Ren Congxin

THE ANISOTROPY OF THE CURRENT-CARRYING CHARACTERISTICS OF YBCO FILM FABRICATED BY MAGNETRON SPUTTERING

The anisotropy of the current-carrying characteristics of YBCO film fabricated by magnetron sputtering has been investigated. It is shown that the critical current density Jc parallel to the (ab) basal plane is highly anisotropic with respect to theta , the angle between the magnetic field and the c axis. This anisotropy increases with increasing magnetic field. In addition to intrinsic pinning, it is suggested that extrinsic pinning from the planar defects of stacking faults may also contribute to anisotropic pinning. The I-V curves also show anisotropy with theta , and at lower voltages they could be well fitted by the power law V=Aln. The value of n decreases with increasing magnetic field and it could be fitted by n=KH-m. n varies periodically with theta as Jc; the higher Jc is, the larger is n.

Effects of flourine ion implantation on superconducting properties of YBa2Cu3O7-x

The effects of fluorine ion implantation on superconductivity in YBa2Cu3O7-x thin films have been studied using resistance measurements and X-ray diffraction patterns. Damage created by nuclear energy loss processes degrades both the transition temperature and the critical current density. However, the onset temperature and X-ray diffraction patterns almost remain the same until the critical fluence of 2.7×1013 ions/cm2. At low ion fluences, the data from measurements suggest that ion implantation does not destroy the superconducting property within granular cells, but destroyes the weak links between grain boundaries. At high ion fluences, the material goes continuously through the metal to semiconductor transition. At still higher fluences a crystalline to amorphous transition occurs, and the sample becomes insulator.

Reactive ion beam etching characteristics of LiNbO3

The dependence of the etch rate for LiNb03 on ion beam energy, beam current density and gas flow rate during reactive ion beam etching (RIBE) with CF4 and CHF3 gases have been examined. The influence of the gas flow rate and the pressure in the target chamber on the etched surface topography have also been investigated. The reason for the surface roughening is discussed. The change of the relative dark conductivity of LiNbO3 surface etched by different ions is given. Experimental results show that RIBE can be successfully applied to etching of the surface acoustic wave devices.

Ar Ion Implantation Induced Tc Degradation of YBa2Cu3O7-x Thin Films

The Ar ion implantation induced changes of structure and transport properties of YBa2Cu3O7-x thin films were studied as a function of fluence. Both the zero resistance temperature Tc and the critical current density Jc decrease rapidly with fluence, however, the transition temperature onset almost remains constant at low fluences. At dose of 1.2 × 1013 Ar/cm2, the sample has a metal to semiconductor phase transition. When the fluence further increases, a crystalline to amorphous phase transition occurs, and the sample becomes insulator.

Superconducting properties and structural perfection of epitaxial YBa2Cu3O7-x thin films

High quality epitaxial YBa2Cu3O7-x thin films have been successfully prepared by dc magnetron sputtering deposition, on (100) and (110) aligned SrTiO3, LaAlO3 and yttria-stabilized zirconia (YSZ) substrates. The films showed zero resistance around 90 K and had a Jc (at 77 K, H = 0) over 106 A/cm2. It was found that superconducting properties and structures of the films were strongly dependent on oxygen pressure and substrate temperature. The epitaxial structure of the films have been studied by x-ray diffraction, Rutherford backscattering and channeling spectroscopy, x-ray double-crystal diffraction and transmission electron microscopy. The experimental results demonstrated that the epitaxial YBa2Cu3O7-x films had excellent superconducting properties and quite perfect structure.