From aperiodic nanolines to imperfect $\sqrt3\times\sqrt3$: a survey of bismuth overlayer structures on Si(001) and Si(111)

Bismuth overlayers on silicon surfaces are of considerable interest because of their surfactant properties in epitaxial germanium growth. Careful control of bismuth deposition parameters can result in a number of different surface structures, from the irregularly spaced, one-dimensional bismuth line system on Si(001) to the different phases of the $\sqrt3 \times\sqrt3$-R30$^\circ$ reconstruction on the Si(111) surface. The leitmotiv underlying all of these overlayer systems is the strain generated by the mismatch between the covalent radii of bismuth and silicon; manifestations of this will be illustrated through scanning tunneling microscope (STM) images. We will explore the evolution from the 2$\times$n reconstruction on (001) to the bismuth line surface, and illustrate the large-scale domain structure of the line system. A new type of defect structure on the bismuth-covered Si(111) surface will be described and examined in the context of surface strain.