Metal Nanoparticles of Various Shapes

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, 209-217

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, 592701

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. B2005, 109, 13857-13870

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)= -29.6 kJ/mol, Δ(12)= -35.8 kJ/mol, Δ(14)= -41.9 kJ/mol,Δ(16)= -48.1 kJ/mol

18. Growth mechanism of gold nanorods 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, 8648-8649

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