1. P.1 Book E2 Section 3.1 Introduction to nanotechnology Colour of gold in nano scale Nano scale Check-point 1 Nano materials What is so special about nano materials? Why do nano materials behave so differently? Check-point 2 3.1Introduction to nanotechnology

2. P.2 Book E2 Section 3.1 Introduction to nanotechnology Colour of gold in nano scale If we keep on cutting the gold bar until it reaches a size of about 100 gold atoms, will it still look glittering yellow? Its colour varies depending on the final size of the gold piece.

3. P.3 Book E2 Section 3.1 Introduction to nanotechnology 3.1Introduction to nanotechnology Nanotechnology is changing and will continue to change our lives in this century. Many even believe that its impact may rival what electricity and internet have brought about.

4. P.4 Book E2 Section 3.1 Introduction to nanotechnology 1 Nano scale Nano generally means extremely small.  originates from a Greek word nanos which means dwarf  symbol: n  as prefix for scientific units: nano = 10 –9 E.g.1 nanosecond (1 ns) = 10 –9 s 1 nanometre (1 nm) = 10 –9 m

5. P.5 Book E2 Section 3.1 Introduction to nanotechnology 1 Nano scale Another unit for measuring length at nano scale is angstrom (symbol: Å): 1 Å = 10 –10 m = 0.1 nm Nano materials: materials with nanometre scale Nano materials are usually defined as materials with at least one dimension less than 100 nm.

6. P.6 Book E2 Section 3.1 Introduction to nanotechnology 1 Nano scale Nano materials have existed in nature even before our existence. E.g.Salt crystals in the ocean air, carbon in soot, DNA molecules in living things Only when we have special tools and methods can we ‘see’ and manufacture nano materials. Nanoscience is the study of nano materials, while nanotechnology is the production and the application of these materials.

7. P.7 Book E2 Section 3.1 Introduction to nanotechnology Check-point 1 – Q1 Express the following lengths in nanometres: (a) A Hong Kong 10-cent coin (thickness 1.15 mm). 1 150 000 nm (b) A hair (diameter 56  m). 56 000 nm (c) A hydrogen atom (diameter 10 –10 m). 0.1 nm

8. P.8 Book E2 Section 3.1 Introduction to nanotechnology Check-point 1 – Q2 If the diameter of a gold atom is about 0.29 nm, estimate the no. of atomic layers of a thin sheet of gold (thickness 100 nm). No. of atomic layers = 100 nm 0.29 nm = 345

9. P.9 Book E2 Section 3.1 Introduction to nanotechnology 2 Nano materials Materials in nano scale exist in various forms. 1.Some surface coatings have only one dimension in nano scale and the other two dimensions in bulk scale. 2.Nano wires and nano tubes have two dimensions in nano scale. 3.Nano particles have all three dimensions in nano scale.

10. P.10 Book E2 Section 3.1 Introduction to nanotechnology 2 Nano materials a Nano particles There are a wide range of nano particles, including metallic, organic, mineral or a mixture of these materials. Many of them naturally exist. E.g.Nano particles of gold and silver have been used as coloured pigments in stained glass since the 10 th century.

11. P.11 Book E2 Section 3.1 Introduction to nanotechnology a Nano particles Gold no longer glitters gold when its size is in the nano scale. The colour of gold depends on the size of the nano particles. size of nano particle: 25 nm size of nano particle: 50 nm size of nano particle: 100 nm

12. P.12 Book E2 Section 3.1 Introduction to nanotechnology 2 Nano materials b Fullerenes The two typical structures of pure carbon: (i) Diamond (ii) Graphite

13. P.13 Book E2 Section 3.1 Introduction to nanotechnology b Fullerenes A new form of carbon, called fullerene (bucky ball) was found in 1985. In its molecules, carbon atoms are arranged in hollow cages with interconnected pentagonal and hexagonal polygons. The first discovered fullerene is C 60.  60 carbon atoms forming a spherical cage

14. P.14 Book E2 Section 3.1 Introduction to nanotechnology 2 Nano materials c Carbon nano tubes In 1991, it was found that carbon atoms can also be arranged in a long cylindrical tube.  Carbon nano tube (CNT)  diameter < a few nanometres CNTs can exist as single-walled (SWCNT) or multi-walled carbon nano tubes (MWCNT)

15. P.15 Book E2 Section 3.1 Introduction to nanotechnology c Carbon nano tubes CNTs have structures similar to an individual graphite sheet being rolled up. Depending on how it is ‘rolled up’, CNT can be classified as armchair, zigzag and chiral types. armchair zigzag chiral

16. P.16 Book E2 Section 3.1 Introduction to nanotechnology c Carbon nano tubes Carbon nano tubes have lots of fascinating properties. For example, (i)it is 100 times stronger than steel of the same size, but only one-sixth as heavy. (ii)it can be bent at large angles and straightened again without damage.  100

17. P.17 Book E2 Section 3.1 Introduction to nanotechnology 2 Nano materials d Nano wires Nano wires are usually slightly thicker than nano tubes (~10 nm).  of many different types (e.g. metallic, semiconducting, insulating and molecular)  potentially useful (e.g. connecting extremely small electronic circuits)

18. P.18 Book E2 Section 3.1 Introduction to nanotechnology 2 Nano materials e Nano sheets and nano films Nano sheets and nano films are very thin layers of materials.  can be used for surface coating  widely used in electronic devices (e.g. semiconductor lasers) Nano materials include nano particles, fullerenes, nano tubes (such as carbon nano tubes), nano wires and nano films.

19. P.19 Book E2 Section 3.1 Introduction to nanotechnology 3 What is so special about nano materials? Objects in nano scale: 1.Their physical and chemical properties are very different from those of the same substances at larger dimensions. E.g.TiO 2 powder changes from white to transparent when reduced to nano scale.  Open up new possibilities that cannot be achieved by objects of ordinary size.

20. P.20 Book E2 Section 3.1 Introduction to nanotechnology 3 What is so special about nano materials? 2.Small in size   amount of physical resources needed for manufacture  less waste when discarded 3.Storage devices will have much higher storage capacity, yet are compact in size. How many $1 coins are needed? Example 1 Objects in nano scale:

21. P.21 Book E2 Section 3.1 Introduction to nanotechnology Example 1 How many $1 coins are needed? Imagine that it is possible to record words on a $1-coin. Each word will occupy an area of 10  10 nm 2 on the coin. How many $1-coins are needed to store the information of all the books in the Hong Kong Central Library (~1.63 million books)? Assume:~1 million words in each book Diameter of an $1-coin = 25.50 mm

22. P.22 Book E2 Section 3.1 Introduction to nanotechnology Example 1 How many $1 coins are needed? Total no. of words = (1.63  10 6 )  (1  10 6 ) = 1.63  10 12 words Area of an $1-coin =  r 2 = 5.11  10 –4 m 2 25.5  10 –3 2 = =  2

23. P.23 Book E2 Section 3.1 Introduction to nanotechnology Example 1 How many $1 coins are needed? No. of recording points in one $1-coin 5.11  10 –4 (10  10 –9 ) 2 = = 5.11  10 12 > 1.63  10 12  Only one $1-coin is needed.

24. P.24 Book E2 Section 3.1 Introduction to nanotechnology 4 Why do nano materials behave so differently? a Surface area effect Size of an object   Surface area per unit volume   Percentage of atoms at the surface  greatly ∵ Atoms are more reactive at the surface than at the centre. ∴ Nano material are more reactive than the same material at ordinary size. Surface area per unit volume Example 2

25. P.25 Book E2 Section 3.1 Introduction to nanotechnology Example 2 Surface area per unit volume (a) Consider a cube of side 1 mm. (i)Surface area per unit volume = ? (ii)Percentage of molecules at the surface = ? Assume: molecules pack closely together and each molecule occupies a volume of 1  1  1 nm 3.

26. P.26 Book E2 Section 3.1 Introduction to nanotechnology Example 2 Surface area per unit volume (a) (i) Surface area to volume ratio: area volume 6d 2 d 3 = = 6000 m –1 6d6d = 6 0.001 =

27. P.27 Book E2 Section 3.1 Introduction to nanotechnology Example 2 Surface area per unit volume No. of molecules at surface  6  (1  10 6 ) 2 = 6  10 12 Total no. of molecules = (1  10 6 ) 3 = 10 18 Percentage of molecules at surface 6  10 12 10 18 = = 0.0006% (a) (ii) No. of molecules on each side = = 1  10 6 1 mm 1 nm

28. P.28 Book E2 Section 3.1 Introduction to nanotechnology Example 2 Surface area per unit volume (b) Repeat (a) for a cube of side 10 nm. (i) Surface area to volume ratio: area volume = 6  10 8 m –1 6d 2 d 3 = 6d6d = 6 10  10 –9 =

29. P.29 Book E2 Section 3.1 Introduction to nanotechnology Example 2 Surface area per unit volume No. of molecules at surface = 488 = 36  10 + 8  8  2 Total no. of molecules = 10 3 = 1000 Percentage of molecules at surface 488 1000 = = 48.8% (ii) No. of molecules on each side = = 10 10 nm 1 nm 36  10 (36 of such 10-molecule rows) 8  8 = 64 (2 of such 64-molecule faces)

30. P.30 Book E2 Section 3.1 Introduction to nanotechnology 4 Why do nano materials behave so differently? b Quantum effect The characteristics of individual atoms become important for materials at nano scale.  requires a new set of physics laws (quantum mechanics) to explain Quantum mechanics also explains the very different optical, electrical and magnetic properties of nano materials from that of bulk materials.

31. P.31 Book E2 Section 3.1 Introduction to nanotechnology Check-point 2 – Q1 (a)Silver particles (total diameters of 3 particles  20 nm) (b)A coating on glass (thickness  370  m) (c)A metal wire (diameter  25 nm) (d)Small tungsten disulfide tube (diameter  0.01  m) (e)Grains of sand (total diameter of 30 grains  3 mm) Yes, 3-D NoNo Is each of the following a nano material? If yes, no. of dimension(s) in nano scale = ? Yes, 2-D NoNo

32. P.32 Book E2 Section 3.1 Introduction to nanotechnology Check-point 2 – Q2 Except the most typical structures like the diamond and graphite, pure carbon can also exist in other forms such as the _________ and ________________. fullerenes carbon nano tubes

33. P.33 Book E2 Section 3.1 Introduction to nanotechnology Check-point 2 – Q3 True or False: Due to their small sizes, it is easier to manufacture nano scale objects. ( T / F )

34. P.34 Book E2 Section 3.1 Introduction to nanotechnology Check-point 2 – Q4 True or False: Due to their small sizes, nano materials produce less waste to the environment when discarded. ( T / F )

35. P.35 Book E2 Section 3.1 Introduction to nanotechnology The End