Surface reconstruction of ultrathin silicon nanosheets

► Discovery of a new surface structure specific to a double-layer Si nanosheet. ► The new surface structure can be labeled as Si(1 1 1)-2 × 2. ► This structure has a larger band gap than the bulk Si(1 1 1)-2 × 1 surface. ► Vibrational properties of the nanosheet reflect the distortion in tetrahedral order. ► This nanostructure is significant for electronic devices and sensor applications.