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objects interact differently with left-circularly-polarized (LCP) and right-circularlypolarized (RCP) light. Their absorption difference under LCP and RCP incidences
is circular dichroism (CD), and the polarization rotation of light interacting with the
chiral objects is optical rotatory dispersion. However, naturally occurring materials
have intrinsically weak chiroptical responses, or circular birefringence, due to the
large mismatch between the wavelength and the sizes of chiral molecules. This weak
response hinders application of chiroptical properties.
Recent advances in artificial chirality in structured materials suggest a possibility
of generating materials that have strong chiroptical properties that far exceed those
found in natural materials, and chiral effects have been observed universally across
different length scales. According to the antenna theory [2], the resonant wavelength
of a single antenna is comparable to its geometric feature size. This principle also
applies to chiral effects; the working wavelength of the chiral effects becomes generally similar to the geometric feature size of the chiral antenna. Therefore, chiral
antennas that operate at wavelengths of micrometers or longer are relatively easy to
fabricate. This principle applies because the optical properties of metals at long wavelengths are well represented as conductor (metallic) [3]. However, the optical properties of metals near the plasma frequency become strongly dispersive and deviate
from those of a perfect conductor. Due to this feature, metallic antennas become
lossy at wavelengths near the visible regime. With these points in mind, fabrication
methods should be considered with regards to the desired working wavelength and
the properties of the material.
Recently, subwavelength metallic particles have been actively investigated for
surface-enhanced Raman scattering [4], photothermal effects [5], and optical
antennas [6] due to their strong near-field enhancement and scattering effects, which
originate from localized surface plasmon resonance (LSPR) coming the collective
oscillations of electrons and photons trapped on the surface of the small particles
[7]. When the particle size is much smaller than the wavelength, the LSPR can
be predicted using the quasistatic theory. Therefore, the metallic antennas near the
visible regime are distinguished from those at longer wavelengths as plasmonic
antennas. The wavelength scaling principle above does not apply to plasmonic
antennas [3], and subwavelength (~10 nm) chiral plasmonic nanoparticles (NPs)
have strong chiral effects in the visible spectrum. In addition, the LSPR wavelength
can be further redshifted without increasing the particle size by using high refractive
index core and plasmonic shell [8, 9].
In this chapter, we discuss a few fabrication methods of chiral structures and their
applications. Sections are divided according to the structure size, because it determines working wavelengths and the fabrication methods, and applications strongly
depend on the working wavelengths.
Y. Yang et al.
objects interact differently with left-circularly-polarized (LCP) and right-circularlypolarized (RCP) light. Their absorption difference under LCP and RCP incidences
is circular dichroism (CD), and the polarization rotation of light interacting with the
chiral objects is optical rotatory dispersion. However, naturally occurring materials
have intrinsically weak chiroptical responses, or circular birefringence, due to the
large mismatch between the wavelength and the sizes of chiral molecules. This weak
response hinders application of chiroptical properties.
Recent advances in artificial chirality in structured materials suggest a possibility
of generating materials that have strong chiroptical properties that far exceed those
found in natural materials, and chiral effects have been observed universally across
different length scales. According to the antenna theory [2], the resonant wavelength
of a single antenna is comparable to its geometric feature size. This principle also
applies to chiral effects; the working wavelength of the chiral effects becomes generally similar to the geometric feature size of the chiral antenna. Therefore, chiral
antennas that operate at wavelengths of micrometers or longer are relatively easy to
fabricate. This principle applies because the optical properties of metals at long wavelengths are well represented as conductor (metallic) [3]. However, the optical properties of metals near the plasma frequency become strongly dispersive and deviate
from those of a perfect conductor. Due to this feature, metallic antennas become
lossy at wavelengths near the visible regime. With these points in mind, fabrication
methods should be considered with regards to the desired working wavelength and
the properties of the material.
Recently, subwavelength metallic particles have been actively investigated for
surface-enhanced Raman scattering [4], photothermal effects [5], and optical
antennas [6] due to their strong near-field enhancement and scattering effects, which
originate from localized surface plasmon resonance (LSPR) coming the collective
oscillations of electrons and photons trapped on the surface of the small particles
[7]. When the particle size is much smaller than the wavelength, the LSPR can
be predicted using the quasistatic theory. Therefore, the metallic antennas near the
visible regime are distinguished from those at longer wavelengths as plasmonic
antennas. The wavelength scaling principle above does not apply to plasmonic
antennas [3], and subwavelength (~10 nm) chiral plasmonic nanoparticles (NPs)
have strong chiral effects in the visible spectrum. In addition, the LSPR wavelength
can be further redshifted without increasing the particle size by using high refractive
index core and plasmonic shell [8, 9].
In this chapter, we discuss a few fabrication methods of chiral structures and their
applications. Sections are divided according to the structure size, because it determines working wavelengths and the fabrication methods, and applications strongly
depend on the working wavelengths.