Ar ion implantation induced electrical and structural changes in epitaxial YBa 2Cu 3O 7- x thin films

Abstract

Epitaxial YBa 2Cu 3O 7- x superconducting thin films were implanted with 180 keV Ar ions at room temperature. Ion implantation induced superconducting and structural changes have been systematically studied with X-ray diffraction, high-resolution transmission electron microscopy (TEM) and electrical measurements. The experimental results showed that the superconducting transport properties of high-quality epitaxial YBa 2Cu 3O 7- x thin films could be controllably modified using Ar ion implantation. The sample went through the metal to semiconductor to insulator transitions with the increasing of fluence. It was found that the critical current density J c and the superconducting transition temperature T c significantly decreased with fluence. However, when J c (at 77 K, H=0) decreased by six orders of magnitude, T c only decreased from 90.5 to 77.5 K. The film implanted with Ar ions became a semiconductor at a fluence of about 1.2x10 13 Ar/cm 2, while its superconducting state completely disappeared for an Ar ion dose of about 2.2x10 13 Ar/cm 2. An Ar ion fluence of 5x10 14 Ar/cm 2 made the sample become amorphous with such high resistivity that it could be treated as an insulator. The TEM micrographs showed that the lattice frame of the sample was nearly unchanged under low fluence ion implantation. Only at high fluence was the structure completely destroyed. We suggest that the degradation of T c and J c may be due to the disordering of the oxygen sublattice, but the crystalline to noncrystalline transition may be caused by the collapsing of the other atomic sublattices.