ELECTRIC-FIELD-INDUCED TRANSITIONS ON THE (110) SURFACES OF NOBLE-METALS

Electric-field effects on the transition between the reconstructed and unreconstructed states of (I 10) noble-metal surfaces in contact with electrolytes are investigated theoretically. Two models of different complexity are used to describe the transitions between the 1 X 2 ''mi ssing row'' and the 1 X 1 structures. These are the Ising model and th e ''step-excitation'' model which is a variant of a solid-on-solid mod el, used earlier in the description of Ising and roughening transition s on (I 10) noble-metal surfaces in ultrahigh vacuum. A suggested proc edure of parametrization of the model parameters with the surface char ge of the metal leads, finally, to a phase diagram in the ''temperatur e-surface-charge-density'' plane. The diagram shows that the transitio n between the reconstructed and unreconstructed states, which follows the charging of the surface towards more positive values, passes throu gh a narrow intermediate region of charges where the surface is disord ered. This is an ''Ising disorder'' and/or roughening, depending on th e type of the model and the relation between basic parameters. This an alysis explains why the transition induced by tuning the electrode pot ential in the electrochemical cell is possible at room temperature, wh ereas these surfaces in ultrahigh vacuum deconstruct at much higher te mperatures; it is in line with the published observations of an interm ediate disordered region by in situ x-ray diffraction and scanning tun neling microscopy.