What is the working principle of atomic force microscope (AFM)?

Responder: anonymous user time: 20 10-02-25 where can I find the best life science academic exchange forum? > > > Atomic Force Microscope (AFM) was designed in 1986. It mainly obtains the microscopic information of the sample surface by detecting the interatomic force between the needle tip and the sample, so the sample is not required to have conductivity. The working principle of AFM is to fix one end of a micro-cantilever beam which is very sensitive to weak force and install a probe at the other end. The tip of the micro-cantilever lightly touches the sample surface, and the tiny repulsive force between the atoms at the tip of the needle tip and the atoms on the sample surface makes the micro-cantilever bend upward. By detecting the position change of the laser spot reflected from the back of the micro-cantilever on the optical detector, it can be transformed into the change of force, because the position change of the reflected spot or the bending change of the micro-cantilever is proportional to the change of force. The bending of micro-cantilever beam is the result of the interaction of many forces, the most common of which is van der Waals force. The small distance between the needle tip and the sample surface will produce different van der Waals forces. By controlling the constant force of the needle tip during scanning and measuring the longitudinal displacement of the needle tip, the microscopic information of the sample surface can be obtained.

AFM has two working modes: constant force mode and constant height mode. In the constant force mode, the scanning head is accurately controlled to move up and down in the longitudinal direction with the change of the surface morphology of the sample, so that the force acting on the micro-cantilever beam is constant, and the surface morphology image of the sample is obtained from the longitudinal movement value of the scanning head. In the constant height mode, the height of the scanning head is fixed, and the surface information of the sample is directly obtained from the deflection information of the micro-cantilever beam in space. SPM has the characteristics of high resolution, continuous and dynamic detection of microscopic information of objects in various environments (vacuum, gas and liquid), and has been rapidly applied to life science research. SPM was first used to study the structure and function of biological macromolecules (DNA, protein, etc.). ) and accumulated a wealth of data in this field.