$\mathrm{GaAs}\left(2511\right)$: A New Stable Surface within the Stereographic Triangle

The atomic structure of GaAs(2 5 11), a hitherto unknown stable surface, has been determined by in situ scanning tunneling microscopy and first-principles electronic structure calculations. This orientation is located within the stereographic triangle, i.e., far away from all low-index surfaces. A low-energy ( $1\times 1$) reconstruction containing arsenic dimers forms on the surface. The analysis of the surface structure shows that, for semiconductor surfaces, the gain in stability due to minimization of the number of dangling bonds is more important than the gain from rendering a semiconducting ground state.