Direct observation of an increase in buckled dimers on Si(001) at low temperature

The first low-temperature scanning-tunneling-microscope (STM) images of Si(001) are presented. It is observed that on cooling to 120 K the number of buckled dimers increases, confirming that dimers have an asymmetric character. Buckled-dimer domains of c(4×2) order are bounded by p(2×2) regions. Defects pin nearby dimers into a buckled configuration and act to smear out the transition to order. At room temperature dimers rapidly switch orientation leading to an averaged symmetric appearance in STM images.