Working principle of atomic force microscopy and its applications
Atomic force microscope is a scanning probe microscope developed on the basic principle of scanning tunneling microscope. The emergence of atomic force microscopy has undoubtedly played a driving role in the development of nanotechnology. Scanning probe microscopy, represented by atomic force microscopy, is a general term for a series of microscopes that use a small probe to scan over the surface of a sample, thus providing high magnification observations. AFM scans provide information about the surface state of various types of samples. Compared with conventional microscopes, the advantage of AFM is that it can be used to observe the surface of a sample at high magnification under atmospheric conditions, and can be used for almost all samples (with certain requirements for surface finish) without the need for any other sample preparation to obtain a three-dimensional topographical image of the sample surface. The scanned 3D image can be used for roughness calculation, thickness, step width, box plot or granularity analysis.
Atomic force microscopy can examine many samples, providing data for surface studies and production control or process development that conventional scanning surface roughness meters and electron microscopes cannot provide.
Basic Principle
Atomic force microscopy uses the interaction force (atomic force) between the surface of the test sample and a fine probe tip to measure the surface topography.
The probe tip is on a small bremsstrahlung 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 3-4 nm, and the force detected between them, less than 10-8 N. The light from the laser diode is focused on the back of the cantilever. As the cantilever bends under the force, the reflected light is deflected, using a bit-sensitive photodetector deflection angle. The collected data is then processed by a computer to obtain a three-dimensional image of the sample surface.
A complete cantilever probe, placed on the sample surface under the control of a piezoelectric scanner, is scanned in three directions in steps of 0.1 nm or less at an accuracy level. Generally, the displacement of the cantilever is kept fixed under the action of the Z-axis of the feedback control as the sample surface is swept in detail (XY-axis). In response to the scanning is the feedback Z-axis value is input into the computer processing, resulting in the observation of the sample surface image (3D image).
Features of Atomic Force Microscope
1. High resolution capability far exceeds the scanning electron microscope (SEM), as well as optical roughness instrument. Three-dimensional data on the sample surface to meet the requirements of research, production, quality inspection more and more microscopic.
2. Non-destructive, probe and sample surface interaction force of 10-8N or less, far less than the previous stylus roughness instrument pressure, so there will be no damage to the sample, there is no scanning electron microscope electron beam damage. In addition, the scanning electron microscope requires non-conductive samples to be coated, while the atomic force microscope is not required.
3. Wide range of applications, can be used for surface observation, size determination, surface roughness determination, granularity analysis, protrusions and pits of the statistical processing, evaluation of film-forming conditions, the size of the protective layer of the determination of the step, the interlayer insulating film flatness evaluation, VCD coating evaluation, evaluation of friction treatment of directional film process, defect analysis.
4. Strong software processing functions, its three-dimensional image display its size, viewing angle, display colour, gloss can be freely set. And can choose the network, contour, line display. Macro management of image processing, the shape of the section and roughness analysis, morphological analysis and other functions.
