1 The nanoscale ‘Nano’ is the unit prefix representing 10 –9. Some common unit prefixes

2 Carbon can exist in two forms in daily life: –Diamond (tetrahedral) –Graphite (hexagonal) Diamond Graphite

3 Carbon atoms can also be arranged in many other ways to produce other forms, e.g. –Carbon nanotube (roll up layer of carbon atoms from graphite) –Fullerene (C-60: 20 hexagons + 12 pentagons) Carbon nanotube R ~ few nm C-60 (a special kind of fullerene) Others: C-70, C-76, C-84, etc R ~ 1 nm

4 exhibits different behaviour than the bulk form. Physical properties of nanomaterials much stronger and stiffer than their bulk forms. both strong and ductile. Badminton racquets made of fibres mixed with carbon nanotubes Mechanical properties

5 Strange optical properties appear in nanomaterials. e,g 1 gold Gold coin (bulk form) Aqueous colloidal gold Particle:10 – 100 nm Brilliant red in color Optical properties e.g.2 Zinc oxide & titanium oxide in nanoscale can block UV that they can be user in sunscreen and cosmetics

6 Most nanomaterials have a lower melting point than their bulk forms. Variation of the melting point of gold nanoparticles with size Thermal properties

7 A CPU heat sink The thermal conductivity of a material depends on its form (e.g. diamond is a good thermal conductor but nanotubes are 2 times better than diamond). A heat sink with carbon nanotubes

8 Some insulators become conductors in their nano forms. e.g. SiO 2 The resistivity of metals (normally small) greatly increases when the metal sample is reduced to nanosize. Electrical properties Magnetic properties Hard disk drives record data using ferromagnetic materials. Most ferromagnetic materials (can keep magnetization) become paramagnetic (cannot keep magnetization) when they are reduced to nano size.

9 Observing at the nanoscale Factors affecting the resolving power of a microscope –Optical aberrations (= image error) of the lenses Limitations of optical microscopes Spherical aberration : due to curve surface Chromatic aberration: due to frequency

10 Factors affecting the resolving power of a microscope –Diffraction of light Light diffracts when it passes through a circular aperture.

11 1.circular lens ~ circular aperture 2.light diffracts when it passes through a lens of an optical device.

12 The diffraction patterns of the two point sources overlap: difficult to resolve them.

13 The Rayleigh criterion Two objects are just resolvable when the first minimum of one diffraction patterns falls on the central maximum of the other. For circular aperture, the minimum angular separation of two resolvable objects is

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15 The resolving power of a microscope is the minimum linear separation (s ) between two resolvable objects. S ~ λ. Assume u ~ f, ~ (s/f) and f > (D/2) S ~ 0.6 λ ~ λ The resolving power of a microscope is limited by λ

16 The transmission electron microscope (TEM) uses electron beams of short wavelengths instead of visible light. Transmission electron microscopes (TEM)

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19 E. Coli ( 大腸桿菌 )Salmonella bacteria ( 沙門氏菌 )

20 Comparison between a traditional optical microscope and a TEM

21 The scanning tunnelling microscope (STM) scans a surface by detecting the changes in the tunnelling current between the probe and the surface. Scanning tunnelling microscopes (STM) An STMProbe of an STM

22 The current is produced by a phenomenon called quantum tunnelling, and is very sensitive to the distance between the tip of the probe and the surface.

23 An iron surface with chromium impurities (little bumps) on it A chain of caesium atoms (orange) on a gallium arsenide surface

24 Iron atoms arranging into a circle on a copper surface Iron atoms arranging to form characters

25 Comparison between the TEM and STM

26 Recent development in nanotechnology The technology used in CPUs nowadays reaches the nanoscale. Electronics and computer hardware

27 A CRT display An FED display (Field emission display) (Efficient electron emitter) FED : 1.Reduce thickness 2.Use less power

28 Material science Badminton racquets made of fibres mixed with carbon nanotubes New bullet-proof vest produced with carbon nanotubes

29 Nanomedicine A nanorobot performing a surgery on a cell 1.Some nanomaterials have specific interactions with special cells 2.target on defective cells/ deliver appropriate treatment 3.nanodoctors: repair cells & defective DNA

30 Energy A solar cell made of nanocrystals of titanium dioxide: To facilitate conversion of solar energy to electrical energy

31 little knowledge about the potential hazards of nanotechnology. Nanoparticles are chemically very reactive : 1.toxic, 2.highly penetrating (even reach DNA and cause DNA mutation), 3.easily absorbed by plants/animals/human body/water sources/food Potential hazards of nanotechnology