Atomic Scale Au/Si(111)-(7×7) Study On Surface Charge Measurement And First Principle Calculation

It has been a convenient method for semiconductor researchers to study the surface adsorption mechanism and the adsorption potential difference between metal and semiconductor,and the probe has become a more accurate method for researchers to study the surface adsorption mechanism of metal at the same time.In this paper,the adsorption structure properties and local contact potential energy difference of Au on Si(111)-(7×7)surface were studied by self-made ultra-high vacuum non-contact Kelvin probe force microscopy,and calculated by differential charge density.The charge density distribution of the lowest energy point of Au adsorbed on Si(111)-(7×7)surface is obtained,and the mechanism of charge transfer between Au atom and Si(111)-(7×7)surface is analyzed.Then,the morphology and local contact potential difference of atomic scale Au adsorbed Si(111)-(7×7)surface are measured at room temperature,and the triangular delocalized adsorption AFM morphology of a single gold atom in the semi crystal cell of Si(111)-(7×7)is obtained,and this phenomenon is analyzed.Finally,combined with simulation and KPFM experiment,the reason for the difference of local contact potential energy difference measurement results in the process of Au adsorption is analyzed.This study is helpful to promote the development of accurate measurement of surface charge of various materials,and is expected to provide some insights into the charge characteristics of metal adsorbed semiconductor surface.The main research contents are as follows:Firstly,various potential measurement methods and the research status of metal adsorption semiconductor surface at home and abroad are reviewed.The existing potential measurement methods are described from three aspects: photoelectric effect,electron beam induced current and electrostatic interaction.At the same time,the research status of metal adsorption on semiconductor surface is also introduced from the charge state in the adsorption process,single atom adsorption and metal nano clusters.Secondly,the principle and measurement method of Kelvin probe force microscope are introduced.This paper mainly introduces the measurement principle of AFM and the relationship between probe and sample force,and focuses on the principle of KPFM,including the definition of work function,contact potential difference and the measurement principle of KPFM system under different types.Next,the components of ultra-high vacuum AFM and KPFM are introduced,including the conditions required for the generation of vacuum system,vacuum pump and vacuum chamber device,the principle of electron beam evaporation source and infrared thermometer,the structure of probe and sample holder,which paves the way for the smooth progress of KPFM experiment.The corresponding Si(111)-(7×7)atom model is established,and through the first principle calculation,the optimal adsorption position of the atom is studied in combination with the adsorption energy and binding energy.Through the calculation of differential charge density,the charge density distribution diagrams of Au adsorbed at different positions on the Si(111)-(7×7)surface are obtained.For the differential charge density of the Si(111)-(7×7)surface with no Au atom adsorbed and the position with the lowest energy of Au adsorbed on the Si surface,To explore the physical problems such as charge transfer and chemical bonding in the adsorption process,and combined with the KPFM experiment at room temperature,the reasons for the difference of LCPD measurement in the experiment are analyzed in detail.