The unique advantages of scanning probe microscopy
The working principle of a scanning probe microscope is based on various physical properties in the micro or mesoscopic range. The interaction between the two is detected by scanning the surface of the studied substance with an extremely fine atomic probe, in order to obtain the surface characteristics of the studied substance. The main difference between different types of SPMs is their needle tip characteristics and the corresponding needle tip sample interaction methods.
The working principle comes from the tunneling principle in quantum mechanics. Its core is a needle tip that can scan on the surface of the sample and has a certain bias voltage between it and the sample, with a diameter of atomic scale. Due to the negative exponential relationship between the probability of electron tunneling and the width of the potential barrier V (r), when the distance between the tip and the sample is very close, the potential barrier becomes very thin, and the electron clouds overlap with each other. By applying a voltage between the tip and the sample, electrons can be transferred from the tip to the sample or from the sample to the tip through the tunneling effect, forming a tunneling current. By recording the changes in tunnel current between the needle tip and the sample, information on the surface morphology of the sample can be obtained.
Compared to other surface analysis techniques, SPM has unique advantages:
(1) It has atomic level high resolution. The resolution of STM in the direction parallel and perpendicular to the sample surface can reach 0.1nm and 0.01nm, respectively, which can distinguish individual atoms.
(2) Real time 3D images of surfaces in real space can be obtained, which can be used for studying surface structures with or without periodicity. This observable performance can be used for studying dynamic processes such as surface diffusion.
(3) The local surface structure of a single atomic layer can be observed, rather than the average properties of the individual image or the entire surface. Therefore, surface defects, surface reconstruction, the morphology 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, and room temperature, and even immerse the sample in water and other solutions without the need for special sample preparation techniques, and the detection process does not damage the sample. These characteristics are particularly suitable for studying biological samples and evaluating the surface of samples under different experimental conditions, such as monitoring the multiphase catalytic mechanism, superconducting mechanism, and electrode surface changes during electrochemical reactions.
(5) By cooperating with Scanning Tunneling Spectroscopy (STS), information about surface electronic structures can be obtained, such as the density of states at different levels of the surface, surface electron wells, changes in surface potential barriers, and energy gap structures.
