1. Metal Nanoparticles of Various Shapes
Jie Gao, Min Xu
Apr. 1, 2007

2. Outline Advantages of metal nanoparticles. Why we need nanorods?
Synthesis of metal nanoparticles.
Synthesis of gold nanorods.
Growth mechanism of gold nanorods.
Synthesis of gold nanoparticles of different shapes.
Advantage of seed-mediated method
Other issues to consider

3. Advantages of Metal Nanoparticle
Strong plasma absorption
Enhance Rayleigh scattering
Surface enhanced Raman scattering

4. Advantage of Metal Nanoparticles
Biological detector
Biological system imaging
Determine chemical information on metallic nanoscale substrate

5. Why we need nanorods? Limitations of nanospheres
S. Eustis, M. A. El-Sayed, Chem. Soc. Rev. 2006, 35,

6. Synthesis of metal nanoparticles
Bottom up method--assemble atoms to nanostructures
1. Nanosphere lithography.
2. Templating, chemical, electrochemical, sonochemical, thermal and photochemical reduction techniques.
Top down method--cut into pieces in nanoscale
1. Photolithography
2. Electron beam lithography

7. Synthesis of metal nanoparticles
Nanosphere lithography
W. Huang, W. Qian, M. A. El-Sayed, Proc. SPIT Int. Soc. Opt. Eng. 2005, 5927,

8. Synthesis of metal nanoparticles
Citrate Reduction Method
Turkevitch in 1951
sodium citrate + HAuCl4

9. Synthesis of metal nanoparticles
Two Phase Reactions
Inverse Micelles
General idea of chemical method: reduction + capping

10. Synthesis of gold nanorods
Seed-mediated method
Two steps: produce seed particles + seed grow into rod
C. J. Murphy, T. K. Sau, A. M. Gole, C. J. Orendorff. J. L. Gou, S. E. Hunyadi, T. Li, J. Phys. Chem. B 2005, 109,

11. Synthesis of gold nanorods

12. Synthesis of gold nanorods
Factors related to the growth
1. Seed size
2. Length of “tails” of CTAB (cetyltrimethylammonium bromide )

13. Synthesis of gold nanorods
dependence of nanorod aspect ratio on seed size

14. Synthesis of gold nanorods
Dependence of aspect ratio on length of tails of CTAB

15. Growth mechanism of gold nanorods
“Zipping” fashion formation of gold nanorods
:C16TAB

16. Growth mechanism of gold nanorods
Planar density of atoms of FCC structure
{111}: 0.907
{100}: 0.785
{110}: 0.555
crystallography picture of gold nanorods:
pentatetradedral

17. Growth mechanism of gold nanorods
tail contribution to the free energy formation of a bilayer on gold
ΔG(10)= kJ/mol, Δ(12)= kJ/mol, Δ(14)= kJ/mol,Δ(16)= kJ/mol

18. Growth mechanism of gold nanorods

19. Synthesis of gold nanoparticles of different shapes
General idea is the same as the growth of gold nanorods (seed-mediated method)
Slightly change the conditions when growing nanorods (concentration of different reactants)
Cubes, hexagon, triangle, tetropods, branched
T. K. Sau, C. J. Murphy, J. Am. Chem. Soc. 2004, 126,

20. Synthesis of gold nanoparticles of different shapes
[AA] increases from A to C and seed concentration increases from C to D. Scale bar = 100 nm

21. Synthesis of gold nanoparticles of different shapes
TEM images showing cubic to rod-shaped gold particles produced with low AA concentration in the presence of small quantity of silver nitrate. [CTAB] is increased (A) to (B, C, D). [Au3+] decreases from B to C, and seed concentration increased form C to D. Scale bar = 100 nm

22. Synthesis of gold nanoparticles of different shapes
TEM images of brached Au nanoparticles, varying in the dimension and number of branches

23. Synthesis of gold nanoparticles of different shapes
Summary of experimental procedure
The concentrations are interdependent
2. Growth mechanism is similar to that of rod

24. Advantage of water seed-mediated method
High yield
Monodisperse
Cheap, easy

25. Other issue to consider
The nucleation process in growth of seed is still mysterious
Limitation in length and aspect ratio
maximum length: ~600nm
maximum aspect ratio: ~25

26. Summary Advantages of metal nanoparticles. Why we need nanorods?
Synthesis of metal nanoparticles.
Synthesis of gold nanorods.
Growth mechanism of gold nanorods.
Synthesis of gold nanoparticles of different shapes.
Advantage of seed-mediated method
Other issues to consider