Surface study and fabrication of low-resistivity contacts on Cu-1234 superconductor

The surface nature of CuBa/sub 2/Ca/sub 3/Cu/sub 4/O/sub 12-/spl delta// (Cu-1234) superconducting ceramics has been characterized by photoemission spectroscopy, and an improvement of their surface electronic structure for high performance contacts has been attempted, In photoemission spectra of the specimens which had been scraped by a diamond file in vacuum, a shift of Ba core signals towards the higher binding energy side and reduction of valency of Cu were observed. This indicates that the surfaces of the conventionally treated Cu-1234 should easily lose oxygen from the vicinity of (BaO)/(CuO/sub 2-y/)/(BaO) blocks. Due to this degradation, a high contact resistivity was observed on interfaces between Au and such surfaces. The annealing in ultra-high vacuum at a low temperature below 150/spl deg/C under atomic oxygen or O/sub 3/ beams developed an intrinsic surface-electronic-structure. Due to the treatment, contact resistivity as low as 1/spl times/10/sup 18/ /spl Omega/ cm/sup 2/ was reproducibly achieved.