Cadmium Modified Rutile Titanium Dioxide (110) Surface Structure And Nature

Using DFT-LDA method we have investigated rutile TiO₂(110) surface relaxationand the adsorption properties of Cd on the TiO₂(110) surface. The stable adsorption site,electron structure and charge transfer for the Cd atoms have been analyzed. The resultsindicate that the relaxation phenomena existed obviously on the TiO₂(110) surface. Therelaxation will influence on properties of system, so surface relaxation must beconsidered in studying surface reaction.At different coverages, different characters have been found. The adsorptionenergy increases with decreasing of coverage. The stable adsorption site for Cd atoms issame on the TiO₂(1×1) surface and TiO₂(1×2) surface, also the optimized geometrieswhich Cd bond with two bridging O atoms and one plane O atom, namely geometry B.On these two surfaces, the Cd 5s and Cd 5p states have obvious interaction, so wepredict that one dimension chain structure has been formed in the direction of [001] ofCd. On the TiO₂(2×1) and TiO₂(2×2) surfaces, Cd presents another geometry which Cdbond with two plane O atoms and one bridging O atom, namely geometry A. Withdecreasing of coverage, the trend to form this geometry increased.After adsorption, Cd atoms lose its electrons. Electrons transfer to bridged oxygenwhich conjoint with Cd and localize on it. The unsaturated bond of oxygen acceptedelectron from Cd atoms. It weakens the bond between bridging O and sixfoldTi andmakes it become longer. The charge of sixfoldTi is close to it in the bulk. FivefoldTiatoms accept little electron, and can not be deoxidized.The action between Cd and bridging O is the main factor which decides whetherthe adsorption is stable. There is a mainly interaction between Cd 4d states and bridgingO 2p states. The Cd 5s states and bridging O 2p have some interaction too. The Cd 5sstates, O 2p states, Ti 3d states appear in the same position, Cd, O and Ti form thespecial metal-oxygen-metal interaction.