composition of the alloy as determined by microanalysis. The bulk materials were first cut into 1 mm thick sheets (1 cm 1 cm), mechanical polished with silicon carbide paper and diamond polishing paste and subsequently electropolished at 40 V for approximately 10 s in a mixed solution of 80% HClO4 and 20% CHCOOH below 0 C. The sheets were then cleaned for 30 min using an ultrasonic bath with acetone, alcohol and deionized water sequentially