1. Light and Nanotechnology : How Do we “See” Something Too Small to See?
Laboratory 04
Light and Nanotechnology : How Do we “See” Something Too Small to See?

2. Objectives
Measure the width of a human hair using a laser pointer and diffraction.
• Synthesize silver nanoparticles, and investigate how color is related to particles.

3. Nanotechnology
Nanotechnology is the technology for design, fabrication and manipulation of nanometre scale systems, in the scale of nm

4. Human hair thickness ~ 50 µm
How Small is nano ?
1 µm = one millionth of a meter
1 nm = one billionth of a meter
≈ 1/50,000 thickness of a hair!
≈ a string of 3 atoms
If we shrunk all distances by 110,000,000,000 X
The sun and earth would be separated by 1 m
A football field would be 1 nm
Human hair thickness ~ 50 µm
110 m
110,000,000 km

5. Why Nanomaterials ?
High Aspect ratio
Quantum Effect

6. Properties of Nanomaterials
Enhanced electrical and heat conductivity
Increased strength, tensile properties
Magnetic properties
Optical properties – color changes with size

7. Silver Nanoparticles Size: 10nm-100nm Chemical formula: Ag
Details: Silver nanoparticles are ultra fine particles of silver. They are ten to a hundred nanometers large, and differ from the bulk silver as they have different colors such as yellow, as opposed to the silver.
This is due to plasmon absorbance:
Incident light rays create oscillation in free electrons on the surface of nanoparticles, causing them to absorb electromagnetic radiation, creating different colors reflected.

8. Synthesis of Silver nanoparticles
Reduction method
Ag + → Ag (Reducing agent NaBH4)
Ag atoms will stick together to form small particles.
Addition of citrate-
Act as a buffer to control pH
Act as a binding agent to limit the growing of nanoparticls
Addition of hydrogen peroxide-
Act as a etching agent , remove silver atoms from less stable nanoparticles.
Silver nanoprism is formed.
Bromide is added to control the size of the nanoprisms.

9. Diffraction of light through a single slity W L
w sin Ɵ = n λ
tan Ɵ = y / L
In this lab, a variation of single slit diffraction is used to measure the width of a human hair; instead of a single slit in a wall.