STEP INSTABILITIES - A NEW KINETIC ROUTE TO 3D GROWTH

Atomic force microscopy studies of Ge/Si(001) molecular beam epitaxy g rowth reveal a crucial new role of surface steps in the 2D to 3D trans ition. At or near step flow we show that S-A steps undergo a stress-dr iven triangular step instability. The resulting spatial variation of s urface strain, although small, can dramatically influence the activati on barrier for 3D island nucleation. This provides a surprising kineti c route for the onset of 3D growth associated with the apex regions of triangular steps.