Construction And Surface Chemistry Of Ultrathin Two-Dimensional Structure On Metal Surface

The ultrathin two-dimensional(2D)structure formed on metal surface is a classic model system for surface catalysis research.Controllable preparation of 2D structures and studies of the interface chemistry and surface reaction,which includes the thin layer structures of graphene-based 2D materials and ultra-thin 2D oxide,will provide solid theoretical foundation and guidance for designing catalysts in actual systems.In this thesis,we focused on the studies in metal-supported single-layer hexagonal boron nitride(h-BN)and single-layer/double-layer ZnO structures,with main achievements shown as the following aspects:(1)A single-layer h-BN/Ni(111)model surface was prepared.We studied the adsorption,desorption and dissociation behaviors of CO on the h-BN/Ni(111)surfaces.It was found that CO can intercalate near-full-layer h-BN structures under ambient conditions.Compared with the clean Ni(111)surface,the desorption temperature of CO at the h-BN/Ni(111)interface was lower,and the desorption temperature was narrower,indicating the confinement effect of h-BN on CO surface chemistry.Besides,CO molecules could dissociate to form nickel carbide and graphitic carbon species at 0.1 mbar CO and 300 ?.(2)h-BN monolayer structures with different defect density have been grown on the surface of Pt(111).We dynamically imaged CO intercalation process under the h-BN structure using near ambient pressure scanning tunneling microscope(NAP-STM)under the near ambient CO pressures for the first time.For the defect-rich h-BN surface,CO intercalation occurred at 2 × 10-8 mbar CO;while the CO intercalation under defect-less h-BN required 0.1 mbar CO.Thanks to tunneling transparency of the top h-BN layer,the adsorption configuration of CO molecules on the Pt(111)surface can be directly imaged with STM.Through the comparison and analysis of the CO adsorption configurations on Pt(111)and h-BN/Pt(111)surfaces under the same conditions,we demonstrated the confinement-induced molecule enrichment effect within the 2D nanospace.(3)The formation of atomic oxygen species and the oxidation of metallic Zn on the surface of Au(111)were investigated.It was found that the oxidizing potential of different oxidants was O3>NO2>O2.Bilayer-ZnO overlayers with different coverages were prepared by molecular beam epitaxy(MBE)method using NO2 as oxidant,while monolayer ZnO with different coverages was firstly grown on Au(111)in O3.We further investigated the water activation and hydrogenation on the different ZnO overlayers.Water can be activated on the ultra-thin ZnO surfaces to form zinc hydroxide at room temperature and near ambient pressure condition,with the ratio of surface hydroxyl groups being 67%.Ultra-thin ZnO surfaces can also be hydrogenated by atomic H species to from the hydoxylated structure,with surface hydroxyl groups in 67%coverage on monolayer ZnO while only 50%on bilayer ZnO.Moreover,intercalation of oxygen at the ZnO/Au(111)interface has been observed when exposing the surface to O3,which can be further reacted with CO under ambient conditions.