Electrochemical Coating of HTSC Materials

The metallization of local regions of HTSC surfaces is being studied in connection with the problem of junction fabrication. In this case, the adhesion that determines the ohmic resistance on the HTSC/metal interface is of greatest importance. 

Another important problem is the elimination of the chemical interactions between contacting phases and also of the diffusion of metal atoms into the oxide bulk [487 89], One example is the operation of commonly used indium junctions, which are convenient because films of this soft metal and its alloys can be applied mechanically [490], This fact stimulates the quest for low-temperature techniques for junction fabrication. It is known that silver, gold, and copper, and also probably platinum [202] and palladium [487], are most suitable because of their weak interaction with HTSCs. 

Unfortunately, the electrodeposition of metals summarized in Table 4 is accompanied by increased HTSC degradation under cathodic polarization [53, 55]. In nonaqueous media, electrocrystallization processes can be inhibited due to the peculiarities of the intermediate Cu+ species solvation [286]. Moreover, the surface morphology of deposits can be adversely affected by the formation of dendrites this can be overcome by the addition of a brightening agent [497]. 

Special studies with ring-disk electrodes showed that only metals with relatively positive deposition potentials silver and mercury [53, 494] and also probably copper can be cathodically deposited on HTSC substrates without partial reduction of the oxide surface. HTSC-silver composites are fabricated by multistage techniques that include an electrodeposition stage [498, 499]. It has been noted during deposition of silver and copper that their incorporation into the BSCCO lattice is possible (0.01 and 0.4 atom per molecule, respectively) with the formation of substituted phases [495]. 

In recent years, electrochemical metallization of semiconductors [500-502], including photoassisted processes [503, 504], has been investigated extensively. The experience gained in these experiments on the controlled deposition of ultrathin films is yet to be applied to HTSCs. 

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