| Investigating the atomic and electronic structures of materials are of great importance to understand their catalytic,electronic,photonic,superconductivity etc.performances;the percentage of surface atoms of material significantly increases with its size decreasing,which fundamently affect its properties.In the past decades,tremendous advances have been made in determining the surface structures of the micro-sized crystals by conventional surface analytical techniques,represented by scanning tunneling microscopy(STM).However,it is still challenging to analyze the surface structure,surface stress,surface dynamics,surface chemistry and surface bonding of nanomaterial,through these conventional surface analytical techniques.Herein,through the state of the art environmental transmission electron microscope(ETEM),spherical aberration corrected TEM and in situ TEM holders in center of electron microscopy of Zhejiang University,we developed a series of methods to study nanomaterial’s surface behaviors under external environment by in situ TEM.Taking TiO2 etc.as examples,in these widely studied systems,we realized determining the surface atomic structure,investigating the atomic structures of minority surfaces and edges,observing surface atomic dynamics,evolution and surface catalytic reaction under external environment.These successful application cases of in situ TEM in those aspects,that the traditional surface analytical methods are difficult to apply,show the great application prospect of in situ TEM in surface science.The main work has been listed as follows:(1)For the first time,we determined atomic structure of TiO2(1×4)-(001)surface from side-view by in situ TEM,and provided the most convincing experimental evidence for the ADM model.This work ended the long-term debate concerning the atomic structure of this reconstructed surface.(2)For the first time,our experiments revealed the atomic structures of TiO2 minority surfaces,such as(102),(103),(301)etc.and several edges between different facets.(3)In oxygen environment and for the first time,we observed the formation process of the TiO2(001)-(1×4)reconstruction and the surface dynamic evolution between“1×3"、"1×5"and "1×4" surfaces,at the atomic scale.Combining DFT calculations,we revealed the stress-driving reconstruction mechanism.(4)Through Cs-corrected STEM,we in situ studied surface stabilities of(101),(100),(001),(102)etc.surfaces of anatase TiO2 simultaneously at the atomic scale.It was found that surface reconstruction and structural evolution would occur at the elevated temperature,to lower the systematic energy.Elaboration of stability of TiO2 from the perspective of surface structure well explained why phase transition temperature of anatase TiO2 nanocrystal is much higher than theoretical value.(5)With Pt nanoparticles clad by graphene as the sample,simultaneous comparison of catalytic activity between different surfaces of Pt was successfully achieved at atomic scale for the first time.Our in situ observations demonstrated that Pt(100)and(110)surfaces have higher catalytic activities than that of Pt(111)surface in catalytic oxidation of graphene.(6)The dynamic structural evolution of MoO2 nanowire in oxygen environment was observed at the atomic scale by our in situ experiments;We revealed an oscillatory dissolution of MoO2 nanowire-tip facets and simultaneous layer-by-layer regrowth of sidewall facets;Combining with DFT calculations,it was found the electron-beam-irradiation caused tip-facets’ oxygen-loss results in the change of the preferential growth facets and drives the morphology reshaping. |
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