Circular dichroism in the interband transitions of achiral metal nanoparticles: TiN and noble metals
- PDF / 511,499 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 16 Downloads / 204 Views
Research Letter
Circular dichroism in the interband transitions of achiral metal nanoparticles: TiN and noble metals Jong-Won Park*, Department of Chemistry and The Photonics Center, Boston University, 590 Commonwealth Avenue, Boston, Massachusetts 02215, USA Address all correspondence to Jong-Won Park at [email protected] (Received 24 January 2018; accepted 6 March 2018)
Abstract A longitudinal field component parallel to the wave vector is generally considered in nonlocal optical response. Longitudinal volume plasmons accompanied by inhomogeneous internal field optically break symmetry for isotropic metal nanoparticles. Here, natural circular dichroism in the interband transitions of TiN nanocubes, Au nanospheres, and Cu nanospheres in solution is presented. A field gradient or volume plasmons exert an electric force and consequently Lorentz force on bound valence-band electrons inside the nanoparticles. It is generalized that interband transitions in nanoparticles intrinsically produce a positive rotational strength and optical right-handedness. Electromechanical chiralty is introduced to explain the optical activity of achiral nanoparticles.
Introduction Chirality exists widely in nature at a variety of scale levels from galaxies to atomic nuclei.[1] The chiral matter with its size smaller than the microscopic level is typically manifested by circular dichroism. Circular dichroism (CD) is the spectral difference in photoabsorption or photoemission between left- and rightcircularly polarized (RCP) light in matter. CD may originate from structural, electronic, or magnetic effects including structural dissymmetry in bulk state[2] and band splitting or electron spin polarization at the surface.[3] Electronic CD spectrometers have been commonly used in conjunction with biological studies, in that difference in absorption of chiral substances between leftcircularly polarized (LCP) and RCP light is measured in the optical and ultraviolet regions. When chiral substances significantly scatter light, circular intensity differential scattering (CIDS) also contributes to the amplitude of CD ellipticity.[4] Most of the CD studies in plasmonics are based on CIDS because of the strong scattering intensity of nanostructures obtained in the typical far-field measurement. Although contribution to the far-field intensity is negligible, near-field effects are crucial in nonlinear optical response, plasmon–molecule interaction, hot-electron generation, and conduction-electron dynamics at a metal surface. In the previous study,[5] we have experimentally demonstrated that spherical metal nanoparticles dispersed in solution produce CD in the surface plasmon resonances, although geometrical chirality is not present in and near
* Present address: Department of Mechanical Engineering, Texas Tech University, Box 41021, Lubbock, Texas 79409, USA
the nanoparticles. We attributed the unexpected CD response to nonlocality or a near-field effect. In particular, spatial variation in the energy transfer from surface plasmons to electrons inside the pl
Data Loading...
