Fig. 6 Cross Configuration.This is the fundamental unit in a dilute dimer row (see Fig. 12.) At lower temperatures this configuration is observed to be stable while at higher temperatures the energy barrier between this and the tie is more easily crossed. This conversion between crosses and ties sometimes leads to row creation, as can be seen on the Rows page of the Gallery. The cross was named by Wingerden et al. (see citations) because the rows on either side of the bright central spot are often strongly buckled. This gives the formation the appearance of an X or a cross.

Fig. 7 Filled vs. Empty State Images of a Cross. The empty state image reveals the cross's flanking monomers which are not visible in the filled state image. Note: the filled and empty state images are aligned; however, rows and troughs trade relative brightnesses under the imaging conditions.

Fig. 10 A-Dimer Pairs, a.k.a Twins. In our normal temperature range, around 400K, the twin is not common, but in a series of room temperature images we were able to observe this formation that had previously been identified by van Dam et al.* Note that the diagram shows the two ad-dimers slightly shifted from the centers of their rows toward each other, it also shows new substrate bonds that are believed to be formed. The skewed appearance of the twins in this image is due to sample drift during the imaging.

Fig. 11 Filled vs. Empty State Images of Twins.This image shows three Twins. The empty state image agrees with the diagram's off-center placement of the dimers in Fig. 11. While the two twins on the left of the image appear as quadruplets in the filled state image, they are seen as two separate twins in the empty state image. Again, the slight skewing of the twins is not a real effect, but is due to sample drift during the imaging.



*A. van Dam, J. van Wingerden, et al., Interactions between absorbed Si dimers on Si(001), Phys. Rev. B. 54 1557-1560 (1996).