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

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metal nanoparticles of various shapes

Metal Nanoparticles of Various Shapes

Jie Gao, Min Xu

Apr. 1, 2007

outline
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
advantages of metal nanoparticle
Advantages of Metal Nanoparticle
  • Strong plasma absorption
  • Enhance Rayleigh scattering
  • Surface enhanced Raman scattering
advantage of metal nanoparticles
Advantage of Metal Nanoparticles
  • Biological detector
  • Biological system imaging
  • Determine chemical information on metallic nanoscale substrate
why we need nanorods
Why we need nanorods?
  • Limitations of nanospheres

S. Eustis, M. A. El-Sayed, Chem. Soc. Rev.2006, 35, 209-217

synthesis of metal nanoparticles
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

synthesis of metal nanoparticles7
Synthesis of metal nanoparticles
  • Nanosphere lithography

W. Huang, W. Qian, M. A. El-Sayed, Proc. SPIT Int. Soc. Opt. Eng.2005, 5927, 592701

synthesis of metal nanoparticles8
Synthesis of metal nanoparticles
  • Citrate Reduction Method

Turkevitch in 1951

sodium citrate + HAuCl4

synthesis of metal nanoparticles9
Synthesis of metal nanoparticles
  • Two Phase Reactions
  • Inverse Micelles

General idea of chemical method: reduction + capping

synthesis of gold nanorods
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

synthesis of gold nanorods12
Synthesis of gold nanorods
  • Factors related to the growth

1. Seed size

2. Length of “tails” of CTAB (cetyltrimethylammonium bromide )

synthesis of gold nanorods13
Synthesis of gold nanorods

dependence of nanorod aspect ratio on seed size

synthesis of gold nanorods14
Synthesis of gold nanorods

Dependence of aspect ratio on length of tails of CTAB

growth mechanism of gold nanorods
Growth mechanism of gold nanorods

“Zipping” fashion formation of gold nanorods

:C16TAB

growth mechanism of gold nanorods16
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

growth mechanism of gold nanorods17
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

growth mechanism of gold nanorods18
Growth mechanism of gold nanorods

Growth mechanism of gold nanorods

synthesis of gold nanoparticles of different shapes
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

synthesis of gold nanoparticles of different shapes20
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

synthesis of gold nanoparticles of different shapes21
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

synthesis of gold nanoparticles of different shapes22
Synthesis of gold nanoparticles of different shapes

TEM images of brached Au nanoparticles, varying in the dimension and number of branches

synthesis of gold nanoparticles of different shapes23
Synthesis of gold nanoparticles of different shapes
  • Summary of experimental procedure
  • The concentrations are interdependent
  • 2. Growth mechanism is similar to that of rod
advantage of water seed mediated method
Advantage of water seed-mediated method
  • High yield
  • Monodisperse
  • Cheap, easy
other issue to consider
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

summary
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