Investigation Of The Dynamic Behaviors And Properties Of Interfacial Water By Atomic Force Microscopy

Interfacial water is ubiquitous in nature,involving physical and chemical process and biological functions.The interaction between water and interface plays an important role in the fields of friction,recognition and expression of organisms,catalysis and electrochemistry.Due to the limitation of research method,the investigation of interfacial water has been confined to the theoretical stage in the past.In recent years,the development of scanning probe microscopy has provided a powerful tool to study the structure,dynamic behavior and properties of interfacial water molecules.However,there are still many problems worthy of discussion for the interface water layer under atmospheric conditions,which need to be further studied and solved.In this thesis,atomic force microscopy is used to explore the factors affecting the dynamic behavior of interfacial water and its effects on the interface properties,including the electrical/magnetic properties,friction properties,etc.The contents of this thesis include the following chapters:Chapter I is a comprehensive introduction of the research background.From the invention of atomic force microscopy,the working principles and main working mode of atomic force microscopy are introduced.The research progress of atomic force microscopy in the field of interfacial water is introduced in detail,including gas-solid interfacial water,liquid-solid interfacial water and solid-solid interfacial water(confined water).Finally,the basis for the selection of the topic and the research content of this thesis are summarized.In chapter Ⅱ,the micro-nano structure and thermodynamic property of icelike water molecules at the interface of graphene and SiO2/Si were investigated by in situ heating atomic force microscopy.The effect of the trapped interfacial icelike water layer on the charge transfer between graphene and SiO2/Si substrate was also investigated.The scanning Kelvin probe microscopy surface potential mapping shows that the graphene is electronically modified by the icelike water layer as the electron density transfers from graphene to icelike water layer,resulting in hole-doping to the graphene,which was also confirmed by the graphene field effects transistor electrical transport measurements.In addition,the density functional calculations provide indepth insight into the electronic contributions of the ice like water layer to the graphene and the charge transfer mechanism.This research will improve our ability to manipulate graphene’s electronic properties for diverse applications such as humidity sensors.In chapter III,magnetic force microscopy based on atomic force microscopy was employed to investigate the effect of confined water on the magnetic property of mechanically exfoliated two-dimensional nanomaterials on mica substrate,such as MoS2 and graphene.By analyzing the phase shift,we found that the MoS2 nanosheets had magnetic response and the presence of confined water weakened the magnetic response of MoS2 to some extent.Similarly,confined water also weakened the magnetic response of graphene on mica.We consider that the presence of confined water affects the charge transfer of MoS2,leading to the change of magnetic response.The results of the surface potential of scanning Kelvin probe microscopy showed that confined water played the role of electron doping on MoS2 and some electrons transferred from confined water to MoS2,result in the change in the magnetic response.The result of this chapter has important guiding significance for regulating the magnetic properties of two-dimensional nanomaterials.In chapter Ⅳ,the microstructure and dynamic behavior of icelike water layer on mica were visualized by high resolution atomic force microscopy and the mechanism of water growth was investigated.The water growth can be well controlled by adjusting mechanical force and line density during the scanning.Additionally,thermal stability and growth state of the ice-like water under the competitive effects of tip-induced and temperature were also investigated.Lateral force microscopy(LFM)was performed to study the friction between the tip and mica surface and the results show that the water adlayer can reduce the friction dramatically.This study indicates the implementability of observation and manipulation of water on substrate under atmospheric conditions,advancing our cognition of interface science.