Differences in Molecular Adsorption Emanating from the (2 × 1) Reconstruction of Calcite(104)

Calcite, in the natural environment the most stable polymorph
of calcium carbonate (CaCO3), not
only is an abundant mineral in the Earth’s crust but also forms
a central constituent in the biominerals of living organisms. Intensive
studies of calcite(104), the surface supporting virtually all processes,
have been performed, and the interaction with a plethora of adsorbed
species has been studied. Surprisingly, there is still serious ambiguity
regarding the properties of the calcite(104) surface: effects such
as a row-pairing or a (2 × 1) reconstruction have been reported,
yet so far without physicochemical explanation. Here, we unravel the
microscopic geometry of calcite(104) using high-resolution atomic
force microscopy (AFM) data acquired at 5 K combined with density
functional theory (DFT) and AFM image calculations. A (2 × 1)
reconstruction of a pg-symmetric surface is found
to be the thermodynamically most stable form. Most importantly, a
decisive impact of the (2 × 1) reconstruction on adsorbed
species is revealed for carbon monoxide.