Preparation And Properties Of Organic/Inorganic Nanostructures On Metal Surfaces

Nanostructures on metal surfaces have received extensive attentions because of its scientific significance and potential application.In the last few years,with the continuous development of experimental technology and computational theory,people have now been able to prepare and analyze nanostructures at the molecular scale.In this thesis,two typical nanostructures,water nanostructure and single-molecule rotor,were chosen as the research object.The scanning tunneling microscopy and density functional theory were used as tools to study their adsorption and properties on the metal surfaces.Studying water nanostructures on metal surfaces is not just of an important first step toward understanding the nature of water and ice,but also offer a possibility to solve practical problems such as environmental protection?water pollution?,clean energy?hydrogen production by decomposing water?,and the like.After decades of hard work,people have proposed a general model for water adsorption on metal surfaces.A single water molecule binds preferentially at the top site of metal atom with the molecular dipole plane nearly parallel to the surface.This binding mode favors interaction of the water 1b₁ delocalized molecular orbital with metal surface.The stronger the water-metal interaction,the lower the adsorption height.It is believed that the incredible richness in the water nanostructures is raised form the competition between the water-water interaction and hydrogen bonding.Especially,the greater the water-metal interaction,the greater the difference in height between water molecules in water hexamers.In addition,the stability of the bilayer structure is dependent on the specific water-metal interaction.In the past,the researches mainly focused on the metals such as copper,silver,ruthenium,palladium and platinum.However,there have been relatively few studies of the adsorption geometries and properties of water on the surfaces of bismuth?Bi?and cadmium?Cd?.Single-molecule rotor is another hot topic in nanoscience.In a molecular rotor,a molecule or a part of a molecule rotates with respect to the surface or another part of the molecule.As a typical nanostructure,it can convert external energy?thermal energy,chemical energy,electric energy or light energy etc.?into mechanical energy at the molecular level.Molecular rotor is an important part to build molecular machinery,such as molecular motors,nano-cars and so on.At present,people often use organometallic macromolecules to build single molecular rotors or molecular motors.However,there have been relatively few studies of the movement or rotation of TMPc on solid surfaces.In this thesis,the structure and adsorption mechanism of water clusters on the Bi?111?surface have been studied by STM experiments and DFT calculations.The effect of electric field on the adsorption of water on the Cd?0001?surface has also been discussed.Besides,single molecular rotor on Bi?111?were also characterized and analyzed at liquid helium and liquid nitrogen temperatures.The rotation of the molecules was controlled by STM tip.The main contents and results are as follows:1.Monodisperse water clusters on the Bi?111?surfaceWater molecules prefer to adsorb on the Bi?111?surface in the hexagonal arrangement to form large-scale arrays.The water hexamers on the Bi?111?surface have only one orientation.Interestingly,the water hexamer appearance in the STM images changes with the bias voltage:three bright spots appear under high bias and black holes under low bias.Theoretical calculations show that the tri-lobed protrusion can be traced to the buckling of the water hexamers on the Bi?111?surface.Further calculation reveals that there is only one orientation of water hexamers because Bi?111?has a special electronic structure and the Pauli repulsive force is minimized at the hollow position.The monodispersity of water clusters is due to the dominant hydrogen bond in the water structure on the Bi?111?surface.Double proton acceptor?less hydrogen bonds?make big?small?clusters less stable.2.The adsorption of water on cd?0001?surface and the effect of electric field on the stabilityThe adsorption of a single water molecule on the Cd?0001?surface is similar to that on other metal surfaces.However,different from Pt?111?and Be?0001?,where some small clusters on the surface are more stable,the larger the water cluster on Cd?0001?surface,the more stable they are.Energy calculations reveal that either single water molecules or small clusters,its adsorption will be enhanced in the presence of applied electric field.Electronic structure analysis reveals that a negative?positive?electric field can strengthen?weaken?the water-cadmium interaction.Structural optimization shows that the orientation of a single water molecule changes under an electric field.However,the formation of hydrogen bonds makes it difficult for water molecules in the cluster to response the electric field.Importantly,the stability of the water bilayer structure will change when the negative electric field is strong enough.3.Monitoring and manipulating single-molecule rotors on the Bi?111?surfaceAt the liquid helium temperature,the manganese phthalocyanine molecule on the Bi?111?surface is statically adsorbed at the top of Bi.Geometries optimization and STM simulation show that the structural change will lead to the change of the topography symmetry in the STM image.At liquid nitrogen temperatures,the manganese phthalocyanine molecules appear as flower-like structure.I-t spectral measurements and energy calculations indicate that the flower-like shape is the low-frequency image of a high-frequency manganese phthalocyanine molecular rotation.Importantly,we achieved the starting and stopping of manganese phthalocyanine rotors by controlling the distance between the molecules with STM tip.