Advanced Optical Materials

A nanocup structure that mimics the Lycurgus cup effect enables nanoplasmonic spectroscopy to be used for colorimetric sensing, requiring only the naked eye or ordinary visible color photography. Enhanced optical transmission from the subwavelength cup structures couples with the localized surface plasmon from metal nanoparticles on the side walls of the cup, creating extraordinary sensitivity and visible color changes. Utility of the sensor for chemical imaging, biomolecular imaging, and integration to portable microfluidics devices for lab-on chip-applications is demonstrated by Liu and co-workers on page 68.

Cebollada and co-workers review on page 10 how the combination of plasmonic and magnetic functionalities gives rise to magnetoplasmonic systems, where both the magneto-optical and plasmonic properties can be engineered. For example, the effect of the magnetic field on the optical properties of these systems can be increased under plasmon excitation. Additionally, in these systems, the wavelength of the propagating surface plasmons can be externally controlled under the application of a magnetic field.

The rendering on the back cover shows the release of a silicon stamp used for the direct thermal imprint of gold over a parylene C bilayer. The periodic high-resolution gold features are nanocut and vertically displaced into the polymer in a single step by V. Auzelyte, J. Brugger, and co-workers on page 50, resulting in a double-layer structure supporting Fano-like surface plasmon resonances in the visible range.

Magnetoplasmonic systems possess both plasmonic and magnetic functionalities. By a smart combination of plasmonic and ferromagnetic materials with magnetooptical activity it is possible to design nanostructures whose magneto-optical properties are enhanced by plasmon resonance excitation, and whose plasmonic properties are modulated by an external magnetic fi eld. These structures fi nd applications in sensing devices as well as in optical communications.

In the multilayer architecture of a polymer solar cell, Martínez-Otero, J. Martorell, and co-workers introduce a highly transparent material as a buffer layer which enhances the reflectivity of the solar device. On page 37, they describe how this results in an optimal optical field distribution to increase light harvesting by the absorber layer, which maximizes the conversion of sun photons into electrical charges by the photovoltaic device.

An optically enhanced architecture can be used to fabricate high-performance polymer solar cells. The basic optical parameters that control light propagation in a layered device are such that an optimal light harvesting is achieved. The general character of such optically enhanced architecture is demonstrated by applying it to two different kinds of low bandgap polymers.

A two-dimensional pyramidal shape metamaterial-based absorber composed of multiple alternating metallic and dielectric thin films is proposed. This pyramid metamaterial absorber is a broadband, wide-angle, omni-directional and polarization-insensitive light absorbing device. The absorption performance of the absorber is excellent, with an absorptivity of nearly 100% at the infrared waveband from 1 μm to 14 μm for normal incidence.

High-resolution multilayer plasmonic nanostructures are made in a single fabrication step by nanocutting a gold and parylene C bilayer.. A silicon stamp is used to cut the gold film and vertically displace the nanocut shapes into the polymer. Periodic Au nanopatterns in single and double-layer configurations are fabricated down to the sub-100 nm range, supporting plasmon resonances in the visible range.

Y.-L. Zhang, H.-B. Sun and co-workers report the facile fabrication of highly efficient SERS substrates from natural rose petals. The unique surface superhydrophobicity and the hierarchical nature of the structures contribute to their high sensitivity and low detection limit.

The green, facile, low-cost and sustainable fabrication of a SERS substrate is reported, through physical vapor deposition of silver on rose petals. The hierarchical structures on the petal contribute to not only the superhydrophobicity, but also E-field enhancements. Therefore, the rose-petal-based SERS substrate shows high efficiency in the detection of R6G, and a detection limit of 10^-9 M is achieved.

A fast and low-power all-optical tunable Fano resonance in a plasmonic microstructure made of gold and polycrystalline LiNbO₃ is realized by combining strong quantum confinement enhancing nonlinearity and near-resonant excitation enhancing nonlinearity. The operating pump intensity is reduced by four orders of magnitude, while a fast response time on the order of a hundred picoseconds and a large tunability are maintained.

A large-area high-density nanoscale Lycurgus cup array is created with 100 times better sensitivity than any other reported nanoplasmonic device. With this device, nanoplasmonic spectroscopy sensing, for the first time, becomes colorimetric sensing requiring only the naked eye or ordinary visible color photography.

Earth abundant broad spectral iron pyrite (fool's gold) nanocrystals are shown by S. Ren and co-workers on page 78 to have great potential in magnetic field responsive photosensing applications

Earth-abundant broad spectral iron pyrite (FeS₂) nanocrystals show great potential in photosensing applications. Tunable photocurrent is observed under the magnetic field effect due to an interdiffusion-controlled diluted magnetic semiconductor phase.

An optically rewritable/reconfigurable patterning method is reported. Circularly polarized (CP) light is employed to write information into cholesteric liquid crystal cells fabricated with a photoaligning boundary layer. Macroscopic scattering areas, patterned via CP light, can be reconfigured into a new pattern by erasing (i.e., returning cell to reflective state) with linearly polarized (LP) light and writing a new pattern with CP light.

A series of water-soluble conjugated polymers with large two-photon absorption cross section are synthesized. PFVCN is found to display high fluorescence brightness and a high singlet oxygen generation capability under two-photon excitation. Its potential application as a promising agent for simultaneous two-photon imaging and two-photon photodynamic therapy are demonstrated.

Self-assembly of macroscopic gold nanosphere–ligand films is demonstrated to produce optical metamaterials. Using phase separation and surface tension gradients nanoparticles are capped with thiol ligands, self-assembled into macroscopic monolayers and transported onto non-functionalized substrates. By measuring the real and imaginary parts of the phase shift of light transmitted through the self-assembled films a positive near-zero index of refraction at visible wavelengths is demonstrated.