With the advancement of technology and the emergence of electron microscopes, different types of these microscopes were created with different working methods. One of the types of microscopes that is widely used today is the atomic force microscope. This microscope does not use electrons like other new microscopes.

The operation of this microscope is based on the force between the tip of the microscope probe and the atoms on the surface. The tip of the microscope probe cannot get closer to the atoms on the surface and the reason is the repulsive force that is created between the two.

Functional modes of atomic force microscope (AFM)

Atomic Force Microscope (AFM) can work in different modes, which are mentioned below:

Contact mode

In this mode, the tip (probe tip) is in contact with the surface, and by moving it on the surface and moving the arm (going up and down based on the height and elevation of the investigated surface), an image of the surface is prepared. For arm displacement measurements, a laser is used that shines on the arm and its reflection is measured on several photodiodes side by side. By moving the arm, the reflection of the emitted laser beam is also moved, and as a result, it is possible to measure the heights and heights on the surface. In the figure below, the basis of operation of atomic force microscopes is shown.

In the contact state, the tip is in the repulsion range and is repelled by the sample surface molecules. At the same time, the rest of the band is in the attraction zone and will be absorbed by the sample. A balance is established between these two forces and the brigade moves based on the surface bumps.

This mode has a high scanning speed and is a suitable option for hard samples with sharp changes in the surface.

Non-contact mode

In this case, the microscope tip vibrates in the resonant frequency range. In this case, using a piezoelectric, they make the arm oscillate. The probe moves on the surface and scans it. The tip is placed near the surface without touching it to measure the weak attraction between the tip and the sample. The reactive forces received in the non-contact mode create a very good vertical resolution. Of course, this mode cannot work in a liquid environment. This fashion is more suitable for the weather.

The scanning speed of this mode is lower than the contact mode, but it causes less damage to the sample and the microscope tip.

Tapping mode

This mode is also the same as the contactless mode. In this state, the pole is oscillating and bringing the tip closer to the surface for slow contact. Then move the tip away from the surface to avoid hitting and damaging it. When the tip of the probe approaches the surface, the amplitude of the pole oscillation decreases. By measuring this fluctuation range, the surface characteristics of the sample can be understood. In this case, the scanning speed is very low. This mode is suitable for soft samples.

Advantages and disadvantages of AFM atomic force microscopy

Advantages:

• High speed
• Very suitable for measuring roughness and surface height
• Can be used on all conductive and non-conductive materials
• Simplicity of sample preparation
• Ability to work in air, vacuum and liquids
• Ability to study biological systems

Disadvantages:

• Limited vertical reading range: This means that if the difference in height and surface hardness is greater than a certain limit, AFM is not able to take proper images.
• Dependence of the obtained information on the type of microscope tip
• The possibility of damaging the tip of the microscope or the sample
• Need special attention for soft samples