interact with external light of a much longer wavelength. Thus, the BCP SA
approach is very promising for fabrication of large-scale and low-cost 3D isotropic
metamaterials.
Indeed, the Wiesner group suggested in a computational study that BCP-derived
3D isotropic metamaterials with a double gyroid morphology may have a negative
refractive index in the visible regime [15]. This exciting result may motivate the
use of other materials derived from bottom-up SA techniques in metamaterials
research [65]. Furthermore, in a subsequent collaborative effort with the Steiner and
Baumberg groups at Cambridge University, aspects of the proposed properties
of the computational studies were seen in alternating BCP gyroid metamaterials
backfilled with gold [38, 66].
6.3 Phononics and Thermoelectric Devices
A phonon is a lattice vibration that mediates transport of sound and thermal waves.
A phononic crystal is a periodic material engineered to control the propagation
of phonon waves. Phononic crystals that manipulate sound waves are sometimes
called acoustic metamaterials. As for photonic crystals, BCP SA may be used for
fabricating phononic crystals. Also similar to the photonics field, one of the main
properties that scientists try to establish in acoustic metamaterials is a phononic
band gap, i.e., a frequency range in which phonons cannot exist in the material.
Similarly to photonic crystals, phononic crystals can manipulate specific phonons
with a wavelength that is comparable to the lattice dimension. For example, a
periodic material with a lattice dimension of centimeters manipulates sound waves,
whereas a material with a lattice dimension of nanometers strongly interacts with
thermal waves. Thus, a phononic crystal derived from BCP SA may be able to
control the flow of thermal waves.
The control of thermal waves in such phononic crystals could be applied to
generate better thermoelectric materials. The figure of merit for thermoelectric
devices, ZT, is proportional to the so-called Seebeck coefficient and to the ratio
of electron conductivity to thermal conductivity [67]. Materials with high electron
and low thermal conductivities promise high figures of merit, thereby leading to
efficient thermoelectric devices. The three parameters are, however, not independent. For example, materials with low thermal conductivity usually have poor
electric conductivity. In order to minimize the thermal conductivity of a material
without the deterioration of electron conductivity, it is desirable to structure the
material with a phononic band gap. The incorporation of phononic band gap
structures into thermoelectric materials can reduce their thermal conductivity in
that phonons (thermal energy carriers) are missing in the phononic band gap
frequency range. Therefore, BCP-derived phononic crystals may in the future
become useful for improving the figure of merit for thermoelectric devices.
Design and Applications of Multiscale Organic–Inorganic Hybrid Materials. . .
285
approach is very promising for fabrication of large-scale and low-cost 3D isotropic
metamaterials.
Indeed, the Wiesner group suggested in a computational study that BCP-derived
3D isotropic metamaterials with a double gyroid morphology may have a negative
refractive index in the visible regime [15]. This exciting result may motivate the
use of other materials derived from bottom-up SA techniques in metamaterials
research [65]. Furthermore, in a subsequent collaborative effort with the Steiner and
Baumberg groups at Cambridge University, aspects of the proposed properties
of the computational studies were seen in alternating BCP gyroid metamaterials
backfilled with gold [38, 66].
6.3 Phononics and Thermoelectric Devices
A phonon is a lattice vibration that mediates transport of sound and thermal waves.
A phononic crystal is a periodic material engineered to control the propagation
of phonon waves. Phononic crystals that manipulate sound waves are sometimes
called acoustic metamaterials. As for photonic crystals, BCP SA may be used for
fabricating phononic crystals. Also similar to the photonics field, one of the main
properties that scientists try to establish in acoustic metamaterials is a phononic
band gap, i.e., a frequency range in which phonons cannot exist in the material.
Similarly to photonic crystals, phononic crystals can manipulate specific phonons
with a wavelength that is comparable to the lattice dimension. For example, a
periodic material with a lattice dimension of centimeters manipulates sound waves,
whereas a material with a lattice dimension of nanometers strongly interacts with
thermal waves. Thus, a phononic crystal derived from BCP SA may be able to
control the flow of thermal waves.
The control of thermal waves in such phononic crystals could be applied to
generate better thermoelectric materials. The figure of merit for thermoelectric
devices, ZT, is proportional to the so-called Seebeck coefficient and to the ratio
of electron conductivity to thermal conductivity [67]. Materials with high electron
and low thermal conductivities promise high figures of merit, thereby leading to
efficient thermoelectric devices. The three parameters are, however, not independent. For example, materials with low thermal conductivity usually have poor
electric conductivity. In order to minimize the thermal conductivity of a material
without the deterioration of electron conductivity, it is desirable to structure the
material with a phononic band gap. The incorporation of phononic band gap
structures into thermoelectric materials can reduce their thermal conductivity in
that phonons (thermal energy carriers) are missing in the phononic band gap
frequency range. Therefore, BCP-derived phononic crystals may in the future
become useful for improving the figure of merit for thermoelectric devices.
Design and Applications of Multiscale Organic–Inorganic Hybrid Materials. . .
285