| The mechanism and process of metal adsorption on semiconductor surfaces have been a popular research subject.Notably,with the advancement of Kelvin probe force microscopy(KPFM)technology in recent years,the characterization of metal adsorption on semiconductor surfaces can achieve higher resolution,providing a more convenient and accurate technical means for studying metal adsorption on semiconductor surfaces.Based on this,the main research content of this paper is as follows: The present investigation utilized non-contact frequency modulation Kelvin probe force microscopy(NC-FM-KPFM)as the analytical technique to investigate the charge distribution and ad-sorption characteristics of individual gold(Au)atoms and clusters on the Si(111)-(7×7)surface,thereby enabling the observation of these phenomena at room temperature.(1)The objective of this study is to investigate the adsorption behavior of Au atoms on the Si(111)-(7×7)surface using a custom-built ultra-high vacuum Kelvin probe force microscopy(KPFM)system.By employing this technique,the adsorption position and topography of Au atoms with varying atomic numbers on the Si(111)-(7×7)surface were analyzed,providing valuable insights into the atomic-scale topography of the system.The scan control capability of the KPFM system allowed for precise measurement of the sample topography,enabling the characterization of individual Au atoms and Au clusters at different adsorption sites on the surface.This approach provides a comprehensive understanding of the adsorption process and the distribution of Au species on the Si(111)-(7×7)surface.The successful characterization of atomic-scale topography provides valuable information that can contribute to the further understanding of the properties and behavior of the Au/Si(111)-(7×7)surface.The results showed that Au adsorbs in both single-atom and cluster forms.Among them,Au clusters with six atoms in a hexagonal structure are adsorbed on the three center adatoms of the faulted half unit cell(FHUC)of Si(111)-(7x7);while single Au atoms are adsorbed on the center adatoms of the un-faulted half unit cell(UHUC).(2)The study investigated the interaction force between Au atoms and surface atoms in Si(111)-(7×7)using ultra-high vacuum Kelvin probe force microscopy.Atomic identification was achieved by analyzing atomic characteristics at specific positions on Au/Si(111)-(7×7).The short-range chemical forces,as well as the attraction and repulsive characteristics of the needle tip during the interaction with the sample,were described using Z Specscopy based atomic force spectrometry measurements.The chemical force of the surface was modified by the low coverage adsorption of Au atoms on Si(111)-(7×7),saturating the surface hanging bonds.The utilization of interatomic force spectroscopy facilitated the identification of distinct Au adsorption sites,including the single Au atomic adsorption site,the Adsorption site of Au cluster,and the Si top atom on the Si(111)-(7×7)surface.This allowed for an improved comprehension of the microscopic interaction mechanism involving Au and Si surface atoms.(3)The current study employed self-made ultra-high vacuum Kelvin probe force microscopy to analyze the charge distribution features of distinct adsorption sites of Au atoms on the surface of Si(111)-(7×7).In this study,we achieved a successful determination of the local contact potential difference at the atomic level for the Au/Si(111)-(7×7)surface.Furthermore,we conducted precise measurements of the atomic-scale morphology and potential difference of individual Au atoms and Au clusters at different adsorption sites on the Si(111)-(7×7)surface.This comprehensive analysis provides valuable insights into the electronic properties and distribution of Au species on the Si(111)-(7×7)surface,contributing to a deeper understanding of the adsorption behavior and surface characteristics of this system.The findings demonstrated that the local contact potential difference image offered valuable insights into the electron distribution.Furthermore,it was observed that both a single Au atom and Au cluster exhibited bright spots at the Si top atom positions,which indicated brighter topography and darker LCPD,and that both a single Au atom and Au cluster displayed positive electrical characteristics on the surface.(4)In this study,through the utilization of differential charge density calculations,an indepth understanding of the underlying mechanisms governing the charge transfer and adsorption characteristics of the Au/Si(111)-(7x7)surface has been achieved.The research findings indicate that,during the adsorption process,Au undergoes charge transfer,leading to a partial loss in charge.Consequently,the work function is locally reduced at the position of the adsorbed atom.The theoretical model presented in this study aligns well with the experimental results,particularly with regard to the short-range force,local contact potential difference,and differential charge density variation across the distance range examined. |
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