The structural and vibrational properties of two-dimensional hexagonal silicon （silicene） and germanium （germanene） are investigated by means of first-principles calculations. It is predicted that the silicene （g...The structural and vibrational properties of two-dimensional hexagonal silicon （silicene） and germanium （germanene） are investigated by means of first-principles calculations. It is predicted that the silicene （germanene） structure with a small buckling of 0.44 ,~ （0.7/k） and bond lengths of 2.28 ,~ （2.44 .~） is energetically the most favorable, and it does not exhibit imaginary phonon mode. The calculated non-resonance Raman spectra of silicene are characterized by a main peak at about 575 cm-1, namely the G-like peak. For germanene, the highest peak is at about 290 cm-1. Extensive calculations on armchair silicene nanoribbons and armchair germanene nanoribbons are also performed, with and without hydrogenation of the edges. The studies reveal other Raman peaks mainly distributed at lower frequencies than the G-like peak which could be attributed to the defects at the edges of the ribbons, thus not present in the Raman spectra of non-defective silicene and germanene. Particularly the Raman peak corresponding to the D mode is found to be located at around 515 cm-1 for silicene and 270 cm-1 for germanene. The calculated G-like and the D peaks are likely the fingerprints of the Raman spectra of the low-buckled structures of silicene and germanene.展开更多
A first principles study on the stability and structural and electronic properties of two-dimensional silicon allotropes on a semiconducfing layered metal-chalcogenide compound, namely SnS2, is performed. The interact...A first principles study on the stability and structural and electronic properties of two-dimensional silicon allotropes on a semiconducfing layered metal-chalcogenide compound, namely SnS2, is performed. The interactions between the two- dimensional silicon layer, commonly known as silicene, and the layered SnS2 template are investigated by analyzing different configurations of silicene. The calculated thermodynamic phase diagram suggests that the most stable configuration of silicene on SnS2 belongs to a family of structures with Si atoms placed on three different planes; so-called dumbbell silicene. This particular dumbbell silicene structure preserves its atomic configuration on SnS2 even at a temperature of 500 K or as a ＂flake＂ layer （i.e., a silicene cluster terminated by H atoms）, thanks to the weak interactions between the silicene and the SnS2 layers. Remarkably, an electric field can be used to tune the band gap of the silicene layer on SnS2, eventually changing its electronic behavior from semiconducting to （semi）metallic. The stability of silicene on SnS2 is very promising for the integration of silicene onto semiconducting or insulating substrates. The tunable electronic behavior of the silicene/SnS2 van der Walls heterostructure is very important not only for its use in future nanoelectronic devices, but also as a successful approach to engineering the bang-gap of layered SnS2 paving the way for the use of this layered compound in energy harvesting applications.展开更多
The idea of stacking multiple monolayers of different two-dimensional materials has become a global pursuit. In this work a silicene armchair nanoribbon of width W and van der Waals-bonded to different transition-meta...The idea of stacking multiple monolayers of different two-dimensional materials has become a global pursuit. In this work a silicene armchair nanoribbon of width W and van der Waals-bonded to different transition-metal dichalcogenide （TMD） bilayer substrates MoX2 and WX2, where X = S, Se, Te is considered. The orbital resolved electronic structure and ballistic transport properties of these systems are simulated by employing van der Waals-corrected density functional theory and nonequilibrium Green＇s functions. We find that the lattice mismatch with the underlying substrate determines the electronic structure, correlated with the silicene buckling distortion and ultimately with the contact resistance of the two-terminal system. The smallest lattice mismatch, obtained with the MoTe2 substrate, results in the silicene ribbon properties coming close to those of a freestanding one. With the TMD bilayer acting as a dielectric layer, the electronic structure is tunable from a direct to an indirect semiconducting layer, and subsequently to a metallic electronic dispersion layer, with a moderate applied perpendicular electric field.展开更多
文摘The structural and vibrational properties of two-dimensional hexagonal silicon （silicene） and germanium （germanene） are investigated by means of first-principles calculations. It is predicted that the silicene （germanene） structure with a small buckling of 0.44 ,~ （0.7/k） and bond lengths of 2.28 ,~ （2.44 .~） is energetically the most favorable, and it does not exhibit imaginary phonon mode. The calculated non-resonance Raman spectra of silicene are characterized by a main peak at about 575 cm-1, namely the G-like peak. For germanene, the highest peak is at about 290 cm-1. Extensive calculations on armchair silicene nanoribbons and armchair germanene nanoribbons are also performed, with and without hydrogenation of the edges. The studies reveal other Raman peaks mainly distributed at lower frequencies than the G-like peak which could be attributed to the defects at the edges of the ribbons, thus not present in the Raman spectra of non-defective silicene and germanene. Particularly the Raman peak corresponding to the D mode is found to be located at around 515 cm-1 for silicene and 270 cm-1 for germanene. The calculated G-like and the D peaks are likely the fingerprints of the Raman spectra of the low-buckled structures of silicene and germanene.
文摘A first principles study on the stability and structural and electronic properties of two-dimensional silicon allotropes on a semiconducfing layered metal-chalcogenide compound, namely SnS2, is performed. The interactions between the two- dimensional silicon layer, commonly known as silicene, and the layered SnS2 template are investigated by analyzing different configurations of silicene. The calculated thermodynamic phase diagram suggests that the most stable configuration of silicene on SnS2 belongs to a family of structures with Si atoms placed on three different planes; so-called dumbbell silicene. This particular dumbbell silicene structure preserves its atomic configuration on SnS2 even at a temperature of 500 K or as a ＂flake＂ layer （i.e., a silicene cluster terminated by H atoms）, thanks to the weak interactions between the silicene and the SnS2 layers. Remarkably, an electric field can be used to tune the band gap of the silicene layer on SnS2, eventually changing its electronic behavior from semiconducting to （semi）metallic. The stability of silicene on SnS2 is very promising for the integration of silicene onto semiconducting or insulating substrates. The tunable electronic behavior of the silicene/SnS2 van der Walls heterostructure is very important not only for its use in future nanoelectronic devices, but also as a successful approach to engineering the bang-gap of layered SnS2 paving the way for the use of this layered compound in energy harvesting applications.
文摘The idea of stacking multiple monolayers of different two-dimensional materials has become a global pursuit. In this work a silicene armchair nanoribbon of width W and van der Waals-bonded to different transition-metal dichalcogenide （TMD） bilayer substrates MoX2 and WX2, where X = S, Se, Te is considered. The orbital resolved electronic structure and ballistic transport properties of these systems are simulated by employing van der Waals-corrected density functional theory and nonequilibrium Green＇s functions. We find that the lattice mismatch with the underlying substrate determines the electronic structure, correlated with the silicene buckling distortion and ultimately with the contact resistance of the two-terminal system. The smallest lattice mismatch, obtained with the MoTe2 substrate, results in the silicene ribbon properties coming close to those of a freestanding one. With the TMD bilayer acting as a dielectric layer, the electronic structure is tunable from a direct to an indirect semiconducting layer, and subsequently to a metallic electronic dispersion layer, with a moderate applied perpendicular electric field.
