GailJ. Brown U. S. Air Force Research Laboratory
John Pendry Imperial College London
David Smith Duke University
NicholasX. Fang Massachusetts Institute of Technology
W5: Poster Session
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
W1: Transformation Optics
Tuesday PM, April 26, 2011
Room 3006 (Moscone West)
9:30 AM - **W1.1
Manipulating Waves Using Acoustic Metamaterials.
CheTing Chan 1 Show Abstract
1 Physics, HKUST, Clear Water Bay Hong Kong
We will describe our ongoing work on using acoustic metamaterials to achieve some interesting wave manipulation effects. Acoustic metamaterials are composite materials in which the effective density and bulk modulus can be tuned by using resonating units embedded inside a host, and the effective values of density and bulk modulus are discussed in the sense of an effective medium theory. Using the technique of transformation optics, we will show that acoustic metamaterials can achieve novel wave manipulation effects such as invisible cloaking. The cloaking effect can be achieved using acoustic metamaterials that either enclose or do not enclose the object to be cloaked. We will also show that there are systems in which the wave manipulation properties can be tuned continuously from meta-material-like to phononic-crystal-like, simply by tuning system parameters. We will then see that in some cases, phononic crystals can be used to create similar wave manipulate effects as acoustic metamaterials. We will see that under certain conditions, some phononic crystals behave as if they are metamaterials with a zero density and zero modulus, and we will see that those zero-density-zero-modulus materials are related to Dirac cone dispersions in the band structure.
10:00 AM - W1.2
Transformational Plasmonics and Gradient Index Plasmonics.
Yongmin Liu 1 , Thomas Zentgraf 1 , Maiken Mikkelsen 1 , Jason Valentine 1 2 , Guy Bartal 1 , Xiang Zhang 1 3 Show Abstract
1 , University of California, Berkeley, California, United States, 2 , Vanderbilt University, Nashville, Tennessee, United States, 3 Materials Science Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Transformation optics has recently attracted extensive interests, because it provides a novel design methodology for manipulating light at will. Although transformation optics in principle embraces all forms of electromagnetic phenomena on all length scales, so far, much less efforts have been devoted to near-field optical waves, such as surface plasmon polaritons (SPPs). Due to the tight confinement and strong field enhancement, SPPs are widely used for various purposes at the subwavelength scale. Taking advantage of transformation optics, here we demonstrate that the confinement as well as propagation of SPPs can be managed in a prescribed manner by carefully controlling the dielectric material properties adjacent to a metal. Since the metal properties are completely unchanged and the transformed dielectric materials can be isotropic and non-magnetic, it provides a straightforward way for practical realizations. We show that our approach can assist to tightly bound SPPs over a broad wavelength range at uneven and curved surfaces, where SPPs would normally suffer from significant scattering losses. In addition, a 180-degree plasmonic bend with almost perfect transmission is designed. We further propose to slowly change the thickness of an isotropic dielectric cladding layer and hence the local effective index of SPPs, instead of directly modifying the permittivity of the dielectric medium. In such a way the propagation of SPPs can be controlled without structuring the metal surface or adding discrete scattering structures on the metal. As the local effective index of SPPs is varied gradually in a truely continuous manner we term our approach gradient index (GRIN) plasmonics, in analogy to the well-known GRIN optics. Applying this method, we design and demonstrate two different devices: a plasmonic Luneburg lens to focus SPPs and a plasmonic Eaton lens to bend SPPs. In comparison with previously reported plasmonic elements, the scattering loss of SPPs in our designs can be significantly reduced since the optical properties are gradually changed. Experimentally we tailor the topology of a dielectric layer adjacent to the metal surface using gray scale lithography. Fluorescence imaging and leakage radiation microscopy are applied to characterize the performance of the designed GRIN plasmonic devices, showing a good agreement with the numerical simulation. We expect that the approach of transformational plasmonics and gradient index plasmonics introduced here will lead to a host of fascinating near-field optical phenomena and devices.
10:15 AM - W1.3
Gold Coated Silicon Nanowire: A Case Study Of Engineering Novel Light-matter Interactions.
Pengyu Fan 1 , Uday Chettiar 2 , Linyou Cao 3 , Farzaneh Afshinmanesh 1 , Nader Engheta 2 , Mark Brongersma 1 Show Abstract
1 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States, 2 Electrical Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States, 3 , University of California, Berkeley, Berkeley, California, United States
Metallic-dielectric coupled nanostructures could have novel optical properties. Hereby we investigated the optical properties of a silicon nanowire coated with a thin shell of gold. We have observed that, depending on the polarization of incident light, not only the gold shell could act as an optical antenna that concentrates light to the nanowire, which will enhance the photoresponse of the nanowire, more interestingly, the gold shell also functions as an optical cloak that drastically reduce the scattering from silicon nanowire, making the silicon nanowire essentially "invisible". This cloaking effect, known as plasmonic cloaking, takes the advantage of the fact that metal and dielectric materials have opposite signs of polarizability which leads to destructive interference of scattering from the gold shell and silicon core and thus cancelling of total scattering. Albeit the suppression of scattering, the silicon nanowire still could efficiently absorb incident light, which generates charge carriers and thus produce a measurable photocurrent signal across the silicon nanowire when it is electrically contacted. As a result, we successfully demonstrated an "invisible" photodetector based on the structure. This study suggests enormous potentials of engineering new types of light-matter interaction based on metallic-dielectric coupled nanostructures and exciting opportunities of realizing devices with novel and complex optical and optoelectronic functionalities.
10:30 AM - **W1.4
Fano Resonances Induced by Chirality and Anisotropy: A Composite-material Based Perspective.
Cheng-Wei Qiu 1 , S. Zouhdi 1 Show Abstract
1 , University Paris Sud, Gif sur Yvette France
Composite materials with chirality and (or) anisotropy give us a new paradigm of achieving intrigue Fano resonance. In this talk, we will first propose a 3D spiral photonic crystal structure with controllable phase shift. The paradoxical high Right-handed (RH) transmission is found surprisingly in RH polarization gap, which is owing to Fano resonances derived from mode interference. The intrinsic mechanism of such a paradox is interpreted by mode coupling theory by analyzing Fourier spectra and chirality of eigenmodes. Then other paradigm to achieve asymmetric Fano resonance is proposed by manipulating radial anisotropy instead of manipulating frequency. A fast-switching radiation pattern is observed in association with Fano resonance under a tiny perturbation of the anisotropy. At different resonant modes (symmetrical or asymmetrical), the corresponding bifurcation and singularities of Poynting vector are investigated for the potential use in calculation of heating, radiation pressure and trapping, etc.
11:00 AM - W1: trans optics
W2: Optical Metamaterials
Tuesday PM, April 26, 2011
Room 3006 (Moscone West)
11:30 AM - **W2.1
Enhanced Near-field Imaging using Surface Plasmons and other Surface Wave Phenomena.
Richard Blaikie 1 , Prateek Mehrothra 1 , John Foulkes 1 , Charles Holzwarth III 1 Show Abstract
1 MacDiarmid Institute for Advanced Materials and Nanotechnology, Department of Electrical and Computer Engineering, University of Canterbury, Christchurch New Zealand
Imaging in the near field offers the opportunity to overcome conventional diffraction limits for high-resolution imaging, high-density data storage or deep-subwavelength lithography. However, the depth of field for simple near-field imaging systems can be severely limited, with the high-resolution imaging region being tightly confined to the close proximity of a near-field probe. Extending the depth of field or pulling the high-resolution imaging region away from the near-field probe would offer additional flexibility, and we have explored the use of plasmonic and other surface-wave phenomena to achieve this goal.In the plasmonic superlensing regime the near field image is projected through a thin single- or multi-layer planar plasmonic lens, and our experiments have shown that the diffraction limit can be overcome, albeit with loss in image fidelity due to surface-roughness-induced artefacts. Reflection-mode plasmonic imaging offers better performance, and improvements in the depth of field of more than a factor of two can be achieved for a number of different imaging modalities: mask-based evanescent near-field optical lithography (ENFOL); evanescent interference lithography (EIL); surface plasmon imaging lithography (SPIL); and far-field controlled absorbance modulation optical lithography (AMOL). The improvements that reflection-mode plasmonic imaging offers to these techniques will be described, together with results showing that other surface-wave phenomena can achieve the same improvements, with more flexibility and better performance in many cases.
12:00 PM - W2.2
Composite Materials for Subwavelength Imaging.
Zsolt Szabo 1 , Yasaman Kiasat 1 , Er Ping Li 1 Show Abstract
1 , Institute of High Performance Computing, Singapore Singapore
One of the promises of metamaterial research is to produce near field lenses with a negative refractive index at optical frequencies for subwavelength imaging. A waveguide approach  and an estimate based on Nyquist-Shannon sampling criteria indicate that a resolution of 100 nm requires unit cell sizes of 20 nm or smaller. At this unit cell size, to fabricate the required negative magnetic response remains a challenge. Nevertheless, for the special case of a transverse magnetic (TM) source, a negative electric permittivity is sufficient to amplify the evanescent components of the source, in order to produce subwavelength images . An optimized superlens fabricated using a multilayer metal-dielectric composite, separated with transparent dielectric layers is presented. The advantages of the proposed configuration can be summarized as follows: a multilayer superlens can offer a larger separation between the source and image compared to a single layer lens  and the use of composite materials instead of bulk metals provides the tunability of the lens  to the frequencies of commercially available laser sources. To design the multilayer composite lens, a transfer matrix based field solver and a gradient based optimization algorithm has been developed. Maxwell Garnett composites formed from a SiO2 host containing Ag or Al spherical or spherical shell nanoparticles with an average size of 5 nm are explored. The possibility to arrange the layers of the lens in periodic and fractal geometries is investigated. The working frequency, filling fractions, number and thickness of layers required to build an optimized superlens are provided.AcknowledgementThe support of Agency for Science Technology and Research (A*STAR) Singapore, Metamaterial Research Program Grant No. 0821410039 is acknowledged.References R. S. Hegde, Zs. Szabó, Y. Kiasat, Y. L. Hor, G. H. Park, E. P. Li and W. J. R. Hoefer, Shedding new light on super-resolution imaging – a spectral domain approach, Fourth International Congress on Advanced Electromagnetic Materials in Microwaves and Optics, Metamaterials 2010, Karlsruhe, Germany, 2010, pp. 492-494.  J. B. Pendry, Negative Refraction makes a perfect lens, Physical Review Letters, vol. 85(18), p. 3966, 2001. L. Solymar and E. Shamonina, Waves in Metamaterials. Oxford, University Press, 2009.  W. Cai, V. Shalaev, Optical Metamaterials: Fundamentals and Applications, Springer, 2010.
12:15 PM - W2.3
Spherical Hyperlens for Two-dimensional Sub-diffractional Imaging at Visible Frequencies.
Junsuk Rho 1 , Ziliang Ye 1 , Yi Xiong 1 , Xiaobo Yin 1 , Zhaowei Liu 1 3 , Hyeunseok Choi 1 , Guy Bartal 1 , Xiang Zhang 1 2 Show Abstract
1 NSF Nanoscale Science and Engineering Center, University of California, Berkeley, Berkeley, California, United States, 3 Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Hyperlens has excited a great deal of interest in recent years, not only because of the intriguing physics but also for its ability of imaging sub-diffractional scale objects into the far-field in a real-time fashion. The major breakthrough emerged with the concept of optical hyperlens, showing the first proof-of-principal for magnifying sub-diffractional images to the far-field as propagating waves. Utilizing alternating dielectric and metallic multilayers in a curved geometry, this metamaterial-based optical device achieves strong optical anisotropy that supports the propagation of waves with very large spatial frequency and, due to the cylindrical geometry, adiabatically compresses its lateral wave vector while the wave propagating outward along the radial direction. Consequently, the sub-diffractional details of objects are magnified and eventually larger than the diffraction limit to be transmitted to the far field. Since the first experimental demonstration of the cylindrical hyperlens in one dimension, newly improved designs as well as fabrication techniques, such as the impedance matched, flat, oblate, the aperiodic and acoustic hyperlens, have been proposed in the framework of transformational optics. Nevertheless, all the experimental demonstrations of hyperlens so far were limited to the one dimensional magnification and ultra-violet (UV) wavelengths whereas for any practical imaging applications [1,2], it is critical to demonstrate the two-dimensional imaging with resolution below diffraction limit at visible spectrum. Here, we present a spherical hyperlens for two-dimensional sub-diffraction limited real-time imaging at visible frequencies without the need of optical scanning or image reconstruction.  Designing a spherical hyperlens with flat hyperbolic dispersion that supports wave propagations with very large spatial frequency, and yet same phase speed, we are able to faithfully resolve sub-diffractional features down to 160 nm, much smaller than the diffraction limit at visible wavelength of 410 nanometers. Such a hyperlens can readily be integrated in conventional microscopes, critically expanding their capabilities beyond the diffraction limit and opening a new realm in real-time nanoscopic optical imaging of biological machineries in living cells. References: Liu, Z., Lee, H., Xiong, Y., Sun, C. & Zhang, X. Science 315, 1686 (2007). Lee, H., Liu, Z., Xiong, Y., Sun, C. & Zhang, X. Opt. Express 15, 15886-15891 (2007). Rho, J., Ye, Z., Xiong, Y., Yin, X., Liu, Z., Choi, H., Bartal, G. and Zhang, X. Accepted to Nature Communications (2010).
12:30 PM - **W2.4
Recent Progresses in Optical Metamaterials.
Xiang Zhang 1 Show Abstract
1 , University of California at Berkeley, Berkeley, California, United States
Metamaterials are artificially designed subwavelength composites that possess extraordinary properties not existing in naturally occurring materials. In particular, they can alter the propagation of electromagnetic waves resulting in negative refraction, subwavelength focusing and even in cloaking of macroscopic objects. Such unusual properties can be obtained by a careful design of dielectric or metal-dielectric composites on a deep sub-wavelength scale. The metamaterials may have profound impact in wide range of applications such as nano-scale imaging, nanolithography, and integrated nano photonics. I will discuss a few recent experiments demonstrating intriguing phenomena associated with Metamaterials. These include subdiffraction limit imaging and focusing, low-loss and broad-band negative-refraction of visible light, negative-index metamaterials and the first cloak operating at optical frequencies; an all-dielectric “carpet cloak” with broad-band and low-loss performance. I will also present our recent demonstration of a deep sub-wavelength plasmonic laser.
W4: Photonic Crystal Metamaterials
Tuesday PM, April 26, 2011
Room 3006 (Moscone West)
4:30 PM - W4.1
Transformation Optics Beyond Effective Medium Regime: A Case for Low-loss Optical Cloaks.
Yaroslav Urzhumov 1 2 , David Smith 1 2 Show Abstract
1 Center for Metamaterials and Integrated Plasmonics, Duke University, Durham, North Carolina, United States, 2 ECE Department, Duke University, Durham, North Carolina, United States
Recently, we have introduced a new class of optical media based on adiabatically modulated, dielectric-only, and potentially extremely low-loss, photonic crystals (PC) . These media represent a generalization of the eikonal limit of transformation optics (TO). The basis of the concept is the possibility to fit some equal frequency surfaces (EFS) of certain PCs with elliptic surfaces, allowing PCs to mimic the dispersion relation of light in anisotropic effective media, including electromagnetic metamaterials. Absent the metallic inclusions that are typical of many implementations of TO media, PCs hold the hope that optical cloaks and other TO devices operating at visible wavelengths can be constructed from optically transparent substances like glasses, whose attenuation coefficient can be as small as 10 dB/km, suggesting the TO design methodology can be applied to the development of macroscopic optical devices than span thousands and millions of wavelengths.TO designs result in inherently complex media, typically requiring the exotic property of superluminal phase velocity (i.e., n<1) combined with anisotropy, spatial gradients of refractive index, or both anisotropy and gradients. Here, we first demonstrate the validity of using modulated PC materials by designing an optical beam shifter, and validating its operation in a finite-element simulation. Then, we present a material distribution that operates as an optical cloak in the eikonal limit, to demonstrate the general ability to control light propagation and mimic TO media with PCs. This all-dielectric device suitable for visible wavelengths is potentially closer to a real invisibility tool than the previously suggested dielectric-only ``cloaking" structures [2,3], since the latter can create optical illusions only for a limited range of view angles.To summarize, we demonstrate both analytically and in device-scale electromagnetic simulations that the concepts of TO can be implemented with Bloch-Floquet waves in adiabatically modulated anisotropic photonic crystals, which can be composed of materials that are macroscopically transparent in the entire visible spectrum. This includes a demonstration of a dielectric-only, rotationally-invariant structure that functions as an optical cloak in the ray-optics limit. This paradigm creates hope for a new class of optical-wavelength devices capable of being scaled to arbitrarily large dimensions.References Y. Urzhumov and D.R. Smith, Phys. Rev. Lett. 105, 163901 (2010). U. Leonhardt, Science 312, 1777 (2006). J. Li and J. B. Pendry. Phys. Rev. Lett. 101, 203901 (2008).
4:45 PM - W4.2
Exceeding the Ergodic Light Trapping Limit Using Photonic and Plasmonic Materials.
Dennis Callahan 1 , Jeremy Munday 1 , Harry Atwater 1 Show Abstract
1 , California Institute of Technology, Pasadena, California, United States
In 1982, Yablonovitch proposed an upper bound on light trapping within textured solar cells using a statistical ray optics treatment. Until only very recently, this limit has been well accepted to apply to almost all cases of solar cells, as their structures could be well described as homogeneous slabs of semiconductor. Renewed interest in accelerating the cost reduction of solar cell technologies has led to many new cell designs utilizing ultrathin or inhomogeneously structured active regions, including designs incorporating nanowires, photonic crystals, plasmonics and metamaterials. Here, we show that the traditional light trapping limit can be exceeded in many of these structures by designing a solar cell in which the active region has an elevated local density of optical states (LDOS) compared to that of the bulk, homogeneous material. Additionally, to practically achieve light trapping exceeding the ergodic limit, the modes of the structure must be appreciably populated via an appropriate incoupling mechanism. We then use these principles to outline a number of possible new solar cell structures that have potential to exceed the ergodic light trapping limit. We find that ultrathin planar solar cells incorporating a plasmonic back reflector can achieve spatially averaged LDOS enhancements of 1 to 3, and a metal-insulator-metal (MIM) structure can achieve enhancements over 50 at a wavelength of 1100 nm, the bandedge of Si. We then extend this to all dielectric planar structures such as the slot waveguide and find that broadband LDOS enhancements are possible utilizing realistic material parameters. We also find that having the active solar cell material within a localized plasmonic or metamaterial resonator can lead to nearly spatially uniform LDOS enhancements above 1000 within the active material. We also examine the possibility of structuring and combining ultrathin solar cells with dispersive dielectric structures such as photonic crystals to exceed the ergodic light trapping limit. We find that LDOS enhancements of ~2-5 inside an untextured, planar solar cell can be achieved by simply placing a photonic crystal above or below the active material. Lastly, we emphasize the importance of fully populating the modes of a given dispersive structure to practically achieve light trapping above the limit. These results can guide the design of future solar cells incorporating dispersive dielectric structures, plasmonics and metamaterials to achieve unprecedented light trapping.
5:00 PM - W4.3
Photonic and Plasmonic Coupling in Gold/Silicon Dioxide Incorporated Colloidal PMMA Photonic Crystals and Inverted Structures.
Sibu Padmanabhan 1 2 , Syara Kassim 1 2 , Maria Bardosova 1 2 , Martyn Pemble 1 2 Show Abstract
1 Tyndall National Institute, University College Cork, Cork, Cork, Ireland, 2 Department of Chemistry, University College Cork, Cork, Cork, Ireland
The bottom-up colloidal syntheses of photonic band gap (PBG) materials or photonic crystals has many advantages over so-called top-down approaches, particularly for the economically viable production of complex 3-dimensional structures. In this work, we have used a modified colloidal crystallization approach in the fabrication of PMMA- based colloidal photonic crystals containing both silicon dioxide and Au nanoclusters in order to study the modifications induced by these materials on the optical properties of the material. The hybrid metal/ oxide/polymer photonic crystal structure was prepared by a colloidal crystallization method and samples further treated to make inverse structures consisting of the 3D hybrid metal/oxide framework. The angle and polarization dependent reflection and transmission spectral features of resulting structures are discussed. The coupling between the plasmonic resonance of the gold and the Bragg diffraction resonances are evident from the nearly-dispersionless behaviour of these features as a function of angle of incidence.  1.P.-T. Miclea, S. G. Romanov, C. M. Sotomayor Torres, Z. Liang, A. Susha and F. Caruso, Mol. Cryst. Liq. Cryst., 2004, 415, 211–219.
5:15 PM - W4.4
Microwave Volumetric Probe Measurements of Field Localization, Zero and Negative Index within Photonic Bandgap MetaMaterial Structures.
Ricky Moore 1 , Eric Kuster 1 , Stephen Blalock 1 , Brian Cieszynski 1 Show Abstract
1 STL, Georgia Tech Research Institute, Atlanta, Georgia, United States
Electromagnetic mode localization within photonic bandgap (PBG) crystals is often evidenced by external measurement of enhanced optical emission from quantum dots or photoemissive polymers that are placed within the structure. In this paper wavelength is decreased and photonic crystal dimensions increased to allow direct insertion of a loop probe in the PBG and directly measure volumetric electromagnetic fields; thereby producing a volume -frequency map of field amplitude and phase within the PBG. The unit cells of the PBG are formed from arrays of 0.0051m x 0.023 m x 0.31m Alumina strips which are suspended in air by surrounding acrylic supports. Strips are spaced 0.033 m in the transverse direction and ~ 0.064m spacing in direction of field propagation. The high aspect structure is a two dimensional PBG. Electromagnetic fields of single, two and three layer PBGs are predicted and these compare well with measurement. Numerical simulations of field localization and PBG reflection and transmission model each layer as formed from sections in which translational invariance along the Z-axis is assumed for for the nth section. In each rectangular block both the permittivity and the permeability can vary. The two polarizations, E parallel to the alumina strip (Y axis) and E perpendicular to the rods (Z axis) can be treated separately. Periodicity along the X axis (propagation direction) implies that the field’s X dependence can be represented as a sum of Floquet modes. The solution to Maxwell’s equations for the PBGs is found by mode matching techniques in combination with a multimode cascade matrix formalism. Two measurement techniques are used and compared to theory. Transmission coefficient is measured using a focused beam, network analyzer based system. Volumetric fields are measured using the loop probe antenna, inserted between Alumina strips of the PBG and translated to different positions within the two dimensional structure. Electric and magnetic field magnitude and phase are measured at 1600 frequencies over the 4-18 GHz band at each of 100 positions. PBG fields are calibrated to probe measurements at identical positions and frequencies but without the PBG present. Both electromagnetic model and measurement shows field localization and effective negative or zero index at multiple frequencies within the 4 to 18 GHz band. Volumetric field magnitudes increase by an order of magnitude and local field phase-frequency derivatives are negative or near zero near localization frequencies. Field localizations and PBG transmission are shown to be sensitive to small perturbations of electrical properties or geometry. Thus measurements of PBGs, perturbed by small cylindrical inserts, allow precision measurements of the insert’s electromagnetic properties.
5:30 PM - W4.5
Characteristic Band Gap Structures of High Dielectric Contrast Photonic Crystals.
Sheng Chao 1 Show Abstract
1 , National Taiwan University, Taipei Taiwan
Conventional photonic crystals exhibit low-lying full band gaps for the dielectric contrast smaller than 15. As the dielectric contrast increases, the band gap patterns change characteristics and exhibit interesting properties. In particular, the dispersion curves near the band gap region become concentrated to the middle band frequencies and exhibit an overall red shift in frequency. For a dielectric column photonic crystal made of a hexagonal lattice of circular cylinders, the maximum full band gap was found at the dielectric contrast as high as 27.5, which is attainable by using ceramics materials. The gap opens at high-lying bands, has simultaneous TM and TE band edges, and exhibit flattened dispersion curves near the band edges. The band gap opening mechanism was elucidated via the Mie scattering resonance model. A correlation between the band gap frequency ranges and the appearance of the Mie resonances was demonstrated. The dispersion curves for the TM and TE modes of the propagating electromagnetic waves have been analyzed separately. TM mode fits in the Mie resonance model more closely than the TE mode. However, it is the TE mode that determines the width of the full band gap. Unlike the low-lying band gaps, analysis on field distributions is not able to show the definite relations between the band gaps and the field localization in specific regions.
W5: Poster Session
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
6:00 PM - W5.1
Highly Ordered Plasmonic Nanogap Arrays via Colloidal Lithography.
Chul-Joon Heo 1 , Yeonho Choi 2 , Su Yeon Lee 1 , Se Gyu Jang 3 , Soojeong Cho 1 , Seung-Man Yang 1 Show Abstract
1 , KAIST, Daejeon Korea (the Republic of), 2 , Korea University, Seoul Korea (the Republic of), 3 , University of California, Santa Babara, Santa Babara, California, United States
We demonstrate a simple and effective method for preparation of hybrid plasmonic probe arrays with precisely controlled nanogap. Deveopment of plasmonic sensors which relies on surface plasmons(SPs) originated from metallic nanostructures makes the nanometer-scale analysis of system available. To materialize the study of biological events in nanometer-scale, design of the metallic platform with strong local field enhancement and high uniformity should be preceded. When two different or identical metal nanostructures are located closely with sub 10 nm gap, strong coupling between two nanostructures extraordinarily large field enhancement responsible for ultra-sensitive recognition can be generated at the nanogap. Nanogap array is fabricated by directional metal deposition onto the nanometer-sized masks sculptured from colloidal particles and polymer thin film. By varying the deposition condition and etching condition for mask preparation, gap size between two different plasmonic structures can be precisely controlled. Highly enhanced electromagnetic (EM) field originated from nanometer-sized gap between two structures enables ultra-sensitive plasmonic detection of biomolecules. Precisely engineered plasmonic nanogap system can covers large area with uniform enhancement which was hard to be achieved for nanogap-based techniques using e-beam lithography or particle assembly. Furthermore, nanometer-sized feature of nanoforest enables recognition of molecules with ultra-small resolution.
6:00 PM - W5.12
Fabrication of Uniformly Ordered Plasmonic Arrays by Using Holographic Lithographically Defined Structure as a Mask.
Hwan Chul Jeon 1 , Chul-Joon Heo 1 , Su Yeon Lee 1 , Seung-Man Yang 1 Show Abstract
1 Chemical and Biomolecular Engineering, KAIST, Daejeon Korea (the Republic of)
Today, surface plasmons (SPs) of the metal nanoparticles (MNPs) are widely studied because of large potential for various applications using their optical properties. However, it is difficult to make MNPs with various arrangements and diverse shapes over large-area using conventional methods. In this study, we demonstrate a novel method for preparation of regularly ordered plasmonic arrays by using holographic lithographically defined polymeric nanostructure as a mask. These periodic metallic nanostructures could be fabricated by using a combination of the mask that was fabricated by prism holographic lithography (HL), reactive ion etching (RIE), e-beam evaporation and lift off procedure of the photoresist (PR). A He-Cd laser beam (325nm) and specific designed top-cut prism had been used to achieve various mask patterns with face-centered cubic (FCC) lattice. The PR film thickness was varied by changing the concentration of epoxy-based resin (SU-8) resin in solvent and spin-speed resulting different layer number of FCC structure. Nanometer-scale empty rooms for metal deposition could be varied as circular, ellipsoidal and smooth-angle triangular shape from the FCC polymeric masks with 1 layer, 2 layers and 3 layers, respectively. And we could further control the internal gap separation by changing the laser exposure time using electronic shutter. After RIE to remove residual pre-coated sacrificial layer, metal deposition was performed by using the highly directional metal deposition. Finally, the large area of periodic homogeneous MNPs could be obtained by using lift off process. Plasmonic features of these periodic MNP arrays with various shapes were characterized by dark field microscopy equipped with spectrometer. Those periodic plasmonic arrays have a potential as a SERS substrate for sensing application.
6:00 PM - W5.13
Discrete and Soluble Plasmonic Architectures via Directed Assembly of Gold Nanorods.
Kyoungweon Park 1 , Dhriti Nepal 1 , Richard Vaia 1 Show Abstract
1 Nanostructured and Biological Materials Branch, Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Fabrication of discrete, soluble plasmonic architectures, such as nanorod pairs, by colloidal approaches offer numerous advantages relative to lithographic techniques, including compositionally asymmetric structures, three dimensional geometries of sub 5 nm gaps, and higher throughput Density driven colloidal assembly, such as by solvent evaporation, yields intriguing structures, including particle chains; however controllability and post-processibility of the final architecture is limited, and the product is nominally comprised of a broad distribution of assembly size and type. Here in, we demonstrate high-yield formation of discrete and soluble plasmonic architectures by arresting flocculation, and stabilizing the assembled product, using bi-functional nanoparticles and reversible modulation of solvent quality. Au nanorods (AuNRs) serve as the initial nano-units ("monomers"). Functionalization of separate faces provides distinct repulsive interparticle potentials, e.g. electrostatic along the AuNR side and steric at the AuNR end. Reducing the electrostatic stabilization specifically drives agglomeration (“polymerization”) along the nanorods sides, while solution stability is maintained by steric repulsion at the nanorod ends. The assembly process is arrested by subsequently increasing the electrostatic stabilization. In a manner analogous to step-growth polymerization, the separation of “reactive” and “non-reactive” regions on the nanoparticle and the ability to externally control “reactivity” enable controlled formation of soluble, discrete plasmonic architectures (”macromolecules”) with yields greater than 50%. The coupled plasmonic resonance of the AuNR pairs agree well with theoretical predictions, and provide a novel intermediate building block for optical devices and sensors.
6:00 PM - W5.2
Unconventional Diffraction Grating at the Molecular Scalesto Create a Huge Acoustic Wave.
Kyung Choi 1 Show Abstract
1 , University of California, Irvine, California, United States
Scientists usually obtain acoustic waves by setting up periodic metal frames to create ‘diffraction grating’. The conventional method, the development of periodic metal frames at the bulk scales, often shows limitations in practical applications. To overcome the limitation, an unconventional diffraction grating system at the molecular scales was developed to create a huge acoustic wave. A periodic alignment of alkyl-chains was molecularly designed in hybrid glasses for creating ‘effective diffraction grating at the molecular scales’. The new family of hybrid glasses doped with Cro/CrOx shows unusual optical properties that hitherto haven’t been discovered. In laser experiments, the doped hybrid glass generates a huge acoustic wave as strong as liquid. The chemical approach is promising to develop a new version of metamaterials.
6:00 PM - W5.3
Ag Nanoparticle Films for Color Applications.
Satoru Hashimoto 1 , Teruyoshi Hirano 2 , Osamu Okitsu 3 , Mizue Ebisawa 4 , Takayasu Suzuki 5 , Shuichi Maeda 5 Show Abstract
1 , HYOUKAKEN Co., Ltd., Sakumacyou, Chiyoda-ku, Tokyo Japan, 2 , HIRANO Consulting Engineer Office, Nishi-Shinbashi, Mitano-ku, Tokyo Japan, 3 , GGK Co.,Ltd., Minato-ku, Tokyo Japan, 4 , TOKYO Metropolitan Industrial Technology Research Institute, Nishigaoka, Kita-ku, Tokyo Japan, 5 Optical and Imaging Science & Technology, TOKAI University, Kitakaname, Hiratsuka-shi, Kanagawa Japan
We describe the preparation and characterization of Ag nanoparticle films for color application.It is well known that Ag nanoparticles absorb visible light of various wavelengths due to surface plasmon resonance and the wavelength depends on particle size, particle shape, and local refractive index. It is also known that Ag nanoparticles can be converted into larger ones by photoinduced method and the light-irradiation process results in Ag nanoparticle films which have a variety of colors depending on the irradiation time. However, this irradiation process requires many hours for the conversion of Ag nanoparticles.Recently, we have discovered a novel and facile method for preparing Ag nanoparticle films for color applications. In our method, Ag nanoparticle films made by sliver mirror reaction are dipped in a solution of a sulfide. The Ag nanoparticle films change their colors depending on the dipping time and the dipping time is at most on the second time scale. The color of the film, initially sliver (shinny white), changes to shinny yellow, red, and blue. In addition, to the best of our knowledge, this is the first time to control the colors of Ag nanoparticle films by using chemicals.Our color-changeable Ag nanoparticle films have a number of potential applications including coating materials, imaging materials and optical memories, since the film is easy to prepare, low cost, and applicable to a large area. On the other hand, it is of great scientific interest to elucidate the mechanism of the color change of our Ag nanoparticle films. Therefore, these Ag nanoparticles have been characterized in terms of their particle size, chemical compositions and optical properties by a wide range of experimental techniques, including scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and visible absorption spectra. For example, our scanning electron microscopy studies indicate that the color of the Ag nanoparticle films depend markedly on the particle size and distribution of the films.
6:00 PM - W5.4
Dependence of Fluorescence Decay Dynamics of Quantum Dots on Metallic Nanostructures.
Chi Ho Fok 1 , Koon Chung Hui 2 , Hock Chun Ong 2 Show Abstract
1 Materials Science and Engineering, The Chinese University of Hong Hong, Hong Kong Hong Kong, 2 Physics, The Chinese University of Hong Kong, Hong Kong Hong Kong
Plasmonics has become an important research area next to the eras of Photonics and Electronics. In particular, it has been considered as one of the most promising candidates for realizing truly nanoscale photonic devices in the future. In the past decade, tremendous amount of effort has been seen worldwide in understanding the basic plasmonic properties of metallic nanostructures, such as extraordinary transmission, superlens effect, negative refraction, etc. While these properties are slowly but surely understood, attention is being shifted towards the study of hybridizing the metallic nanostructures with active materials such as light emitters, nonlinear optical materials, ferroelectrics, etc. The integration of passive plasmonic system with functional materials will allow one to realize active plasmonic control in which the system has the ability of not only generating and transmitting signals but also modulating, processing, switching and detecting them. For example, by combining the metallic nanostructures with light emitting materials, the light intensity or the emission lifetime can be modulated by controlling the SPP field strength. However, since the field strength is so highly geometry dependent that slight variation in the structure of the plasmonic system can have strong influence in the outcomes, a full and detailed understanding in how geometry affects the optical properties of light emitting materials is thus of great importance. Here, we have systematically studied the spontaneous emission lifetime of CdSe-based quantum dots (QDs) attached on various metallic nanostructures with different sizes, shapes, periodicities, etc. By using fluorescence lifetime imaging and two-photon luminescence microscopy, we are able to study the fluorescence decay dynamics of QDs and nearby electric field strength quantitatively. In addition, by varying the geometry of the arrays to obtain different decay lifetimes and coupling efficiencies for different electromagnetic resonance modes, we have studied their influences on the fluorescence dynamics of QDs. In fact, strong correlation is found between the radiative rate of electromagnetic modes and the spontaneous emission rate of QDs; faster radiative decay leads to higher spontaneous emission rate. As a result, our results point to a direction to engineer the spontaneous emission rate of fluorescence materials by controlling the geometry of metallic nanostructures.
6:00 PM - W5.5
New Array-based Surface Plasmon Resonance Sensors with Extremely High Figure of Merit and On/Off Ratio.
Sze Lung Wong 1 , Lei Zhang 1 , Chung-yu Chan 1 , Hock Chun Ong 1 Show Abstract
1 Physics, The Chinese University of Hong Kong, Hong Kong Hong Kong
Surface plasmon resonance (SPR) spectroscopy, which relies on detecting the local change of refractive index in the proximity to the metal surface upon binding of target analytes to receptors, has become one of the leading methods for label-free bio and chemical detection. By monitoring the spectral shift of SPR reflection dip/transmission peak, it is possible to detect the presence of target analytes at low concentration. Metallic array is particularly attractive for making SPR sensor since it concentrate electromagnetic field in a very small mode volume, thus possibly increasing the sensitivity for small molecule detection. However, as the plasmonic effect is so highly geometry dependent that slight modification of the structure can lead to large variation in the outcome, it is of great important to understand how one can design the geometry of metallic array to achieve the highest possible sensitivity. Here, we lay out our approach in rationally design metallic array with extremely high figure of merit, defined as sensitivity/linewidth, and on/off ratio. In fact, we find the bulk and surface sensitivities are strong function of the period of array. On the other hand, the linewidth is governed by the decay lifetime of surface plasmon polariton. Longer lifetime leads to narrower linewidth. In fact, we find reducing the size of individual basis of the array has significant effect on prolonging the SPP lifetime. As a result, by carefully tailoring the geometry of the arrays, we are able to realize the figure of merit larger than 120/RIU, which surpasses those of Kretschmann and nanoparticle counterparts, and, to our knowledge, is the highest by far. Finally, by orthogonally orienting the incident and detection polarizers to eliminate the non-resonant background from the reflectivity spectra, the SPP profiles changes from Fano to Lorentzian, improving the on/off ratio to 104. We will detect the binding of avidin to biotinylated surfaces with almost single molecular sensitivity.
6:00 PM - W5.6
Synthesis and Characteristics of Large-scale Helix-coiled Plasmonic Metal Nanowire Assemblies.
Weon-Sik Chae 1 , Eun-Mee Kim 1 , Jin-Seung Jung 2 Show Abstract
1 Gangneung Center, Korea Basic Science Institute, Gangneung, Gangwon, Korea (the Republic of), 2 Department of Chemistry, Gangneung-Wonju Nanotional University, Gangneung, Gangwon, Korea (the Republic of)
Recently, plasmonic metal nanostructures (PMN) have attracted great attention for their abundant physical and chemical characteristics such as tunable surface plasmon resonances, efficient electron scavenging, surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence. By now, PMNs have been synthesized in different dimensions, shapes, morphologies in a nanometer scale. Wet chemical routes readily enable a large quantity of gold nanoparticles, while anisotropic and more complicated morphologies can be obtained through templating routes.In this study, PMNs with a complicated morphology of helix-coiled nanowire assembly were fabricated in a centimeter scale through a templating route. A unique composite system of mesoporous silica filled anodic aluminum oxide membranes was used as a template, where the narrow nanopores inside the confined silica phase provide a room for electrodeposition of plasmonic metals (gold and silver). A key step to the plasmonic metal nanowire replicas with a high quality in a large scale is slowing down deposition rate at a low temperature using a pulsed chronoamerometry method.The resulting helix-coiled PMNs were easily released from the composite templates by treating simply with HF, and basically characterized by steady-state absorption and emission spectroscopic tools. In particular, fluorescence lifetime imaging microscopy revealed interesting time-resolved emission characteristics in a picoseconds time regime in a single nanowire scale as well as the large assembled scale. From SERS experiments, we first found that helix-coiled metal nanowires showed distinctly enhanced molecule sensing efficiency than those from simple smooth nanowires. Furthermore, the helix-coiled gold nanowire assemblies also showed notable hydrogen peroxide sensing efficiency as an amperometric sensor. Hence, it is expected that the unique helix-coiled plasmonic metal nanowires, which could be synthesized in a large scale, would be an advanced functional nanomaterials in ranged application areas.
6:00 PM - W5.8
Improved Dielectric Properties in Template-stripped Plasmonic Films.
Jong Hyuk Park 1 , Prashant Nagpal 1 , Sang-Hyun Oh 2 , David Norris 3 Show Abstract
1 Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota, United States, 2 Department of Electrical and Computer Engineering, University of Minnesota, Minneapolis, Minnesota, United States, 3 Department of Mechanical and Process Engineering, ETH Zürich, Zürich Switzerland
The template stripping fabrication method can offer an approach to smooth patterned metals for plasmonics and metamaterials. While reduced surface roughness through this approach has previously been demonstrated, its ability to improve the dielectric function and electrical resistivity of the obtained metals has not been thoroughly investigated. Here, we report the effect of template stripping on the physical properties of silver films. Films were prepared with different surface roughness using conventional metal deposition and template stripping. The dielectric functions of the resulting films were compared using ellipsometry. The template-stripped surfaces with the smallest roughness exhibited dielectric functions with the largest negative real component and the smallest imaginary component. This indicates that the template-stripped surface will exhibit higher conductivity and less loss. The total electrical resistivity of the template-stripped films, even including the contribution due to electron scattering at surfaces, is close to that of bulk silver. Conventionally-deposited surfaces have much higher values. As a result of the improved surface properties, the propagation length of surface plasmon polaritons on the template-stripped surfaces is estimated to be 10 times longer than the conventionally-deposited surfaces.
6:00 PM - W5.9
Enhancement of Photoluminescence Emission from InGaN/GaN Multiple Quantum Wells via Coupling to Surface Plasmons in Two-dimensional Silver Array.
Cheng-Hsueh Lu 1 , Chia-Chun Lan 1 , Chuan-Pu Liu 1 2 , Yen-Lin Lai 3 Show Abstract
1 Department of Materials Science and Engineering , National Cheng Kung University, Tainan Taiwan, 2 Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan Taiwan, 3 , Genesis Photonics Inc, Tainan Hsien Taiwan
III-nitride semiconductor based light emitting diodes (LEDs) with high internal quantum efficiencies are indispensable for developing high bright solid-state lighting devices. Recently, significant attention has been paid to the enhancement of light emission efficiency from InGaN/GaN multiple quantum wells (MQWs) by coupling to surface plasmons (SPs). In this work, a novel approach to enhance the emission efficiency from InGaN/GaN MQWs via coupling to SPs in a periodic two-dimensional silver array is demonstrated. A higher internal quantum efficiency as well as a higher light extraction efficiency are achieved by the practice of engraving an array of nano-holes into the p-GaN cladding layer followed by partial filling with silver metals. By top excitation and collection, we demonstrate a two-fold enhancement in peak photoluminescence intensity. This nano-engraving technique offers a practical approach to overcome the limitation of the exponentially decayed SP field, and is feasible for use with solid state lighting application.
GailJ. Brown U. S. Air Force Research Laboratory
John Pendry Imperial College London
David Smith Duke University
NicholasX. Fang Massachusetts Institute of Technology
W6: Metamaterials for Photonics
Wednesday AM, April 27, 2011
Room 3006 (Moscone West)
9:30 AM - **W6.1
Recent Progress in IR Metatronics.
Nader Engheta 1 Show Abstract
1 Department of Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
I will present an overview of our most recent results in developing the paradigm of metatronics, in which the concept of metamaterials and plasmonic optics may provide us with the useful platform for the three fields of “electronics”, “photonics” and “magnetics” to be considered together seamlessly under one umbrella [N. Engheta, Physics World, 23(9), 341 (2010); N. Engheta, Science, 317, 1698-1702 (2007).] I will discuss my group’s most recent experimental results in demonstrating the proof of the concept of metatronics in the infrared regime, from 8 to 14 microns. We have shown, using the Fourier-Transform Infrared (FTIR) spectroscopy, that nanorods made of low-stressed Si3N4 with deeply subwavelength cross sectional dimensions function as lumped circuit elements at the IR wavelengths [Y. Sun, B. Edwards, A. Alu, and N. Engheta, “Experimental Realization of Optical Lumped Nanocircuit Elements at Infrared Wavelengths,” submitted]. This concept of lumped circuit elements provide us with a new set of "alphabets" for micro- and nanophotonics. Using the circuit theory we have obtained the quantitative values of these lumped circuit elements, and we have now experimentally verified these quantitative values. In addition to these experimental results, we have also expanded our theoretical works on metatronics into other platforms such as graphene, proposing the possibility of using graphene as a new paradigm for metatronic circuitry, i.e., single-atom-thick metatronic circuitry. We will also give an overview of these recent results.
10:00 AM - W6.2
Photonics Platform at 1/20th of the Wavelength.
Volker Sorger 1 , Ziliang Ye 1 , Rupert Oulton 1 , Yuan Wang 1 , Guy Bartal 1 , Nitipat Pholchai 1 , Ertugul Cubukcu 1 , Xiang Zhang 1 2 Show Abstract
1 , UC Berkeley, Berkeley, California, United States, 2 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
With the ongoing trend for increased electronic or photonic device performance and simultaneously mitigating power consumption, the reduction of device feature sizes on a component level is paramount. While metal-based nanostructures can theoretically achieve this goal, wave guiding with deep sub-wavelength confinement is still to be verified, especially with technologically relevant semiconductor materials, which exacerbate intrinsic propagation losses. Here we report a direct experimental observation of ultra-small guided waves in a metal-semiconductor waveguide design featuring broadband operation with a superior figure-of-merit relevant for nanophotonic building blocks. Nearfield scanning optical microscopy (NSOM) reveals mode sizes as small as about 50 x 60 nm2 at visible and near-infrared wavelengths demonstrating a viable photonics platform down to 1/20th of the wavelength. We furthermore demonstrate strong coupling (beta-factor = 75% and Purcell-Factor = 60) of molecular emission into such waveguide, which is the first step towards a single photon all-optical switch. This novel waveguide-platform allows for highly integrated photonic components and circuits such as on-chip light sources, fast modulators and non-linear optics within only a few wavelengths.
10:15 AM - W6.3
MWIR and LWIR Tunable Polarmetric Scatterometery.
Stephen Nauyoks 1 , Michael Marciniak 1 Show Abstract
1 Engineering Physics, Air Force Institute of Technology, Dayton, Ohio, United States
A Schmitt Measurement System’s Complete Angle Scatter Instrument (CASI) can discretely measure the reflection and transmission hemispheres of scattered light. The automated sample holder allows the angle of incidence to be varied from up to 80 degrees depending on the size of the sample. Thus the bidirectional scattering distribution function (BSDF) could be found for a variety of incident angles. Our CASI system was modified with the addition of a dual rotating retarder, which allows the BSDF measurement to broken down into each Mueller element. This makes the system unique to commercial systems such as Woollam’s IR-VASE which only measure the Mueller matrix elements for the specular reflection. The system was further modified with the addition of six tunable Quantum Cascade Lasers (QCL) by Daylight Solutions. These lasers can be tuned from 4.35 to 9.71 µm with exclusions from 4.55 to 4.74 µm, 5.67 to 5.76 µm, and 6.54 to 7.40 µm. Because of limitations of production capabilities and incomplete material models it can be difficult to manufacture novel sub-wavelength materials that resonate at very specific wavelengths. This can limit the use of lasers to characterize these materials. However, with the tunablility of the QCLs it is possible to characterize novel nano- and micrometer sized structured materials, for example photonic crystals, plasmonic structures and optical meta-materials, at both the very specific resonance frequencies, near the resonant frequency and away from resonant frequency. This allows for a fuller understanding of the material being studied. This novel full polarimetric ellipsometry technique for characterizing nano- and micrometer sized structures will be demonstrated and its capabilities explored.
10:30 AM - W6.4
Room Temperature Sub-diffractional Plasmon Laser.
Renmin Ma 1 , Rupert Oulton 1 , Volker Sorger 1 , Guy Bartal 1 , Xiang Zhang 1 2 Show Abstract
1 , UC Berkeley, Berkeley, California, United States, 2 , Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Plasmon lasers are a new class of coherent optical amplifiers that generate and sustain light well below its diffraction limit. Their intense, coherent and confined optical fields can enhance significantly light-matter interactions and bring fundamentally new capabilities to bio-sensing, data storage, photolithography and optical communications. However, metallic plasmon laser cavities generally exhibit both high metal and radiation losses, limiting the operation of plasmon lasers to cryogenic temperatures, where sufficient gain can be attained. Here, we present room temperature semiconductor sub-diffraction limited laser by adopting total internal reflection of surface plasmons to mitigate the radiation loss, while utilizing hybrid semiconductor-insulator-metal nano-squares for strong confinement with low metal loss. High cavity quality factors, approaching 100, along with strong λ/20 mode confinement lead to enhancements of spontaneous emission rate by up to 18 times. By controlling the structural geometry we reduce the number of cavity modes to achieve single mode lasing.
10:45 AM - W6.5
A Single Nanorod Plasmonic Switch.
Stephan Link 1 Show Abstract
1 Chemistry and Electrical & Computer Engineering, Rice University, Houston, Texas, United States
Although building optical analogs of electronic circuits with dimensions much smaller than the incident wavelength has become possible by using localized and propagating surface plasmons, active control in plasmonics still presents a major roadblock. Here we show how to externally turn the polarized scattering intensity of the longitudinal surface plasmon resonance from individual gold nanorods completely on or off using applied voltages as a low 4V. This plasmonic switch takes advantage of the unique electro-optical properties of a nematic liquid crystal. Individual gold nanorods were isolated between planar electrodes and covered with the liquid crystal 5CB. Using single particle spectroscopy we found that the polarization of light scattered by the longitudinal plasmon resonance of a single nanorod can be rotated reversibly by 90 degrees. We demonstrate that the response time of this plasmonic switch follows the dynamics of the electric field induced reorientation of the liquid crystal director.
11:00 AM - W6: Meta photon
W8: Plasmonic Coupling
Wednesday PM, April 27, 2011
Room 3006 (Moscone West)
2:30 PM - **W8.1
Applications of Plasmonic Oligomers, Metamaterials, and Nanoantennas.
Harald Giessen 1 Show Abstract
1 4th Physics Institute, University of Stuttgart, Stuttgart Germany
We present an overview of 2D and 3D plasmonic oligomers , metamaterials, and nanoantennas which are utilized for different purposes. Stacked 3D metamaterials can be used as perfect absorbers, which give angle and polarization independent absorption beyond 90% in the visible and near-infrared region . Utilizing transition metals as well as plasmonic induced transparency schemes , the application of sensors for liquids and gases becomes feasible . Cavity enhancement allows for tailoring the spectral resonances of plasmonic systems and results in very high figures of merit for the sensor schemes [5,6]. Arranging plasmonic substructures in 3D geometries, chirality can result as optical property. Using this method allows for the construction of novel broadband circular polarizers with large angle acceptance angles. Nanoantennas can aid the sensing and nonlinear properties of plasmonic nanostructures as well. We are going to discuss applications in this area as well. Transition from isolated to collective modes in plasmonic oligomers. M. Hentschel, M. Saliba, R. Vogelgesang, H. Giessen, A. P. Alivisatos, and N. Liu; Nano Lett. 10, 2721 (2010). Infrared perfect absorber and its application as plasmonic sensor. N. Liu, M. Mesch, T. Weiss, M. Hentschel, and H. Giessen; Nano Lett. 10, 2342 (2010). Planar metamaterial analog of electromagnetically induced transparency for plasmonic sensing. N. Liu, T. Weiss, M. Mesch, L. Langguth, U. Eigenthaler, M. Hirscher, C. Sönnichsen, and H. Giessen; Nano Lett. 10, 1103 (2010). Hydrogen sensor based on metallic photonic crystal slabs. D. Nau, A. Seidel, R.B. Orzekowsky, S.-H. Lee, S. Deb, and H. Giessen; Opt. Lett. 35, 3150 (2010). Cavity plasmonics: Large normal mode splitting of electric and magnetic particle plasmons induced by a photonic microcavity. R. Ameling and H. Giessen; Nano Lett. 10, 4394 (2010). Cavity-enhanced localized plasmon resonance sensing. R. Ameling, L. Langguth, M. Hentschel, M. Mesch, P. V. Braun, and H. Giessen; Appl. Phys. Lett. 97, 253116 (2010).
3:00 PM - W8.2
Resonant Properties of Plasmonic Resonator Antennas.
Edward Barnard 1 , Ernst Jan Vesseur 2 , Toon Coenen 2 , Ragip Pala 1 , Albert Polman 2 , Mark Brongersma 1 Show Abstract
1 , Stanford University, Stanford, California, United States, 2 , FOM Institute AMOLF, Amsterdam Netherlands
A combined theoretical and experimental study of wavelength-scale plasmonic resonator antennas is presented. Using full-field electromagnetic simulations and analytical optical antenna models, we are able to derive simple and intuitive design rules to achieve antennas with a desired set of optical properties (field enhancement, scattering cross section, absorption cross section, and resonant frequency) based on their geometric properties. As part of these design rules we are able to quantify reflection phase and understand this quantity in terms of the end-face near-field. With these design rules, we have constructed resonance maps that allow a designer to choose an antenna structure that provides desired resonant properties for a specific application. We then apply these design rules to create antennas that resonantly enhance absorption on thin silicon detectors as well as enhance emission of cathodoluminescence (CL). Through spatial and spectral mapping of both photocurrent and CL we clearly show the fundamental and higher-order resonant modes of these antennas. With CL we are also able to map the spatial distribution of these resonant modes with 10 nm resolution. In addition to these specific demonstrated applications, the results of this study enable optical engineers to more easily design a myriad of plasmonic devices that employ optical antenna structures, including nanoscale photodetectors, light sources, sensors, and modulators. Additionally the understanding of phase may be critical to designing resonant elements for metamaterials.
3:15 PM - W8.3
Fabry-Perot Effect on Dimer Nanoantennas.
Alessia Polemi 1 , Kevin Shuford 1 Show Abstract
1 Chemistry, Drexel University, Philadelphia, Pennsylvania, United States
It is well known that metallic nanoparticles support plasmonic modes, whose resonance is strongly dependent on the metal dispersion, the shape of the particles, and the environment where the particles are located. It has also been shown in the recent literature that these nanoparticles function as optical antennas, in a manner analogous to radio antennas. In the optical domain, if a quantum emitter is coupled to the antenna mode, the antenna enhances the interaction between the emitter and the radiation field. The presence of the antenna and of the local environment strongly modifies the transition rates of the emitter, and the antenna properties are modified by the presence of the emitter. Thus, the whole system must be regarded as coupled. The appropriate coupling between the antenna and its local environment and the quantum emitter can be exploited to enhance transition rates, modify the angular emission, and enhance directivity and gain. In this work, we investigate the interaction between a single quantum emitter with dimer nanoantennas through a Fabry-Perot structure realized as an appropriate combination of two dielectric layers. This kind of Fabry-Perot dielectric configuration is well known in the microwave region as a structure to increase the antenna efficiency. Here, this concept is transposed to the optical domain. The single emitter is coupled to the dielectric structure, which produces a wide aperture field on top of the dielectrics with the same polarization of the emitter. This purely polarized aperture field can be used to excite one or more conveniently spaced nanoantennas. We demonstrate by 3D numerical calculations that the directivity and excitation rate of a single dimer is significantly enhanced. Also, we show how multiple dimers arranged in an array configuration can be enhanced due to the wide aperture field generated by only one emitter.
3:30 PM - W8.4
Power Flow Analysis of Emitter Decay Via an Optical Antenna.
Kevin Chih-Yao Huang 1 , Min-Kyo Seo 2 , Young Chul Jun 2 , Mark Brongersma 2 Show Abstract
1 Electrical Engineering, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States
Current methods to calculate the emission enhancement of a quantum emitter coupled to an optical antenna of arbitrary geometry rely on analyzing the total Poynting vector power flow out of the emitter or the dyadic Green functions from full field numerical simulations. Unfortunately, these methods do not provide information regarding the nature of the dominant energy decay pathways. We present a new approach to this problem that allows for a rigorous separation, quantification, and visualization of the emitter output power flow captured by an antenna and the subsequent reradiation power flow from the antenna to the far field. Furthermore, it can be used to calculate emission into free space and antenna-supported decay channels while enabling separate optimization of the input and output power flow of the antenna thus opens up new design strategies for strongly interacting emitter/ antenna systems used in sensing, active plasmonics and metamaterials, and quantum optics.
3:45 PM - W8.5
Differentiating the Roles of Surface Plasmon Polaritons in Excitation and Spontaneous Emission Rates and Outcoupling Efficiency Enhancement from Nanoantenna Arrays.
Kay Fung Chan 1 , Koon Chung Hui 1 , Yau Chuen Yiu 1 , Hock Chun Ong 1 Show Abstract
1 , The Chinese University of Hong Kong, Hong Kong Hong Kong
As it is anticipated one day light-emitting diodes (LEDs) will replace conventional light bulbs and fluorescent tubes, how to increase the light emission efficiency of LEDs has become a mainstream research and development. To increase the overall emission efficiency, both internal quantum and light extraction efficiencies have to be improved. Surface plasmon polaritons (SPPs), which support strongly localized field on metal surface, have recently been proposed to increase both internal quantum and light extraction efficiencies. In fact, by placing the plasmonic systems in close proximity to the photoactive materials, increase in light emission has been widely reported, pointing to a positive direction towards surface plasmon mediated emission enhancement. However, to fully understand the underlying mechanism, it is of great importance to differentiate the roles of SPPs in the modification of excitation and spontaneous emission rates and light outcoupling efficiency such that a rational approach can be developed in the future in designing suitable plasmonic system for any given light-emitting material. Here, we combine angle-, temporal-, and spatially-resolved photoluminescence and photoluminescence excitation spectroscopy to study the emission enhancement arising from metallic nanoantenna arrays. By comparing the angle-resolved reflectivity and photoluminescence and photoluminescence excitation mappings, it is possible to identify all possible electromagnetic modes excited on the arrays and to study their contribution to the excitation and emission enhancements. As a result, both Bloch-like propagating and localized SPPs have been identified unambiguously and studied quantitatively. In addition, the effects of different types of SPPs on the modification of spontaneous emission rate have been addressed by fluorescence lifetime microscopy. Compared with Bloch-like SPPs, localized SPPs are found to have stronger effects on emission enhancement, which is in good agreement with our theoretical simulation.
4:00 PM - W8: Plas Coup
W9: Metamaterial Resonators
Wednesday PM, April 27, 2011
Room 3006 (Moscone West)
4:30 PM - W9.1
Dynamic Tuning of Infrared Metamaterials via Mechanical Deformation of an Elastomeric Substrate.
Imogen Pryce 1 , Yousif Kelaita 1 , Emily Warmann 1 , Koray Aydin 1 , Ryan Briggs 1 , Harry Atwater 1 Show Abstract
1 Thomas J. Watson Laboratories of Applied Physics, California Institute of Technology, Pasadena, California, United States
Active metamaterials, which control the resonant response of a material by incorporating dynamic components at the unit cell level, represent a new class of resonant structure designs. Increasing the tunability of a metamaterial system is important for the development of a number of devices including modulators, tunable filters, and concentrators. Various approaches, ranging from electrical probing of single unit cells to thermal actuation, have been used to demonstrate amplitude modulation and frequency tuning of the resonant response. In this work, we exploit the mechanical deformation of a compliant substrate to achieve greater than linewidth tunability of the resonant frequency of coupled split ring resonator (SRR) based metamaterials and discuss how highly compliant cantilever mechanical designs can be used to reduce the force requirements.We investigate SRR designs fabricated using a hard/soft nanolithographic pattern transfer technique. Arrays of 100 nm thick Au resonators are patterned over 100 μm by 100 μm squares by e-beam lithography on a sacrificial Si substrate. The Au patterns are functionalized using a monolayer of 3-mercaptopropyl trimethoxysilane in order to improve adhesion to the PDMS. PDMS is cured on the patterns, and the Si is back etched leaving a free-standing PDMS substrate patterned with SRR arrays. Reflection spectra of the arrays are measured using FTIR spectroscopy between 1.5 and 8 µm. Both experimental and simulated results for the tunable SRR arrays will be presented. We show that though mechanical deformation can be used to change the capacitance of a single SRR and shift the resonant frequency, in order to achieve more significant tunability, we must introduce different designs. We show that using coupled resonators and through the incorporation of more complex mechanical features, linewidth tunability can be achieved with up to 10 times less force than in our previous work. Full field electromagnetic simulation is used to corroborate the experiments and guide the design of coupled resonators with particular resonant frequencies. Finite element method modeling of the mechanical deformation will be discussed with a view to understanding how high compliance mechanical designs can be achieved.Of particular interest for sensing applications is the enhanced detection of molecular infrared vibrational modes with compliant metamaterials. We show that the mechanical tunability can be used to optimize alignment with various IR vibrational modes and enhance the surface enhanced infrared absorption signal from these modes. We will also discuss how coupling the bright mode resonance, from either a vibrational mode or a single nanowire antenna, to the dark mode resonance of a split wire pair in a dolmen-type structure induces a Fano-like dip in the reflection spectra. We demonstrate how mechanical manipulation can be used to modulate the vibrational mode intensity and ultimately induce an on-off response.
4:45 PM - W9.2
Surface Plasmon Enhanced Photocurrent in GaN Based UV Photodetectors - Plasmonics for Shorter Wavelengths.
Serkan Butun 1 2 , Ekmel Oezbay 1 2 3 Show Abstract
1 Nanotechnology Research Center, Bilkent University, Ankara, Ankara, Turkey, 2 Department of Physics, Bilkent University, Ankara, Ankara, Turkey, 3 Department of Electrical and Electronical Engineering, Bilkent University, Ankara, Ankara, Turkey
Integration of plasmonic nano-structures with solid-state devices has opened a new way to incorporate light into integrated circuits (IC). IC elements become smaller gradually along with the technological advancements. We reach a point that electrons are no longer carrying information fast enough. Photons are expected to replace electrons in ICs. Therefore photodetectors will be one of the core components of future ICs. However, reduction of absorption cross section is the main setback for miniaturization of the volume of a photodetector. A properly designed plasmonic antenna positioned on top of a photodetector can guide and focus the light in sub-wavelength dimensions. Metal semiconductor metal (MSM) type photodetectors are very convenient for this type of work. Since, metal contact surfaces can easily be structured intelligently. Main drawback, on the other hand, is that a significant portion of incident light is blocked by the MSM contacts before reaching the active region. A suitable plasmonic antenna may also help to collect light that is incident upon the contacts. Invention of blue-ray disks is a practical example of the importance of using shorter wavelengths. The reason is that, light with shorter wavelength can be focused in a much tighter area thereby decreasing the device size significantly. This tendency to make devices smaller necessitates the development of optical components to form a bridge between photons and electrons in short wavelength regions.Here, we report on design and fabrication of a plasmonic UV lens to be used as an optical antenna on a GaN based UV photodetector. Aluminum gratings of various periods ranging from 180 nm to 300 nm were fabricated. Ellipsometric measurements were carried out to determine the resonant wavelength. A special high quality so called semi-insulating GaN epitaxial layer was grown on c-plane sapphire by metalorganic chemical vapor deposition. 300 nm apart Ni/Al MSM contacts were formed on GaN. Top surface of the contacts were covered with Al gratings with designed period. Spectral photoconductivity and current voltage measurements were carried out and compared to control samples which have no plasmonic lens. An overall 3 fold enhancement in photocurrent was achieved. This work proved that Al having a high bulk plasma frequency can be used for plasmonic devices for UV region. This is the shortest wavelength reported plasmonic optoelectonic device in the literature as well.
5:00 PM - **W9.3
Scan Angle Enhancement of Phased Array Antennas Using a Negative Index Material Lens.
Minas Tanielian 1 , Tai Lam 1 , David Vier 1 , Jean Nielsen 1 , Claudio Parazzoli 1 Show Abstract
1 Elect. Comm. and Sensing Technology, Boeing Research and Technology, Seattle, Washington, United States
We present the design, optimization, fabrication, and measurement of a NIM lens to steer phased array antenna beams to the horizon. The conformal mapping technique of transformation optics is utilized in the design process to facilitate with lens fabrication. A new dual polarization unit cell is designed to avoid the issues associated with short cut wires. The lens is measured using an actual phased array antenna and it demonstrates down to-the-horizon scanning as designed, although material losses are somewhat high.
GailJ. Brown U. S. Air Force Research Laboratory
John Pendry Imperial College London
David Smith Duke University
NicholasX. Fang Massachusetts Institute of Technology
W10: Novel Fabrication Processes
Thursday AM, April 28, 2011
Room 3006 (Moscone West)
10:00 AM - W10.1
In Situ Characterisation of Tunable Ag Nanoparticles Arrays Grown by Glance Angle Deposition.
Ruggero Verre 1 , Karsten Fleischer 1 , Sumesh Sofin 1 , Nial McAlinden 1 , John McGilp 1 , Igor Shvets 1 Show Abstract
1 Physics, CRANN, Trinity College of Dublin, Dublin 2 Ireland
One-dimensional Ag nanoparticle arrays below the diffraction limit have been grown on step bunched vicinal c-plane Al2O3 in ultra-high vacuum using deposition at a glancing angle. The substrates were obtained via high temperature annealing in a furnace and their morphology can be tuned by modifying the annealing conditions. The following self-assembly growth combines the high throughput of colloidal chemistry with the nanoparticle (NP) long range order attainable usually via lithographic techniques. The average NP diameter and inter-particle distance is around 15 nm and 22 nm respectively and with standard deviations of 20%. Such ordered structures have never been reported before with similar techniques. The structures showed a strong optical anisotropy in the visible region with a shift between longitudinal and transverse resonant modes bigger than 1 eV. This phenomenon has been attributed to the combined effects of both shape anisotropy and strong inter-particle interaction. The presence of the resonant shift provides an estimate of the decay length in a waveguiding process along such structures to be over 10 μm. Furthermore, due to the presence of “hot spot” area in the inter-particle sites, the structure is appealing for surface enhanced Raman spectroscopy measurements. Reflection Anisotropy Spectroscopy (RAS) has been used for the first time on such structures, to monitor optical anisotropy in-situ, during the growth. The relevant optical properties were determined as a function of deposition angle, Ag thickness, substrate temperature and morphology. In particular, tunability of the peaks can be attained by changing the deposition parameters and measuring the spectra during the growth. The peak related to polarization along the chain axis can be changed in a range of more than 100 nm.The combination of both glancing deposition and in-situ monitoring allows to choose the resonant energy of the structures without interrupting the process and gives hints on the growth process of NP with a narrow morphological dispersion.A simple phenomenological model was finally developed to reproduce the features seen in the spectra. With this model it was possible to use the inhomogeneous broadening as a guide to the nanoparticle dispersion and to find the angle which provides the best long range order without the need of any microscopy technique. We have developed a tool to effectively grow and monitor strongly anisotropic samples for dichroic, waveguiding or biosensing purposes whose properties can be tuned once the optimisation of the parameters governing the growth has been regulated. F.Cuccureddu et al, Nano Lett. 8 (10), 3248 - 3256 (2008)
10:15 AM - W10.2
A New Approach to the Formation of Supported Gold Nanostructures.
Robert Hughes 1 , Svetlana Neretina 1 Show Abstract
1 Mechanical Engineering, Temple University, Philadelphia, Pennsylvania, United States
While the vast majority of gold nanostructures have been produced using solution-based synthetic protocols it is well-understood that a significant number of potential applications require that the nanostructures be supported by a substrate in a manner which renders them immobile. Oxide substrates provide an excellent platform for the formation of supported gold nanostructures due to their chemical and thermal stability, crystallographic perfection, wide variety of accessible surface reconstructions, lower surface free energies, and resistance to gold diffusion. Numerous routes exist for the production of such structures including the attachment of functionalized solution-based nanoparticles to the surface, growth off of surfaces seeded with linked nanoparticles, lithographically patterning continuous thin films, thermal dewetting, spinodal dewetting, vapor phase epitaxy and nanosphere lithography. Among these various techniques those utilizing self-assembly stand out as an attractive means for forming such structures over large areas. Forming a heteroepitaxial relationship between the gold nanostructure and the underlying substrate provides the additional means to engineer the shape, size and crystallographic orientation of the nanostructures through substrate imposed strains, epitaxy, crystallographic symmetries, substrate surface morphology, interface chemistry and wettability. Heteroepitaxial growth pathways also allow for the use of surface acting agents which fundamentally alter the nanostructure growth modes by inhibiting adatom motion and, thus, preventing the equilibrium state from being achieved. The work presented will demonstrate how such agents, acting in a heteroepitaxial environment, can fundamentally alter nanostructure shape. Examples will include the transformation of nanostructures from the equilibrium Wulff shape to hexagonal-shaped tablets.
10:30 AM - W10.3
Sub-100nm Patterning of Gold Nanorods on Polymer-derived Surface Patterns.
Dhriti Nepal 1 , M. Serdar Onses 2 , Kyoungweon Park 1 , Michael Jespersen 1 , Folusho Oyerokun 1 , Paul Nealey 2 , Richard Vaia 1 Show Abstract
1 Nanostructured and Biological Materials Branch, Wright Patterson Air Force Base, Wright Patterson , Ohio, United States, 2 Department of Chemical and Biological Engineering, College of Engineering, University of Wisconsin – Madison, Madison, Wisconsin, United States
Directed and self assembly concepts provide intriguing avenues to fabricate translationally-ordered nanoparticle arrangements, but lack the robustness to reproducible deliver complex spatial organization across macroscopic length scales that is comparable to traditional lithographic-deposition concepts. The crucial challenge is to determine how to best synergize the salient features of assembly and lithography to provide fabrication routes that enable new devices architectures. Here, the assembly of gold nanorods (AuNRs, width ~15-30 nm, aspect ratio ~2-6, nanomolar aqueous dispersion) onto sub-100 nm polymer derived surface patterns (PDSP) is examined to determine the conditions necessary for selective absorption and to understand the impact of commensurate length scales (i.e. confinement regime) on the ordering of the Au NRs. Using site-specific functionalization to tune the surface property of the Au NRs, CTAB-free polyethylene glycol (PEG) and PEG- mercaptopropane sulfonate (MS) functionalized Au NRs have been created. At the appropriate pH, MS-AuNRs selectively interact via acid-base or electrostatics with cationic surfaces, such as poly2-vinyl pyridine (P2VP). In contrast, PEG-Au NRs preferentially absorb to hydrophobic surfaces, such as polystyrene (PS), analogous to protein adsorption on hydrophobic interface. This preferential interaction enables selective Au NRs absorption and thus replication of the underlying PS-P2VP pattern down to 25 nm line widths. In contrast to prior studies on spherical nanoparticles, the NRs organization and orientation strongly depend on both size and pitch of the pattern, and the size and architecture (aspect ratio) of the rods. Large scale organization of such patterns provide novel anisotropic optical properties arising from hybridized plasmon modes associated with the engineered coupling of the AuNR plasmon resonances.
10:45 AM - W10.4
Use of Thin Sectioning (Nanoskiving) to Fabricate Nanostructures for Plasmonics.
Darren Lipomi 1 , George Whitesides 1 Show Abstract
1 Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States
This paper reviews nanoskiving—a simple and inexpensive method of nanofabrication—and its applications in plasmonics. Nanoskiving requires three steps: i) deposition of a metallic, semiconducting, ceramic, or polymeric thin film onto an epoxy substrate (which may be topographically patterned); ii) embedding this film in epoxy, to form an epoxy block, with the film as an inclusion; and, the key step, iii) sectioning the epoxy block into slabs with an ultramicrotome. These epoxy slabs, which can be 30 nm – 10 μm thick, contain nanostructures whose lateral dimensions are equal to the thicknesses of the embedded thin films, and thus can be as thin as 10 nm. Each successive slab is a quasi copy of the preceding slab. When combined with soft lithographic molding and other processes, nanoskiving can replicate patterns of structures that can be transferred to almost any substrate, and that would be difficult or impossible to generate by conventional methods of fabrication. Nanostructures produced include single-crystalline nanowires of gold, and two-dimensionsal arrays of rings, crescents, counterfacing split rings, cylinders, stacked rings, coaxial cylinders, and other structures. These arrays of structures can be composed of metals, semiconductors, dielectrics, and polymers, singly or in combination. Optical applications of structures produced by nanoskiving include surface plasmon resonators, plasmonic waveguides, and frequency-selective surfaces.
11:00 AM - W10: Novel Fab
W11: Plasmonics II
Thursday PM, April 28, 2011
Room 3006 (Moscone West)
11:30 AM - **W11.1
Tuning Electric and Magnetic Responses as Structure Evolves in Metamaterial.
Mu Wang 1 , Xiong Xiang 1 , Ru-Wen Peng 1 , Wei-Hua Sun 1 , Ling Qin 1 Show Abstract
1 , Nanjing University, Nanjing China
Here we focus on simultaneous realization of pure magnetic and electric responses by changing topological structures of the building block in an array of metallic structure. The building block changes from double-layered orthogonally rotated symmetric H-shaped metallic pattern to un-symmetric U-shaped metallic pattern, and eventually to helix. In an assembly of U-shaped resonators, pure magnetic and electric responses are realized at high (ωH) and low (ωL) frequencies, respectively. By rotating the polarization of incident light for 90°, the magnetic and electric responses can be switched at the same frequency . By moving the shorter metal bar at the end of two longer parallel bars towards the center of the bars, the U-shaped resonator gradually evolves to an H-shaped resonator. Meanwhile, ωH and ωL approach each other, and overlap eventually. This means that the negative refractive index can be achieved without changing the polarization of incident light . By connecting U-shaped pattern on different layers, the building block can be transformed into a helix. The metallic helices with different chirality are used to assemble an optically-nonactive metamaterial . With linearly polarized incident light, pure electric or magnetic resonance can be selectively realized, which leads to negative permittivity or negative permeability accordingly. Our calculated results are supported by the experimental measurements. The physical processes involved in these evolutions are discussed based on the investigations of field distributions and surface current distributions on the metallic structures.  Xiang Xiong, et al.,Switching the electric and magnetic responses in a metamaterialPhys. Rev. B80, 201105(R) (2009) Xiang Xiong, et al., Tuning electric and magnetic responses as structure evolves in metamaterial, to be published Xiang Xiong, et al., Optically-nonactive assorted helices array with interchangeable magnetic/electric resonance, to be published, http://arxiv.org/abs/1012.2623
12:00 PM - W11.2
Broadband Plasmonic Microlenses Based on Patches of Nanoholes.
Hanwei Gao 1 , Jerome Hyun 2 , Min Hyung Lee 1 , Lincoln Lauhon 2 , Teri Odom 2 Show Abstract
1 , University of California, Berkeley, Berkeley, California, United States, 2 , Northwestern University, Evanston, Illinois, United States
This work reports a new type of diffractive microlens based on finite-areas of 2D arrays of circular nanoholes (patches). The plasmonic microlenses can focus single wavelengths of light across the entire visible spectrum as well as broadband white light with little divergence. The focal length is determined primarily by the overall size of the patch and is tolerant to significant changes in patch substructure, including lattice geometry and local order of the circular nanoholes. The optical throughput, however, depends sensitively on the patch substructure and is determined by the wavelengths of surface plasmon resonances. This simple diffractive lens design enables millions of broadband plasmonic microlenses to be fabricated in parallel using soft nanolithographic techniques.
12:15 PM - W11.3
A Nanoplasmonic-electrochromic Optical Switch.
Amit Agrawal 1 , Ceren Susut 1 , Ben McMorran 1 , Gery Stafford 1 , Henri Lezec 1 , Alec Talin 1 Show Abstract
1 CNST, NIST, Gaithersburg, Maryland, United States
Nanoplasmonic devices with active, low-voltage control over their optical properties are attractive for variety of applications such as optical communications and sensing. In this paper we demonstrate active control over the transmission characteristics of nanoscale slits and slit-groove pairs fabricated in Au films using a thin layer of an electrochromic dye Prussian Blue selectively deposited in the slits. By electrochemically switching the dye from absorbing to non-absorbing state, we achieve high contrast in transmitted light with a voltage <1 V. The coupling of light into surface plasmons allows for electrochromic films only a few monolayers thick to modulate much higher light intensity compared to conventional electrochromic optical switches with similar dye thickness. We fabricated the nanoscale slits using a focused ion beam, and we deposit the dye using a modified electrodeposition method which will be described in the talk. In addition to experimental data, we will present modeling results which will help guide the development of future devices based on this principle.
12:30 PM - W11.4
Self-assembly of Au Nanoparticles on Gratings for High Sensitivity and High Fidelity SERS Detectors.
Aiqing Chen 1 , Alexandra Joshi-Imre 2 , A. Eugene DePrince III 2 , Arnaud Demortiere 2 , Elena Shevchenko 2 , Leonidas Ocola 2 , Stephen Gray 2 , Ulrich Welp 1 , Vitalii Vlasko-Vlasov 1 Show Abstract
1 Material Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 2 Center for Nanoscale Materials, Argonne National Laboratory, Argonne, Illinois, United States
Surface enhanced Raman spectroscopy (SERS) is a powerful analytical technique capable of detection and recognition of tiny amounts of chemicals through their unique vibrational modes. SERS is largely based on the enhancement of the light intensity in hot spots on nano-structured metals, such as rough metal films or aggregates of metal nanoparticles (NPs). Poor control of randomly distributed hot spots causing poor reproducibility and low fidelity of the SERS spectra poses the major challenge for the numerous potential application of SERS including chemistry, medicine, pharmaceutical, and national security. A possible solution of the problem could be a construction of regular arrays of closely spaced metal elements e.g. using electron beam lithography (EBL). Unfortunately, resolution limitations and relatively low efficiency make the task of the EBL fabrication of required nanometers gaps quite unpractical. In this work we demonstrate a bottom up manufacturing of SERS-active substrates with well-controlled arrays of regular hotspots in a hierarchical architecture allowing multi-stage light amplification. The arrays are made using self-assembly of 80nm Au NPs in lithographically defined gratings on 100 nm Ag films. The first stage of amplification results from the grating assisted transformation of light into surface plasmons in the Ag film and confinement of light energy into surface fields. Periodic modulations on the film surface form the distributed Bragg resonator and assist the enhancement through intense standing waves. Further enhancement of light fields is provided by controlled and reproducible hot spots in the gaps of self-assembled regular arrays of Au NPs. The grating effect due to the periodic structure enables also an efficient directional emission of the Raman light at the Bragg angle. In our structures 1D rectangular profile gratings were fabricated by e-beam lithography using a negative tone hydrogen silsesquioxane (HSQ) resist on top of a 100 nm Ag/10 nm SiO2 film on Si substrates. The grating period was 450 nm and the trench width varied to accommodate 2, 3 or 4 NPs. The self-assembly of gold NPs on gratings was implemented using solvent evaporation techniques. By careful control of surface stabilizers on NPs and proper assembly conditions (optimized concentration of NPs, surface tension of solvent, temperature, and evaporation rate), we obtained well-ordered arrays of NPs extended over more than 100x100 microns^2 areas of grating structures. Spectral characterization of samples reveals unique optical resonances of the self-assembled Au NP arrays on Ag gratings, which are well reproduced in our numerical simulations. We analyze contributions from different components of our hierarchical SERS-active substrates and demonstrate high fidelity SERS spectra from 5nm CdSe quantum dots and Rhodamine 6G solutions.
GailJ. Brown U. S. Air Force Research Laboratory
John Pendry Imperial College London
David Smith Duke University
NicholasX. Fang Massachusetts Institute of Technology
W14: Acoustic Metamaterials
Friday AM, April 29, 2011
Room 3006 (Moscone West)
10:00 AM - **W14.1
From Newton's Cradle to New Materials: Nonlinear Acoustic Crystals.
Chiara Daraio 1 Show Abstract
1 Aeronautics and Applied Physics, California Institute of Technology, Pasadena, California, United States
The bouncing beads of Newton's cradle fascinate children and executives alike, but their symmetric dance hides complex dynamic behavior. Lift a bead on one side off a chain of a few suspended beads, let it swing back: one bead bounces off on the other side. Do the same with a long chain of beads: several beads bounce off on the other side. This represents an example of nonlinear wave dynamics, which can be exploited for a variety of engineering applications. By assembling grains in crystals or layers in composites such that they support nonlinear waves, we are developing new materials and devices with unique properties. We have constructed acoustic lenses that allow sound to travel as compact bullets that can be used in medical applications, have developed new materials for absorbing explosive blasts, and are exploring new ways to test aircraft wings and railroad tracks nondestructively with the help of nonlinear waves.
10:30 AM - W14.2
An Acoustic Directional Antenna with Isotropic Materials.
Christopher Layman 1 , Theodore Martin 1 , Gregory Orris 1 Show Abstract
1 , Naval Research Lab, Washington, District of Columbia, United States
New acoustic metamaterial devices offer promising applications, ranging from tunable sound blocking with superior efficiency, to acoustical diodes. Transformation acoustics (TA), relying on the invariance of field equations under coordinate transformations, in conjunction with metamaterial features, has further expanded the range of functionalized acoustic materials. However, for a large variety of devices based on TA, such as ones relying on Pendry’s concept, physical realization remains limited owing to the requirement of anisotropic effective properties. Here we examine the behavior of a directional four-wave acoustic antenna, designed from finite embedded coordinate transformations (FECT), which eliminate the constraint of anisotropy by way of a suitable conformal mapping. The two dimensional antenna consist of a square rod with an inhomogeneous and isotropic distributed mass density and bulk modulus designed from the FECT perspective. The rod is embedded in an acoustically matched matrix and subsequently subjected to an internal coaxially line source to evaluate its transmitting performance across a large bandwidth. Passive characteristics are also studied by probing the antenna with a point source-receiver setup. Experimental data is compared to both established analytical FECT models and full-wave simulations. This work is supported by the Office of Naval Research.
10:45 AM - W14.3
Transmission Line Acoustic Cloak for Ultrasound Waves.
Nicholas Fang 1 2 , Shu Zhang 2 , Jun Xu 1 2 Show Abstract
1 MechE, MIT, Cambridge, Massachusetts, United States, 2 MechSE, UIUC, Urbana, Illinois, United States
We present here the first practical realization of a low-loss and broadband acoustic cloak for underwater ultrasound. This metamaterial cloak is constructed with a network of acoustic circuit elements, namely serial inductors and shunt capacitors. Our experiment clearly shows that the acoustic cloak can effectively bend the ultrasound waves around the hidden object, with reduced scattering and shadow. Due to the non-resonant nature of the building elements, this low loss (~6dB/m) cylindrical cloak exhibits excellent invisibility over a broad frequency range from 52 to 64 kHz in the measurements. The low visibility of the cloaked object for underwater ultrasound shed a light on the fundamental understanding of manipulation, storage and control of acoustic waves. Furthermore, our experimental study indicates that this design approach should be scalable to different acoustic frequencies and offers the possibility for a variety of devices based on coordinate transformation.
11:00 AM - W14: Acoustic
W15: Plasmonics IV
Friday PM, April 29, 2011
Room 3006 (Moscone West)
11:30 AM - W15.1
Plasmo-photonic Nanowire Arrays for Large-area Surface-enhanced Raman Scattering Sensors.
Joshua Caldwell 1 , Orest Glembocki 1 , Francisco Bezares 1 , Nabil Bassim 3 , Ronald Rendell 1 , Mariya Feygelson 1 , Maraizu Ukaegbu 4 , Loretta Shirey 1 , Sharka Prokes 1 , James Long 2 , Charles Hosten 4 Show Abstract
1 Electronic Science and Technology, Naval Research Laboratory, Washington , District of Columbia, United States, 3 Materials Division, Naval Research Laboratory, Washington, District of Columbia, United States, 4 Chemistry Department, Howard University, Washington, District of Columbia, United States, 2 Chemistry Division, Naval Research Laboratory, Washington, District of Columbia, United States
Methods for exploiting surface enhanced Raman scattering (SERS) to enable Raman spectroscopy for detection of trace concentrations or stand-off detection of species of interest and for single molecule detection have been an area of intense research since the discovery of the SERS effect in the 1970's. While single molecule detection has been reported at localized ‘hot-spots’ in systems of coupled plasmonic particles, for most chem-bio sensing applications, a more evenly distributed plasmonic field is desired to improve sensing reproducibility and reliability. To make such sensors, large arrays (>100 um) of SERS-active nanoparticles are desirable, a size that extends well beyond the incident wavelength. Thus grating other photonic effects may mediate optical interactions among individual nanoplasmonic structures and must be understood. Here we have characterized such arrays comprising lithographically fabricated Ag- and Au-coated vertical semiconductor nanorods. The nanorod diameter and pitch was varied in a range extending from 15-315 nm. SERS measurements at a variety of incident wavelengths from a monolayer coverage of benzene thiol illustrated that there was a strong diameter dependence, with a distinct peak in the SERS intensity observed at a specific diameter. This optimal diameter varied with the various structural and excitation parameters, with average enhancement factors extending up to 5x108 for optimal arrays. In contrast, the influence of the interpillar gap and/or pitch were much less pronounced, with only a slowly increasing SERS intensity being observed as the interpillar gap was widened. This is contrary to theory, where it was predicted that at tightly spaced pillars (<20nm) long-range coupling would lead to larger SERS response. Spatial mapping with ~1 um resolution was used to illustrate the high degree of uniformity of the SERS intensity within individual arrays. Finite-element solutions to Maxwells equations were carried out within COMSOL Multiphysics using both the quasi-static and full-wave modes to model the field intensities and distributions within our structures. The experimental results were found to compare favorably in expected SERS intensity as a function of both incident wavelength and pillar diameter with the COMSOL simulations.
11:45 AM - W15.2
The Effects of Surface Plasmons on a Two-photon Absorbing Chromophore Film on Sub-wavelength, Gold Triangles.
Jarrett Vella 1 , Augustine Urbas 2 Show Abstract
1 , Air Force Research Laboratory, Materials and Manufacturing Directorate, General Dynamics Information Technology, Wright-Patterson AFB, Ohio, United States, 2 , Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, Ohio, United States
There is currently an interest in exploiting the evanescent electromagnetic fields of surface plasmons to alter the optical properties of chromophores. This alteration can result in the improved efficiency of organic solar cells, light emitting devices, and molecular sensors, among others. Here the effects of surface plasmons on the optical properties of an organic chromophore will be presented. A two photon absorbing chromophore was deposited onto a film of sub-wavelength sized, gold triangles whose plasmon resonance was tuned to the two-photon absorption wavelength of the chromophore. The effects of the gold triangles on the nonlinear optical properties of the chromophore were determined by performing z-scan and two photon fluorescence measurements. To determine the interaction between the gold triangles and the singlet photoexcited state of the chromophore, steady-state absorption and luminescence measurements, as well as the decay kinetics of the chromophore, were studied.