Advanced Optical Materials Issue 2 is live, with twelve contributions from leading research groups and covering the whole range of light–matter interactions.

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Table of Contents: Advanced Optical Materials, Issue 2

• Front Cover

  • Photonic Crystals: Photoresponsive Block Copolymer Photonic Gels with Widely Tunable Photosensitivity by Counter-Ions (Adv. Mater. 23/2012) (page OP89)

    Youshin Ahn, Eunjoo Kim, Jinho Hyon, Changjoon Kang and Youngjong Kang

    Article first published online: 12 JUN 2012 | DOI: 10.1002/adma.201290136

    

    Block copolymer photonic gels exhibiting multiple colors in response to near-UV radiation are demonstrated by Y. Kang and co-workers on page OP 127. The counterions pairing with the polyelectrolyte in the gel layers determine the photosensitivity of photonic gels. The simple replacement of ions can make the photonic gels either highly sensitive or insensitive to near-UV. The illustration shows ionic signaling giving “STOP” and “GO” cues for the photoresponse of these photonic gels.

• Inside Front Cover

  • Microlens Arrays: Fabrication of Microlens Arrays with Well-controlled Curvature by Liquid Trapping and Electrohydrodynamic Deformation in Microholes (Adv. Mater. 23/2012) (page OP90)

    Xiangming Li, Yucheng Ding, Jinyou Shao, Hongmiao Tian and Hongzhong Liu

    Article first published online: 12 JUN 2012 | DOI: 10.1002/adma.201290137

    

    Y. C. Ding, J. Y. Shao, and co-workers demonstrate a creative and economic method for manufacturing large-area microlens arrays (MLAs) with controllable curvature and supersmooth surfaces. On page OP 165, the production of a concave MLA is achieved by electrohydrodynamically deforming the surface of a photocurable prepolymer trapped in microhole array which has been etched onto a doped silicon wafer. The concave MLA is then used as a master to generate the convex MLA via vacuum micromoulding.

• Back Cover

  • Metamaterial Electromagnetic Wave Absorbers (Adv. Mater. 23/2012) (page OP181)

    Claire M. Watts, Xianliang Liu and Willie J. Padilla

    Article first published online: 12 JUN 2012 | DOI: 10.1002/adma.201290138

• Editorial

  • Metamaterials Top the Advanced Materials Charts (page OP97)

    Article first published online: 12 JUN 2012 | DOI: 10.1002/adma.201290141

• Progress Report

  • Metamaterial Electromagnetic Wave Absorbers (pages OP98–OP120)

    Claire M. Watts, Xianliang Liu and Willie J. Padilla

    Article first published online: 25 MAY 2012 | DOI: 10.1002/adma.201200674

    

    A review of metamaterial perfect absorbers, their applications (both potential and realized) and an overview and critique of current work taking place in the field is presented.

• Frontispiece

  • Electrochromic Materials: Electrochemical Optical-Modulation Device with Reversible Transformation Between Transparent, Mirror, and Black (Adv. Mater. 23/2012) (page OP121)

    Shingo Araki, Kazuki Nakamura, Kanae Kobayashi, Ayako Tsuboi and Norihisa Kobayashi

    Article first published online: 12 JUN 2012 | DOI: 10.1002/adma.201290142

    

    A novel electrochromic device with three optical states – transparent, specular mirror, and black – is demonstrated by N. Kobayashi and co-workers on page OP 122. The cell i
    s constructed by sandwiching gel electrolyte-containing silver nitrate between one flat and one particle-modified in-dium thin oxide electrode. The optical states can be switched by altering the potential across the two electrodes.

• Communications

  • Electrochemical Optical-Modulation Device with Reversible Transformation Between Transparent, Mirror, and Black (pages OP122–OP126)

    Shingo Araki, Kazuki Nakamura, Kanae Kobayashi, Ayako Tsuboi and Norihisa Kobayashi

    Article first published online: 10 MAY 2012 | DOI: 10.1002/adma.201200060

    

    A novel electrochromic device with three optical states, transparent, specular mirror, and black, is demonstrated. The cell is constructed by sandwiching gel electrolyte containing silver nitrate between one flat and one particle-modified indium thin oxide electrode. The optical states can be switched by altering the potential across the two electrodes. All changes are reversible and show good stability over 2500 cycles of testing.

  • Photoresponsive Block Copolymer Photonic Gels with Widely Tunable Photosensitivity by Counter-Ions (pages OP127–OP130)

    Youshin Ahn, Eunjoo Kim, Jinho Hyon, Changjoon Kang and Youngjong Kang

    Article first published online: 10 FEB 2012 | DOI: 10.1002/adma.201103767

    

    Block copolymer photonic crystalscomprising polyelectrolyte hydrogels exhibit strong reflective multicolors in response to near-UV radiation. Due to unique volume transition of swollen gels, the photonic gels show high photosensitivity, and which can be widely tunable by exchanging counter-anions. Multicolor photonic patterns created by photolithography can be repeatedly fixated and reactivated by sequentially exchanging counter-anions with different photosensitivity.

  • Light-Driven Plasmonic Color Filters by Overlaying Photoresponsive Liquid Crystals on Gold Annular Aperture Arrays (pages OP131–OP135)

    Yan Jun Liu, Guang Yuan Si, Eunice S. P. Leong, Ning Xiang, Aaron J. Danner and Jing Hua Teng

    Article first published online: 21 MAR 2012 | DOI: 10.1002/adma.201104440

    

    Light-driven plasmonic color filters are demonstrated by integrating gold annular aperture arrays with photoresponsive liquid crystals (LCs). Upon photoirradiation, a nematic−isotropic phase transition of the LCs arises from the trans–cisphotoisomerization of photochromic LCs. As a consequence, the effective refractive index experienced by the impinging light changes, modulating the transmission intensity.

  • Metal–Polymer–Metal Split-Dipole Nanoantennas (pages OP136–OP142)

    Deirdre M. O’Carroll, James S. Fakonas, Dennis M. Callahan, Martin Schierhorn and Harry A. Atwater

    Article first published online: 22 MAR 2012 | DOI: 10.1002/adma.201103396

    

    The conjugated polymer semiconductor poly(3-hexylthiophene), (P3HT), is integrated directly into the slot region of resonant plasmonic split-dipole nanoantennas. The P3HT radiative emission rate is enhanced by a factor of up to 29, in experiment, and 550 for the ideal case, due to the large local density of optical states in the nanoantenna slot region. Additionally, the theoretical modified luminescence quantum efficiency is shown to increase from 1% to 45% for optimized nanoantenna parameters.

  • Realization of Variable Three-Dimensional Terahertz Metamaterial Tubes for Passive Resonance Tunability (pages OP143–OP147)

    Chen Zaichun, Mohsen Rahmani, Gong Yandong, Chong Tow Chong and Hong Minghui

    Article first published online: 22 MAR 2012 | DOI: 10.1002/adma.201104575

    

    A three-dimensional metamaterial tube is fabricated by rolling up 2D metamaterials on flexible PEN substrate. This novel 3D design of metamaterials can be used to effectively tune the resonance frequency by varying its diameter. Meanwhile, it can also be applied in material identification with a solid-core metamaterials tube.

  • Label-Free, Coupler-Free, Scalable and Intracellular Bio-imaging by Multimode Plasmonic Resonances in Split-Ring Resonators (pages OP148–OP152)

    Yueh-Chun Lai, Hsin-Cheng Lee, Shu-Wen Kuo, Cheng-Kuang Chen, Hsieh-Ting Wu, Oscar K. Lee and Ta-Jen Yen

    Article first published online: 15 MAY 2012 | DOI: 10.1002/adma.201200291

    

    Intracellular imaging by exciting multimode resonances in spilt-ring resonators (SRRs) is presented. With advantages such as being label-free, coupler-free, having a tunable spectrum range and in

    tracellular detection length, SRR microscopy is a strong competitor for surface plasmon resonance microscopy for observing cells. Its capability for constructing refractive index distribution images of cells is demonstrated. SRR microscopy offers a much simpler optical configuration and better penetration depth for truly whole-cell imaging applications.

  • Radiative Lifetime Modification of LaF3:Nd Nanoparticles Embedded in 3D Silicon Photonic Crystals (pages OP153–OP158)

    Hailong Ning, Agustin Mihi, Joseph B. Geddes III, Masao Miyake and Paul V. Braun

    Article first published online: 9 MAY 2012 | DOI: 10.1002/adma.201104769

    

    The photonic density of states (DOS) of a silicon inverse photonic crystal is probed using the radiative emission of LaF₃:Nd nanoparticles. These emitters are embedded as a thin planar defect within the interior of photonic crystals with varying silicon filling fractions. The alignment of the narrow emission of the particles with the high and low photonic DOS regions is achieved. The time-resolved measurements reveal that the radiative lifetime of the embedded Nd³⁺ is strongly influenced by the surrounding DOS provided by the silicon inverse opals.

  • Low Threshold, Amplified Spontaneous Emission from Core-Seeded Semiconductor Nanotetrapods Incorporated into a Sol–Gel Matrix (pages OP159–OP164)

    Yile Liao, Guichuan Xing, Nimai Mishra, Tze Chien Sum and Yinthai Chan

    Article first published online: 18 MAY 2012 | DOI: 10.1002/adma.201200121

    

    Wet-chemically synthesized CdSe seeded CdS nanotetrapods incorporated into silica matrices have been explored as high performance nanocrystal-based optical amplifiers. Varying the physical dimensions of the tetrapods allowed for room temperature biexcitonic amplified spontaneous emission (ASE) at wavelengths corresponding to either the CdSe core or CdS arms, while higher pump intensities resulted in ASE from a higher CdSe excited state. These results collectively indicate that such heterostructured tetrapods can facilitate tunable, multiple-wavelength lasing across a wide spectral range from a single nanostructure.

  • Fabrication of Microlens Arrays with Well-controlled Curvature by Liquid Trapping and Electrohydrodynamic Deformation in Microholes (pages OP165–OP169)

    Xiangming Li, Yucheng Ding, Jinyou Shao, Hongmiao Tian and Hongzhong Liu

    Article first published online: 22 MAR 2012 | DOI: 10.1002/adma.201104625

    

    The microlens array (MLA) or micromirror array (MMA) is one of the most important units in many optical devices and photoelectronic systems. The paper presents a process for fabricating an MLA with well-controlled curvature by liquid trapping and electrohydrodynamic deformation in microholes. The approach has been shown capable of generating large-area and high-quality MLAs or MMAs economically.

  • Can Nanotubes Make a Lens Array? (pages OP170–OP173)

    Ranjith Rajasekharan, Haider Butt, Qing Dai, Timothy D. Wilkinson and Gehan A. J. Amaratunga

    Article first published online: 9 MAY 2012 | DOI: 10.1002/adma.201200296

    

    Reflective binary Fresnel lenses fabricated so far all suffer from reflections from the opaque zones and hence degradation in focusing and lensing properties. Here a solution is found to this problem by developing a carbon nanotube Fresnel lens, where the darkest man-made material ever, i.e., low-density vertically aligned carbon nanotube arrays, are exploited.

• Frontispiece

  • Hierarchical Electrohydrodynamic Structures for Surface-Enhanced Raman Scattering (Adv. Mater. 23/2012) (page OP174)

    Pola Goldberg-Oppenheimer, Sumeet Mahajan and Ullrich Steiner

    Article first published online: 12 JUN 2012 | DOI: 10.1002/adma.201290143

    

    On page OP 175, U. Steiner and co-workers destabilise polymer trilayer films using an electric field to generate separated micrometre-sized core-shell pillars, which are further modified by selective polymer dissolution to yield polymer core columns surrounded by a rim and micro-volcano rim structures. When coated with gold and decorated with Raman active probes, all three structure types give rise to substantial enhancement in surface-enhanced Raman scattering (SERS). Since this SERS enhancement arises from each of the isolated structures in the array, these surface patterns are an ideal platform for multiplexed SERS detection.

• Full Paper

  • Hierarchical Electrohydrodynamic Structures for Surface-Enhanced Raman Scattering (pages OP175–OP180)

    Pola Goldberg-Oppenheimer, Sumeet Mahajan and Ullrich Steiner

    Article first published online: 4 APR 2012 | DOI: 10.1002/adma.201104159

    

    Electrohydrodynamic (EHD) instabilities are employed to create hierarchical structures including, pillars, coaxial morphologies and rims with sub-micrometer edges, which are further used as substrates for surface-enhanced Raman scattering (SERS). 1.0 × 10⁷ SERS enhancements from isolated rims and coaxial patterns are observed. Since SERS enhancement arises from each of the isolated structures in the array, EHD-patterned substrates provide optimal platforms for high-throughput SERS detection, where each of the individual EHD structures can be used to detect a different molecular component.