First principles study of silicene symmetrically and asymmetrically functionalized with halogen atoms

Using first principles calculations with the hybrid exchange-correlation functional, we systematically investigated the structural and electronic properties of silicene symmetrically and asymmetrically (Janus) decorated with halogen elements. The calculations show that all the functionalized systems are direct-band-gap semiconductors. Even more remarkable, by carefully selecting the adsorption adatoms on silicene and applying elastic tensile strain, a direct-band-gap semiconductor with any value between 0.98 and 2.13 eV can be obtained. The formation energies indicate that all the silicene derivatives should be formed experimentally. The present study suggests a rather practical way for gap opening and modulation of silicene.