The KPFM Measurement Of Au Atoms Absorbation On Si(111)-7×7 Surface At Atomic Resolution

Surface potential distribution is a very important property of materials,which affects various physical and chemical processes on the surface of materials,such as work function,chemical reaction,catalyst and chemical bond.The Kelvin Probe Force Microscope(KPFM)is one of the most powerful techniques for measuring surface potential and can be used to study the surface charge distribution of semiconductors,insulators and thin films at the atomic or nanometer scale.A major advantage of the technology is that it is not limited by materials,and many of the breakthroughs in high-resolution imaging have been made on surfaces that are inaccessible to other imaging technologies.KPFM is used to characterize the nanoscale surface potential by measuring the contact potential difference(CPD)between the cantilever tip and the sample.The frequency modulated mode KPFM(FM-KPFM)is highly sensitive to short-range interactions and has high spatial potential resolution,which enables real potential images at atomic scale to be obtained.In this paper,the self-built FM-KPFM measurement system was used to realize the measurement of KPFM on the surface of Si(111)-7 × 7adsorbed by Au with atomic resolution.The main research contents are as follows:The research status of Kelvin Probe Force Microscope at home and abroad is reviewed firstly and the principle of Kelvin Probe Force Microscope and the relationship between the forces of probe samples are introduced.Secondly,the system structure of the ultrahigh vacuum atomic force microscope is introduced.Including vacuum device,evaporation source,phase-locked amplifier,feedback control system.A high conductivity conductive probe was prepared by physical vapor deposition(PVD),in which a nanoscale iridium film was coated on the tip of a silicon-based probe.Scanning electron microscopy(SEM),transmission electron microscopy(TEM)and energy dispersive spectrometer(EDS)were used to characterize the prepared probe,and the effectiveness of the self-made conductive probe was verified,laying a foundation for the next KPFM experiment.Au atoms were evaporated on a clean Si(111)-7 × 7 surface using an electron beam evaporation source.The surface morphology of Au/Si(111)-7×7 at atomic scale and the high resolution measurement results of local contact potential difference(LCPD)were obtained by using a self-made ultra-high vacuum NC-FM-AFM/KPFM system at room temperature.The measured results show that Au atoms are easily adsorbed at the position of unfaulted half unit cell(FHUC).The corresponding model and physical explanation are also given.In conclusion,in this study,the morphology and potential of gold atoms on Si(111)-7×7surface were successfully measured by a self-made conductive probe under the Kelvin probe force microscope system with ultra-high vacuum,and the precision measurement of atomic resolution KPFM on the sample surface was realized,which plays an important role in promoting the development of precision measurement field.