A NOVEL BIDIRECTIONAL STEP-FLOW GROWTH MODE - C-60 ON GE(100) AND GAAS(110)

A novel epitaxial step-flow growth mechanism is revealed in the growth of C-60 overlayers on Ge(100) and GaAs(110) surfaces using scanning t unneling microscopy. in contrast to the conventional step-dow growth m ode, molecules attached to a substrate atomic step protrude well above its top edge and hence create an inverted step. This new step in turn acts as a nucleation site for subsequent growth over the upper terrac e, and flows in the direction of ascending steps, in conjunction with the step flow on the lower terrace in the direction of descending step s. This bi-directional step-flow growth mode is a direct consequence o f a large out-of-plane lattice mismatch, and thus should be common in the growth of large molecules or clusters on monoatomically stepped su bstrates. (C) 1997 Elsevier Science B.V.