Scanning probe microscopy's unique advantages
The working principle of Scanning Probe Microscopy is based on various physical properties in the microscopic or mesoscopic range, and the interaction between them is detected by means of a very fine probe of atomic linearity scanning above the surface of the substance under study, in order to obtain the surface properties of the substance under study, the main difference between the different types of SPMs lies in the differences in the characteristics of their needles and their corresponding ways of interacting with the samples of the needles.
The principle of operation is derived from the tunneling through principle in quantum mechanics. At its core is a tip that can scan over the sample surface with a certain bias voltage between it and the sample, and whose diameter is on the atomic scale. As the chance of electron tunnelling shows a negative exponential relationship with the width of the potential barrier V(r), when the distance between the tip of the needle and the sample is very close, the potential barrier between them becomes very thin, and the electron clouds overlap each other, and by applying a voltage between the tip of the needle and the sample, the electrons can be transferred from the tip to the sample or from the sample to the tip of the needle through the tunneling effect to form a tunnel current. By recording the changes in the tunneling current between the tip and the sample, information on the surface morphology of the sample can be obtained.
SPM has unique advantages over other surface analysis techniques:
(1) High resolution at the atomic level, with resolutions of 0.1 nm in the parallel and 0.01 nm in the perpendicular direction to the sample surface, where individual atoms can be resolved.
(2) A three-dimensional image of the surface in real space can be obtained in real time, which can be used for the study of periodic or non-periodic surface structures, and this observable performance can be used for the study of dynamic processes such as surface diffusion.
(3) It is possible to observe the local surface structure of a single atomic layer rather than the individual image or the average nature of the entire surface, and thus it is possible to directly observe surface defects, surface reconstruction, the morphology and location of surface adsorbates, and surface reconstruction caused by adsorbates.
(4) It can work in different environments, such as vacuum, atmosphere, room temperature, etc., and can even immerse the sample in water and other solutions, which does not require special sampling techniques and does not damage the sample during the detection process. These features are particularly suitable for the study of biological samples and the evaluation of the sample surface under different experimental conditions, such as for the multiphase catalytic mechanism, superconductivity mechanism, and the monitoring of electrode surface changes during electrochemical reactions.
(5) In combination with scanning tunneling spectroscopy (STS), information about the electronic structure of the surface can be obtained, such as the density of states at different levels of the surface, the surface electron traps, the variation of the surface potential barriers and the energy gap structure.
