Figure 1 shows two consecutive images of an Au(lll) terrace immersed in an acidic solution containing traces of CI" ions and polarized at positive potentials. The progressive growth of the holes, one atomic diameter deep, provides clear evidence that the corrosive attack takes place preferentially at their edges, probably because the simultaneous binding of more than one chloride ion to the same gold atom is required to cause the formation and desorption of the water-soluble AuCLt complex.

Fig. 1. Two consecutive images of the same 267 nm x 267 nm area of an Au(ll 1) electrode in 10 mM H2S04 +10 |xM NaCl under conditions of anodic corrosion. E=0.95 V/SCE and E^ = -650 mV with I, = 2 nA and a W tip.

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