Research On Properties Of Silicene Based On First-principles

Silicene,the two-dimensional single-atomic-layer silicon film with whose structure and electrical properties similar to graphene,has attracted widespread attention due to the unique potential of being compatible with silicon-based semiconductors.Herein,based on the first-principles calculation method,the structure,electrical and optical properties of silicene and Si?3×3?/Ag?4×4?epitaxial silicene?containing the Ag?111?substrate?have been calculated and researched with the aid of the Materials Studio,aiming to analyze the effect of the substrate on the properties of the silicene.Taking surface decoration of adsorption into consideration,the effect of single alkali metal?AM,such as Li,Na,K?adatom on the structure,electrical and optical properties of silicene has been studied,while the migration characteristics of single AM adatom on the surface of silicene also have been explored.Furthermore,the hydrogen storage characteristics of AM adatoms-decorated silicene have been investigated,exploring the influence of AM component?e.g.,Li?and mixed decoration of AM?e.g.,Li and Na?on the hydrogen storage performance.The conclusions are as follows:The band gap of silicene is 0 eV and presents the peculiar property of the Dirac-Fermion,whose?and?*energy bands near the Fermi energy level intersect with each other at the K point of the Brillouin zone.Due to the hybridization of the Ag substrate with Si atoms,the energy band of silicene is opened with a band gap of 0.29 eV.Silicene tends to absorb ultraviolet light and visible light,while the light absorption efficiency of silicene is decreased under the influence of the Ag substrate.Besides,electrons in silicene tend to absorb the incident electrons with energies of 8.10 eV and 2.25 eV by the use of the inelastic interaction,while the energy absorption tendency of the electrons in silicene slightly shifts toward the lower energy direction under the effect of the Ag substrate.Overall,the Ag substrate has a wide influence on the structure,electrical and optical properties of the silicene.The introduction of single Li,Na or K atom opens an energy band gap of 0.142 eV,0.074eV,and 0.066 eV,respectively,presenting characteristics of N-type semiconductor.It can be found that the hybridizations of Li-s,Na-s/p and K-s/p orbitals with Si-p orbitals play a significant role in the ionic bonding of Li,Na,K adatoms with silicene,respectively.Additionally,AM adatoms reduce the light absorption efficiency,and lower the energy loss peak at 8.10 eV with a shift toward the lower energy direction.The transition state search results show that the AM atoms are consistent in the migration selection between the adjacent hollow sites on the surface of silicene.The migration path is hollow-valley-hollow,and the corresponding migration barriers are 0.22 eV,0.14 eV and 0.10 eV,respectively.In general,different single AM adatom-decorated silicene have many similar properties in terms of structure,electrical,optical,and migration characteristics owing to the adsorption of the same family elements in periodic table.When it comes to the hydrogen storage properties of AM adatoms-decorated silicene,it is clearly observed that the maximum hydrogen storage capacity of Li-decorated silicene system increases with the enhance of the Li component.When the Li component raises up to 0.50,Li atoms are saturated with the maximum hydrogen storage capacity of 11.46 wt%and the average adsorption energy of 0.34 eV/H₂,well meeting the hydrogen storage standard set by the U.S.Department of Energy and meaning that the hydrogen storage can be theoretically improved by increasing the Li adsorption component to a saturated level.It can also imply that reasonably enhance the component of AM can effectively lead to a higher hydrogen storage capacity of silicene.In the case of Li-Na-decorated silicene,each Li and Na atom can absorb up to three and six hydrogen molecules,respectively,resulting in hydrogen storage capacity of 6.65 wt%with the average adsorption energy of 0.29eV/H₂.It can be mentioned that the maximum hydrogen storage capacity of Li-Na-decorated silicene is between that of Li-decorated and Na-decorated silicene under the same adsorption component,which shows that the mixed decoration of AM can tune the hydrogen storage performance of the single kind of AM adatoms-decorated silicene to a certain extent.Furthermore,combined with the analysis of the Mulliken charge population,the charge density difference and the density of states,it can be observed that the charge-induced electrostatic interaction and the orbital hybridization are the key factors of the hydrogen storage for AM adatoms-decorated silicene.