When history developed into the 1980s, a new surface analysis instrument based on physics and integrating a variety of modern technologies-the scanning probe microscope (STM)-was born. STM not only has a very high spatial resolution (up to 0.1nm in the lateral direction and better than 0.01nm in the longitudinal direction), it can directly observe the atomic structure of the material surface, and it can also manipulate atoms and molecules, thus transforming human Subjective will is imposed on nature. It can be said that the scanning probe microscope is an extension of human eyes and hands and the crystallization of human wisdom.
The working principle of the scanning probe microscope is based on various physical properties in the microscopic or mesoscopic range. The interaction between the two is detected by scanning an ultra-fine probe of atomic lines above the surface of the substance being studied, in order to obtain the results of the interaction between the two. To study the surface properties of matter, the main difference between different types of SPM is their tip properties and their corresponding way of tip-sample interaction.
The working principle comes from the tunnel penetration principle in quantum mechanics. Its core is a tip that can scan on the surface of the sample and has a certain bias voltage between it and the sample. Its diameter is on the atomic scale. Since the probability of electron tunneling has a negative exponential relationship with 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 each other. When a voltage is applied, electrons can be transferred from the tip to the sample or from the sample to the tip through the tunnel effect, forming a tunnel current. By recording the changes in tunneling current between the tip and the sample, information on the surface morphology of the sample can be obtained.
Compared with other surface analysis technologies, SPM has unique advantages:
(1) With atomic-level high resolution. The resolution of STM in the directions parallel to and perpendicular to the sample surface can reach 0.1nm and 0.01nm respectively, and single atoms can be resolved.
(2) The three-dimensional image of the surface in real space can be obtained in real time, which can be used to study surface structures with or without periodicity. This observable performance can be used to study dynamic processes such as surface diffusion.
(3) The local surface structure of a single atomic layer can be observed, rather than the individual image or the average properties of the entire surface. Therefore, surface defects, surface reconstruction, the shape and position of surface adsorbed bodies, and the effects caused by adsorbed bodies can be directly observed. Surface reconstruction, etc.
(4) It can work in different environments such as vacuum, atmosphere, and normal temperature, and can even immerse samples in water and other solutions. No special sample preparation technology is required, and the detection process will not damage the samples. These features are particularly suitable for studying biological samples and evaluating sample surfaces under different experimental conditions, such as monitoring of heterogeneous catalytic mechanisms, superconducting mechanisms, and electrode surface changes during electrochemical reactions.
(5) In conjunction with Scanning Tunneling Spectroscopy (STS), information about the surface electronic structure can be obtained, such as the density of states at different levels on the surface, surface electron traps, changes in surface potential barriers, and energy gap structures.
