Ca/Si(111) "3x1" reconstruction was the first anisotropic surface structure that I have studied looking for one-dimensional behavior. The quotation marks around "3x1" assignment are because of some controversy of the actual atomic arrangement: essentially almost all studies with diffraction techniques (LEED, RHEED) produce a typical 3x1 pattern. STM observations however indicate a 3x2 arrangement, which agrees with photoemission results. In fact, recent model of a 3x2 reconstruction in a similar Ba-induced system suggests the most elegant way to reconsile the various experimental observations.
An STM image of the rows of this reconstruction shows a "zig-zag" pattern typical for other 3x1 reconstructions on Si(111) (mostly alkali-induced).
9x3 nm2 filled states image (experiment in collaboration with F.M. Leibsle (UMKC))
There are two main types of structural models proposed for these zig-zag chains. First model (left image below) associates the observed bright protrusions with actual atoms (or atomic orbitals) arranged in a zig-zag manner. Models of the second type (right image below) assume a chain of ring-like structures instead, and associate the bright spots with two edges of the rings.
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Grey circles on the above images represent the protrusions seen in STM images,
unit cells for the structures are outlined with thick dashed lines.
While even some basic considerations such as typical bond lengths are not very consistent with a simple zig-zag chain of atoms, the ring-like model tends to explain the observed STM images well. Another strong supporting evidence for the ring-like structural element is the observation of the edge row features. Basically rows on the boundaries of the 3x1 domains are of bright-dark-bright structure consistent with the ring-like structural units, but not consistent with a double-wide-bright-dark structure expected for a chain-like arrangement.
Does this surface have a 1D metallic band? Go on to the PES results for the answer!
