Surface Plasmon Resonance in Metallic Nanoparticles and Nanostructures

Transcription

1 Surface Plasmon Resonance in Metallic Nanoparticles and Nanostructures Zhi-Yuan Li Optical Physics Laboratory, Institute of Physics, CAS Beijing 18, China January 5-9, 7, Fudan University, Shanghai Challenges and Opportunities in Nano-Optics Workshop

2 Outlines 1. Introductions. SPR in metallic nanoparticles of complex geometries 3. Local field enhancement in metallic nanoparticles 4. Synthesis and applications of metallic nanoparticles 5. Plasmonics in metallic nanostructures 6. Conclusions

3 Introductions Metal nanostructures and nanoparticles have found applications in a wide variety of areas: Catalysis, optics, optoelectronics, information storage, biological and chemical sensing, and surface-enhanced Raman scattering. By tailoring the size and shape of metal nanoparticles, one can tune their intrinsic properties for a range of applications. Fabrication of metallic nanostructures and nanoparticles: 1. Top-down physical technologies: lithography techniques, template approach. Bottom-up chemical technologies: synthesis of nanoparticles, nanowire, self-assembly technique, etc.

4 SPR in Metallic Nanoparticles Surface plasmon modes in metal surfaces E = E exp( ik x x k z z)exp( iω t) k = ε ε x k ε = 1 k 1 kn1 ε1 + ε Surface Plasmon in Metallic Nanoparticles: far smaller than incident wavelength, do not support true localized SP wave modes, but rather resonant scattering modes.

5 A simple example: small nanoparticles as a point dipole r r r P = α Eloc (r ) 3 α = r ε ( ω) ε ( ω)]/[ ε ( ω) + ε ( ω)] [ 1 1 If at certain frequency α ε1( ω) = ε ( ω), P r Scattering/Absorption/Extinction Resonance Happens. Must be metal materials. Depends on dispersion ε 1 ( ω) The dominant physical mechanism is not the existence of localized surface eigenmode, but rather the match of polarizability of the dipole.

6 SPR in Au and Ag spherical solid nanoparticles 1.5 Water background Optical Spectra silver Q ext Q sca Q abs R=15nm Optical Spectra gold Q ext Q sca Q abs R=15nm Optical Spectra W avelength (µ m) Q ext Q sca Q abs R=5nm Wavelength (µ m) Optical Spectra Q ext Q sca Q abs R=5nm Optical Spectra W avelength (µ m) Q ext Q sca Q abs R=5nm W avelength (µ m) Optical Spectra W avelength (µ m) Q ext Q sca Q abs R=5nm

7 Nanocube and Cubic Shell Nanoparticles Solid non-spherical particles Q ext Q sca Q abs a=39nm b=33nm t=3nm gold cube in water a=4nm Q ext Q sca Q abs Wavelength (µm) gold shell Wavelength (µm) Wavelength (µm) Empty shell particles Q ext Q sca Q abs a=36nm b=3nm t=3nm silver cube in water a=4nm Q ext Q sca Q abs gold shell Wavelength (µm)

8 Gold nanorods: Tuning of SPR wavelength via aspect ratio Optical Spectrum D=nm, L=3nm Q ext Q sca Q abs Wavelegnth (µm) Optical Spectrum D=nm, L=4nm Q ext Q sca Q abs Optical Spectrum Wavelegnth (µm) D=nm, L=6nm Q ext Q sca Q abs Wavelegnth (µm) 5 D=nm, L=8nm 6 D=nm, L=1nm Optical Spectrum Optical Spectrum Q ext Q sca Q abs Wavelegnth (µm) Wavelegnth (µm)

9 Metal Nanostructures of Different Shapes Chemical synthesis methods

10 Local Field Enhancement Questions: 1. Correlation of field enhancement with SPR peak. Correlation of field enhancement with geometry of metallic particles

11 Ag Polyhedron nanoparticles in water background B.Wiley et al, J. Phys. Chem. B 11, (6). Cover Feature article Long wavelength SPR is related with the sharp corners

12 Disk-shape nanoparticles. Incident wave normal to disk plate

13 Ag triangular plate particle y 4 surface E pattern surface x Extinction Cross Section (1-1 m ).5 triangular plate h=5nm a=43nm h=1nm X-polarization Wavelength (µm) center h=1nm particle SPR 64nm center h=5nm particle SPR 78nm

14 Ag-Au alloy ring particle E pattern Transverse Mode SPR 91nm E surface Optical Coefficient Ag:Au=:1 Alloy ring D out =16nm D in =1nm h=3nm Q ext Q sca Q abs center Wavelength (µm)

15 Silver Rectangular Bar in Water z y x Optical Cross Section (1-1 m ) Longitudinal mode a=15nm b=55nm c=5nm C ext C sca C abs Optical Cross Section (1-1 m ) Wavelength (µm) Transverse mode a=15nm b=55nm c=5nm C ext C sca C abs Wavelength (µm)

16 89nm, Longitudinal Mode SPR YZ plane at Particle Center XZ plane at Particle Center XZ plane at Particle Upper Surface YZ plane at Particle Right Surface XY plane at Particle Center XY plane at Particle Front Surface

17 51nm, Transverse Mode SPR 4 - YZ plane at Particle Center XZ plane at Particle Center XZ plane at Particle Upper Surface YZ plane at Particle Right Surface 4 XY plane at Particle Center XY plane at Particle Front Surface

18 Synthesis and Applications of Novel-Geometry Metallic Nanoparticles Chemical synthesis of nonspherical silver nanoparticles: bottom-up scheme Ethylene glycol

19 Synthesis of Ag nanocube particles SEM images of four typical examples of Ag nanocubes: (A-C) cubes of 3, 5, and 11 nm in edge length and, and (D) truncated cubes of 1 nm in dimension. Synthesis with aid of polyo process using PVP. Growth along (111) direction. Single crystal cube with six (1) faces. J. Chen et al., Nano Letters, 5, Vol. 5, pp

20 Au nanoparticles of complex geometry Galvanic replacement reaction on Ag nanocube particles leads to Au nanocages Ag + HAuCl4 Au

21 Applications of New Metallic Nanoparticles Gold nanocages: Size 3-4nm wall thickness 3-5nm J. Chen et al., Nano Letters, 5, Vol. 5, pp ; B. Wiley et al., MRS Bulletin, 5, Vol. 3, pp ; C. Hu et al., Optics Letters, 5, Vol. 3,

22 Imaging Contrast Agents in Optical Coherence Tomography Theory C abs C sca = = m m OCT Measurement λ 8nm C abs C sca = = m m

23 J. Chen et al., Advanced Materials 17, 555 (5). Issue 18 Strong absorption effect of light by Au nanocages TEM images of Au nanocages (~55 nm in edge length) before (A) and after (B) exposure to a camera flash light. The insets are the enlarged TEM images, with the scale bars being 5 nm. The nanocages have melted and became spherical droplets due to the photothermal effects.

24 Thermal Therapeutic Applications J. Chen et al., Advanced Materials 17, 555 (5). Issue 18 Bioconjugation Gold nanocage has 5 orders of magnitude larger absorption cross section than ICG dye

25 Synthesis kinetics and dynamics of nanoparticles probed by optical spectra Upper panel: vials containing gold nanocages (suspended in water) that were prepared by titrating silver nanocubes with different volumes of HAuCl 4 solution. Lower panel: extinction spectra recorded from aqueous suspensions of these gold nanocages, with the volume of HAuCl 4 solution labelled on each curve. M. Hu et al., Chem. Soc. Rev. 35, 184 (6)

26 5. Fabrication and Characterization of Complex Nanostructures in Metal Thin Films Surface plasmonics in metallic nanostructures microfabrication techniques for metal thin films New physics: anomalous transmission through metallic holes arrays directional emission through nanostructured slits/holes New applications: ultrasmall optoelectronical devices and integrated circuits sensitive bio/chemical sensors Questions: Relations of far-field transmission spectra with near-field optical properties?

27 Dual Pass-Band Cross Dipole Fractal Slit Arrays a1=1.8 µm, a=.8 µm d=1.5 µm w=1nm Two-Order Fractal Metallic Nanostructures Mei Sun et al., Phys. Rev. B 74, (6)

28 Far-Field Transmission Spectrum.5.6 Two-Order Structure First-Order Structure Second-Order Structure.4.5 Transmission.3..1 Theory Experiment Transmission Wavelength(µm) Wavelength(µm)

29 Near-Field Optical Patterns Electric-field intensity pattern Y (µm) Y (µm) X (µm) λ =1.68um X (µm) λ = 5.um

30 Nanostructures of Anisotropic Geometry: H-Pattern a 3 d a 1 a y x w w a1=a=.5 µm, d=1.1 µm, w=1nm, h=1nm

31 Transmission Spectrum: Strong Polarization Dependence Transmission o 3 o 45 o 6 o 9 o gold film Wavelength (nm) Experimental and theoretical results Transmission Transmission x-polarized Wavelength (nm) y-polarized.5. Mei Sun et al., Phys. Lett. A, in press (7) Wavelength (nm)

32 Optical-Near Field Pattern at Transmission Peaks.4.. d=1.1um, λ=1.53um, x-pol d=1.1um, λ=1.65um, y-pol d=1.1um, λ=1.68um, x-pol d=1.1um, λ=3.6um, y-pol

33 Summary By tailoring the geometries of metal nanoparticles and nanostrutures, one can tune their intrinsic properties for a range of applications. 1. Geometry, composite, and background sensitive: Chemical and biosensors. Easy tunning of SPR to particular wavelength windows 3. Local field enhancement: SERS 4. Optical probe for nanoparticle synthesis dynamics and kinetics. 5. Nanophotonics functional elements and devices, information and energy applications 6. New applications? Depend on design and synthesis of new nanostructures

34 Collaborators: 1. Experimental group in Chemistry Department, University of Washington, Seattle, USA Prof. Younan Xia, Jingyi Chen, B. Wiley, Dr. Yugang Sun, Dr. Yujie Xiong, Dr. Cang Hu et al., Metallic Nanoparticles. Photonic crystal group in Optics Physics Laboratory, IoP, CAS Prof. Daozhong Zhang, Dr. Mei Sun, Metallic Nanostructures 3. Prof. Sishen Xie, experimental group, IoP, Composite Metallic Nanoparticles 4. Prof. Meng Chen, Dept. Chem., Fudan University, Metallic Nanoparticles Financial supports: Bai-Ren Ji-Hua project, CAS, China 973 Project, Outstanding Young Scientist Fellowship, NSFC