4] and/or pulsed laser deposition [5,6]. Usually Mg-B or B amorphous precursor films are first deposited, which must then be annealed at high temperatures in order to build the MgB 2 structure.…”

Section: Introductionmentioning

confidence: 99%

RBS characterization of MgB₂superconducting films annealedex situandin situ

Cheang-Wong

Jergel

Chromík³

et al. 2003

The elemental composition and depth profiles of MgB2 films prepared by successive e-beam evaporation as well as by thermal co-deposition of Mg and B components were investigated by Rutherford backscattering spectrometry (RBS). In the case of films deposited by e-beam evaporation we studied both Mg-B precursors and appropriate MgB2 films grown on glassy carbon, Si(100) and J-sapphire substrates annealed in situ. For the films co-deposited by thermal evaporation on R-sapphire substrates and annealed ex situ we investigated superconducting MgB2 films only. The Tco values of all MgB2 films ranged from 21 to 30 K. Because of a very fine granular structure of the annealed films, confirmed also by SEM observations, we could not identify any MgB2 phase from x-ray diffraction (XRD) patterns. On the other hand, Mg2Si phase has been detected by XRD on the film–substrate interface for the superconducting film deposited on Si(100) substrate. The RBS measurements were performed with a 3.1 MeV 4He+ beam. Under these conditions, the 16O(α,α)16 elastic resonance allowed us to detect oxygen in all studied samples especially in B layers. The depth profiles of precursors prepared by successive e-beam evaporation showed clearly the multilayer film structure consisting of B and Mg layers. A strong interdiffusion between B and Mg layers may be observed after an in situ annealing, but still some degree of non-homogeneous component distribution may be observed. On the other hand, the MgB2 films co-deposited by thermal evaporation and annealed ex situ are much more homogeneous, but a higher content of oxygen is present.