Si Monomer Trapping at Steps and Islands on the Si(001) Surface*

Image 1: Dual-polarity images of a submonolayer of Si atoms deposited on the Si(001) surface. The filled (occupied) states image is on the left and empty (unoccupied) states image is on the right. The image contrast is highly bias dependent. The single-dimer-wide island in the upper right (arrow) appears as a broad band in the filled states and as two thinner stripes in the empty states. Individual monomers can be seen in the empty states images bound at the end of the rebonded-SB dimer rows. (See also Image 5 below.) (GIF 81kb)



Image 2: Model of the Si(001) surface. There are two types of steps on the surface. Step segments that are perpendicular to the substrate dimer rows are called SA and steps that are parallel to the substrate dimer rows are called SB. Furthermore, SB steps that terminate on the substrate dimer rows are called rebonded SB and those that terminate between the substrate dimer rows are called nonbonded SB. Monomers (labeled "M") can become trapped at the ends of rebonded-SB type dimer rows with a binding activation barrier of ~1.0 eV. While the ends of rebonded-SB dimer rows are active sites for the capture of monomers, nonbonded-SB and SA steps are inert. (GIF 11kb)



Image 3a), b): STM movie images of a monomer swapping between two traps terminating on the same substrate dimer row. These data were acquired at 105 C. The two traps are separated by 11 and 3 lattice sites in a)[left] and b)[right] respectively. (MPEG format 107kb, 118kb)



Image 4a), b): STM movie images of a monomer swapping between nearest-neighbor traps. The swapping rate is about an order of magnitude faster between nearest-neighbor traps than between isolated traps. a)[left] Two traps located at neighboring dimer rows of a small island. b)[right] A monomer shared by 4 neighboring traps located at an SB step. (MPEG format 73kb, 84kb)



Image 5: Dual-polarity images of deposited Si atoms at an SB step acquired at room temperature. The filled states image is on the left and empty states image is on the right. Many of the trap sites located at the step are occupied by monomers. Although clearly evident in the empty states image, this type of information would be difficult to obtain from filled-state imaging. (GIF 66kb)