Silicene on Zirconium Carbide (111)

A silicon monatomic layer (i.e., silicene) forms an ordered phase on the surface of ZrC(111) in the 2 ? 2 periodicity of the substrate. For the first time, phonon dispersion relations were measured using high-resolution electron energy loss spectroscopy (HREELS) on a silicene sheet. The atomic structure and phonon dispersions were calculated using ab initio density functional theory. Nearly all the surface-localized phonon modes were well reproduced, and especially the dipole-active phonon modes well corresponded to the peaks in the specular HREEL spectrum. The optimized atomic structure was a distorted silicene on the Zr-terminated ZrC(111), in which the ?3 ? ?3 unit cell of Si6 coincides with the 2 ? 2 unit of the substrate ZrC(111). In the unit cell, one Si atom sits on the on-top site of the Zr substrate; three atoms are placed at the bridge sites of the substrate; and two other atoms are on the 3-fold hollow sites above the third layer (C) and above the fourth layer (Zr). This structure is prevalent on several metal substrates.