Dimer strings, anisotropic growth, and persistent layer-by-layer epitaxy

We propose that molecular-beam epitaxy of Si on Si(001) can proceed by nucleation and anisotropic growth of dimer strings. Such anisotropic growth, which changes orientation from layer to layer, imposes topological constraints of growth and can explain recently observed, puzzlingly persistent oscillations in surface diffraction intensities. We speculate that a complete picture for such epitaxy can be based on strings, coupled with an understanding of nucleation rules at steps and on terraces. © 1989 The American Physical Society.