Onset of step antibanding instability due to surface electromigration

Heating by a direct electric current can produce step bunches:on vicinal se miconductor surfaces. Under extreme conditions, steps crossing from one bun ch to another bend sufficiently to create bands of steps of the opposite si gn (antibands). Unusual large scale scanning tunneling microscopy images re veal a mechanism where field-induced concentration gradients produce a spat ially variable step velocity that drives the antiband formation. A continuu m step model :allows quantitative analysis of crossing step shapes, yieldin g an effective charge for the diffusing adatoms of q(eff) = 0.13 electron u nits at 1270 degrees C.