When history developed to the 1980s, a new surface analysis instrument-scanning probe microscope (STM) was born, which was based on physics and integrated with many modern technologies. STM not only has a high spatial resolution (up to O.1nm in horizontal direction, but better than O.01nm in vertical direction), it can directly observe the atomic structure on the surface of matter, but also manipulate atoms and molecules, thus imposing human subjective will on nature. It can be said that the scanning probe microscope is the extension of human eyes and hands and the crystallization of human wisdom.
The working principle of scanning probe microscope is based on various physical properties in microscopic or mesoscopic range, and the interaction between them is detected by scanning the ultra-fine probe with atomic linearity above the surface of the studied substance, so as to obtain the surface characteristics of the studied substance. The main difference between different types of SPM lies in their needle tip characteristics and the corresponding interaction modes of needle tip samples.
(1) It has high resolution at atomic level. The resolution of STM in the direction parallel to and perpendicular to the sample surface can reach 0.1nm and 0.01nm respectively, so that a single atom can be distinguished.
(2) The three-dimensional image of the surface in real space can be obtained in real time, which can be used to study the surface structure with or without periodicity, and this observability can be used to study the dynamic processes such as surface diffusion.
(3) The local surface structure of a single atomic layer can be observed instead of the average properties of an individual image or the whole surface, so surface defects, surface reconstruction, the shape and position of surface adsorbents, and surface reconstruction caused by adsorbents can be directly observed.
(4) It can work in different environments such as vacuum, atmosphere, normal temperature, etc., and even the sample can be immersed in water and other solutions, without special sample preparation technology, and the detection process has no damage to the sample. These characteristics are especially suitable for studying biological samples and evaluating the surface of samples under different experimental conditions, such as heterogeneous catalytic mechanism, superconducting mechanism, monitoring the changes of electrode surface during electrochemical reaction and so on.
(5) With scanning tunneling spectroscopy (STS), information about the surface electronic structure can be obtained, such as the density of states at different levels of the surface, the surface electron trap, the change of the surface barrier and the energy gap structure.
