A STRAIN-RELIEVE TRANSITION IN EPITAXIAL-GROWTH OF METALS ON SI(111)(7X7)

Pronounced RHEED specular beam intensity oscillations have been observ ed during the growth of several metals on a Si(111)(7 X 7) substrate a t low temperature (100 K), showing that the metals grow in a layer-by- layer fashion. For all metals studied three regimes can be distinguish ed. Up to one or two monolayers the variation of the reflected intensi ty is due to changes in the surface structure rather than surface morp hology. Next, a limited number of oscillations with an ill-defined per iod appears. Most surprisingly, however, in most cases a sudden reviva l of the oscillations with a much more regular period is observed. It is suggested that this phenomenon is caused by a transition from a lat tice-matched to a relaxed layer-by-layer growth mechanism.