Water adsorption lifts the (2 × 1) reconstruction of calcite(104)

The adsorption of water on calcite(104) is investigated in ultra-high vacuum by density functional theory (DFT) and non-contact atomic force microscopy (NC-AFM) in the coverage regime of up to one monolayer (ML). DFT calculations reveal a clear preference for water to adsorb on the bulk-like carbonate group rows of the (2 × 1) reconstructed surface. Additionally, an apparent water attraction due to carbonate group reorientation suggest island formation for water adsorbed on the reconstructed carbonate group rows. Experimentally, water is found to exclusively occupy specific positions within the (2 × 1) unit cell up to 0.5 ML, to form islands at coverage between 0.5 and 1 ML, and to express a (1 × 1) structure at coverage of a full monolayer. At low coverage, water exclusively occupies one specific position within the (2×1) unit cell of calcite(104)−(2×1). At higher coverage, water gradually lifts the (2×1) reconstruction until the fully water covered surface expresses a (1×1) structure.