Troubleshooting for the Condenser Lifting Mechanism of Microscopes
The basic principle of an atomic force microscope is as follows: one end of a microcantilever, which is extremely sensitive to weak forces, is fixed, and a tiny probe tip is mounted at the other end. The tip gently contacts the sample surface. Owing to the extremely weak repulsive force between the atoms on the probe tip and those on the sample surface, by keeping this force constant during scanning, the microcantilever with the tip moves up and down perpendicular to the sample surface, following the equipotential surface defined by the interaction force between the tip and sample surface atoms. Using optical detection or tunneling current detection methods, the positional change of the microcantilever at each scanning point can be measured, so that information about the surface topography of the sample can be obtained. In the following, we take the atomic force microscope employing laser beam deflection for force detection (Laser-AFM), a commonly used member of the scanning probe microscope family, to elaborate on its working principle.
Throughout the entire imaging and detection process of the system, the distance between the probe and the tested sample is maintained at the nanometer scale (10⁻⁹ m). If the distance is too large, surface information of the sample cannot be acquired; if the distance is too small, both the probe and the tested sample will be damaged. The feedback loop functions as follows: during operation, it receives the magnitude of the probe-sample interaction force from the probe, and adjusts the voltage applied to the vertical axis of the sample scanner. This drives the sample to extend or retract, thereby regulating the probe-sample separation and in turn stabilizing the magnitude of the probe-sample interaction force to realize feedback control. Therefore, feedback control constitutes the core operating mechanism of this system.
This system adopts a digital feedback control loop. Users can control the characteristics of the feedback loop by setting parameters including the reference current, integral gain and proportional gain in the parameter toolbar of the control software.
