The Working Principle and Applications of Atomic Force Microscopes
1, Basic principles
Atomic force microscopy uses the interaction force (atomic force) between the surface of a sample and the tip of a fine probe to measure the surface morphology.
The probe tip is on a small flexible cantilever, and the interaction generated when the probe contacts the sample surface is detected in the form of cantilever deflection. The distance between the sample surface and the probe is less than 3-4nm, and the force detected between them is less than 10-8N. The light from the laser diode is focused on the back of the cantilever. When the cantilever bends under the action of force, the reflected light is deflected, and a position sensitive photodetector is used to deflect the angle. Then, the collected data is processed by a computer to obtain a three-dimensional image of the sample surface.
A complete cantilever probe is placed on the surface of the sample controlled by a piezoelectric scanner and scanned in three directions with a step width of 0.1 nm or less in horizontal accuracy. Generally, when scanning the sample surface in detail (XY axis), the Z-axis controlled by the displacement feedback of the cantilever remains fixed and unchanged. The Z-axis values that provide feedback on the scanning response are input into the computer for processing, resulting in an observation image (3D image) of the sample surface.
Characteristics of Atomic Force Microscopy
1. The high-resolution capability far exceeds that of scanning electron microscopes (SEM) and optical roughness meters. The three-dimensional data on the surface of the sample meets the increasingly microscopic requirements of research, production, and quality inspection.
2. Non destructive, the interaction force between the probe and the sample surface is below 10-8N, which is much lower than the pressure of traditional stylus roughness meters. Therefore, it will not damage the sample and there is no electron beam damage problem of scanning electron microscopy. In addition, scanning electron microscopy requires coating treatment on non-conductive samples, while atomic force microscopy does not.
3. It has a wide range of applications and can be used for surface observation, size measurement, surface roughness measurement, particle size analysis, statistical processing of protrusions and pits, evaluation of film formation conditions, size step measurement of protective layers, flatness evaluation of interlayer insulation films, VCD coating evaluation, evaluation of friction treatment process of oriented films, defect analysis, etc.
4. The software has strong processing capabilities, and its 3D image display size, viewing angle, display color, and gloss can be freely set. And network, contour lines, and line displays can be selected. Macro management of image processing, analysis of cross-sectional shape and roughness, morphology analysis, and other functions.
