Uniform, self-organized, seven-step height Pb/Si(111)-(7X7) islands at lowtemperatures

An unusual growth mode has been observed during low temperature growth at T =185 It in the system Pb/Si(lll)-(7 x 7) with the formation of uniform seve n-step, steep-edged, flat-top islands up to coverages theta=7.5 ML. The evi dence is based on the spot profile analysis-low-energy electron diffraction diffracted intensity distribution as a function of k(parallel to), k(z) th e parallel and normal components of the momentum transfer which show sevenf old oscillations over the range in k(z) where single step oscillations are expected. The formation of these highly uniform, self-organized structures implies that unconventional kinetic mechanisms operate at these low tempera tures.