Question

Explain construction and working of atomic force microscope.

Answer 1

An Atomic Force microscope (AFM) consists of following components:
1.LASER
2.Photodiode
3. Cantilever with a sharp tip
4.Detector and feedback circuit
5.Pizoelectric scanner
WORKING OF ATOMIC FORCE MICROSCOPE :

1.AFM consists of microscope cantilever with a sharp tip (probe) at its end used to scan the specimen surface.

2.The cantilever is typically silicon or silicon nitride with the tip radius of curvature of the orders of nm. Basically, AFM is modified TEM in which limitations of TEM is overcomed. When the tip is bought close to the sample, force between the tip and sample leads to the deflection of the cantilever according to the Hook`s law. Instead of using an electrical signal, the AFM relies on forces between the atom on the tip and in the sample.

3.The force present in the tip is kept constant and the scanning is done. As the scanning continues, the tip will have vertical movements depending upon the topography of the sample. The force present in the tip is kept constant and the scanning is done. As the scanning continue the tip will have vertical movement depending upon the topography o the sample.

4.A LASER beam is used to have a record of vertical movement of the needle. This information is later converted into visible from using photo diode. Depending upon the situation, AFM measures different types of forces like a Vander Waal’s forces, capillary force, mechanical contact force etc.