Optical Properties of Gold Nanoparticles Outline Introduction Size

Outline: • • • Introduction Size Dependence Shape Dependence Temperature Dependence Encapsulating Layers Conclusion

Introduction: • New optical properties which are observed neither in molecules (2 nm and

Plasmon A Plasmon is quantized oscillation in the density of an electron gas. It

Introduction: • It can be explained by combining the classical Drude model with the

Size Dependence: • Plasmon bandwidth – λ >> 2 R, 2 R < 25

Summery of the size of the gold nanoparticles Diameter [nm] Mean Standard λmax Deviation

Shape Dependence: • Family of alumina membranes that contain Au nanoparticles. • Aspect ratio

Aspect ratio of the resulting Au nanoparticles, and color of the Nanoparticle-containing membrane Coulombs

Temperature Dependence: • Dephasing of the surface plasmon electron motion is a result of

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Optical Properties of Gold Nanoparticles

Outline: • • • Introduction Size Dependence Shape Dependence Temperature Dependence Encapsulating Layers Conclusion

Introduction: • New optical properties which are observed neither in molecules (2 nm and smaller) nor in bulk metals. • Presence of a strong band in the visible region of the absorbance (for spherical gold nanoparticles at about 520 nm). • It attributed to surface plasmon oscillation modes of the conduction electrons (6 selectorons for gold).

Plasmon A Plasmon is quantized oscillation in the density of an electron gas. It is due to electron-electron interactions. Surface plasmon: Two-dimensional fluctuations at the surface.

Introduction: • It can be explained by combining the classical Drude model with the Mie theory for light absorption and scattering by spheres. • Sensitive to: – Size Dependence – Shape Dependence – Encapsulating Layers – Temperature Dependence –…

Size Dependence: • Plasmon bandwidth – λ >> 2 R, 2 R < 25 nm Intrinsic size effects, Dipole approximation – 2 R > 25 nm Extrinsic size effects, higher order terms contribute • λmax – Intrinsic size effects – Extrinsic size effects

λmax

Summery of the size of the gold nanoparticles Diameter [nm] Mean Standard λmax Deviation [%] [nm] 8. 9 13 517 14. 8 12 520 21. 7 9 521 48. 3 11 533 99. 3 11 575

Shape Dependence: • Family of alumina membranes that contain Au nanoparticles. • Aspect ratio (length divided by diameter) – a/b < 1 Oblate or pancake-like – a/b = 1 Spheroid – a/b > 1 Prolate or needle-like

Aspect ratio of the resulting Au nanoparticles, and color of the Nanoparticle-containing membrane Coulombs of gold plated Particle length (nm) Particle aspect ratio Membrane color 0. 05 20 0. 38 Turquoise 0. 065 24 0. 46 Sky Blue 0. 05 28 0. 54 Blue Purple 0. 10 40 0. 77 Magenta 0. 10 70 1. 3 Violent 0. 20 140 2. 7 Ruby Rod 0. 40 400 7. 7 Red 0. 70 600 12 Scarlet 1. 33 1200 23 Ferrari Red

Temperature Dependence: • Dephasing of the surface plasmon electron motion is a result of electron-electron repulsion rather than electron-phonon interactions.

Encapsulating Layers: • Au@Si. O 2