Research On Hydrogen Bond Networks And Dynamics At Water-solid Interfaces

Water-solid interfaces play a crucial role in our daily life due to its ubiquitousness nature.The key to fully understand water-solid interfaces relies on revealing the microscopic nature of hydrogen bond networks,including their atomic structures,interfacial interactions,and related dynamics.With atomic-scale spatial resolution,Scanning Tunneling Microscope(STM)has presented unparalleled advantages in researches on water-solid interfaces.In this thesis,the hydrogen bond networks,interfacial interactions,as well as hydrogen bond dynamics on noble metal surfaces are explored using a home-build low temperature STM.In order to further explore the photo-induced dynamic behaviors in hydrogen bond,pump-probe laser system has been integrated into STM to obtain ultimate temporal and spatial resolution simultaneously.The contents of this thesis are as follows:1.Characterization of water clusters on Au(111)surface.With an STM tip functionalized by a water molecule,we have realized molecule-resolved STM imaging of various water clusters on Au surface,including water trimers,tetramers,pentamers and hexamers.The high resolution topographs provide deterministic evidence for the coplanar configuration of water hexamers,which is further corroborated by the first principle calculations in which the van der Waals correction has been properly implemented.Theconsistence between experimental observations and theoretical calculations not only solves the long-term debate on the configuration of water hexamer, but also directly manifests the crucial role of van der Waals interaction in constructing hydrogen bond networks.2.One-dimensional water chains and hydrogen bond dynamics.Two types of one-dimensional(1D)water chains,Armchair and Zigzag,are observed on noble metal surface with molecular resolution for the first time.By injecting tunneling electrons,various hydrogen bond dynamic behaviors are observed in 1D water chains,including chain reconfiguration and proton transfer through hydrogen bond chain.3.Upgrading of an ultrafast time-resolved scanning tunneling microscope.For more efficient coupling between laser and STM junction,we designed and fabricated a new STM scanner.The pulse delay system is upgraded to extend the measurement range to a longer time scale.New experimental scheme has been implemented to obtain higher signal to noise ratio.Finally,the upgraded system has been tested on a GaAs sample,demonstrating simultaneously temporal and spatial imaging of electronic density of states.