Laboratory 04
Light and Nanotechnology : How Do we
“See” Something Too Small to See?
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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.
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Nanotechnology
Nanotechnology is the technology for design,
fabrication and manipulation of nanometre scale
systems, in the scale of 1-100 nm
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
110,000,000 km
Human hair
thickness ~ 50 µm
110 m
Why Nanomaterials ?
High Aspect ratio
Quantum Effect
Specific Surface Area of Nanoparticles
Surface / km2/m3
1000
800
600
400
200
0
0
100
200
300
400
500
600
Radius /nm
700
800
900
1000
Properties of Nanomaterials
Enhanced electrical and heat conductivity
Increased strength, tensile properties
Magnetic properties
Optical properties – color changes with size
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.
Synthesis of Silver nanoparticles
Reduction method
Ag + →
Ag (Reducing agent NaBH4)
Ag atoms will stick together to form small particles.
Addition of citrateAct as a buffer to control pH
Act as a binding agent to limit the growing of nanoparticls
Addition of hydrogen peroxideAct 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.
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Diffraction of light through a single slit
y
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.
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