Atomic Force Microscope: Construction, Working, and Nanomaterial Synthesis
Atomic Force Microscope (AFM)
Principle
The various types of forces experienced by the probe while scanning the sample surface scatter a laser signal, which produces a 3D image of the sample.
Diagram
- Optical fiber
- Photodetectors
- Laser beam
- Reflective surface
- Probe
- Cantilever
- Sample
Construction and Working
The AFM consists of a probe with a sharp tip fitted to a cantilever. The radius of the tip is 1 nm, and the length of the cantilever is around 10 nm.
The cantilever surface is highly reflective. A laser beam is incident on the cantilever through an optical fiber. The reflected laser beam is collected by photodetectors.
As the probe is moved over the sample, the tip experiences a force, due to which the cantilever undergoes a deflection.
The force is detected by a series of photodetectors, which collect the laser beam scattered at different directions due to the deflection of the probe.
This creates a 3D image carrying information of the surface of the sample.
Different Techniques to Synthesize Nanomaterials
Ball Milling
It is a mechanical method in which small, hard steel balls are kept in a container filled with powder of bulk material. The container spins about itself while rotating in a circular path about its axis. This causes the milling balls to collide with the powder of bulk material and with each other. This collision results in a reduction in the size of the bulk material and produces nanoparticles.
Sputtering
It is a process in which a solid target material is kept in an evacuated chamber, and an inert gas (He or Ar) is introduced into it at low pressure. A substrate is placed in front of the target material. A target material is bombarded with high-energy ions to eject atoms from the target surface. The ejected atoms travel through the vacuum chamber and condense onto a substrate. This forms a thin film of coating on a substrate. Sputtered thin films are used in optical coatings for lenses, mirrors, and displays.
Vapor Deposition
In this method, the material is initially heated to form a gas and is allowed to deposit on a solid surface under vacuum conditions, which forms nanopowders on the surface of the solid. This method is very useful for producing composite materials.
Applications of Nanomaterials
Self-Cleaning Glass
Nanoparticles like titanium dioxide are coated on a glass surface to make it photocatalytic and hydrophilic, which keep the glass clean.
Stain-Resistant Clothing
Hydrophobic nanoparticles like zinc oxide are coated on clothes, which create a water-repellent surface, thus making them stain-resistant.
Scratch-Resistant Coating
Nanoparticles like alumina (Al2O3) are coated on the glass to make it scratch-resistant.
Insulation Materials
Nanocrystalline materials like aerogel, which are porous and extremely light, are used as insulators in aerospace or building insulation.
Cutting Tools
Nanocomposite materials like tungsten carbide are used to create cutting tools with exceptional hardness and wear resistance.
High-Sensitivity Sensors
Sensors made of nanocrystalline materials are extremely sensitive to changes in their environment. These sensors are used as smoke detectors or ice detectors on aircraft wings.