STM Research Of CO Adsorption On Cu(?) And Cl Adsorption On Silicene

As we all know that more than 80% catalysis is gas- solid catalyst in the world,which involves in the interaction between gas and solid surface.Because the CO adsorption activation on transition metals activate the important role of the catalytic process of CO, so CO adsorption have been the widely studied subject.Here we present a study of CO adsorption on Cu(?) and study it with scanning tunneling microscopy.During long period of adsorption under Ultra High Vacuum,there are many kinds of CO structures on Cu(?). While the adsorption time is short,CO will adsorb on Cu(?) around the defect firstly.As the adsorption time increase,there two kinds of structures,hexagonal(4× 4)and(6× 6),under LN2 temperature.But these two structures is unstable,because they one structure can transform to the other one.And there are also two structures,hexagonal(?3× ?3)R300 and honeycomb(4×4),under LHe temperature,.But the honeycomb(4×4)phase will occur phase change under LHe temperature and domain boundaries appear,and there are two angles between these boundaries,600 and 1200.Silicene,the Si analogue of graphene, is a promising material for electronic applications while it supplies an ideal interface with existing Si devices and takes advantage of tractable material technology. It is found that buckled silicene is a zero-gap semiconductor with bands crossing linearly at the Fermi level,which may attribute a massless Dirac fermion character to charge carriers. This possible extremely high carrier mobility makes silicene an ideal material, especially in FETs.However, compared with the bulk 4-fold coordination, the surface Si atoms in silicene are unsaturated. Thus, the reactive surface should be stabilized upon adsorption of foreign atoms to saturate the dangling bonds.In this dissertation,the halogenation of monatomic silicene sheet on Ag(?) was studied by scanning tunneling microscopy.We successfully synthesized silicene on Ag(?) using molecular beam epitaxy. Silicon can form various structures on Ag(?), according to the substrate temperature and coverage.Of these phases, the Ag-(4 × 4) or silicene-(3×3) is the simplest and most well understood one,We chose this phase as the model system for chlorine adsorption?Chlorine can adsorb on different Si atoms with different coverage.Chlorine will adsorb on the upper-buckled Si atoms,when the coverage is low.when the coverage of chlorine is saturated,the configuration of buckled Si atoms will change and there will be seven upper-buckled Si atoms,instead of six.Thus the unit cells apparently moves.but the lateral position of the whole lattice is fixed unchanged.In this configuration,there are six upper-buckled Si atoms in one half unit cell,and one upper-buckled Si atom in the other half unit cell.Once chlorine atoms adsorb on these seven upper-buckled Si atoms,the buckle degree of Si atoms will increase.The final adsorption structure share the same period with silicene-(3×3),but the two half unit cell is non mirror symmetry.