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Absorption and Scattering Spectroscopy of Single Metallic Nanoparticles

The excitation of the surface plasmon oscillation of metallic nanoparticles gives rise to both absorption and scattering. The spectral position of the plasmon resonance is determined by the particle size and shape as well as the dielectric properties of the local environment and the metal. Ensemble extinction spectroscopy measures the sum of both absorption and scattering and averages over all nanoparticle sizes and shapes present within the detection volume. To eliminate inhomogeneous broadening of the surface plasmon resonance due to distributions in particle size, shape, and environment, single particle spectroscopy techniques can be applied to investigate separately the radiative (scattering, fluorescence) and nonradiative (absorption) plasmonic properties of individual metallic nanoparticles. Because optical microscopy is limited in resolution by diffraction, we furthermore correlate the optical response with the morphology of the nanoparticles using scanning electron microscopy (SEM). The goal is to determine the plasmonic properties of anisotropic nanostructures that are used as sensors or biological probes and for comparison to more complex nanoparticle assemblies.

The figure above shows an SEM image (left) of individual gold nanorods and the corresponding dark-field scattering image (middle). The same nanoparticles are identified in the electron and optical microscopes using patterned substrates with identification marks. The single particle scattering spectra (right) show the longitudinal surface plasmon resonance. The homogeneous linewidth can be related to the dephasing of the coherent electron oscillation, which occurs on the timescale of a few femtoseconds.

To measure the nonradiative response of the surface plasmon oscillation, we have implemented photothermal heterodyne imaging. Heating of an individual nanoparticle due to plasmon absorption caused by a modulated excitation beam induces a temperature dependent refractive index modulation in the nanoparticle and its surrounding medium, which is probed optically with a second laser beam. Using polarization sensitive excitation, the direction of the plasmon oscillation is interrogated, which can then be used to determine the orientation of non-spherical nanoparticles.

The figure above shows the photothermal intensity of two single gold nanorods as a function of polarization of the excitation beam (left). The intensity reaches a maximum for excitation polarized parallel to the long rod axis. The two traces are out of phase by 90 degrees indicating that the two nanorods are orientated orthogonal to each other. This is confirmed by correlated SEM imaging (right).


  1. J. Olson, S. Dominguez-Medina, A. Hoggard, L.-Y. Wang, W. -S. Chang and S. Link Optical characterization of single plasmonic nanoparticles Chem. Soc. Rev (ASAP) link
  2. C. P. Byers, B. S. Hoener, W.-S. Chang, M. Yorulmaz, S. Link, and C. F. Landes Single-Particle Spectroscopy Reveals Heterogeneity in Electrochemical Tuning of the Localized Surface Plasmon J. Phys. Chem. B (ASAP) link
  3. C. A. Thibodeaux, V. Kulkarni, W.-S. Chang, O. Neumann, Y. Cao, B. Brinson, C. Ayala-Orozco, C.-W. Chen, E. Morosan, S. Link, P. Nordlander, and N. J. Halas Impurity-Induced Plasmon Damping in Individual Cobalt-Doped Hollow Au Nanoshells J. Phys. Chem. C (ASAP) link
  4. A. Hoggard, L.-Y. Wang , L. Ma, Y. Fang,G. You,J. Olson, Z. Liu, W.-S. Chang, P. M. Ajayan and S. Link, Using the Plasmon Linewidth to Calculate the Time and Efficiency of Electron Transfer between Gold Nanorods and Graphene. ACS Nano 7, 11209 (2013) link
  5. Y. Fang, W.-S. Chang, B. Willingham, P. Swanglap, S. Dominguez-Medina, S. Link, Plasmon emission quantum yield of single gold nanorods as a function of aspect ratio. ACS Nano 6, 7177 (2012). link
  6. W.-S. Chang, S. Link, Enhancing the Sensitivity of Single Particle Photothermal Imaging with Thermotropic Liquid Crystals. J. Phys. Chem. Lett. 3, 1393 (2012). link
  7. B. L. Sanchez-Gaytan, P. Swanglap, T. J. Lamkin, Z. Fakhraai, S. Link, S.-J. Park, Synthesis and Optical Properties of Spiky Gold Nanoshells. J. Phys. Chem. C 116, 10318 (2012). link
  8. W.-S. Chang, B. Willingham, L. S. Slaughter, S. Dominguez-Medina, P. Swanglap, S. Link, Radiative and Nonradiative Properties of Single Plasmonic Nanoparticles and Their Assemblies. Acc. Chem. Res. 45, 1936 (2012). link
  9. L. S. Slaughter, W.-S. Chang, S. Link, Characterizing Plasmons in Nanoparticles and Their Assemblies with Single Particle Spectroscopy. J. Phys. Chem. Lett. 2, 2015 (2011).link
  10. A. Tcherniak, S. Dominguez-Medina, W.-S. Chang, P. Swanglap, L. S. Slaughter, C. F. Landes, S. Link, One-photon plasmon luminescence and its application to correlation spectroscopy as a probe for rotational and translational dynamics of gold nanorods. J. Phys. Chem. C 115, 15938 (2011). link
  11. A. Tcherniak, J. W. Ha, S. Dominguez-Medina, L. S. Slaughter, S. Link, Probing a century old prediction one plasmonic particle at a time. Nano Lett. 10, 1398 (2010). link
  12. L. S. Slaughter, W.-S. Chang, P. Swanglap, A. Tcherniak, B. P. Khanal, E. R. Zubarev, S. Link, Single-particle spectroscopy of gold nanorods beyond the quasi-static limit: Varying the width at constant aspect ratio. J. Phys. Chem. C 114, 4934 (2010). link
  13. W.-S. Chang, J. W. Ha, L. S. Slaughter, S. Link, Plasmonic Nanorod Absorbers as Orientation Sensors. Proc. Natl. Acad. Sci. USA, 107, 2781 (2010). link