The Nanopyramidal Reconstruction of Cu 2 O(111): a Long-standing Surface Puzzle Solved by STM and DFT

International audienceDespite the importance of cuprous oxide for industrial applications, the precise structure of its most stable reconstructed surface remains unknown. Here, by a combination of highresolution STM measurements and simulations based on a DFT-HSE approach, we challenge the previous interpretations of the Cu 2 O(111) (√ 3× √ 3)R30 • surface reconstruction, based on the removal of 1/3 of the under-coordinated surface oxygen atoms. We show that these models do not satisfy the shamrock-type features found by STM, i.e. their position in the Cu-O ring centers, the orientation towards the surface O cus atoms and the topographic height in the STM images. Moreover, they are thermodynamically unstable with respect to moving the vacancy subsurface, a property not recognized before which seems specific to the Cu 2 O (111) surface. We propose a nanopyramidal model of the (√ 3× √ 3)R30 • surface reconstruction which is free from all these shortcomings. Here, the shamrock protrusions seen in STM are formed by three copper adatoms located at the center of the Cu-O rings and capped by an oxygen atom. This structure profoundly differs from existing models of the Cu 2 O(111) surface, and would change common perceptions on its reactivity