The working principle and application of atomic force microscopy
Atomic force microscopy is a scanning probe microscope developed based on the basic principle of scanning tunneling microscopy. The emergence of atomic force microscopy undoubtedly played a driving role in the development of nanotechnology. Scanning probe microscopy, represented by atomic force microscopy, is a series of microscopes that use a small probe to scan the surface of a sample, providing high magnification observation. Atomic force microscopy scanning can provide surface state information of various types of samples. Compared with conventional microscopes, the advantage of atomic force microscopy is that it can observe the surface of the sample at high magnification under atmospheric conditions, and can be used for almost all samples (with certain requirements for surface smoothness), without the need for other sample preparation processes, to obtain a three-dimensional morphology image of the sample surface. And can perform roughness calculation, thickness, step width, block diagram, or particle size analysis on the 3D morphology images obtained from scanning.
Atomic force microscopy can detect many samples and provide data for surface research, production control, or process development, which conventional scanning surface roughness meters and electron microscopes cannot provide.
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 cantilever, and the interaction generated when the probe contacts the surface of the sample is detected in the form of cantilever deflection. The distance between the sample surface and the probe is less than 3-4 nm, and the force detected between them is less than 10-8 N. The light from the laser diode is focused on the back of the cantilever. When the cantilever is bent under the action of force, the reflected light deflects, and a position sensitive photodetector is used to detect the deflection 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 accuracy. Generally, when scanning the sample surface in detail (XY axis), the Z-axis controlled by the displacement feedback of the cantilever is kept fixed and unchanged. The Z-axis values, which are feedback to the scanning response, are input into the computer for processing, resulting in an observed image (3D image) of the sample surface.
The characteristics of atomic force microscopy
1. The high resolution capability far exceeds that of scanning electron microscopy (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 in scanning electron microscopy. In addition, scanning electron microscopy requires coating treatment on non-conductive samples, while atomic force microscopy does not require it.
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, film formation condition evaluation, size step measurement of protective layers, flatness evaluation of interlayer insulation films, VCD coating evaluation, friction treatment process evaluation of oriented films, defect analysis, etc.
4. The software has strong processing capabilities, and its 3D image display can freely set its size, perspective, display color, and gloss. And network, contour lines, and line displays can be selected. Macro management in image processing, analysis of cross-sectional shape and roughness, morphology analysis, and other functions.
