Study On The Structure Stability And Ta Adsorption On MgF₂ Surfaces By Density Functional Theory

MgF2 crystal is widely used in the design and development of various optical thin films and multilayer photonic crystals, because of its following properties:high hardness, good thermal stability, low refractive index, higher transmissivity in the ultraviolet, visible and infrared range, low absorption and wide bandgap etc. For the interface of multilayer structures will impact its optical properties, the research on the interface structures of multilayer is very important. This paper selected and studyed the surfaces of MgF2 from its atomic level; Yet most experiments and theoretical calculation are focused on the thermal stability and bond properties of MgF2 bulk structure, its surface structural stability and its microcosmic principle is unclear, So how to simulate and expound these phenomenons from atomic level is very significant and important.While the interdiffusion in multilayer may also impact its optical properties by making the bandgap became narrow, the properties of some atoms adsorbed on MgF2 surfaces were also studied. The main contents are as follows.(1) The structural stability of four low index surfaces of MgF2 were studied using the first-principle pseudopotential plane-wave method. The total energy and surface energy were calculated, the stability of the four surfaces were compared, and the reason of different surface stability of MgF2 were also explained through the density of state and charge density distribution. The results show that the structural stability of MgF2 surfaces decreases in the following order:MgF2(110), MgF2(011), MgF2(010) and MgF2(001). The density of states of MgF2 shows that the DOS near Fermi energy and the production of new surface states are maily contributed by F 2p state. And more bonding electrons are in low level areas in (110) sueface, furthermore, due to the influence of surface, the charges of Fluorine atoms gather to the surface, which makes the surface electronegative and its activity increase.(2) The adsorption models of Ta on MgF2 (110) surface were also build and geometric optimized in this paper, the adsorption models were stable in structure. Systematically study wre carried on the adsorption of Ta on different positions of MgF2 (110) surface, the most easily adsorption position was given and explained. The results of the study indicate that:The adsorption of Ta on MgF2 (110) surfaces is chemical adsorption, and Ta apts to adsorb on the top site of F atoms, Charge density shows that after Ta adsorded on the surface, the charges of Ta atom transfered to F atoms.