10 Realization of Artificial Chirality in Micro-/Nano-Scale …
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Fig. 10.7 The chiroptical response of two-turn gold nanohelix. a Geometrical features of the
nanohelix structure. b Normalized circular dichroism spectra of left-handed and right-handed
nanohelices; inset: TEM image of the nanohelices. c Circular dichroism spectra of one-turn and twoturn nanohelices grown under different cooling conditions. d Circular dichroism spectra simulated
using a model of (a). The inset shows the discrete dipole model used in the simulation. e Side-view
SEM images of left-handed (top left) and right-handed (bottom left) Mg nanohelices; scale bar: 200
nm. Right panel: top view of a left-handed array of nanohelices. f Extinction spectra in response
to unpolarized (E T ) and circularly polarized light (E L , E R ). g Circular dichroism spectra of 178nm-thick film containing nanohelices of left or right handedness in air. (a–d) from [26], (e–g) from
[29]
~170 K, particularly for materials that have high surface energy, such as noble metals.
The fabricated wafer-scale helical nanostructure array (a 3 inch wafer can support
roughly 10
11 particles) can be released in the solution and can form uniform/isotropic
chiral medium. The advantage of this approach is that the wavelength range in
which chiral properties occur can be controlled by using an appropriate material
for fabrication.
Magnesium (Mg)-based chiral NPs that work in the ultraviolet (UV) spectral
range have been demonstrated [29]. Mg is widely used as a UV plasmonic material
because in the UV region Mg has substantially high far-field absorption efficiency
and strong near-field enhancement. Furthermore, Mg has high diffusion rate, so the
Mg nanohelix structure should be sculpted in a far cooler condition ~100 K. However,
Mg is highly reactive in air, so the nanohelix should be coated with a thin layer of
HfO 2 or Al 2 O 3 to prevent structural and chemical deformation (Fig. 10.7).
Multi-turn nickel and silver nanohelix structures show specular reflectance in the
visible-and-NIR spectrum [30]. The associated optical reflectance spectrum showed
minima at wavelengths that coincided with the total height of nanohelices; this result
demonstrates the existence of LSPR along the axis of nanohelices. This further
251
Fig. 10.7 The chiroptical response of two-turn gold nanohelix. a Geometrical features of the
nanohelix structure. b Normalized circular dichroism spectra of left-handed and right-handed
nanohelices; inset: TEM image of the nanohelices. c Circular dichroism spectra of one-turn and twoturn nanohelices grown under different cooling conditions. d Circular dichroism spectra simulated
using a model of (a). The inset shows the discrete dipole model used in the simulation. e Side-view
SEM images of left-handed (top left) and right-handed (bottom left) Mg nanohelices; scale bar: 200
nm. Right panel: top view of a left-handed array of nanohelices. f Extinction spectra in response
to unpolarized (E T ) and circularly polarized light (E L , E R ). g Circular dichroism spectra of 178nm-thick film containing nanohelices of left or right handedness in air. (a–d) from [26], (e–g) from
[29]
~170 K, particularly for materials that have high surface energy, such as noble metals.
The fabricated wafer-scale helical nanostructure array (a 3 inch wafer can support
roughly 10
11 particles) can be released in the solution and can form uniform/isotropic
chiral medium. The advantage of this approach is that the wavelength range in
which chiral properties occur can be controlled by using an appropriate material
for fabrication.
Magnesium (Mg)-based chiral NPs that work in the ultraviolet (UV) spectral
range have been demonstrated [29]. Mg is widely used as a UV plasmonic material
because in the UV region Mg has substantially high far-field absorption efficiency
and strong near-field enhancement. Furthermore, Mg has high diffusion rate, so the
Mg nanohelix structure should be sculpted in a far cooler condition ~100 K. However,
Mg is highly reactive in air, so the nanohelix should be coated with a thin layer of
HfO 2 or Al 2 O 3 to prevent structural and chemical deformation (Fig. 10.7).
Multi-turn nickel and silver nanohelix structures show specular reflectance in the
visible-and-NIR spectrum [30]. The associated optical reflectance spectrum showed
minima at wavelengths that coincided with the total height of nanohelices; this result
demonstrates the existence of LSPR along the axis of nanohelices. This further