Characteristics of Scanning probe microscopy
When the history developed to the 1980s, a new type of surface analysis instrument, Scanning probe microscopy (STM), based on physics and integrating various modern technologies, was born. STM not only has high spatial resolution (up to O.1nm horizontally and better than O.01nm vertically), it can directly observe the atomic structure of material surfaces, but also manipulate atoms and molecules, thereby imposing human subjective will on nature. It can be said that Scanning probe microscopy is the extension of human eyes and hands, and the crystallization of human wisdom.
The working principle of Scanning probe microscopy is based on various physical properties in the microscopic or mesoscopic range. The interaction between the two is detected by scanning the atomic linear extremely fine probe above the surface of the studied material to obtain the surface characteristics of the studied material. The main difference between different types of SPMs is their tip characteristics and the corresponding Mode of action of tip samples.
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. Since the probability of electron tunneling has a negative exponential relationship with the width of the barrier V (r), when the distance between the tip and the sample is very close, the barrier between them becomes very thin, and the Electron cloud overlaps with each other. 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 tunnel 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 whole surface, so the surface defects, Surface reconstruction, the shape and position of the surface adsorbents, and the Surface reconstruction caused by the 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 applicable to the study of biological samples and the evaluation of sample surfaces under different experimental conditions, such as the monitoring of Heterogeneous catalysis mechanism, superconducting mechanism, and electrode surface changes during electrochemical reaction.
(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.
