Working principle and application of atomic force microscope
Atomic force microscope and its application
Atomic force microscope is a scanning probe microscope developed from the basic principle of scanning tunneling microscope. The emergence of the atomic force microscope has undoubtedly played a role in promoting the development of nanotechnology. The scanning probe microscope represented by the atomic force microscope is a general term for a series of microscopes that use a small probe to scan on the surface of the sample to provide high-magnification observation. AFM scanning can provide information on the surface state of various types of samples. Compared with conventional microscopes, the advantage of atomic force microscopy is that it can observe the sample surface at high magnification under atmospheric conditions, and can be used for almost all samples (with certain requirements for surface finish), without other sample preparation processing, the sample surface can be obtained 3D image of the . It can also perform roughness calculation, thickness, step width, block diagram or particle size analysis on the scanned 3D topography image.
AFM can detect many samples and provide data for surface research and production control or process development, which cannot be provided by conventional scanning surface roughness meters and electron microscopes.
1. Basic principles
The atomic force microscope uses the interaction force (atomic force) between the detection sample surface and the tiny probe tip to measure the topography of the surface.
The probe tip is on a small flexible cantilever, and when the probe touches the sample surface, the resulting interaction 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 a laser diode is focused on the back of the cantilever. When the cantilever bends under the force, the reflected light is deflected using a position-sensitive photodetector deflection angle. Then the collected data is processed by computer to obtain a three-dimensional image of the sample surface.
The complete cantilever probe is placed on the surface of the sample controlled by the piezoelectric scanner and scanned in three directions with a precision level of 0.1nm or less. Typically, the cantilever's displacement feedback-controlled Z-axis remains constant while detailed scanning (XY-axis) is performed on the sample surface. The Z-axis value which is the feedback of the scanning response is input into the computer for processing, and the observation image (3D image) of the sample surface is obtained.
Second, the characteristics of the atomic force microscope
1. High resolution capabilities far exceed those of scanning electron microscopes (SEM), and optical roughness meters. The three-dimensional data of the sample surface 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 less than 10-8N, which is much lower than the pressure of the previous stylus roughness meter, so it will not damage the sample, and there is no electron beam damage problem of the scanning electron microscope. In addition, scanning electron microscopy requires coating of non-conductive samples, while atomic force microscopy does not.
3. It can be used in a wide range of applications, such as surface observation, size measurement, surface roughness measurement, particle size analysis, statistical processing of protrusions and pits, evaluation of film forming conditions, measurement of protective layer size steps, evaluation of flatness of interlayer insulating films, VCD Coating evaluation, evaluation of friction treatment process of oriented film, defect analysis, etc.
4. The software has strong processing functions, and its three-dimensional image display size, viewing angle, display color, and gloss can be set freely. And can choose network, contour line, line display. Macro management of image processing, cross-sectional shape and roughness analysis, topography analysis and other functions.
