Symposium Organizers
Jennifer A. Dionne Stanford University
Luke A. Sweatlock Northrop Grumman Space Technology
Gennady Shvets University of Texas-Austin
Luke P. Lee University of California-Berkeley
D1: Plasmon Nanophotonics I
Session Chairs
Tuesday PM, April 06, 2010
Room 2008 (Moscone West)
9:00 AM - **D1.1
Active Plasmonics.
Harry Atwater 1
1 Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractNanoscale light localization in plasmonic structures enables large changes in the optical properties of materials within small volumes to manifest themselves via very strong changes in light transmission and emission. I will illustrate this concept with several examples, including i) a dramatic modulation of the complex dielectric function of conducting oxide thin films by carrier modulation in nanometer-thickness layers in plasmonic metal-insulator-metal waveguide structures, and ii) large increases in the spontaneous emission rate for for "Wantecas" or waveguide/antenna/cavity structures containing III-V semiconductor and quantum dot heterostructures.
9:30 AM - **D1.2
Nonlinearity in ENZ Plasmonics and Metactronics.
Nader Engheta 1
1 Electrical and Systems Engineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractIn this talk, I give an overview of my group’s recent work in exploring the role of nonlinearity in several plasmonic phenomena which involve extreme metamaterials, e.g., epsilon-near-zero (ENZ) structures. We will discuss our results in combining scattering-cancellation-based plasmonic cloaking with the second-harmonic generation, the role of optical nanoantennas in enhancing the nonlinearity in optical materials, and the effect of nonlinear optical materials when combined with ENZ structures to provide nonlinear lumped optical elements in metamaterial-inspired optical nanocircuitries – metactronics (N. Engheta, Science, 317, pp. 1698-1702 (2007)). The enhancement of second-harmonic generation using proper design of nanoantennas may lead to composites with strong second harmonic effects. The nonlinear elements, that are formed by the combination of ENZ structures with nonlinear optical materials, may act as optical switches at the nanoscale, leading to the possibility of optical manipulation and switching using metactronic circuits. In this talk, we will present our recent results in these areas, will discuss the physical meaning behind our theoretical findings, and will forecast future directions in these areas.
10:00 AM - D1.3
Ultra-high Purcell Factors in Plasmonic Whispering Gallery Resonators.
Ernst Jan Vesseur 1 , Toon Coenen 1 , F. Javier Garcia de Abajo 2 , Albert Polman 1
1 , FOM Institute AMOLF, Amsterdam Netherlands, 2 , Instituto de Optica - CSIC, Madrid Spain
Show AbstractSurface plasmon polaritons propagating through a circular V-groove in a Au surface give rise to whispering gallery resonances. We have investigated the nature, ordering and confinement of these plasmonic resonances both in theory and experiment. The ring resonator supports a rich set of modes with increasing radial and azimuthal order that can be controlled by the diameter, depth and opening angle of the circular groove. Here, we show that the plasmonic whispering gallery modes can confine light to a very small volume, resulting in a broadband Purcell factor as large as 2000. The plasmonic ring resonances can be used to study enhanced light-matter interaction.Ring resonators were made in a single-crystalline Au surface by focused ion beam milling. Ring diameters of 200-1000 nm were studied, with groove depths of 100-500 nm. We excite the resonator modes using a 30 keV electron beam in a scanning electron microscope equipped with a new mirror design, that enables –for the first time– the angle-resolved collection of cathodoluminescence radiation from the sample. We study the angle-resolved emission patterns from ring resonators with intentional shape distortion, in order to break the mode symmetry, and study coupled resonators, in which two ring cavities are placed within each other’s near field.Theoretical studies of the dispersion in linear V-grooves were made using boundary-element-method (BEM) calculations of the local density of optical states (LDOS). We find that the dispersion is higher for grooves with a narrow opening angle and is highest for the lowest order mode (mode index up to 3). In a circular V-groove, these groove modes are resonant when the circumference of the ring equals an integer number of plasmon wavelengths. We determine the resonances of these circular ring resonators using axially symmetric BEM. We find that the resonant wavelengths agree well with the dispersion of plasmons in a linear groove, even in grooves with a circumference of only a single plasmon wavelength. This shows that groove plasmons are strongly confined to the groove and that their dispersion is not influenced significantly by a sharp bend.From the spectral width of the resonances we derive the quality factor Q=15-50. These values are slightly lower than one would expect based on the dispersion of groove plasmons, which is attributed to radiation losses of the whispering gallery resonant modes. Using BEM we calculate the electric field in the groove and find that for rings with a shallow groove (100 nm) with a small groove width (10 nm) the mode volume of the lowest-order ring resonances can be as small as 0.00073 λ^3. As a result, the Purcell factor of the ring resonances can be well over 2000. The high Purcell factor at low Q enables strong and broadband interaction between emitters and modes of the resonator. Preliminary measurements on the enhanced spontaneous emission of ATTO 680 dye in the V-groove cavities will be presented.
10:15 AM - D1.4
Hybrid Optical Elements Based on Transformation Optics.
Thomas Zentgraf 1 , Jason Valentine 1 , Jensen Li 1 , Nicholas Tapia 1 , Xiang Zhang 1 2
1 Mechanical Engineering, University of California, Berkeley, California, United States, 2 Material Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractTransformation optics has provided a new design methodology allowing an unprecedented manipulation of light propagation, enabling exciting new applications. However, transformation optics can also help to improve the performance and functionality of conventional optical elements. Since typical optical elements possess only a single functionality, and work only in a single direction, they cannot be utilized for light manipulation in the other two spatial directions. We demonstrate that transformation optics can provide a new route for designing and integrating multiple and dissimilar optical elements into one footprint. Such a level of interchangeable dual-functionality cannot be obtained with conventional optical designs. Our approach is based on a quasi-conformal mapping of the optical space in order to realize two different elements within the same footprint for the device. We implement the spatially transformed permittivity profile into a silicon-on-insulator waveguide system by simply pattern the waveguide slab with sub-wavelength air holes. In this fashion different optical elements with two independent functionalities are realized. The performance of the optical elements is measured at 1500 nm and compared to numerical simulations. Using transformation optics as a design methodology provides more flexibility in architecture together with a way to build compact highly integrated optical devices. Furthermore, the technique is fully compatible with standard semiconductor fabrication technologies used for electronics and silicon photonics.
D2: Photophysics and Devices
Session Chairs
Tuesday PM, April 06, 2010
Room 2008 (Moscone West)
11:00 AM - *D2.1
Metamaterials as Platform for Modelling Physical Phenomena and Elemental Base of Nanophotonic Devices.
Nikolay Zheludev 1
1 Optoelectronics Research Centre, University of Southampton, Southampton United Kingdom
Show AbstractPatterning of thin metal films on the sub-wavelength scale can yield a range of functionalities invaluable for nanophotonic application. This includes mimicking properties of conventional bulk media such as anisotropy and gyrotropy, but most importantly nanoscale patterning can lead to new functionalities. This includes high-epsilon media, stop bands and narrow resonances with strong dispersion useful in optical delays. Nano-structured films can be electromagnetically “invisible”, enforce asymmetry of light’s propagation in the opposite directions, create sub-wavelength far-filed concentrations of light and form the basis of coherent source of electromagnetic radiation, the “lasing spaser”. Functionalized with nonlinear media such as carbon nanotubes and phase change glasses they provide enhanced ultrafst nonlinearities at very low power levels and electrooptical switching functionality while superconducting metamaterial offer an incredible new opportunities for developing nonlinear and quantum devices. Electromagnetic metamaterials also provide a flexible platform for mimicking and modeling a broader physical realm. Keystone physics ideas and phenomena such as Electromagnetically Induced Transparency, Bose-Einstein Condensation, the Mössbauer Effect, the Meissner Effect, the Bunn effect, parity violation in atoms and the concept of anion and anapole are among those that could be intriguingly close mimicked in classical electromagnetic meta-materials.For references please visit: http://www.nanophotonics.org.uk/niz/publications/
12:00 PM - **D2.2
Negative Radiation Pressure.
Henri Lezec 1 , Kenneth Chau 1 2
1 , National Institute of Standards and Technology, Gaithersburg, Maryland, United States, 2 Engineering, University of British Columbia, Okanagan, Kelowna, British Columbia, Canada
Show AbstractWe demonstrate that free-space electromagnetic radiation is able to exert a negative pressure on a slab of ponderable material. It is shown that this becomes possible when the material is both left-handed [1] - having a negative refractive index resulting from simultaneously negative values of electric permittivity and magnetic permeability - and dissipative. Though left-handed materials do not exist in nature, they can be realized in the form of artificial metal-dielectric metamaterials. Here we characterize the radiation- pressure response of an optical-frequency, volumetric metamaterial based on stacked Ag/Si/Ag plasmonic waveguides, each designed to be left-handed over most of the visible spectrum with a negative refractive index varying broadly over this range. A fully-absorbing flat slab of this metamaterial integrated onto a low-stiffness cantilever is shown to experience a pull when illuminated at normal incidence by a plane-wave of free-space wavelength located in the range 460 nm to 600 nm. An analytic model describing the net radiation pressure, which takes into account both Lorentz and dissipative forces, is developed and validated by comparison to the spectral dependence of the measured pressure on the metamaterial. The model reveals that the real part of the effective refractive index of the metamaterial contributes to a proportionately-large, negative dissipative force, which, when it exceeds the always-positive Lorentz force, results in a net negative pressure on the object. 1) V. Veselago, Sov. Phys. Usp. 10, 509 (1968).
12:30 PM - **D2.3
Plasmonic Solar Cells.
Albert Polman 1
1 Center for Nanophotonics, FOM-Institute AMOLF, Amsterdam Netherlands
Show AbstractSuitably engineered metal nanostructures, integrated with thin-film solar cell designs, can strongly increase the solar cell efficiency and reduce its thickness. In this talk, I will review two plasmonic light trapping geometries that we have successfully studied: (1) metal nanoparticle arrays placed at the surface of crystalline Si solar cells and (2) the use of a textured metal backcontact on amorphous Si thin film solar cells.Metal nanoparticles at the surface act as efficient scatterers of light, causing a redistribution of light in the solar cell and thus an enhancement of the effective path length. We experimentally demonstrate clear enhancements of the photocurrent due to near-infrared light that is otherwise poorly absorbed in the cell and present finite-difference time domain simulations on the light scattering in a range of nanoparticle geometries, focusing on the physical effects that lie behind the light trapping.Metallic nanoparticles are integrated with the metallic backcontact of thin-film amorphous Si solar cells using substrate-conformal soft-imprint lithography. The nanopatterned solar cells show strongly enhanced photocurrents in the 550-800 nm spectral range, demonstrating efficient light trapping. Using a novel technique, angle-resolved photocurrent spectroscopy, we identify the coupling between the incident and scattered light and the waveguide modes in the solar cell. Using an optimized light scattering geometry we demonstrate the first high-efficiency amorphous Si solar cell with a thickness no more than the p-n junction thickness of only 160 nm.Our work can be applied on any thin film solar cells geometry and material.
D3: SPP and Photon Sources I
Session Chairs
Tuesday PM, April 06, 2010
Room 2008 (Moscone West)
2:30 PM - **D3.1
A Silicon-based Electrical Source of Surface Plasmon Polaritons.
Robert Walters 1 , Ihor Brunets 2 , Jurriaan Schmitz 2 , Albert Polman 1
1 Center for Nanophotonics, FOM Institute for Atomic and Molecular Physics, Amsterdam Netherlands, 2 MESA<sup>+</sup> Institute for Nanotechnology, University of Twente, Enschede Netherlands
Show AbstractThe optical excitation of surface plasmon polaritons (SPPs) using an external laser is impractical for many future applications, especially those in chemical or biological sensing where minimum cost and maximum parallel functionality will be beneficial or requisite. The development of electrically excited sources of SPPs is therefore of critical importance for future integrated plasmonic device technology.We have designed and fabricated silicon-based electrical sources of SPPs in the metal-insulator-metal (MIM) waveguide geometry. In these devices, optically thick gold cladding layers surround a semi-insulating layer of alumina containing optically active silicon nanocrystals. The nanocrystals are excited through an impact ionization process when a current is applied through the insulator layer. For sufficiently thin insulator layer thicknesses, the only radiative decay pathway available to excited nanocrystals is decay into the symmetric TM0 plasmon mode of the MIM waveguide, resulting in efficient coupling and SPP emission in the near-infrared.Our fabrication process is designed to be potentially back-end compatible with CMOS microelectronics. The optically active insulator layer was obtained by sequential atomic layer deposition (ALD) of Al2O3 (at 300°C) and low pressure chemical vapor deposition (LPCVD) of silicon nanocrystal layers (at 325°C) without vacuum break. This process flow results in smooth and abrupt interfaces and allows precise control of the insulator layer thickness and the location of the nanocrystals. Membranes are then chemically etched to allow electrical and optical access to both interfaces of the structure. We further process our samples using focused ion beam milling to precisely define an array of out-coupling grating structures. When a current is applied to our device, we observe emission from the out-coupling grating structures. Our analysis of these measurements shows that this light originates from electrically generated SPPs that scatter out of the waveguide. We will discuss our experiments, design strategies in the context of the underlying mode structure of the waveguide, and future integrated sensor geometries incorporating similar plasmon sources.
3:00 PM - **D3.2
Plasmon Generation by Swift Electrons.
Javier Garcia de Abajo 1
1 , CSIC, Madrid Spain
Show AbstractElectron beams can be controlled with nanometer resolution and positioned on a metallic sample to excite both localized and propagating plasmons. The analysis of the energy lost by the electrons and the resulting light emission are excellent ways of mapping these excitations with unmatched combination of energy and space resolution. But electrons can also be employed to produce on-demand excitation of plasmons with nanometer resolution. We will discuss recent developments in these techniques and explore new trends and applications.
3:30 PM - D3.3
Plasmon-enhanced Spontaneous Emission From Erbium-doped Silicon-rich Silicon Oxide in MOS Waveguides.
Aaron Hryciw 1 , Oleksandr Savchyn 2 , Pieter Kik 2 , Mark Brongersma 1
1 Geballe Laboratory for Advanced Materials, Stanford University, Stanford, California, United States, 2 CREOL, The College of Optics & Photonics, University of Central Florida, Orlando, Florida, United States
Show AbstractThe realization of a CMOS-compatible on-chip light source exhibiting high-frequency modulation and high power efficiency is necessary for monolithically-integrated Si photonics systems. It is therefore unfortunate that many attractive Si-based light-emitting materials, such as rare-earth-doped Si nanocomposites, can also possess long radiative recombination lifetimes and/or low internal quantum efficiencies (IQEs). However, by incorporating a thin light-emitting layer into a metal–oxide–semiconductor (MOS) structure, the emission can be coupled to propagating surface plasmon polariton modes, effecting large radiative rate enhancements (~50×, according to semi-classical spontaneous emission rate calculations) across a broad, non-resonant wavelength range, with an associated increase in IQE. We investigate this effect theoretically and experimentally at 1.5 μm for erbium-doped silicon-rich silicon oxide (SRSO:Er) in a Ag/SRSO:Er/Si/SiO2 structure, which has the additional advantage of coupling the emission preferentially into a single well-defined Si slab waveguide mode. This work suggests a new class of on-chip light-sources for integrated photonics, enhancing the well-understood electrical characteristics of MOS structures with new plasmonic functionality.
3:45 PM - D3.4
Plasmonic Resonator Antennas for Enhanced Emission and Detection of Light.
Edward Barnard 1 , Ana Brown 1 , Ragip Pala 1 , Aaron Hryciw 1 , Mark Brongersma 1
1 Materials Science & Engineering, Stanford University, Stanford, California, United States
Show AbstractA combined theoretical and experimental study of detectors and emitters enhanced by wavelength-scale plasmonic resonator antennas is presented. These antennas support standing surface plasmon-polariton (SPP) waves that enable substantial concentration of light at a set of well-defined resonant frequencies. From experiments and full-field simulations, it is now well-established that the resonant frequencies critically depend on the exact antenna geometry (size and shape) and the optical properties of the metal. 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. 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 and enhance emission of Er-doped Si nanocrystal films. In addition to these specific 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.
D4: Enhanced Emission and Nanoantennas
Session Chairs
Tuesday PM, April 06, 2010
Room 2008 (Moscone West)
4:30 PM - **D4.1
Three-dimensional Optical Metamaterials and Nanoantennas: Chirality, Coupling, and Sensing.
Harald Giessen 1 , Na Liu 1
1 , University of Stuttgart, Stuttgart Germany
Show AbstractMetallic metamaterials have shown a number of fascinating properties over the last few years. A negative refractive index, negative refraction, superlenses, and optical cloaking are some of the ambitious applications where metamaterials hold great promise.We are going to present fabrication methods for the manufacturing of 3D metamaterials [1]. We are investigating their coupling properties and the resulting optical spectra. Hybridization of the electric [2] as well as the magnetic [3] resonances allows us to easily understand the complex optical properties. Lateral as well as vertical coupling can result in EIT-like phenomena [4, 5]. These phenomena allow to construct novel LSPR sensors with a figure of merit as high as five [6].The connection between structural symmetry and their electric as well as magnetic dipole and higher-order multipole coupling will be elucidated. It turns out that stereometamaterials [7], where the spatial arrangement of the constituents is varied (see figure), reveal a highly complex rotational dispersion. The chiral properties are quite intriguing and can be explained by a coupled oscillator model. Our three-dimensional stacking approach allows also for the fabrication of 3D nanoantennas, which are favorable for emitting and receiving radiation from quantum systems.References[1] Na Liu, Hongcang Guo, Liwei Fu, Stefan Kaiser, Heinz Schweizer, and Harald Giessen: Three-dimensional photonic metamaterials at optical frequencies, Nature Materials 7, 31 (2008).[2] N. Liu, H. Guo, L. Fu, S. Kaiser, H. Schweizer, and H. Giessen: Plasmon Hybridization in Stacked Cut-Wire Metamaterials, Advanced Materials 19, 3628 (2007)[3] Na Liu, Liwei Fu, Stefan Kaiser, Heinz Schweizer, and Harald Giessen: Plasmonic Building Blocks for Magnetic Molecules in Three-Dimensional Optical Metamaterials, Advanced Materials 20, 3859 (2008).[4] Na Liu, Stefan Kaiser, and Harald Giessen: Magnetoinductive and Electroinductive Coupling in Plasmonic Metamaterial Molecules, Advanced Materials 20, 4521 (2008).[5] Na Liu, N. Liu, L. Langguth, T. Weiss, J. Kästel, M. Fleischhauer, T. Pfau, and H. Giessen: Plasmonic EIT analog at the Drude damping limit, Nature Materials 8, 758 (2009).[6] Na Liu, T. Weiss, M. Mesch, L. Langguth, U. Eigenthaler, M. Hirschner, C. Sönnichsen, and H. Giessen: Planar metamaterial analog of electromagnetically induced transparency for plasmonic sensing, Nano Lett. 9 (2009), available online.[7] Na Liu, Hui Liu, Shining Zhu, and Harald Giessen: Stereometamaterials, Nature Photonics 3, 157 (2009).
5:00 PM - D4.2
Plasmonic Vertical Beaming and Electrical Modulation of Optical Antenna Coupled Quantum Dot Emission.
Young Chul Jun 1 , Mark Brongersma 1
1 Geballe Laboratory for Advanced Materials, Stanford university, Stanford, California, United States
Show AbstractRecently, optical antennas based on metal nanostructures attracted great attention due to their unique ability to concentrate light into a deep subwavelength volume. It holds promise for many new applications requiring tight confinement of optical fields. At the same time, optical antennas are found to be very useful for modifying emission from nearby fluorescent molecules or quantum dots (QD). Strong nearfield coupling makes their emission efficiently coupled to optical antennas, then re-radiated into freespace. In this talk, we present our optical and electrical measurements on semiconductor QD emission in a metal slit-groove optical antenna. First, we show that the lifetime and polarization of QD emission in metal nanoslits are strongly modified due to surface plasmon coupling of QD emission, and its out-coupled light can be collimated vertically into a narrow angle with optimized side grooves. We experimentally demonstrate and visualize this vertical beaming, using a confocal scanning of QD emission. In the second part of the talk, we present our measurements on the stark shift modulation of quantum dot emission. Two side metal plates of metal slits are used as electrical contact pads, and we apply modulated electrical signals to dynamically control QD emission. We present both time-resolved measurements and frequency domain lock-in measurements of QD emission intensity modulation. Through these measurements, we precisely analyze and quantify the electrical modulation of QD emission. Large QD spontaneous emission enhancement in optical antenna structures can potentially enable gigahertz-level direct modulation of QD emission. Our experimental demonstrations may open the door to novel applications in spectroscopy, sensing, and optoelectronic devices.
5:15 PM - D4.3
Enhancing Spontaneous Emission in III-V and Quantum Dot Semiconductor Plasmonic Core-shell Nanoresonators.
Carrie Hofmann 1 , F. Javier Garcia de Abajo 2 , Harry Atwater 1
1 Materials Science, California Institute of Technology, Pasadena, California, United States, 2 Instituto de Optica, CSIC, Madrid Spain
Show AbstractResearchers have devoted considerable effort to enhancing spontaneous emission from light emitters using plasmonic nanostructures. Si quantum dots (QDs) and III-V semiconductors are exciting materials systems to explore because they have high internal quantum efficiency and a well-established growth technology. If dramatic enhancements are achieved, ultra-fast, nanoscale light emitting diodes could be realized. Here, we investigate a deeply subwavelength core-shell nanowire resonator consisting of a semiconductor core clad uniformly with a shell of Ag, and demonstrate that high Q/V and ultrafast spontaneous emission rates are achievable in subwavelength devices.
Theoretical calculations of four specific core-shell resonators will be discussed, namely: (Si QDs in SiNx)-Ag, and III-V core-shell resonators with longitudinally heterostructured cores (InGaP/GaAs/InGaP)-Ag, (AlAs/AlGaAs/AlAs)-Ag, and (GaN/InGaN/GaN)-Ag. The core-shell nanoresonator geometry allows precise control of the local density of optical states (LDOS), and thus the radiative emission rate, by changing the dimensions of the semiconductor core. For maximum enhancement in the emission rate, we design the resonator such that the lowest order longitudinal resonance occurs at the same energy as the band-edge emission of the semiconductor core. We then determine the LDOS, quality factor, Q, and effective mode volume, V, as well as the enhancement in the radiative and total decay rates (Γrad and Γtot, respectively, normalized to decay in vacuum, Γ0), and the corresponding quantum efficiency, η=Γrad/Γtot. For all resonators, we see very high confinement within the semiconductor core and moderate quality factors, resulting in high Q/V and large enhancements in the radiative emission rate. Numerical results for these resonators are summarized in the table below.
Experimentally, we fabricate (Si QD in SiNx)-Ag and (GaN/InGaN/GaN)-Ag core-shell nanoresonators from semiconductor thin films using electron beam lithography, reactive ion etching, RF magnetron sputtering, and Ar plasma etching. Optical characterization from a combination of dark-field reflection and white-light transmission spectroscopy, as well as with both time- and spatially-resolved microphotoluminescence, will be presented. This work demonstrates the promise of subwavelength plasmonic structures for enhancing the emission rate of active semiconductor materials.
5:30 PM - D4.4
Far-field Measurement of Ultra-small Plasmonic Mode Volume using Optical Force Method.
Shuang Zhang 1 , Yong-shik Park 1 , Yongmin Liu 1 , Thomas Zentgraf 1 , Xiang Zhang 1
1 , Univ California Berkeley, Berkeley, California, United States
Show AbstractLight-matter interaction is greatly enhanced in cavities with tightly confined optical mode, where the mode volume, defined as the total electromagnetic energy stored in the cavity divided by the maximum energy density, determines the interaction strength. In particular, incorporating gain medium to the tightly confined mode (‘hot-spot’) facilitates applications such as efficient light emitting devices, enhanced spontaneous emission and nano-lasers. Nano-scale metallic elements can provide ultra-small cavity mode by utilizing the strong plasmonic confinement. The experimental determination of the mode volume of plasmonic elements is therefore of fundamental importance. Mapping the electric field distribution using near-field scanning optical microscopy (NSOM) may disturb the field distribution hence prevent a reliable measurement of the mode volume. Here, we develop a general, non-pertubative technique to experimentally determine the mode volume of plasmonic resonators in the far field through a unique optical force method. We implement this method to experimentally determine the mode volume of plasmonic loop antennas operating at the mid-infrared spectral region. To our knowledge, this technique represents the first attempt to measure the mode volume of plasmonic elements without requiring any near-field information. The mode volumes were shown to be at least 3 orders of magnitude less than the wavelength cube, leading to an estimation of extremely large Purcell factors. The optical antennas, with suitable gain medium placed inside their feeding gap, will lead to enormous enhancement of the spontaneous emissions.
5:45 PM - D4.5
Hybridized Plasmonic Excitations in Complex Nanocavities and Development of A Single-polarized Antenna Array.
Ahmet Yanik 1 , Ronen Adato 1 , Shyamsunder Erramilli 2 , Hatice Altug 1
1 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States, 2 Physics , Boston University, Boston, Massachusetts, United States
Show AbstractPlasmonic nanoantennas, with a potential to reshape the photonics field by converting light to sub-wavelength scale localized surface plasmons, are at the core of new exciting opportunities [1-2]. The phenomenon of extra-ordinary light transmission (EOT) through the sub-wavelength cavity arrays in optically thick metals films is another example of an interesting physical effect due to the surface plasmons [3]. This phenomenon is generally related to the propagating surface plasmon polaritons (SPP) created by the periodic perturbations in the metal surface supplying the extra momentum [3-4]. This widely accepted description, on the other hand, clearly separates the concepts of antenna theory and the EOT phenomenon. Likewise, work on optical antennas reported to date has been focused on isolated metallic nanostructures such as nanoparticles, nanoshells, nanorods and bow tie antennas [5-6].In a recent work, we have presented a quasi-static model incorporating the basic antenna principles similar to the isolated nano-antennas to explain the EOT phenomena [7]. We showed that EOT phenomena in complex cavities can be explained by hybridization of elementary plasmonic excitations in a much similar way to widely known hybridization effects in nanoshells [7]. Experimentally measured red-shifting of the plasmonic resonances of the rectangular coaxial-apertures with respect to those of the simple rectangular aperture arrays are successfully described and the asymmetric nature of the plasmonic resonances are explained in relation to strong shape anisotropies. Further enhancement of the extra-ordinary light transmission is also predicted by the model and experimentally demonstrated for the coaxial rectangular cavities. We also demonstrate that our structures enable enhanced polarization control surpassing the performance of commercially available holographic wire grid polarizers in the mid-infrared region of the spectrum. In this talk we will present these results. [1] K. Seungchul et al, Nature 453, 757 - 760 (05 Jun 2008)[2] S. Nie and S. R. Emory, Science 275, 1102 (1997).[3] T. W. Ebbesen et al, Nature, 391, 667 (1998).[4] A. A. Yanik et al, Appl. Phys. Lett. 93, 081104 (2008).[5] K.B. Crozier et a l, Journal of Applied Physics, vol. 94, pp. 4632-42 (2003).[6] E. Prodan et al, Science, 302, 419 (2003).[7] A. A. Yanik et al,Optics Express, Vol. 17 Issue 23, pp.20900-20910 (2009).
Symposium Organizers
Jennifer A. Dionne Stanford University
Luke A. Sweatlock Northrop Grumman Space Technology
Gennady Shvets University of Texas-Austin
Luke P. Lee University of California-Berkeley
D5: Plasmon Photovoltaics
Session Chairs
Wednesday AM, April 07, 2010
Room 2008 (Moscone West)
9:00 AM - **D5.1
Enhancing Solar Cells With Localized Surface Plasmons.
Kylie Catchpole 1
1 Centre for Sustainable Energy Systems, Australian National University, Canberra, Australian Capital Territory, Australia
Show AbstractLocalized plasmon excitations on metal nanoparticles are a promising way of increasing the efficiency of solar cells. Because of the weak absorption of light by silicon, it is necessary to increase the light path within the solar cell to obtain maximum efficiency. Conventional solar cells achieve this by using a surface texture with feature sizes of several microns, but this approach is not applicable to the next generation of thin film solar cells. Plasmon excitations on metal nanoparticles close to the semiconductor surface can strongly scatter light and direct it into the active layer, because of the high polarizability of the semiconductor.We review the state-of-the-art in plasmonic photovoltaics and describe the role of the major mechanisms involved. In particular, we describe new results in the design and fabrication of plasmonic scattering arrays and the prospects for enhancing solar cells by making use of plasmonic modes other than simple dipoles. In addition, we outline future prospects for plasmonic photovoltaics.
9:30 AM - D5.2
Ultrathin Film a-Si:H Solar Cells With Nanostructured Plasmonic Back Reflectors.
V. Ferry 1 , M. Verschuuren 2 , H.b. Li 3 , C. h. van der Werf 3 , R.e. Schropp 3 , H. Atwater 1 , A. Polman 4
1 , California Institute of Technology, Pasadena, California, United States, 2 , Philips Research, Eindhoven Netherlands, 3 , Utrecht University, Utrecht Netherlands, 4 , FOM Institute AMOLF, Amsterdam Netherlands
Show AbstractWith thin film a-Si:H photovoltaics approaching gigawatt production, the optimization of light absorption is a critical parameter for improving cell efficiency and reducing cost. So far, light trapping in thin solar cells is accomplished by scattering from a randomly textured back contact layer. In this work, we have designed and fabricated thin (500 nm) and ultrathin (150 nm) film a-Si:H cells with nano-patterned back contact Ag layers, where the back reflector is designed to enhance absorption via coupling of incident free space light into localized resonant modes and propagating guided wave modes. Nanoscale surface morphology has non-optical device performance benefits as well: reducing the surface topography of the rear contact relative to random texturing improves film conformality and semiconductor electronic quality.Regular square arrays of Ag nanocorrugations with diameters 150 – 225 nm and pitch 500 and 700 nm were made. A flat film of Ag and a randomly textured Ag surface were used as references. The regular patterns were made using substrate conformal imprint lithography (SCIL), a technique which allows for large area, high fidelity patterning and is amenable to scaled-up photovoltaic production. The patterned substrate and the rough sample are processed simultaneously to minimize deposition variation. The cells are standard n-i-p a-Si:H grown by 13.56 MHz PECVD, with a 100 nm ZnO:Al spacer layer between the Ag back contact and the a-Si:H, and an 80 nm ITO top contact that also serves as an antireflection coating. Compared to the flat reference cell, the 500 nm thick cells show a 32% increase in short circuit current density (Jsc) for the 500 nm pitch patterns, and 27% increase for the 700 nm pitch patterns. The particle size had only minor effects on photocurrent. Spectral measurements show that the enhanced photocurrent results primarily from the 550 – 800 nm region; light in the 350 - 550 nm spectral range is absorbed directly in the cell before interacting with the back contact scatterers. In ultrathin configurations, the absorption enhancement from controlled coupling to propagating longitudinal modes is more pronounced; the Jsc in the cells with 500 nm pitch is 47% higher than in the flat reference cell. Moreover, the Jsc of these patterned cells exceeds the randomly textured cell by 8.5%. Spectral response measurements show that this enhancement is mainly in the 500 – 700 nm region of the spectrum.Calculations have shown that the height of the nanostructures within the semiconductor controls the coupling fraction of incident light to each waveguide mode. We analyze the achievable absorption enhancements through an optimization of the nanopattern to preferentially couple to those modes with the highest semiconductor absorption fraction. In summary, we have shown that, through appropriate design of metallic nanostructures, the performance of ultrathin a-Si:H solar cells can be improved beyond that of surface texturing.
9:45 AM - D5.3
Enhanced Absorption in Amorphous Silicon Solar Cells Using Plasmonic and Photonic Crystals – Measurement and Simulation.
Rana Biswas 1 2 , Ben Curtin 2 , Vikram Dalal 2
1 Physics & Astronomy; Ames Laboratory, Iowa State University, Ames, Iowa, United States, 2 Microelectronics Research Center; Electrical and Computer Engineering, Iowa State University, Ames, Iowa, United States
Show AbstractWe investigate both experimentally and theoretically plasmonic and photonic crystals for enhancing thin film silicon solar cells. Thin film amorphous silicon (a-Si:H) solar cells suffer from decreased absorption of red and near-infrared photons, where the photon absorption length is large. We first simulate 1) plasmonic crystals of metallic nano-cylinders on top of solar cells and 2) photonic crystal back-reflectors consisting of hole arrays, with a rigorous scattering matrix routine where Maxwell’s equations are solved in Fourier space. A plasmonic array of nano-cylinders on top of an ITO coated a-Si:H solar cell strongly enhances the absorption at long wavelengths (above 600 nm) by ~10%. Optimized array pitch is near 600-700 nm with a small diameter (160 nm), to minimize reflection losses. The dependence with the ITO thickness will be discussed. Alternatively, simulations of photonic crystal back reflectors predict maximal light absorption for a pitch of 700-800 nm for hole arrays in silver or ZnO/Ag back reflectors, with absorption increases of ~12%. The photonic crystal improves over the ideal randomly roughened back reflector (or the ‘4n**2 limit’) at wavelengths near the band edge. We then fabricated metallic photonic crystal back-reflectors using photolithography and reactive-ion etching. We conformally deposited a-Si:H solar cells on triangular lattice hole arrays on silver back-reflectors. The photonic crystal has a pitch of 760 nm and triangular lattice symmetry. Electron microscopy demonstrates excellent long range periodicity and conformal a-Si:H growth. The measured quantum efficiency increases by 7-8 %, relative to a flat reflector reference device, with enhancement factors exceeding 6 at near-infrared wavelengths. We discuss the dependence of the enhancement on the depth of the photonic crystal. These results will be compared to experimental results on randomly roughened Ag/ZnO back reflectors. Enhancement with c-Si will be discussed. The photonic crystal back reflector strongly diffracts light and increases optical path lengths of solar photons.
10:00 AM - D5.4
Optoelectronic Design Concepts for GaAs Plasmonic Solar Cells.
Jeremy Munday 1 , Dennis Callahan 1 , Harry Atwater 1
1 Applied Physics, Caltech, Pasadena, California, United States
Show AbstractRecently, light management schemes involving the addition of plasmonic scattering objects have been proposed as a way to increase light collection in photovoltaic devices; however, the potential for plasmonic photovoltaics can extend beyond simply increased light collection. Here we discuss design principles that include: (a) design of scatterers that provide absorption enhancements better than those obtained with antireflection coatings, and (b) other, often overlooked, potential benefits of such as (i) increased surface conductivity in plasmonic arrays and (ii) the ability to tailor the electromagnetic fields within the cell to improve the generation and collection of charge carriers. To this end, we present a combination of Finite-Difference Time-Domain (FDTD) simulations, electronic device simulations, and experimental results for ultrathin (50-200 nm) GaAs solar cells to study the possible benefits of plasmonic photovoltaics over traditional photovoltaics. 2D electromagnetic simulations are used to determine the spatially varying carrier generation rates from the imaginary part of the dielectric function and the electromagnetic field profiles, which are integrated over the AM 1.5 spectrum. Optimization procedures are used to vary the size (30-200 nm) and period (0.1-1.0 μm) of front and back scatterering structures. For an array of 50 by 150 nm silver plasmonic back scatterers, which do not penetrate into the semiconductor to avoid detrimentally affecting electronic device performance, we show a ~20% absorption enhancement is possible for a 200 nm thick GaAs cell. Device simulations show that reducing the thickness of the cell, which reduces the dark current, can increase the open circuit voltage by 5-10%. Further, device simulations can be coupled to the electromagnetic simulations in order to determine the efficiency of charge collection upon generation. Initial experimental results for ultrathin GaAs solar cells show device improvements upon incorporating plasmonic structures due to increased absorption and sheet conductivity; however, further improvements in the fabrication procedure are necessary to achieve the full benefit of plasmonic nanoparticles. Finally, we will discuss the possibility of combining all of the above benefits in order to achieve an ultrathin film solar cell that could surpass the efficiency of a traditional solar cell.
10:15 AM - D5.5
Designing and Developing a Metallic Nanoconcentrator Electrode for a Lateral Multijunction Photovoltaic Cell.
Trudie Wang 2 , Peter Peumans 1
2 Mechanical Engineering, Stanford University, Stanford, California, United States, 1 Electrical Engineering, Stanford University, Stanford, California, United States
Show AbstractMultijunction photovoltaic (PV) cells consisting of epitaxial layers currently have power conversion efficiencies exceeding 40% [DOE]. However, the requirement to match the maximum power point current at each junction limits the cell to the layer that produces the lowest current and makes theoretical efficiencies of greater than 45% practically unattainable. To circumvent this limit, we propose a structure that is capable of splitting the solar spectrum laterally using junctions placed alongside one another. These junctions are formed from nanowires (NWs) with varying bandgaps positioned above a patterned, nanostructured metal electrode and achieves efficient carrier collection through lateral separation of the spectrum. The electrode acts as a network of plasmonic nanoantennas that play the critical role of spectral splitting and lateral concentration. Because the antennas can be designed to have separate contact points for each NW, photocurrent matching becomes unnecessary. The design of the electrode is the focus of this research, with the main challenge being to show that it can spectrally split and concentrate optical wavelengths so that enhanced absorption of energy occurs within NWs placed where there is maximum field enhancement by the antennas. To demonstrate this functionality, a ring resonator antenna was modeled using finite difference time domain (FDTD). The local electric field is shown to enhance by ~70x at resonance and the resonant frequency was found to depend on the geometry and material of the metal and the surrounding medium, as well as orientation of the incident wave. The location of the resonance peak was most sensitive to the thickness to diameter ratio of the ring and the field is focused primarily along the ring axis and enhanced uniformly within the cavity, providing concentration with less metal compared to other structures and hence less absorption loss. Optical absorption increased as a consequence of optical energy that lingers and makes multiple passes within the structure. Intimate contact with the NW makes the rings more sensitive to the refractive index. In addition to enhancement within the ring, confined field enhancement between rings was demonstrated. To take advantage of this geometrical phenomenon, we modeled a periodic array of Ag ring resonators with a NW inside and a NW of a different material placed in the gap between. The motivation for placement of a NW in the gap was for enhanced absorption in both a different spatial and spectral region. Inside the ring, a III-V ternary compound with tunable bandgap is selected for the NW since the cavity resonance mode is more sensitive to the ring geometry than the gap and so the bandgap can be tuned to take advantage of this. The resulting spectral response shows that the geometry is both effective at spectral splitting and optical field concentration, and hence a candidate for a lateral multijunction cell.
D6: SPP and Photon Sources II
Session Chairs
Wednesday PM, April 07, 2010
Room 2008 (Moscone West)
11:00 AM - **D6.1
Molding the Flow of Light at the Nanoscale.
Mark Brongersma 1
1 , Stanford University, Stanford, California, United States
Show AbstractScaling of chipscale electronic and photonic devices to smaller and smaller dimensions has enabled faster, more power-efficient and inexpensive components. It has also brought about a myriad of new challenges. One very important challenge is the growing size mismatch between electronic and photonic components. Plasmonics can form an efficient bridge between the worlds of nano-electronics and micro-photonics. In this presentation, I will show that this bridge can take many forms and that it is valuable to develop general optimization strategies.
11:30 AM - **D6.2
New Functional Metamaterials for TeraHertz EM Field Engineering and Laser Beam Shaping.
Federico Capasso 1 , Nanfang Yu 1 , Qi Jie Wang 1 , Mikhail Kats 1 , Jonathan Fan 1 , Suraj Khanna 2 , Lianhe Li 2 , A. Giles Davies 2 , Edmund Linfield 2
1 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 2 School of Electronic and Electrical Engineering, University of Leeds, Leeds United Kingdom
Show AbstractTerahertz waves are loosely bound to metallic surfaces since the surface plasmon dispersion is very near the light-line. As shown by Pendry and coworkers the dispersion can be tailored to create strongly bound surface waves by patterning the surface with metamaterials (spoof surface plasmons). In this work we demonstrate the application of this concept to electron devices.We have chosen quantum cascade lasers (QCL), which at THz frequencies have very large divergence approaching 180 deg. By designing and implementing suitable metamaterials on the facets of 3 THz GaAs/AlGaAs QCLs we have achieved beams with excellent collimation (~ 10 degree divergence in orthogonal axes) and high optical power throughput. These concepts are widely applicable to electronic devices.
12:00 PM - **D6.3
Dark Optical Nanocircuits With Surface Plasmon Polaritons.
Hongkun Park 1 , Abram Falk 1
1 Chemistry, Chemical Biology and Physics, Harvard University, Cambridge, Massachusetts, United States
Show AbstractGenerating and controlling single surface plasmon polaritons (SPPs) is a key requirement for quantum plasmonics. In this talk we will discuss strategies for accessing the single-SPP regime using chemically grown nanostructures. An important component of our efforts is employing electrical interfaces that efficiently generate and detect SPPs in the near field, thereby bypassing the need for far-field optics. Moreover, by coupling colloidal quantum dots to silver nanowires, we can generate and measure single SPPs in the near field. Finally, we can modify the quantum dot emission spectrum with silver nanowire resonators. These efforts are moving us closer to the goal of fabricating completely dark optoelectronic circuits that will control SPP quanta without any reference to the far field.
12:30 PM - D6.4
Sub-wavelength Plasmon Laser.
Volker Sorger 1 , Rupert Oulton 1 , Thomas Zentgraf 1 , Ren-Min Ma 2 , Christopher Gladden 1 , Lun Dai 2 , Guy Bartal 1 , Xiang Zhang 1 3
1 , NSF Nanoscale Science and Engineering Centre, Berkeley, California, United States, 2 Peking University, State Key Lab for Mesoscopic Physics and School of Physics, Peking University, Beijing China, 3 , Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractLaser science has tackled physical limitations to achieve higher power, faster and smaller light sources. The quest for ultra-compact laser that can directly generate coherent optical fields at the nano-scale, far beyond the diffraction limit of light, remains a key fundamental challenge. Microscopic lasers based on photonic crystals, metal clad cavities and nanowires can now reach the diffraction limit, which restricts both the optical mode size and physical device dimension to be larger than half a wavelength. While surface plasmons are capable of tightly localizing light, ohmic loss at optical frequencies has inhibited the realization of truly nano-scale lasers. Recent theory has proposed a way to significantly reduce plasmonic loss while maintaining ultra-small modes by using a hybrid plasmonic waveguide. Using this approach, we report an experimental demonstration of nano-scale plasmonic lasers producing optical modes 100 times smaller than the diffraction limit, utilizing a high gain Cadmium Sulphide semiconductor nanowire atop a Silver surface separated by a 5 nm thick insulating gap. Direct measurements of emission lifetime reveal a broad-band enhancement of the nanowire’s exciton spontaneous emission rate by up to 6 times due to the strong mode confinement and the signature of apparently threshold-less lasing. Since plasmonic modes have no cut-off, we show down-scaling of the lateral dimensions of both device and optical mode. As these optical coherent sources approach molecular and electronics length scales, plasmonic lasers offer the possibility to explore extreme interactions between light and matter, opening new avenues in active photonic circuits, bio-sensing and quantum information technology.
D7: Metamaterials I
Session Chairs
Wednesday PM, April 07, 2010
Room 2008 (Moscone West)
2:30 PM - **D7.1
The Magical World of Metamaterials.
Ekmel Ozbay 1
1 Nanotechnology Research Center, Bilkent University, Ankara Turkey
Show AbstractIn this talk, we will review experimental and theoretical studies performed on left-handed metamaterials (LHM). The metamaterials exhibit quiet unusual electromagnetic properties such as negative refraction, negative phase velocity, subwavelength focusing, subwavelength cavities and enhanced transmission.
3:00 PM - D7.2
Broadband Measurement of Amplitude and Phase of Metamaterials.
Petru Ghenuche 1 2 , Stephane Collin 1 , Nathalie Bardou 1 , Riad Haidar 2 , Jean-Luc Pelouard 1
1 , Laboratoire de Photonique et de Nanostructures (LPN-CNRS), Route de Nozay, 91460, Marcoussis France, 2 , ONERA, The French Aerospace Lab, Chemin de la Huniere, F-91761, Palaiseau Cedex France
Show AbstractEngineering the index of metamaterials is obtained by carefully designing the resonances of the inner structures, leading even to simultaneously negative permittivity and permeability, a recipe for negative index materials [1].
In this work we present a method to determine the effective index of refraction together with high-resolution dispersion diagram measurement of metamaterials. The intensities of several diffraction orders produced by a metamaterial diffraction grating are measured by angle-resolved experiments. They provide an interferometric measurement of the amplitude and phase of the metamaterial transmission and reflection coefficients [2].
The metamaterials, with a split ring resonator as a cell [3], have been fabricated by e-beam lithography onto silicon substrates and metal evaporation of 2 and 40 nm thick titanium and gold films, followed by a lift-off process. This method allows reproducible sub-50 nm features of the structures over large surfaces (9 mm2 with 2.5x107 cells) in one run. Several arrays were created on the same substrate: a continuous metamaterial matrix and a diffraction grating of metamaterials with the same cell.
The set-up used allows a high accuracy, independent control of the excitation and detection angles (angular resolution of 0.5 degrees) for the reflection and transmission measurements [4]. The measurements are taken by means of a Fourier transform spectrometer in the wavelength range of 0.6-16 μm.
A first set of measurements are dedicated to the dispersion diagrams of the material, allowing the characterization of the cell. In the grating case, the diffraction orders of the transmission and reflection have been measured from 0 to 60 degrees with 0.2 degrees increments. The measured intensities of the 0-th and 1-th diffraction orders are used to derive the complex coefficients (amplitude and phase) of the optical transmission and reflection, which permits the determination of the refractive index by using the retrieval procedure [5].
The fine control of the geometry of the nano-resonators of each cell allows to tune both amplitude and phase of the wave transmitted through the metamaterial layer. This opens up new degrees of freedom for the engineering of opticalindex and the conception of new optical elements.
[1] Shalaev, V. M., Nat. Photonics 1, 41 (2007),
[2] Zhang S., et al., Phys.Rev.Lett. 95, 137404 (2005),
[3] Kante B., et al., Phys. Rev. B 80, 035108 (2009),
[4] C. Billaudeau, et al., Opt. Lett. 33, 165 (2008),
[5] Menzel C., et al., Rev. B 77, 195382 (2008).
3:15 PM - D7.3
Experimental Determination of Principal Permittivities and Hyperbolic Equi-frequency Surfaces in Silver Nanowire Arrays.
Joerg Schilling 1 2 , Jyotirmayee Kanungo 1
1 Dept. of Physics, Queen's University Belfast, Belfast United Kingdom, 2 ZIK "SiLi-nano", Martin-Luther-Universitaet Halle-Wittenberg, Halle Germany
Show AbstractUniaxial anisotropic metamaterials with an indefinite permittivity or permeability tensor gained considerable interest recently, as they exhibit hyperbolic equi-frequency surfaces for one polarisation and therefore allow the propagation of waves with very large wave vectors. This property for instance allows to transform incident evanescent waves into propagating waves within the metamaterial. Of special practical interest is the case when the permeability is isotropic and equal to 1 while the permittivity perpendicular to the optical axis (ε⊥) is positive and the permittivity parallel to it (εII ) is negative. Theory predicts that a corresponding structure for the visible and near infrared can be realised in form of an array of parallel aligned standing metal nanowires in a dielectric matrix and that the TM-polarisation (magnetic field perpendicular to the optical axis) exhibits the hyperbolic equi-frequency surface.Here we present an experimental determination of the hyperbolic equi-frequency surfaces of TM (p-) polarised light propagating within a silver nanowire array and the experimental derivation of the values of εII and ε⊥ in a wide spectral range in the visible and near IR ( 600nm < λ0 < 1300nm). To this purpose we performed angular resolved transmission measurements on a 1.7μm high alumina film containing the silver nanowire array. The spectra show clear oscillations due to the interference of the multiple reflected beams at top and bottom surface (Fabry-Perot resonances). The condition for a maximum in transmission is π m=kz d, where m is the order of the resonance, d the thickness of the film and kz the wave vector component across the film thickness. Knowledge of m and d therefore allows the determination of kz . In addition kx, the lateral wave vector component, is obtained from the angle of incidence so that finally the equi-frequency surfaces in the kx-kz plane are mapped from the experimental transmission data resulting in a hyperbola for the TM polarisation and a classic circle for the TE polarisation. Furthermore the relationship between the spectral peak position and the angle of incidence can be converted to a simple linear equation. From a corresponding linear fit of the angle dependent peak positions for TE and TM polarisation the principal permittivities ε⊥ and εII are finally determined.These experimentally determined values for ε⊥ and εII agree very well with effective medium calculations using a 2D Maxwell-Garnett approach for ε⊥ and a simple Wiener formula for εII. An advantage of the described experimental method is, that it is based on the spectral shift of extrema in the transmission curves and not on the absolute values of transmission or reflection measurements. The impact of scattering losses on the results (e.g. due to surface roughness or inhomogeneity of the sample) is therefore strongly reduced.
3:30 PM - D7.4
Stretchable Near-infrared Metamaterials With Large Frequency Tunability.
Imogen Pryce 1 , Koray Aydin 1 , Yousif Kelaita 1 , Harry Atwater 1
1 , California Institute of Technology, Pasadena, California, United States
Show AbstractMetamaterials with novel electromagnetic properties such as artificial magnetism, negative refraction, and cloaking have garnered increasing interest in recent years. Thus far, most metamaterial designs have been limited to fixed, narrow frequency range of operation determined by the size of the constitutive resonator elements. Ideally, the response of a metamaterial to an incoming electromagnetic wave would be tunable and controllable to enable incorporation within active optoelectronic devices. Here, we introduce a design for frequency tunable metamaterials based on the elastic deformation properties of the polymer polydimethylsiloxane (PDMS), where greater than linewidth (350 nm) tunability can be achieved. We demonstrate the first mechanically tunable metamaterial in the near infrared, where modifying the distance between coupled resonator elements drastically changes the resonance frequency.
Split-ring resonators (SRR) are commonly used in designing metamaterials over a broad range of frequencies from the microwave to the near infrared. Designing metamaterials at optical frequencies is rather challenging due to the size effects and fabrication difficulties. A common approach is to fabricate U-shaped SRR structures, whose resonance is determined by the effective inductance and capacitance. Here, we propose an alternative metamaterial design in which nanowire-SRR coupling is used as an additional design parameter. The distance between each SRR and wire is varied between 50 nm and 100 nm. As the PDMS substrate is uniaxially stretched this distance increases, changing the coupling between the SRR and the nanowire and inducing a shift in resonance. This allows further engineering of the metamaterial resonant response and the operating frequency.
Arrays of 100 nm thick Au SRRs, 400 nm by 400 or 500 nm are patterned over a 100 μm region via electron beam lithography on Si substrates. The Au is functionalized using 3-mercaptopropyl trimethoxysilane in order to improve adhesion to PDMS. PDMS is then cured on the patterns, and the Si wafer is back etched leaving a free-standing PDMS substrate patterned with SRR arrays. Reflection spectra of the SRR arrays are measured using FTIR spectroscopy between 1.4 and 5.0 µm.
Both experimental and simulation results for the mechanically tunable SRR arrays will be presented. Preliminary results show that the resonant peak position can be shifted by up to 350 nm, a full linewidth shift for an initial nanowire to SRR spacing of 60 nm. There is a hysteresis associated with this shift, but we will also show that the resonance can be tuned elastically by up to 240 nm. Finite-difference time-domain full field electromagnetic simulation is used to corroborate the experiments and guide the design of more complex resonator elements. Complimentary optomechanical measurements for various deformations and polarizations will be discussed as part of a comprehensive assessment of stretchable metamaterials.
3:45 PM - D7.5
Black Metamaterials: Broadband, Ultra-thin Plasmonic Super Absorbers for Unpolarized Visible Light.
Koray Aydin 1 , Ryan Briggs 1 , Harry Atwater 1
1 Thomas J. Watson Laboratories of Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractIt is of significant interest to be able to design and construct "black" materials, with nearly complete broad-band absorption across the visible spectrum. Silicon nanowires and carbon nanotubes have been previously shown to efficiently absorb the entire visible light spectrum in thick absorber layers. Thin-film "black" materials are not easy to obtain and not readily available in nature. Here, we propose using highly reflective metals and nonabsorbing dielectrics to construct black metamaterials. Nanostructured metal surfaces, such as gratings, nanoparticles, and slits, can yield strong absorption of light due to plasmonic resonances. In particular, metal-insulator-metal (MIM) slot resonators have been previously shown to achieve total absorption of light over a narrow frequency interval. We introduce here a MIM plasmonic resonator yielding an average of 85% absorption between 380 and 720 nm.
Full field electromagnetic simulations have been used to study the absorption spectrum of 260-nm thick Ag/SiO2/Ag MIM absorber, with a 60-nm SiO2 middle layer sandwiched between 100-nm Ag layers. The top Ag layer is structured as an array of crossed trapezoidal resonators, with an in-plane periodicity of 300 nm. We show that the trapezoidal elements yield resonances for a broader wavelength regime than rectangular structures. Calculated magnetic and electric field intensity profiles indicate that resonances at different wavelengths arise from different parts of the trapezoid. Crossed trapezoidal resonator arrays provide an in-plane symmetry, assuring that the absorber is resonant both for transverse-electric (TE) and transverse-magnetic (TM) polarizations of incident light. The calculated field components confirm that the observed broad-band absorption behavior arises from the localized MIM resonances.
Plasmonic absorbers were fabricated by patterning the top Ag layer using electron beam lithography. Transmission and reflection spectra through the absorber structure were measured using an inverted optical microscope. Arrays of trapezoidal resonators showed a broader spectral absorption compared to conventional gratings. We observed an average of 70% total absorption between 380 and 720 nm. We will present the numerical simulation, fabrication and experimental characterization of several resonators and compare their absorption performances in detail. We will discuss the possibility of achieving higher absorption using multi-layer MIM stacks, paving the way towards ultra-thin black metamaterials.
4:30 PM - **D7.6
Transforming Light with Metamaterials.
Vladimir Shalaev 1 , A. Kildishev 1 , S. Xiao 1 , V. Drachev 1 , A. Boltasseva 1
1 School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana, United States
Show AbstractOne of the most unique properties of light is that it can package information into a signal of zero mass and propagate it at the ultimate speed. It is, however, a daunting challenge to bring photonic devices to the nanometer scale because of the fundamental diffraction limit. Metamaterials can focus light down to the nanoscale and thus enable a family of new nanophotonic devices. Metamaterials, i.e. artificial materials with rationally designed geometry, composition, and arrangement of nanostructured building blocks are opening a gateway to unprecedented electromagnetic properties and functionalities that are unattainable with naturally occurring materials. We review this exciting field and discuss the recent, significant progress in developing metamaterials for the optical part of the electromagnetic spectrum. Specifically, we report on our recent world’s smallest nanolaser (collaborative work with Norfolk State University and Cornell), describe the phenomena of artificial magnetism across the whole visible and negative refractive indices in the optical range, and demonstrate a broadband cloaking in the visible based on tapered waveguides (collaboration with BAE and Towson University). A new, powerful paradigm of engineering space for light with transformation optics, which can enable a family of new applications including a planar magnifying hyperlens and optical black hole, will be also discussed.
5:00 PM - **D7.7
Deterministic Aperiodic Structures for Nanophotonics and Nanoplasmonics Device Applications.
Luca Dal Negro 1
1 , Boston University, Boston, Massachusetts, United States
Show AbstractDeterministic Aperiodic Structures (DAS) are generated by the mathematical rules of L-systems and number theory, manifest unique light localization and transport properties associated with a great structural complexity, and can be fabricated on-chips using conventional nano-lithographic techniques. When combined with metal-dielectric nanostructures, they give rise to large energy gaps like periodic media (i.e. photonic-plasmonic crystals) and highly localized, enhanced field states like disordered random media, including the formation of Anderson-localized modes, forbidden in periodic scattering media. However, contrary to random media, DAS possess controllable transport properties from ballistic to anomalous diffusion (slower diffusion than classical random walks) and strongly localized field states with large fluctuations of the photonic mode density – essential attributes to achieve spatio-temporal energy localization and to enhanced light-matter coupling, i.e. radiative rates of fluorescent molecules, absorption cross-sections, non-linear optical processes on the nanoscale. In particular, DAS fabricated using metal/dielectric nanoparticles can be utilized to develop novel nanophotonics structures for a variety of technological applications, including Surface Enhanced Raman (SERS) sensing, optical detectors, and enhanced light-emitting and nonlinear components for nanoplasmonics. In this talk, by combining dark-field scattering characterization, micro-photoluminescence and near-field optical measurements with accurate electrodynamics calculations based on semi-analytical scattering theories, I will discuss electromagnetic coupling, resonant scattering3, colorimetric sensing, light emission and enhanced Raman scattering in two-dimensional metal-dielectric arrays based on deterministic aperiodic sequences. In particular, I will focus on the broadband plasmonic scattering and localization properties of Fibonacci, Thue-Morse and Rudin-Shapiro lattices fabricated by Electron-Beam Lithography (EBL) on transparent quartz substrates. Finally, I will consider the design of novel plasmonic DAS ideally suited for broadband light emission enhancement and energy harvesting on chip-scale devices capable of producing the behavior of purely random systems to an arbitrary degree of accuracy.
5:30 PM - D7.8
Resonant Coupling to a Dipole Absorber Inside a Metamaterial: Hybridization of the Negative Index Response.
Svyatoslav Smolev 1 , Z. Ku 1 , S. Brueck 1 , I. Brener 2 , M. Sinclair 2 , G. Ten-Eyck 2 , W. Langston 2 , L. Basilio 2
1 Center for High Technology Materials, University of New Mexico, Albuquerque, New Mexico, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractFrom earlier theoretical work and practical implementation, understanding of negative index metamaterials has advanced rapidly. For some applications it’s interesting to consider the coupling between the metamaterial resonance and an absorbing species located in the metamaterial unit cell. We modeled a fishnet metamaterial with the dielectric spacer layer containing a simple Lorentzian electric-dipole resonance and found a classical anti-crossing behavior. Detection of absorption in novel sensors and use of absorption excitation to alter and switch the metamaterial optical properties are the possible applications.Simple resonance coupling model was constructed to investigate the effect of adding a dielectric with a dipole absorption peak to a fishnet metamaterial. Anti-crossing behaviors and an exchange of oscillator strength as metamaterial structural resonance is tuned through the absorption resonance were obtained. Rigorous coupled wave analysis, an algorithm used to calculate the normal incidence transmission and reflection of periodic structures, was used for detailed numerical modeling. Response of the fishnet structure with a dielectric material without an absorber shows only a single resonant peak, resulting from the coupling of the broadband negative ε with the structurally resonant negative µ associated with the LC circuit between the two metal plates. With the addition of a dipole absorber in the dielectric, the fishnet exhibits doubly resonant behavior. Presence of an electric dipole resonance in the dielectric of the fishnet structure manifests itself in a modification of the magnetic permeability, which in turn modifies the negative index behavior. Anti-crossing behavior of the two resonances is obtained. RCWA calculation and the simple model are in good agreement.A set of experimental samples were fabricated using standard lithographic processing. An Al-BCB-Al fishnet structure was used. Transmission data was obtained by FTIR. Plotting positions of the resonance peaks in the transmission response against ω0 clearly shows coupling between the resonances with hybridization behavior We demonstrate a novel resonant coupling between the structural resonance in the permeability of a fishnet and a material resonance in the dielectric spacer layer. The resonances in the permeability and the negative index response exhibit anti-crossing behavior. We simulate this using a simple analytic model, as well as rigorous coupled wave analysis (RCWA). A theoretical model and experimental data are in good agreement and clearly demonstrate hybridization of structural and material resonances. Detailed results will be presented at the meeting.
5:45 PM - D7.9
Three-dimensional Negative Refraction With a Negative Refractive Index in Plasmonic Waveguide Arrays.
Ewold Verhagen 1 , Rene de Waele 1 , Albert Polman 1
1 Center for Nanophotonics, FOM Institute AMOLF, Amsterdam Netherlands
Show AbstractAchieving a negative index of refraction at optical frequencies is one of the most important goals in metamaterials research. With resonator-based metamaterials it has proven very difficult to reach the necessary magnetic response in the visible frequency regime, where absorption losses limit performance. We show theoretically that it is possible to achieve a negative refractive index in stacked geometries of plasmonic slab waveguides.The proposed material is expected to reach a figure of merit as high as ~10 in the blue to green spectral region, a value that is comparable to theoretical estimates for resonator-based metamaterials only in the near-infrared. The material is based on metal-insulator-metal (MIM) slab waveguides. These are known to exhibit negative refraction in the plane of the slab because they can sustain a surface plasmon mode that exhibits antiparallel phase and energy velocities, for frequencies above the surface plasmon resonance frequency. We show that when we consider a stack of such MIM waveguides, light can also negatively refract in the plane perpendicular to the slabs. This means that the waveguide stack acts as a metamaterial that exhibits a negative index for a broad range of angles in all dimensions. We explain the effect in terms of coupling between the waveguides. The direction in which energy is transferred between adjacent waveguides in the stack determines the refraction behavior. It is shown that this direction is related to the symmetry of the surface plasmon mode. This fact can be exploited to achieve a three-dimensional negative index by carefully tailoring the distance between the waveguides to vary the coupling-induced refraction from positive to negative. The response of the resulting metamaterial can be described in terms of equifrequency contours, which relate the allowed wavevectors in the material to the direction of energy flow. This allows an intuitive understanding of the refraction behavior and left-handed wave propagation in this metamaterial, and it relates those phenomena directly to the underlying physical mechanism of waveguide coupling. The concepts developed in this work can be readily extended to more complex waveguide geometries, for example to achieve a negative refractive index for all polarizations. We will discuss the possibility of applying this relatively simple geometry for lensing applications. Moreover, this work may inspire new metamaterial designs to tailor the flow of light in the context of transformation optics in general.
D8: Poster Session I
Session Chairs
Thursday AM, April 08, 2010
Salon Level (Marriott)
9:00 PM - D8.1
Photoexcitation of Volume Plasmons in Metallic Nanoshells.
Katja Hoeflich 1 2 , Ulrich Goesele 2 , Silke Christiansen 1 2
1 , Institute of Photonic Technology, Jena, Thuringia, Germany, 2 II, Max Planck Institute of Microstructure Physics, Halle, Saxony-Anhalt, Germany
Show AbstractIt has long been known that a vanishing permittivity enables longitudinal electromagnetic waves. The corresponding collective eigenmodes called volume plasmons should not be photo excitable in classical electrodynamics due to the transversal nature of light. Thus, the typical volume modes are known to be excitable via particle beams only. We investigate typical scattering problems for a plane wave incident on a metallic nanoshell consisting of different combinations of metals and dielectric materials via solving the Helmholtz-equation. For spherical geometries the Helmholtz equation can be solved exactly [1,2]. In the textbook of Bohren and Huffman [3] Fortran codes for the calculation of Mie coefficients (after Mie [1] and Aden [2]) are given which permit to calculate optical spectra, e.g. the extinction efficiencies of spherical nanoshells. Remarkably, in the case of silver shells on various cores (e.g. metal or dielectric) the Mie extinction efficiencies have a local maximum at the natural plasma frequency corresponding to the photoexcitation of a volume plasmon. The existence and position of this high energy mode is independent of both the shell's thickness with respect to the core diameter and the core material but dependent on a vanishing shell permittivity. Therefore, we term it a volume plasmon [4]. As expected, the silver volume plasmon is fixed at around 330 nm which corresponds to the experimentally determined value of the silver plasma frequency at 3.8 eV.For explanation we present a simple physical picture which is supported by analytical examples on silver and gold nanoshells on various cores. This picture is in agreement with former experimental and theoretic work on metallic slabs in which the photo-excited volume mode was observed [5]. With variations of the shell permittivity ranging from primitive Drude metal to realistic silver to artificial metals (i.e. non existant metals that show a well selected optical behavior, e.g. a vanishing permitivity at a given wavelength) we investigate the existence and physical nature of the respective high-energy resonances. Furthermore, we are interested in the modifications of volume plasma excitations due to the near-field character of the photoexcitation and therefore study different dielectric media around the shell.The analytical calculations are supported by finite element simulations which can visualize both the electric field strength in any slice through the spherical particle and therefore unveil surface or volume character of plasmon modes and furthermore the boundary charge distributions showing their symmetry.[1] Mie, G.; Annalen der Physik 25 (1908).[2] Aden, A.L. and Kerker, M.; Appl. Phys. 22, 1242 (1951).[3] Bohren, C.F. and Huffman, D.R.; Absorption and Scattering of light by small particles (John Wiley & Sons, 1983).[4] Höflich, K.; Gösele U. and Christiansen, S.; Phys. Rev. Lett. 103, 087404 (2009).[5] Steinmann, W; et al. Phys. Stat. Sol. 28, 437 (1968).
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Plasmonic Oscillations in Metal Nanoparticle Arrays Engineered by Electron Beam Lithography.
Urcan Guler 1 , Rasit Turan 1
1 Physics, Middle East Technical University, Ankara Turkey
Show AbstractThe optical behavior of metal nanoparticles with different geometries is of great interest for the plasmonic resonances in the visible and infrared region. Recently this interest has grown due to a wide range of potential applications including biosensing and photovoltaics where the nanoparticles behave as optical nanoantennas which couple the incoming electromagnetic wave into the underlying device effectively. Electron Beam Lithography (EBL), being an excellent nanomanufacturing tool, enables us to fabricate well defined network of nanoparticles with varying sizes. In this study, the EBL was used to fabricate and examine a wide range of properties of localized plasmonic oscillations induced in Au and Ag nanoparticles on different substrates. We also focused on the fabrication issues such as the optimization of parameters affecting the resulting particle geometry. In general, particle arrays with smaller lattice constants were found to be affected by proximity more than those with larger inter-particle distance. Both transmission and reflection spectra of nanoparticle arrays were studied and discussed in terms of expected resonance conditions. The variation of the resonance peak position with the particle size and the lattice constant of the network was determined and tested against the theoretical results generated by the Discrete Dipole Approximation model. Aside from the size dependence of resonance peaks, the effect of shape asymmetries caused by the manufacturing steps on the resonance peaks were systematically studied using linearly polarized illumination. Elliptical nanoparticles with small axis ratios were found to induce single broad resonance peaks under unpolarized illumination when lattice constants were relatively small, whereas, for the case of larger lattice constants, separate peaks corresponding to the two axes of the ellipsoid were observable. This effect was studied in a series of experiments attempting to understand the relation between the resonance peak and the lattice constant of the particle network. Finally, nanoparticle arrays patterned on the surface of photovoltaic devices were studied experimentally to verify the absorption enhancement due to the localized surface plasmon oscillations at resonance frequencies.
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Gold Nanocone Near-field Scanning Optical Microscopy Probes.
M. Fleischer 1 2 , A. Weber-Bargioni 2 , M. Altoe 2 , A. Schwartzberg 2 , B. Zeeb 1 , P. Schuck 2 , S. Cabrini 2 , D. Kern 1
1 Institute of Applied Physics, University of Tuebingen, Tuebingen Germany, 2 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States
Show AbstractNear-field scanning optical microscopy (NSOM) can be applied to collect simultaneous high-resolution topographical and sub-diffraction limited optical information from a surface. Both the spatial resolution and the optical near-field enhancement depend strongly on the properties of the scanning probe. The spatial resolution of topographical as well as optical imaging directly correlates with the probe tip radius. The near-field enhancement depends on the probe tip geometry, material, dimensions, and radius of curvature. Furthermore it depends on the plasmonic resonance frequency of the probe tip, or rather the probe tip / sample configuration, with respect to the frequency of excitation. Therefore recently a lot of effort has gone into the design of optimized scanning probes. Most commonly, apertureless scanning probes consist in electrochemically etched gold wires. In order to create a more well-defined, strongly localized light-source at the probe tip, single gold spheres or rods have been placed on cantilevers and glass fiber tips [1-5]. Alternatively, bowtie antennas have been added at the apex of cantilever tips [6,7]. In our approach, a single gold cone with dimensions on the order of 100 nm is positioned at the apex of a SiN cantilever tip. When optically excited, the cone acts as an optical antenna with a strong near-field enhancement near the cone apex. The cone geometry combines a sharp tip radius down to less than 10 nm for high spatial resolution with a larger body for efficient antenna excitation. By tuning the size, i.e. base diameter and height, of the cone, the plasmon resonance frequency can be tailored according to application. To fabricate the gold cone probes, a previously developed method for the fabrication of arrays of cones based on ion milling of gold films [8] was combined with a process for the positioning of bowtie-antennas on cantilever tips by means of electron beam induced deposition [7]. The composition and microscopic structure of the gold cone tips was investigated by transmission electron microscopy. The size-dependent resonance frequency was studied on arrays of individual gold cones of different heights on glass using darkfield scattering microscopy. For this configuration, typical resonance wavelengths in the region around 600 nm were observed.The fabrication process and first examples of nanocone near-field probes will be presented together with an overview over the structural and optical properties of the gold cones. [1] T. Kalkbrenner et al., J. Microsc. 202, 72 (2001) [2] S.-K. Eah et al., Appl. Phys. Lett. 86, 031902 (2005)[3] Z.H. Kim and S.R. Leone, J. Phys. Chem. B 110, 19804 (2006)[4] M.T. Wenzel et al., Opt. Express 16, 12302 (2008) [5] T. Taminiau et al., Nano Lett. 7, 28 (2007) [6] J.N. Farahani et al., Phys. Rev. Lett. 95, 017402 (2005)[7] A.F.F. Weber-Bargioni et al., submitted (2009) [8] M. Fleischer et al., submitted (2009)
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The Role of the Driving Field in Using Rear-located Plasmonic Nanoparticles as Light-trapping for Solar Cells.
Fiona Beck 1 , Sudha Mokkapati 1 , Albert Polman 2 , Kylie Catchpole 1
1 Center for Sustainable Energy Systems, Australian National University, Canberra, Australian Capital Territory, Australia, 2 Center for Nanophotonics, FOM-Institute AMOLF, Amsterdam Netherlands
Show AbstractPlasmonic scattering arrays can increase the absorption of light in solar cells. Silver nanoparticles can be designed to support localised surface plasmons with strong scattering resonances and low absorption. These can be deposited on the surface of a solar cell, isolated from the semiconductor surface by dielectric spacer layers (which can include passivation layers). If the near-field of the excited surface plasmon resonance overlaps sufficiently with the optically dense semiconductor scattered light can be efficiently coupled into the active layer of the cell. As a result a significant fraction of incident light is scattered over a large angular range into the cell and trapped, leading to an increased path length of light in the active region of the cell and ultimately to an enhanced photocurrent. When located on the front illuminated surface of the solar cell plasmonic scattering arrays can provide both anti-reflection and light-trapping. However, suppression of absorption within the solar cell occurs at wavelengths below resonance due to Fano interference. This is detrimental to the total photocurrent of the cell, especially when the plasmon resonance is red-shifted in order to optimise the particles for light-trapping in Si cells, as absorption is reduced over a wide bandwidth in the visible region. Rear located particles can provide long wavelength light-trapping in Si solar cells while avoiding suppression at shorter wavelengths. Additionally, this configuration allows light-trapping and anti-reflection to be independently optimised. Using a simple self - assembly technique for nanoparticle fabrication on the rear of the cell, and tuning the nanoparticle resonance to the vicinity of the band-gap of Si, we report a 27% increase in photocurrent, over the light trapping spectral region 750-1180 nm, for 22 μm thick c-Si cells incorporating a traditional dielectric antireflection coating. We experimentally identify asymmetry in the light-trapping provided by nanoparticles located on the front and the rear of thin Si solar cells. We show by numerical calculation that this asymmetry is due to differences in the magnitude of the scattering cross-section of the nanoparticles of up to a factor of 3.7, and not in the efficiency of coupling to the substrate, which does not change. This location dependent variation is attributed to differences in the electric field strength, derived from a simple analytical model at the position of the particle. Furthermore we calculate that the normalised scattering cross-section of a front-located nanoparticle varies from 2-8 depending on the intensity of the driving field. From this result we conclude that the role of the driving field is crucial in the design of plasmonic scattering arrays for light trapping applications and must be considered separately for front and rear located particles.
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Tuning Dispersion in Rhombic Plasmonic Crystals.
Wei Zhou 1 , Hanwei Gao 2 , Teri Odom 2 1
1 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States, 2 Chemistry, Northwestern University, Evanston, Illinois, United States
Show AbstractThis paper describes the angle-dependent optical properties of rhombic plasmonic crystals. We demonstrated that degeneracies in plasmonic crystals could be lifted—which results in increased numbers of plasmon resonances within a fixed wavelength range—by reducing the lattice symmetry and by exciting along low symmetry directions. Unlike previous work that has focused primarily on high-symmetry lattices (square and hexagonal), we fabricated rhombic plasmonic crystals and carried out a comprehensive investigation on the effects of different excitation conditions. These low-symmetry lattices provide extensive opportunities to tailor plasmon resonances, which will have important implications for applications that rely on efficient SPP coupling using free-space light. In addition, we observed strong coupling between different SPP modes at the same wavevector and energy in the form of anti-crossings. In these regions, the SPP propagation significantly slows down and the near-field intensity of SPPs is further enhanced. These anti-crossings were found to depend significantly on the local refractive index and the excitation direction, which could be useful for chemical and biological sensing. Most importantly, our new fabrication method can produce high-quality nanostructures with various unit cell shapes and with different symmetry lattices.
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New Device Geometry Design for Plasmonic Enhanced Light Absorption.
Ching-Mei Hsu 1 , Yi Cui 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractThin film solar cells promise to reduce the material usage in solar energy production. An ideal absorber material is one that absorbs light efficiently at film thicknesses less than or equal to the minority carrier diffusion length. The use of such a material would improve on current thin film cells by increasing open-circuit voltage (Voc), short-circuit current (Jsc) and overall power conversion efficiency. In conventional crystalline silicon cell designs, wavelength-scale surface texturing with a feature size of 2-10um is applied on the front or back of the cell to enhance the coupling of light into the device. However, for thin film solar cells, which have 1-2um film thicknesses, such surface texture is not suitable. In addition, absorbers deposited on rough surfaces typically have poor material quality; the increased surface area due to surface texturing also enhances surface recombination rate. A novel approach that has been pioneered recently is to incorporate metal nanoparticles to enhance light scattering in solar cells. In this study, we will tune the surface plasmon resonance of metal nanoparticles to reduce the transmission loss in the long wavelength and enhance light absorption and photocurrent generation for thin film silicon solar cells. We also demonstrate a new device geometry to decrease the parasitic absorption in the metal nanoparticles. Different dielectric materials will be deposited to study the effects of redshifted resonances in solar cells by characterizing their optical properties and external quantum efficiencies to confirm the corresponding photocurrent enhancement.
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Enhancement of the 1.54μm Er3+ Emission From Aperiodic Plasmonic Arrays.
Ashwin Gopinath 1 , Selcuk Yerci 1 , Svetlana Boriskina 1 , Rui Li 1 , Nate Lawrence 1 , Luca Dal Negro 1
1 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractPeriodic and Aperiodic Au nanoparticle arrays of varying degree of disorder and interparticle separations were fabricated on light emitting Er:SiNx substrates using electron beam lithography. Upto 3.6 times enhancement of the emission observed at 1.54μm in aperiodic nanoparticle arrays, while the comparable periodic nanoparticle arrays resulted in quenching of the PL. accompanied The observed modification of the radiating properties in the periodic and periodic nanoparticle arrays are explained based on radiating plasmon coupling, supported by transmission data and PL decay measurements through the periodic and aperiodic nanoparticle arrays with interparticle separation in the 25nm-500nm range. The results presented in this work are further supported by rigorous Generalized Mie Theory (GMT) and Finite Difference Time Domain (FDTD) based simulation. The ability to use the photonic-plasmonic modes in aperiodic nanoparticle arrays for engineering light emitting devices represents an exciting potential for devices based on silicon technology.
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Plasmonic Optical Nanosensor for Remote Pressure Measurement.
Baxter McGuirt 1 , Matthew Howell 1 , David Carroll 1
1 , Wake Forest University, Winston-Salem, North Carolina, United States
Show AbstractThere is significant clinical demand for small, inexpensive devices which can measure interstitial pressure in a minimally invasive fashion. Currently, large mechanical gauge devices or expensive MEMS devices are used for such measurements. We have proposed a nanoparticle-based sensor for pressure measurement based on the surface plasmon interactions of silver nanoparticles. By adding 5-20nm diameter silver nanoparticles to a PDMS matrix we have created a nanocomposite material which displays sensitivity to pressure through plasmon resonance shifts. Absorption spectra of these materials have been taken at various external pressures and show changes indicative of plasmonic interactions. SEM and confocal microscopy have been used to examine the behavior of the nanoparticles within the composite. These investigations have shown that the natural aggregation behavior of the silver nanoparticles creates large clusters within the composite, which we observe to significantly enhance the expected pressure response. Such nanocomposite materials show strong promise for clinical use as a cheap and effective tool for diagnostic procedures.
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Hyperbolic Dispersion and Slab Lensing in Ag Nanowire Aligned Arrays.
Jerrold Kielbasa 1 , Baxter McGuirt 1 , Junping Zhang 1 , Jungho Park 1 , Burak Ucer 1 , Richard Williams 1 , David Carroll 1
1 Physics, Wake Forest University, Winston-Salem, North Carolina, United States
Show AbstractAligned Ag nanowires were grown in ordered AAO templates to build a uniaxial metamaterial exhibiting hyperbolic dispersion. Hyperbolic dispersion has been shown to result in negative refraction in similar materials. The AAO-Ag nanowire composite has been optically investigated with white light and thin film angle-dependent reflectometry. It has also been used as a flat slab lens to image parallel slits. White light angle-dependent reflectometry shows that the Brewster’s angle shifts from ≈ 57 degrees for wavelengths ≤ 400 nm to ≈ 50 degrees for wavelengths > 400 nm. A decrease in the Brewster’s angle occurs with a change in sign of ε//, which is necessary for hyperbolic dispersion. Thin film angle-dependent reflectometry has been used to obtain the optical constants from the sample based on interference fringes. An NSOM was used to map the electromagnetic field above the sample while it was used as a slab lens to image parallel slits. The Fresnel fringes resulting from the slits have been used to determine the optical path length for light passing through the sample.
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Large-area Imprinted Metal-nanoparticle Arrays to Enhance Efficiency of Si Solar Cells.
Maarten Hebbink 1 , Claire van Lare 1 , Marc Verschuuren 2 , Rene de Waele 1 , Albert Polman 1
1 , FOM institute Amolf, Amsterdam Netherlands, 2 , Philips Research, Eindhoven Netherlands
Show AbstractEfficiency improvement and reduction of material costs are important issues to make solar cells commercial. Thin silicon solar cells are promising to drastically reduce the price of solar energy, but are also less efficient than standard thick Si solar cells since the optical path length is much shorter than the absorption length in the red part of the spectrum. Light trapping by scattering from metal nanoparticles opens the possibility to overcome this problem: sunlight will be scattered preferentially into the silicon layer due to the higher optical density of states in the silicon. In combination with a highly reflecting bottom layer, this geometry causes light to scatter back and forth through the silicon layer, enlarging the optical path length. The scattering also results in an angular redistribution of light in the Si layer, further enhancing the optical path length.In this work, we investigate the fraction of light that is coupled into the substrate. The transmission into Si can be tuned by changing the nanoparticle shape and size and array pitch.We use Finite Difference Time Domain (FDTD) simulations to study the optimum metal nanoparticle geometry (size, shape, pitch) for nanoparticles on a thick Si wafer and compare the optical properties to conventional cells with and without a standard silicon nitride-coating. To confirm our simulation results experimentally we fabricate large-area samples using Substrate Conformal Imprint Lithography (SCIL), which is a low-cost technique that provides the possibility to pattern large-area nanoparticle arrays on substrates. We compare measured diffraction patterns to simulation results for a variety of cell geometries and angles of incidence, and provide physical insights in the light trapping mechanism.
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An Optical Cloak Using Dielectrics.
Jason Valentine 1 , Jensen Li 1 , Thomas Zentgraf 1 , Guy Bartal 1 , Xiang Zhang 1
1 , University of California, Berkeley, Berkeley, California, United States
Show AbstractRecent theories including transformation optics and conformal mapping have proposed that cloaking devices are in principle possible, given the availability of the appropriate medium. Indeed, utilizing metamaterials, the first cloaks have recently been demonstrated at microwave frequencies. However, such cloaks have utilized resonant metamaterials, which are difficult to scale to optical frequencies and result in high loss and narrow bandwidth. We report the first experimental realization of a cloak working at optical wavelengths. The cloak, deemed a ‘carpet cloak’, conceals an object that is placed under a curved reflecting surface by imitating the reflection of a flat surface. It is designed with quasi-conformal mapping which allows it to be implemented with non-resonant, isotropic metamaterials. The cloak is experimentally demonstrated using an all dielectric metamaterial which enables broadband and low-loss invisibility at a wavelength range of 1400-1800 nm.
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Tuning the Optical Properties of Gold Nanoantennas in the Infrared.
Daniel Weber 1 , Frank Neubrech 1 , Javier Aizpurua 2 , Annemarie Pucci 1
1 Kirchhoff Institute for Physics, Heidelberg University, Heidelberg Germany, 2 Centro de Fisica de Materiales, Spanish Council for Scientific Research and Donostia International Physics Center, Donostia - San Sebastian Spain
Show AbstractGold nanoantennas are of great interest for spectroscopic applications due to their plasmonic properties. Excited resonantly by electromagnetic radiation, they are able to strongly enhance the local electromagnetic field. This effect, which is particularly strong for metal antennas in the infrared (IR), can be exploited for surface-enhanced vibrational spectroscopy, e.g. surface-enhanced Raman scattering (SERS) or surface-enhanced infrared spectroscopy (SEIRS).In this paper, we report on the optical properties of gold nanoantennas in the IR spectral range, i.e. the dependence of their plasmonic resonance from different parameters (width and length of the antennas, coupling of antennas and geometrical arrangement, different preparation techniques, different substrates). The samples, nanowires of good crystalline quality and circular cross-sections, were prepared electrochemically at the GSI, Darmstadt (Germany), and transferred onto IR transparent substrates (e.g. KBr, CaF2). Stripe-like nanoantennas with rectangular cross-sections being polycrystalline were prepared lithographically by cooperation partners in Stuttgart (Germany), Troyes (France) and Tsukuba (Japan) on different substrates (ZnS, quartz glass, Si). The measurements were performed by IR microscopic spectroscopy, in our lab and at the synchrotron light source ANKA, Karlsruhe Institute of Technology.Keeping all other geometrical antenna parameters constant, a linear dependence of the resonant wavelength from the antenna length is observed in all cases. [1,2] This property allows it to very precisely tune the spectral resonance position to desired values for any application. In order to study the influence of coupling and of the geometrical arrangement also, nanoantenna arrays with different gap sizes between the antennas (both perpendicular (y-direction) and parallel (x-direction) to the long wire axis) were investigated. The consequences of antenna interaction in such arrays will be shown.
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Broadband Optical Absorption Enhancement in Thin Film Solar Cells Using Periodic and Aperiodic Textures.
Ragip Pala 1 , Justin White 1 , Mark Brongersma 1
1 Geballe Laboratory for Advanced Materials , Stanford University, Stanford, California, United States
Show AbstractA combined computational and experimental study optimizing plasmon-enhanced absorption in thin film solar cells is presented. We investigate different cases where 2-dimensional periodic/aperiodic arrays of metal nanostructures sit above or below the active material. We develop basic design rules for the realization of broadband absorption enhancements for such structures, by simultaneously taking advantage of 1) the high near-fields surrounding the nanostructures close to their surface plasmon resonance frequency and 2) the effective coupling to waveguide modes supported by the Si film through an optimization of the array properties. In order to verify our computational results, we have fabricated Schottky-Barrier Si solar cells and metal nanowires of varying shape and periodicity on top of the cell. Large enhancements in the short-circuit photocurrent density have been achieved in agreement with our theoretical predictions.
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Engineering and Characterization of Resonant Optical Antennas.
Matthias Wissert 1 , Andreas Schell 1 , Konstantin Ilin 2 , Michael Siegel 2 , Uli Lemmer 3 , Hans-Juergen Eisler 1
1 Light Technology Institute, DFG Heisenberg Group 'Nanoscale Science', Karlsruher Institut fuer Technologie, Karlsruhe Germany, 2 Institute for Micro- and Nanoelectronic Systems, Karlsruher Institut fuer Technologie, Karlsruhe Germany, 3 Light Technology Institute, Karlsruher Institut fuer Technologie, Karlsruhe Germany
Show AbstractOptical antennas can provide localized highly enhanced fields when excited resonantly [1,2], which makes them ideally suited for applications such as biosensing or Raman spectroscopy. We have recently preformed a comprehensive study of optical antenna parameters for gold nanoantennas comprised of two arms of length 25 to 65 nm each coupled by a 20 nm gap [3], which allows, via dark-field microscopy, to examine the resonance behavior when antenna arm length, the gap length, or the antenna width is varied. We observe that antenna coupling via a small gap does indeed not only provide highly localized near-fields, but also increases the far-field scattering intensity compared to a single antenna arm without its counterpart by a factor of 8.In the meantime, we also confirmed that such antennas with about 90 nm arm length, when excited resonantly via a laser operated at 800 nm, show a strong TPL-white-light response (similar to results e.g. in [4] or [5]). A systematic study reveals that not only the white-light intensity emitted clearly depends on the length of the antenna arms, but that also in this case the white-light response is significantly enhanced, even when compared to structure of the length of single arms. Experimentally measured white-light intensity plotted versus the antenna arm length shows that, while very limited for uncoupled single antenna arms, white-light can be observed for a wide range around the peak resonance wavelength for two arm antennas with a 20 nm gap.REFERENCES:[1] J. Aizpurua, G. Bryant, L. Richter, F. García de Abajo, B. Kelley and T. Mallouk.Optical properties of coupled metallic nanorods for field-enhancement spectroscopy,Phys. Rev. B 71, 254320 (2005). [2] O. Muskens, V. Giannini, J. Sánchez, and J. Gómez-Rivas. Optical scattering resonances of single and coupled dimer plasmonic nanoantennas, Optics Express 15, 17736 (2007).[3] M.D. Wissert, A.W. Schell, K. Ilin, M. Siegel, and H.-J. Eisler. Nanoengineering and characterization of gold dipole nanoantennas with enhanced integrated scattering properties, Nanotechnology 20, 425203 (2009).[4] P. Mühlschlegel, H.-J. Eisler, O.J.F. Martin, B. Hecht, and D.W. Pohl. Resonant Optical Antennas, Science, 308, 1607 (2005).[5] P. Ghenuche, S. Cherukulappurath, T. Taminiau, N. van Hulst, and R. Quidant. Spectroscopic Mode Mapping of Resonant Plasmon Nanoantennas, Phys. Rev. Lett. 101, 116805 (2008).
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Plasmonic Gallium Nanoparticle Synthesis on Supports.
Yang Yang 1 , Pae Wu 2 , Tong-Ho Kim 2 , Henry Everitt 1 2 , April Brown 2
1 Department of Physics, Duke University, Durham, North Carolina, United States, 2 Department of Electrical and Computer Engineering, Duke University, Durham, North Carolina, United States
Show AbstractMetallic nanoparticles(NPs) are of great interest for plasmonic applications. However, the synthesis of NP ensembles on solid supports tailored for specific optical properties remains challenging. Current research is focused primarily on Ag and Au, which are both limited in their plasmonic tunability. Theoretical studies of optical properties reveal gallium’s(Ga) promise as a UV plasmonic material(Zeman & Schatz, JPC 91 634). Ga NPs possess high thermal stability, long lifetimes (months) and a wide plasmonic spectral range. We have shown local surface plasmon resonant(LSPR) Ga NPs at wavelengths as low as 190nm while Ag and Au nanostructures are limited to 370nm and 520nm, respectively. Recently, we reported SERS exploiting Ga NPs.(Wu et al., JACS 131 12032)
Ga NPs synthesized using molecular beam epitaxy(MBE) are optically monitored by in situ spectroscopic ellipsometry(SE). The system enables us to study the control of the NP plasmonic properties as the fundamental nucleation dynamics are revealed by in situ SE data. We reported that Ga NPs display different formation dynamics depending upon the surface charge of the supports(Wu et al., Langmuir 25 924). Herein, we report that by synthesizing NPs under either static(no incoming flux) or dynamic(growing) conditions with simultaneous desorption of Ga at high temperatures(580°C~760°C), we can significantly narrow the ensemble size distribution, thus elucidating the competing mechanisms, ripening and desorption, driving NPs evolution on solid supports.
Ga desorption is negligible at growth temperatures T<580°C, but above 760°C no Ga adsorption occurs(Choi et al., APL 89 181915). Ga NPs evolution on Al2O3 follows a predicted Volmer-Weber growth behavior moving through stages of nucleation to coalescence and finally ripening. Monitoring the NP formation process by in situ SE, we observe an accelerated red shift of the NPs' LSPR at elevated growth temperatures compared to NPs synthesized at 300K, which correlates with a more rapid growth of the mean NP radius. Under static, high temperature conditions Ga desorption drives a shrinking mean NP radius. Comparing NPs with equivalent LSPR wavelength, a synthesis temperature of 700°C yields a NP density around 60/μm2 compared with 450/μm2 for samples synthesized at 300K. In addition, for the same LSPR wavelength, the FWHM of the size distribution for samples grown at 700°C is 0.38rmean compared to 0.79rmean for NPs grown at 300K. That is, higher growth temperatures enhance the ripening since the higher Ga surface diffusion rates act as the driving force for narrowing the NP size distribution.
In summary, exploiting in situ SE enables both control of the plasmonic properties and concurrent characterization of the growth process. We are able to narrow the NP ensemble size distribution without changing its major plasmonic features. NPs with narrower size distribution are critical for achieving improved plasmonic applications performance.
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Effective Parameters of Terahertz Metamaterials Fabricated With Microfluidic-jetted Technique.
Zsolt Szabo 1 , Yew Li Hor 1 , Li Er-Ping 1
1 , Institute of High Performance Computing, Singapore Singapore
Show AbstractThe microfluidic-jetted technique is a convenient approach to fabricate metamaterial structures at micrometer scale. On a copper clad polymide substrate, a single layer of split ring resonators and microstrip arrays are fabricated. A bulk metamaterial for terahertz frequencies can be made by stacking together several metamaterial layers. The resulting structure will have novel mechanical properties, because the polymide substrate is lightweight and flexible.The fabricated metamaterials are characterized by the effective medium theory in the frequency range of 0.1-2 THz. A parameter retrieval procedure based on Kramers-Krönig relations is presented to retrieve the effective metamaterial parameters from calculated S parameters. The accuracy of the algorithm is demonstrated by retrieving the effective material parameters of a homogenous slab. Then the procedure is applied to determine the effective permeability and permittivity of the metamaterial layers. Finally, the limits of the effective medium theory and of the developed algorithm are studied by increasing the thickness of the metamaterial, and observing the convergence of the retrieved electromagnetic material parameters to a bulk value. The predictions of the model are verified by measured transmission data.The presented results will demonstrate that the Kramers-Krönig relation gives a suitable approximation for the real part of the refractive index. When the metamaterial is thick as compared to the wavelength, more than one branch of the logarithmic function is involved in the final results. As the optical thickness becomes comparable to the wavelength, the effective medium theory cannot be applied anymore.AcknowledgementThe authors wish to acknowledge the support of A*STAR SERC Metamaterial Research Grant No. 0821410039.
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Plasmon Coupling in Gold Nanocube Clusters.
Chen Huanjun 1 , Shao Lei 1 , Wang Jianfang 1
1 Physics, Physics Department, The Chinese University of Hong Kong, Hong Kong China
Show AbstractAssembly of noble metal nanocrystals gives rise to extraordinary plasmonic properties that are distinct from those of isolated nanocrystals. The electric field enhancement in the gaps among assembled metal nanocrystals is usually much larger than that associated with isolated nanocrystals. The gaps therefore function as ‘hot spots’ for enhancing a variety of optical signals. Ordered assemblies of metal nanocrystals can also exhibit collective plasmonic properties, which form the basis for the creation of metamaterials. Furthermore, clusters composed of ordered metal nanocrystals provide a platform for studying the transition from the localized plasmon resonance associated with isolated nanocrystals to the propagating one associated with metal/dielectric interfaces.Previous studies on the plasmon coupling have mainly focused on dimers of metal nanocrystals with varying gaps. No systematic investigations have been carried out to understand the dependence of the plasmon coupling on the number of nanocrystals and their spatial arrangement. We have prepared clusters that are composed of tow-dimensionally ordered gold nanocubes and investigated their plasmonic properties (Small 5, 2111, 2009). The number and spatial arrangement pattern of the nanocubes vary among different clusters. The plasmon resonances of the nanocube clusters have been found to be highly dependent on both the number and ordering of the nanocubes in the clusters. In general, each cluster exhibits a plasmon resonance around 550 nm. As the clusters become larger and more asymmetric, they show more plasmon resonance peaks that are shifted to longer-wavelength regions. Finite-difference time-domain calculations reveal that the plasmon resonance centered at 550 nm for all the clusters originates from the coupling of the vertically oriented dipole in the nanocube with its image dipole in the ITO substrate. The plasmon resonance peaks in the longer-wavelength region arise from the coupling among horizontally oriented dipoles in different nanocubes. The gold nanocubes in the clusters were further welded together by thermal treatment. The plasmon peaks of the thermally treated clusters generally become sharper and are red shifted. These studies can not only help in understanding the plasmon coupling in metal nanocrystal clusters but also offer a potential approach to the tailoring of the plasmonic properties for advanced spectroscopic applications.
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Angle- and Energy-resolved Plasmon Coupling Between Gold Nanorods.
Lei Shao 1 , Huanjun Chen 1 , Kat Choi Woo 1 , Jianfang Wang 1 , Haiqing Lin 1
1 Physics, The Chinese University of Hong Kong, Hong Kong China
Show AbstractInteractions between localized surface plasmon resonances (LSPRs) of metallic nanocrystals have attracted much attention, because they can be utilized in many applications ranging from plasmon-based optoelectronic instruments to single biomolecule detection. A number of experimental and theoretical experiments have studied the dependence of the coupling-induced plasmon shift on the interparticle spacing and found that the plasmon shift increases exponentially as the interparticle spacing is gradually decreased. Gold nanorods (NRs) exhibit both the transverse and longitudinal plasmon resonance modes. The longitudinal plasmon mode is polarized along the length axis. Both the excitation and the scattering of the longitudinal plasmon mode are linearly polarized along the length axis. The polarization-dependent plasmonic properties of gold NRs allow not only for the orientation detection with polarized single-particle microscopy but also for the investigation of the dependence of the plasmon coupling on the relative orientation of gold NRs.We have carried out systematic studies on the dependence of the plasmon coupling in gold NR dimers on their relative orientations and LSPR energies. The NRs were assembled together in an end-to-end manner. The resultant angle between the two NRs in each dimer varied over a wide range. Two plasmon resonance modes were observed in the NR dimer system. They arise from the plasmon hybridization between the two NRs in each dimer and correspond to the bonding and antibonding modes. The intensity ratio between the antibonding and bonding modes were seen to decrease exponentially as a function of the NR angle. A simple dipolar model has been proposed to describe the observed exponential variation. The variation trend has also been confirmed with finite-difference time-domain calculations. In addition, an anti-crossing behavior in the coupling diagram of the NR dimers has also been observed for the first time. This result shows that the plasmon resonance energies of nanoparticle dimers can be tuned by varying the plasmon energy of each nanoparticle component, instead of changing the interparticle spacing. The latter is undesirable because an increase in the spacing will dramatically reduce the local electric field enhancement. We have further studied the effect of the nanocrystal shape on the plasmon coupling. We believe that our results will be useful for developing complex plasmon-based optoelectronic devices and ultrasensitive plasmon sensors. The NR dimers can also potentially function as building blocks for the construction of metamaterials.
Symposium Organizers
Jennifer A. Dionne Stanford University
Luke A. Sweatlock Northrop Grumman Space Technology
Gennady Shvets University of Texas-Austin
Luke P. Lee University of California-Berkeley
D9: Nanoparticle Plasmonics I
Session Chairs
Thursday AM, April 08, 2010
Room 2008 (Moscone West)
9:30 AM - **D9.2
Plasmon Resonances of Charged Gold Nanoparticles: Spectral Shift and Damping.
Thomas Klar 1
1 , Technical University of Ilmenau, Ilmenau Germany
Show AbstractPlasmon spectroscopy of single, charged gold nanoparticles is used in order to monitor the interaction of charged gold nanoparticles in aqueous solution with the solvent. Depending on the applied potential, different regimes can be studied in which the gold nanoparticles either act as “simple” spherical capacitors of constant capacitance, as capacitors with charge tuneable capacitance (leading to a nonlinear charge - voltage relationship), or in which repeated oxidation / reduction cycles allows for shaping of nanoparticles. The results are of importance to such diverse fields as SERS, nanoparticle based catalysis and biosensing.
10:00 AM - D9.3
Nanoscale Characterization of Individual Metal Nanoparticles by their Scattering and Luminescence Patterns.
Tina Zuechner 1 , Frank Wackenhut 1 , Antonio Virgilio Failla 1 2 , Alfred Meixner 1
1 Nanooptics, Institute of Physical Chemistry, Tuebingen University, Tuebingen Germany, 2 , Max Planck Institute for Developmental Biology, Tuebingen Germany
Show AbstractWe present a powerful and versatile confocal microscopy technique to characterize single metal nanoparticles and to probe their environment on the nanoscale. To our knowledge, this is the only technique that allows with a single image to determine the shape and the orientation of a metal nanorod, i.e. the orientation can be determined within a fraction of one degree, and to simultaneously measure the local environment with high accuracy. In addition to the topological information, i.e. the position and the orientation, even the dynamics of the metal particle’s rotation and translation can be tracked with high sensitivity. Confocal microscopy in both reflection (scattering) and fluorescence (luminescence) mode is used in combination with azimuthally and radially polarized doughnut modes (vector beams). In the scattering mode, the detected field consists of the sum of the light directly reflected at the interface and the light scattered from the individual particles. Since the resulting patterns sensitively depend on the particle’s polarizability, particles of different shapes can be distinguished via their characteristic patterns. [1, 2] Moreover, the 2D orientation of single metal nanorods is directly visualized in the confocal scans and can be extracted from the scattering patterns with an accuracy better than 0.5°. [3] Particles fixed at an interface have been observed as well as the spontaneous motion of floating particles. [4] At the same time, dielectric interfaces can be probed on the nanoscale. [4, 5] Even slight variations in the refractive index at one interface can turn the sign of the image contrast, [5] underscoring the potential use of the technique in sensing applications. The influence of the excitation wavelength on both the scattering and luminescence patterns is further studied. Additionally, we found that the luminescence spectra from single particles vary. Our experimental results are compared with theoretical calculations achieving a quantitative understanding of the image formation process.[1] A.V. Failla, H. Qian, H. Qian, A. Hartschuh, A.J. Meixner, Nano Lett. 6, 1374-1378 (2006).[2] T. Züchner, A.V. Failla, A. Hartschuh, A.J. Meixner, J. Microsc. 229, 337-343 (2008).[3] A.V. Failla, S. Jäger, T. Züchner, M. Steiner, A.J. Meixner, Opt. Express 15, 8532-8542 (2007).[4] T. Züchner, F. Wackenhut, A.V. Failla, A.J. Meixner, Appl. Surf. Sci. 255, 5391-5395 (2009).[5] T. Züchner, A.V. Failla, M. Steiner, A.J. Meixner, Opt. Express 16, 14635-14644 (2008).
10:15 AM - D9.4
Spectral Response of Dynamically Coupled Nanoparticle Dimers.
Jennifer I. L. Chen 1 , Yeechi Chen 1 , David Ginger 1
1 Chemistry, University of Washington, Seattle, Washington, United States
Show AbstractWe report single-particle spectroscopy studies of discrete Au nanoparticle dimers linked by oligonucleotides. In contrast with most studies of dimers in the context of plasmon rulers, we have used large Au dimers with close spacings (Au nanoparticles of sizes 30 – 100 nm with gaps of 5 - 10 nm) that allow us to distinguish both the bonding plasmon mode (red-shifted from the free particle resonance by up to 200 nm) as well as a bluer Fano resonance when light is polarized parallel to the dimer-axis. We demonstrate the actuation of these supported dimers using oligonucleotide linkages that undergo hairpin conformational changes, in addition to their intrinsic different stretching behaviors in solvents. We use this ability to modulate the dimer spacing on the sub-10 nm scale to study the distance-dependent scattering properties of the two resonances. We correlate our optical studies with simulations from electrodynamic theory and particle-size correlations using SEM imaging. We discuss the implications of supported active dimers for both scattering-based biosensing and optical field-enhancements.
10:30 AM - D9.5
Excitation Energy Transfer from Organic Dyes to Metal Nanoparticles: Modeling Based on Quantum Mechanical Approaches.
Angel Sanchez-Gonzalez 2 , Aurora Munoz-Losa 2 , Sinisa Vukovic 3 , Stefano Corni 1 , Benedetta Mennucci 2
2 Department of Chemistry and Industrial Chemistry, University of Pisa, Pisa Italy, 3 Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkely, California, United States, 1 , INFM-CNR National Research Center S3, Modena Italy
Show AbstractOne of the processes that may intervene in plasmonic applications based on metal nanoparticles is the excitation energy transfer (EET) between organic molecules and the metal nanostructure. For example, such process is involved in the use of metal nanoparticles as nanometric rulers [1], and it is one of the fundamental steps in the working mechanisms of a spaser, the surface-plasmon analogous of a laser [2]. Description of the EET is routinely based on Förster theory. However, for systems with complex electronic excitations such as metal nanoparticles, Förster theory provides only an approximate microscopic picture of the phenomenon. In this contribution, we shall present our theoretical results in the modeling of dye-nanoparticle EET [3,4]. In particular, we have applied to this problem two different models developed from our group [5,6]. One uses a quantum mechanical description, at the Time Dependent Density Functional Theory (TDDFT) level, for both the dye and the nanoparticle, the other exploits the same TDDFT description of the dye and a continuum electrostatic description of the nanoparticle. The solvent (or an embedding matrix) is included in the model as a (further) dielectric medium. The comparison between the quantum mechanical and the continuum dielectric models of the metal nanoparticle, keeping the same quantum description for the dye, allow identifying intrinsic quantum size effects, as well as effects due to the loss of surface plasmon excitatons in small metal clusters. Investigations on the role of the solvent in controlling EET and a theoretical assessment of the Förster approximation have been also performed.[1] Seelig, J.; Leslie, K.; Renn, A.; Kuhn, S.; Jacobsen, V.; van de Corput, M.; Wyman, C.; Sandoghdar, V. Nano Lett. 2007, 7, 685;[2] M. A. Noginov, G. Zhu, A. M. Belgrave, R. Bakker, V. M. Shalaev, E. E. Narimanov, S. Stout, E. Herz, T. Suteewong, U. Wiesne. Nature 460, 1110 (2009)[3] Muñoz-Losa A., Vukovic S., Corni S., Mennucci B., J. Phys. Chem. C 2009, 113, 16364.[4] Sanchez-Gonzales, A.; Muñoz-Losa A., Vukovic S., Corni S., Mennucci B., submitted.[5] Iozzi, M. F.; Mennucci, B.; Tomasi, J.; Cammi, R. J. Chem. Phys. 2004, 120, 7029[6] Corni, S.; Tomasi, J. J. Chem. Phys. 2003, 118, 6481
11:30 AM - **D9.7
Controlling Dispersion in Metal Nanoparticle Arrays.
Teri Odom 1 2
1 Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Materials Science and Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractThis talk will describe the fabrication and characterization of large-area (> cm2), two-dimensional arrays of plasmonic nanoparticles (NPs). These NP arrays were patterned using a combination of soft interference lithography, etching, and template stripping. Different array symmetries could be created by changing the exposure conditions and range from square to hexagonal to rhombic. Angle-resolved transmission measurements were found to depend sensitively on the NP shape as well as the incident polarization direction. Compiled dispersion diagrams indicated that these arrays supported unusual band structure. The protein sensing possibilities of these new plasmonic structures will be discussed.
12:00 PM - D9.8
Plasmonic Nano Structures via Electron Beam Induced Deposition.
Katja Hoeflich 1 2 , Joerg Petschulat 3 , Norik Janunts 3 , Michael Becker 1 2 , Ren Bin Yang 2 , Nadine Geyer 2 , Andreas Berger 1 2 , Thomas Pertsch 3 , Silke Christiansen 1 2 , Ulrich Goesele 2
1 , Institute of Photonic Technology, Jena, Thuringia, Germany, 2 Exp. Dep. II, Max Planck Institute of Microstructure Physics, Halle, Saxony-Anhalt, Germany, 3 ZIK - Nano Optics, Institute of Applied Physics, Friedrich Schiller University, Jena, Thuringia, Germany
Show AbstractIn the growing field of plasmonics composite nanostructures that contain noble metal components of various geometries are designed to exploit their unique optical properties as e.g. near field behavior, cloaks of invisibility and optical data transmission properties. The basic principle is the spatially strongly localized surface plasmon-polariton (LSP) which means the coupling of an evanescent electric field (a photon) to surface density oscillations of the free electron gas (a plasmon). A wealth of methods has been used to create plasmonic nanostructures. Many of them lack the control needed to realize nanostructures of choice.We use the focused electron beam in a dual beam instrument (FEI xP Dual Beam Nova Nanolab 600) for the direct write of plasmonic nanostructures. We start from the deposition of structures consisting of a matrix of carbonaceous material in which single crystalline gold nanocrystals of a few nanometers in diameter are dispersed by e-beam cracking of an organo-metallic precursor gas (dimethyl-gold(III)-acetylacetonate). Therewith, it is possible to fabricate high precision nano-structures of a few tens of nanometers in diameter with various shapes on any conductive substrate. We will present needles and pillars with tip diameters down to 10 nm as well as helices with up to 7 windings and a diameter of 150 nm. Furthermore we can produce pairs of needles that face each other and run oblique to the substrate surface. Thereby, gaps between the tips of the needles can be realized that are on the order of 5 nm. These needle-pairs can be used as a reproducible substrate for surface enhanced Raman spectroscopy (SERS), especially when the needles are in addition covered with an evaporated silver layer. For testing of the SERS templates Raman spectra of methyl violet as a model analyte are captured. Due to the decomposition of an organo-metallic precursor gas the carbon content of the structures is predominant. To densify the gold content and realize pure gold nano-needles, the carbon is oxidized using ozone and water vapor treatment at moderate temperatures. The structures thereby largely retain their shapes and obtain a multi-crystalline structure of pure gold. We present optical spectra of as-written composite and ozone treated multi-crystalline gold nanostructures that are realized on indium-tin-oxide (ITO) coated glass substrates. From the spectra of these nanostructure ensembles an effective permittivity is calculated and the response of the corresponding as-deposited and modified bulk material can be deduced.
12:15 PM - D9.9
Multiscale 3D Patterning of Nanoparticle Assemblies for Plasmonic Devices.
Robert Carles 1 , Cosmin Farcau 1 , Gerard Benassayag 1 , Caroline Bonafos 1 , Beatrice Pecassou 1
1 , CEMES - Toulouse University, Toulouse France
Show AbstractMost of the currently available lithographic techniques for metal nanoparticles (NPs) fabrication are developed for two-dimensional (2D) arrays. The metal NPs are usually generated on top of a solid substrate support and are exposed to the ambient. Recently we have shown that ULE-II can be a promising technique for the wafer-scale fabrication of silver (Ag) NP planar arrays embedded in a silica (SiO2) on silicon substrate [1,2]. Here we extend the applicability of ULE-II to generate embedded, sub-surface gratings and 2D arrays of Ag NPs assemblies. The sub-surface positioning of the metal nanostructures allows the extension in the third dimension, for example by a subsequent patterning of the free, flat SiO2 surface. By choosing the appropriate SiO2 thickness we engineer the optical properties of the substrate, in order to obtain anti-reflective effects and optical amplification at the film surface.Nanometer-sized Ag NPs exhibiting surface plasmon resonance are synthesized at few-nanometers below the free silica surface. This distance is controlled by the kinetic energy of the implanted ions, thus offering an original way to manipulate optical or electronic processes in the near-field regime. By implantation through a stencil placed in contact with the SiO2 surface, different embedded plasmonic architectures (lines, dot arrays, gratings) made of NP metallic assemblies are fabricated. This provides a means to control photonic waveguide like modes in the plane of the surface. By a careful design, all three effects described above (optical interference, plasmon resonance and near-field coupling) can be concurrently combined, to maximize the efficiency of optical field enhancement at the SiO2 surface. More specifically Ag+ ions of very low energy (3-10 keV) are implanted in a silica layer (240 nm thick) with fluences ranging between 1015-1016 ions/cm2. A stencil containing different sized and shaped apertures (squares, slits, and dashed slits) was prepared by focused ion beam milling of a 200 nm thick Si3N4 membrane. As for example slit gratings have a slit width of 200 nm and periods of 600 and 900 nm. Maps of the optical induced architectures have been recorded using elastic scattering (white-light and dark-field illuminations), Raman scattering, in correlation with structural mapping (SEM, AFM). These results demonstrate that, although the surface remains structurally flat and chemically uniform, the opto-electronic response reflects the multiscale 3D patterning.Envisioned applications include surface-enhanced spectroscopies (Raman, luminescence), non-linear materials, photovoltaics, waveguiding, optical sensing.[1] W. A. Murray, W. L. Barnes, Adv. Mater., 19 (2007) 3771.[2] R. Carles, C. Farcau, C. Bonafos, G. Benassayag, B. Pecassou, A. Zwick, Nanotechnology, 20 (2009) 355305.[3] R. Carles, C. Farcau, J. Campos, C. Bonafos, G. Benassayag, A. Zwick, Mater. Res. Soc. Symp. Proc. 1182 (2009) 1182-EE09-21.
12:30 PM - D9.10
Optical Probing of Conductance Mechanism in Au Nanoparticle Assemblies With Surface Plasmons.
Jae Young Ahn 2 , Hasan Kesserwan 1 , Michele Albrecht 1 , Eun Ju Her 2 , Seung Ho Moon 3 , Jung-tak Jang 3 , Jinwoo Cheon 3 , Tae Hee Kim 2 , Jean-Yves Bigot 1
2 Department of Physics, Ewha Womans University, Seoul Korea (the Republic of), 1 Institut de Physique et Chimie des Matériaux de Strasbourg, CNRS, University of Strasbourg, Strasbourg France, 3 Department of Chemistry, Yonsei University, Seoul Korea (the Republic of)
Show AbstractControlling the transport properties of charges in nanocomposites is important for many applications in new emerging nonvolatile memory devices, such as conductive bridge random-access memory (RAM), resistive-RAM, memristor-based memory as well. From a fundamental point of view it is therefore desirable to investigate the mechanisms that may hinder or enhance the electron transport. Here, we report about an innovative approach towards that goal performed on assemblies of Au nanoparticles having different conductance properties. It is based on a simultaneous optical probing of the surface plasmon (SP) resonance under variable applied currents. We show that the (SP) resonance is an efficient reporter of the conductance properties as it is sensitive to both the charges and dielectric environment surrounding the nanoparticles. In addition, it allows for a local probing of the conductance variations as the laser beam can be tightly focused between the electrodes. The experiments have been made on compact assemblies of Au nanoparticles with 6 nm in size diameter with their ligands totally (sample S1) or partially (Sample S2) removed from their initial colloidal suspensions. The four-probe d.c. conductivity measurements show that S1 has a quasi-ohmic behavior with a fixed resistance of 1 mΩ. In contrast, S2 displays a variable resistance between typically 20 kΩ and 100 Ω when increasing the current from 100 nA up to a few mA. The (SP) are studied by measuring the spectrum of the light scattered resonance (typically near the wavelength 530 nm). The incident light comes from a laser continuum generated in a sapphire crystal by self-phase modulation of femtosecond pulses. They are focused to a ~100 μm spot between the electrodes. This set-up also allows for a time dependent study of the (SP) dynamics in the nanoparticles. The variation of the current in sample S2 leads to a complex variation of the resistance which switches between meta-stable states as observed in the V-I characteristics. Simultaneously, the surface plasmon resonance reduces or increases depending on the current switching. The detailed spectral behavior of the (SP) resonances will be reported for the two samples and as a function of the current behavior. The corresponding switching will be discussed in the context of charges dynamics and structural changes of the ligands.
12:45 PM - D9.11
Nanocrystal-Molecule Nanostructures: Quantifying Formation Yield of Plasmonic Dimers.
Claire Barrett 1 , Gaetan Leveque 2 , Nicolas Sassiat 1 , Aidan Quinn 1
1 Nanotechnology Group, Tyndall National Institute, University College Cork, Cork Ireland, 2 Photonic Sources Group, Tyndall National Institute, University College Cork, Cork Ireland
Show AbstractRecent developments in the design and synthesis of plasmonic building blocks as active elements for biosensing and photoconductive devices have the potential to revolutionize emerging technology markets across multiple sectors including healthcare, security and energy conversion. Size-similar, chemically-synthesised gold nanocrystals ( 20 – 50 nm core diameter) represent attractive candidates, in particular, due to the prospects for formation of plasmonic nanocrystal-molecule(s)-nanocrystal dimers via controlled mixing of nanocrystals with linker molecules [1]. We report on development of processes for controlled formation of nanocrystal-molecule nanostructures in solution and on real-time monitoring of the evolution of the optical response via UV-visible absorption spectroscopy, correlated (off-line) with scanning electron microscopy analysis of the nanostructure distribution. These solution-based processes offer the potential for formation of plasmonic dimers and manipulation of their optical properties during assembly through selection of the appropriate nanocrystal diameter, and also edge-edge separation, which is governed by the geometry of the linker molecule. Using the Generalized Multiparticle Mie Method to simulate the extinction spectrum of a nanocrystal dimer, we demonstrate that the evolution of the measured absorption data for a nanocrystal solution following linker addition can be quantitatively analysed to extract the relative proportions of linked nanocrystal-nanocrystal dimers, as well as isolated nanocrystal “monomers”, at each time step. This analysis also provides additional insight into the kinetics of dimer formation and complements modelling efforts based on random-walk and rate-equation approaches.Finally, we discuss the potential of this technique for development of simple, solution-based plasmonic biosensors with nanomolar detection limits. [1] Barrett, C.; Doyle, H.; Lévêque. G; Redmond, G.; Lydon, D. P.; Spalding, T.R. & Quinn, A.J. Mat. Res. Soc. Symp. Proc. 1154, B06-07 (2009).
D10: Bioplasmonics and SERS
Session Chairs
Thursday PM, April 08, 2010
Room 2008 (Moscone West)
2:30 PM - **D10.1
Plasmons in Strongly Coupled Metallic Nanostructures.
Peter Nordlander 1
1 Physics, Rice University, Houston, Texas, United States
Show AbstractInterference and coherence effects such as subradiance, superradiance, EIT and Fano resonances (FR) have been the subject of extensive research in atomic and molecular physics. Recently it has been realized that plasmonic nanostructures offer a highly tunable platform for the systematic studies of such effects. In this talk, I will show how plasmonic coherence effects provide a powerful mechanism for increasing the electric field enhancements generated by plasmons of relevance for surface enhanced spectroscopies such as SERS and SEIRA and LSPR sensing. Examples of systems that will be discussed are: a quantum description of the plasmons in closely coupled nanoparticle dimers, FR in heterodimers and small nanoparticle clusters of D6h symmetry (Septamers), FR in nonconcentric nanoshells and nanomatryushkas, FR in planar ring-disk systems and FR in the nanoparticle near substrate systems.
3:00 PM - D10.2
Surface Enhanced Vibrational Spectroscopy of Proteins With Plasmonic Nanoantenna Arrays.
Ronen Adato 1 2 , Ahmet Yanik 1 2 , Jason Amsden 3 , David Kaplan 3 , Fiorenzo Omenetto 4 , Mi Hong 5 , Shyamsunder Erramilli 6 , Hatice Altug 1 2
1 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States, 2 Photonics Center, Boston University, Boston, Massachusetts, United States, 3 Biomedical Engineering, Tufts University, Medford, Massachusetts, United States, 4 Biomedical Engineering & Physics, Tufts University, Medford, Massachusetts, United States, 5 Physics, Boston University, Boston, Massachusetts, United States, 6 Physics & Biomedical Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractInfrared absorption spectroscopy is a powerful tool for functional studies of bio-molecules. The method enables direct access to vibrational fingerprints of the molecular structure whose energies correspond to wavelengths in the mid-infrared spectral region (3-20 μm). Although intrinsic absorption cross-sections are nearly 10 orders of magnitude larger than corresponding Raman cross-sections, they are still small in comparison with those of fluorescent labels. Sensitivity improvements are therefore required for the method to be applicable to single molecule / molecular layer studies. One promising approach is to leverage the strongly enhanced near-field that accompanies the plasmonic excitations of nanoscale metal particles. The method has been employed extensively in Raman scattering (SERS) [1] and in analogy, the application to infrared absorption - surface enhanced infrared absorption (SEIRA) spectroscopy - has also been demonstrated [2].The bulk of previous SEIRA experiments, however, have obtained enhancements via chemically prepared or roughened metal surfaces. The stochastic nature of these substrates limits enhancement due to the poor spectral overlap of the plasmonic resonances with the vibrational modes of interest [2,3]. The result is weaker absorption signals and a lack of reproducibility in measurements. In contrast, engineered plasmonic antennas support well defined resonances with strong local fields. These resonances can be readily tuned throughout the mid-infrared in order to maximize field enhancement at the frequency corresponding to a given vibrational mode [4,5]. In a recent work, we demonstrate the use of lithographically patterned arrays of nanoantennas to enhance the absorption signature of the protein Amide-I and II backbone vibrations [5]. Strong absorption minima are observed in the reflectance spectra of antenna substrates coated with a 2 nm thick layer of the protein silk fibroin [6]. Significantly, by examining both periodic and disordered antenna arrays, we show that the higher quality factor resonances achievable with periodic arrangements can be used to obtain significant enhancements in absorption signals. By tuning array periodicity, we show that signals can be enhanced 104 – 105 leading to the direct measurement of vibrational spectra of proteins at zepto-mole sensitivity levels [5]. In this talk we will present these results. [1] K. Kniepp et al. Phys. Rev. Lett., 78, 1667 (1997).[2] K Ataka & J Heberle, Anal. Bioanal. Chem., 308, 47 (2007).[3] M Osawa & M Ikeda, J. Phys. Chem., 95, 9914 (1991).[4] F Neubrach et al., Phys. Rev. Lett., 101, 157403 (2008).[5] R Adato et al., Proc. Nat. Acad. Sci. USA, early edition (week of 26 October, 2009).[6] B D Lawrence et al., J. Mater. Sci., 43, 6967 (2008).
3:15 PM - D10.3
Focusing Plasmons in Nanoslits for Highly Localized Surface Enhanced Raman Scattering.
Pol Van Dorpe 1 , Chang Chen 1 2 , James Hutchison 2 , Hiroshi Uji-i 2 , Johan Hofkens 2 , Liesbet Lagae 1 3 , Gustaaf Borghs 1 3
1 BIONE/FNS, Imec , Leuven Belgium, 2 Department of Chemistry, K.U.Leuven, Leuven Belgium, 3 Physics Department, K.U.Leuven, Leuven Belgium
Show AbstractWe propose and demonstrate a novel nanoslit based plasmonic cavity on a freestanding membrane as a metal substrate for (bio)chemical analysis via surface enhanced Raman scattering (SERS)[1]. Moreover, we applied a novel technique to demonstrate the high spatial localization of SERS in this device[2]. The design of this device is inspired by two areas of enormous current interest, the control, manipulation and confinement of light via the excitation of surface plasmon polaritons (SPPs) on metal nanostructures for SERS sensing applications, and the DNA sequencing methods based on nanopore ionic fluidics. We applied numerical simulations and optical spectroscopy to demonstrate the function of the nanoslit cavity in collecting and focusing SPPs to the nanoslit. SPP coupling across the nanoslit (6~7nm width) ensures a high SERS enhancement factor (>106) for molecules chemisorbed in the nanoslit region. FDTD simulations also indicate an extremely localized volume for SERS enhancement in the nanoslit region. To examine this, we have developed a simple, universal and direct method to experimentally map the local field distribution of a SERS active nanostructure and to demonstrate indeed the high spatial localization of the SERS hot spot by using a well controlled nanoscale deposition technology. By using a modified electron beam induced deposition technique (EBID), we were able to locally deposit carbanaceous nanoparticles at dedicated positions near the hot spot of the plasmonic cavity and we were able to confirm the high spatial confinement of the SERS signal. Moreover, we also developed a kinetic model of near-field photon degradation of analytes in SERS hot spots by studying the laser exposure time effect. It not only further proves the localization of SERS, but also describes a new method for mapping the spatial distribution of field enhancement by using the slope of the photo-degradation curves. As this is independent on the absolute SERS intensity, it is less prone to inaccuracies induced by e.g. inhomogeneities of the target molecule distribution.[1] C. Chen et al “Focusing Plasmons in Nanoslits for Surface Enhanced Raman Scattering” Published online in Small-DOI:10.1002/smll.200901312[2] C. Chen et al, Direct Evidence of High Spatial Localization of Hot Spots in Surface Enhanced Raman Scattering, Accepted for publication in Angewandte Chemie
4:00 PM - **D10.4
Sensing Biomolecular Interactions by Localized Surface Plasmon Resonance.
Kathryn Mayer 1 , Seunhyung Lee 2 , Feng Hao 1 , Peter Nordlander 1 , Jason Hafner 1 2
1 Physics & Astronomy, Rice University, Houston, Texas, United States, 2 Chemistry, Rice University, Houston, Texas, United States
Show AbstractNoble metal nanoparticles exhibit sharp spectral extinction peaks at visible and near-infrared frequencies due to the resonant excitation of their free electrons, termed localized surface plasmon resonance (LSPR). Since the resonant frequency is dependent on the refractive index of the nanoparticle surroundings, LSPR can be the basis for sensing molecular interactions near the nanoparticle surface. Gold nanorods and bipyramids were synthesized and bound to glass substrates, yielding uniform films with plasmon resonant extinction. Antibodies were conjugated to the nanoparticles to create a label-free immunoassay based on LSPR shifts from simple extinction measurements. Antibody binding kinetics were measured and the sensitivity was compared for nanorods and bipyramids, as well as different molecular spacings between the nanoparticle and capture antibodies. The extreme localization of the sensing volume by sharp nanoparticle tips may also enable label-free single molecule detection. The LSPR immunoassay was also carried out on single gold bipyramids by dark field microspectroscopy to detect single molecule undbinding events. LSPR sensing could thus be a powerful addition to the current toolbox of single molecule detection methods since it probes interactions on long time-scales and under relatively natural conditions.
4:30 PM - **D10.5
Plasmon Rulers for Measuring Dynamical Distance Changes in Biological Macromolecular Assemblies.
Paul Alivisatos 1 2
1 , Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Chemistry, University of California at Berkeley, Berkeley, California, United States
Show AbstractThe intensity and spectral signature of light scattering from Au nanocrystals depends strongly upon their separation. This phenomenon can be used to construct a spectroscopic ruler for monitoring the assembly and deformations of macromolecular complexes. The ruler consists of two particles joined by an oligonucelotide or peptide. The oligo or peptide motion changes the distance between the particles resulting in a change in the light scattering. These plasmon rulers can be used to study the mechanisms of DNA cleavage by restriction enzymes. A second application involves the study of protease activity and caspase 3 activation in apoptosis. New nanocrystal molecules consisting of pyramidal and chiral arrangements of metallic and semiconductor nanocrystals will also be described.
5:00 PM - D10.6
Plasmonic Droplet to Detect Low Concentrations of Bacteria Using Surface Enhanced Raman Spectroscopy (SERS).
Young Geun Park 1 2 3 , Yeonho Choi 4 , Debkishore Mitra 1 2 , Kalpit Shah 1 , Taewook Kang 3 , Luke Lee 1 2
1 Bio Engineering, UC Berkeley, Berkeley, California, United States, 2 Biomolecular Nanotechnology Center, UC Berkeley, Berkeley, California, United States, 3 Chemical and Biomolecular Engineering, Sogang University, Seoul Korea (the Republic of), 4 Department of Biomedical Engineering, College of Health Science, Korea University, Seoul Korea (the Republic of)
Show AbstractWe report a novel nanoplasmonic, droplet-based structure to instantaneously detect low concentrations of bacteria using surface enhanced raman spectroscopy (SERS). The pico-liter volume droplets containing single bacteria are formed using a microfluidic device. Plasmonic properties at the droplets’ surface interface are achieved by selective and uniform attachment of gold nanoplasmonic particles to the droplets’ surface. The droplets are then shrunk to form contact between the encapsulated bacteria and the plasmonic probes at the droplets’ surface. This resulting large contact surface area between the bacteria and the probes enables high SERS enhancement. Using this pico-liter plasmonic droplet, we can instantaneously detect and differentiate various encapsulated bacterial strains without further incubation time. This technology will open new doors for fast diagnostics and point of care.
5:15 PM - D10.7
Nano-scale Plasmonic Motors Driven by Light.
Ming Liu 1 , Thomas Zentgraf 2 , Yongmin Liu 2 , Guy Bartal 2 , Xiang Zhang 2
1 AS&T, UC Berkeley, Berkeley, California, United States, 2 NSF Nanoscale Science and Engineering Center, UC Berkeley, Berkeley, California, United States
Show AbstractThe ability to provide rotational locomotive force within nanoscale is critical for various nanosystems, ranging from DNA unfolding and sequencing, to active Micro-Electro-Mechanical Systems (NEMS). However, conventional rotating techniques, including optical tweezers, magnetic tweezers and electrokinetic forces, put constrains on material choices, and require the objects to be a few microns to gain sufficient torques. Here, we demonstrate a significantly large rotation force, generated by a nano-scale plasmonic structure which is illuminated with a simple linearly- or nonpolarized light. We show that a plasmonic particle with size of 1/10 of the excitation wavelength is capable of driving the rotation of a silica microdisk, 4,000 times larger in volume. By merely varying the wavelength of the incident light, we can control the rotation velocity and direction. The tiny dimensions along with the tremendous torque, on the order of 10 pN*nm, may have applications in untwisting DNA and single molecules even in vivo.
5:30 PM - D10.8
Role of Charge-transfer in the SERS of a Single Non-resonant Molecule.
Zee Hwan Kim 1
1 Department of Chemistry, Korea University, Seoul Korea (the Republic of)
Show AbstractWe measured the surface-enhanced Raman scattering (SERS) from individual gold nanoparticle –aminobenzenethiol (ABT) monolayer – gold film junctions to investigate the role of charge-transfer (CT) in the single-molecule SERS (SM-SERS). Despite mild electromagnetic field enhancement (104-105) and high surface density of ABT-molecules (~200 molecules / hotspot) at the junctions, we observe clear spectral and temporal signatures of CT- assisted SM-SERS. The results implicate that only a few molecules at the junction site have significant CT-enhancement of ~100, whereas the rest of the molecules are only weakly CT-active. Furthermore, the results also indicate that overall (chemical and electromagnetic) enhancement of ~107 is already sufficient to observe the SERS of a single non-resonant molecule, which starkly contradicts wide-spread belief on the SERS of single molecules in general.
5:45 PM - D10.9
Nanoporous Substrate With Mixed Nanoclusters for Surface-enhanced Raman Scattering.
Sehoon Chang 1 2 , Srikanth Singamaneni 2 , Hyunhyub Ko 2 , Vladimir Tsukruk 2 1
1 School of Polymer, Textile, and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractRapid detection of plastic and liquid explosives is an urgent need due to various societal and technological reasons. We employed a novel design of surface enhanced Raman scattering (SERS)-active substrate based on porous alumina membranes decorated with metal nanoparticles. In this study, we demonstrated a trace level detection of several important hazardous chemicals such as dinitrotolene (DNT), trinitrotoluene (TNT), and hexamethylenetriperoxidediamine (HMTD) by fast, sensitive, and reliable Raman spectroscopic method. By applying these SERS substrates, we achieved near molecular-level detection (about 15 - 30 molecules) of DNT and TNT from wet phase. Former trace level detection scheme is challenging due to the lack of common optical signatures (fluorescence, absorption in UV-vis range) or chemical functionality of peroxide-based liquid explosives such as HMTD. To overcome this challenge, we employed photochemical decomposition approach and analyzed chemical fragments using SERS substrates. We suggest that tailored polymer coating, mixed nanoclusters with coupled plasmon resonances, and laser-induced photocatalytic decomposition are all critical for achieving this unprecedented sensitivity level.
D11: Poster Session II
Session Chairs
Friday AM, April 09, 2010
Salon Level (Marriott)
9:00 PM - D11.1
Etching and Growth: An Intertwined Pathway to Ag Nanocrystals with Exotic Shapes.
Claire Cobley 1 , Matthew Rycenga 1 , Fei Zhou 2 , Zhi-Yuan Li 2 , Younan Xia 1
1 Biomedical Engineering, Washington University in St Louis, St Louis, Missouri, United States, 2 , Institute of Physics, Chinese Academy of Sciences, Beijing 100080 China
Show AbstractWhen a second aliquot of AgNO3 was added to a polyol synthesis, Ag nanocubes evolved into anisotropically-truncated octahedrons due to oxidative etching and overgrowth. Three adjacent faces of the nanocube grew more rapidly than the other three faces, generating a non-centrosymmetric structure that is half truncated cube, half octahedron. Both oxidative etching and rapid addition of AgNO3 solution played a critical role in the mechanism. The localized surface plasmon spectra of these unusual nanostructures displayed a new peak when compared to the seed cubes. These structures were also investigated as surface-enhanced Raman substrates. Interestingly, despite the sharp corners, the overall enhancement factor was slightly lower than what would be predicted based on studies of Ag nanocubes with a similar size. This is likely due to the fact that though the nanocrystal has sharp corners, all of them are opposite a flat face instead of another corner, leading to a weaker dipole polarization.
9:00 PM - D11.10
Plasmonic Nanogalaxies: Multiscale Aperiodic Arrays for Surface-enhanced Raman Sensing.
Ashwin Gopinath 1 , Svetlana Boriskina 1 , Ranjith Premasiri 2 , Bjoern Reinhard 2 , Lawrence Ziegler 2 , Luca Dal Negro 1
1 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States, 2 Department of Chemistry, Boston University, Boston, Massachusetts, United States
Show AbstractThe accurate and reproducible control of intense electromagnetic fields localized on the nanoscale is essential for the engineering of optical sensors based on the surface-enhanced Raman scattering (SERS) effect. In this work, using rigorous generalized Mie theory (GMT) calculations and a combined top-down/bottom-up nanofabrication approach, we design and experimentally demonstrate 108 spatially averaged, reproducible SERS enhancement in deterministic aperiodic Au nanostructures with varied length scales. Deterministic aperiodic arrays of 200 nm diameter nanocylinders are first fabricated using electron-beam lithography on quartz substrates, and smaller size (30 nm diameter) Au nanoparticles are subsequently positioned by in situ Au reduction at regions of maximum field enhancement. These multiscale structures, which we call “plasmonic nanogalaxies”, feature a cascade enhancement effect due to the strong electromagnetic interactions of small satellite nanoparticles with localized fields in aperiodic arrays of nanocylinders. The development of SERS substrates based on aperiodic arrays with different length scales provides a novel strategy to engineer plasmon-enhanced biosensors with chemical fingerprinting capability. In particular, we have also included perspectives on applying these novel nano-galaxies for reliable detection of bacteria (E-coli and Staphylococcus) as well as identification of different nucleotides.
9:00 PM - D11.11
Nanoscale Photopolymerization Using Optical Near-field at the Vicinity of Silver Nanoparticles.
Claire Deeb 2 , Libai Huang 3 , Jerome Plain 2 , Alexandre Bouhelier 4 , Lavinia Balan 1 , Carole Ecoffet 1 , Renaud Bachelot 2 , Pascal Royer 2 , Olivier Soppera 1
2 Laboratoire de Nanotechnologie et d’Instrumentation Optique LNIO-ICD FRE CNRS 2848, CNRS - UTT, Troyes France, 3 Radiation laboratory, University of Notre Dame, Notre Dame, Indiana, United States, 4 Département Nanosciences, Institut Carnot de Bourgogne CNRS-UMR 5209, CNRS - Université de Bourgogne, Dijon France, 1 Institut de Sciences des Matériaux de Mulhouse CNRS LRC 7228, CNRS - IS2M, Mulhouse France
Show AbstractWe propose in this paper a novel approach to characterize local electromagnetic field of metallic nanostructures by photo-polymerization. This entails the use of silver colloidal nanoparticles (CNP) as nanoantennas to trigger the photopolymerization. Silver nanoparticles were attached to glass slides that werefunctionalized with an amine-terminated self-assembled monolayer. A photosensitive formulation consisting of dye molecules, amine molecules and monomers was utilized tocharacterize the optical near field. Threshold condition under which photo-polymerization occurs was determined for the photosensitive formulation. Irradiation intensities below the threshold were used when CNPs were present, so that the photo-polymerization could only occur in close proximity to the metallic nanoparticles (MNP) due to enhanced optical near-field near MNPs. AFM was employed to image of MNP before and after irradiation.Photopolymer lobes were found to form only on the ends of CNPs and along the polarization of irradiation laser. Our data also demonstrated that the size of the photopolymer lobes corresponded directly to electric field strength. Particular attention was paid to the influence of photonic and physico-chemical parameters on the spatial extend of the polymerization. Using the photosensitive formulation is a way to access locally to the spatial distribution of the optical near field created by localized surface plasmons of metallic nanoparticles. Moreover, the hybrid nanoparticles formed by the metal core surrounded by an anisotropic polymer shell possess original optical properties.Such approach is a demonstration of sub-wavelength photopolymerization using optical near-field and it constitutes a powerful tool to study photochemistry at the nanoscale.
9:00 PM - D11.13
Plasmonic Photocurrent Enhancement in Silicon-on-Insulator Devices Due to Colloidal Silver Nanoparticles.
Birol Ozturk 1 , Eric Schiff 1 , Anthony Terrinoni 1 , Hui Zhao 1 , Fehmi Damkaci 2 , Baojie Yan 3 , Jeff Yang 3 , Subhendu Guha 3
1 Physics, Syracuse University, Syracuse, New York, United States, 2 Chemistry, SUNY Oswego, Oswego, New York, United States, 3 , United Solar Ovonic LLC, Troy, Michigan, United States
Show AbstractA layer of silver nanoparticles created by thermal annealing of evaporated silver films (annealed nanoparticles) can increase the photocurrents in silicon-on-insulator devices by up to twenty-fold, possibly by improving the trapping of light in the thin silicon film [1]. Significant enhancements were restricted to wavelengths greater than 800 nm, which are weakly absorbed in the SOI. Here we report a significant enhancement of photocurrents at shorter wavelengths (500-650 nm) by using layers obtained from colloidal silver nanoparticles. We also report our interpretation of the photocurrent enhancement in terms of underlying quantum efficiencies; even with the fairly large photocurrent enhancements that have been reported, quantum efficiencies remain well below the stochastic light-trapping limit.Stabilizer-free colloidal silver nanoparticles were chemically synthesized and immobilized on the silicon-on-insulator (SOI) device surfaces in an evenly distributed fashion by an established polymer encapsulation method [2]. Photocurrent measurements on these devices showed up to two times enhancement in the 500-650 nm spectral range with the addition of silver nanoparticles. Smaller enhancements were observed in the longer wavelengths in contrast to previous measurements with annealed silver films [1]. Moreover, we discovered that colloidal and annealed silver nanoparticle addition results in frequency shifts in the photocurrent spectra. We have also prepared similar polymer-encapsulated silver nanoparticle layers on nanocrystalline silicon solar cells with conducting oxide layers on top. There is no substantial quantum efficiency enhancement on these cells; experiments with thinner conducting oxide layers are in progress.This research has been partially supported by the U. S. Department of Energy through the Solar America Initiative (DE-FC36-07 GO 17053). Additional support was received from the Empire State Development Corporation through the Syracuse Center of Excellence in Environmental and Energy Systems.[1] S. Pillai, K. R. Catchpole, T. Trupke, M. A. Green; Surface plasmon enhanced silicon solar cells, J. of Appl. Phys., Vol. 101, No. 9. (2007), 093105[2] D. D. Evanoff, Jr., G. Chumanov; Size-Controlled Synthesis of Nanoparticles: I. ‘Silver-Only’ Aqueous Suspensions via Hydrogen Reduction, J. Phys. Chem. B, 2004, 108(37), 13948.
9:00 PM - D11.14
Enhanced Absorption in Silicon Films Using Silver Nanoparticles.
Jeffrey Clarkson 1 , Philippe Fauchet 2
1 Materials Science, University of Rochester, Rochester, New York, United States, 2 Electrical and Computer Engineering, University of Rochester, Rochester, New York, United States
Show AbstractRecently, metallic nanoparticles on top of photovoltaic cells have been used to increase photon capture and localize incident light into absorbing layers [1-4]. This has been proposed as an alternative to current surface texturing techniques in part because it is compatible with thin-film photovoltaic cells. Additionally, the response of the photovoltaic cell can be adjusted throughout the solar spectrum by tuning the particle morphology and composition, and local environment. To this end, we report controlling the plasmon response of random nanoparticle arrays by tuning their morphology and local environment.Ag nanoparticles were formed by annealing discontinuous films deposited via electron beam evaporation. The particle shape is most closely represented by an oblique spheroid with an average effective diameter ranging from 70 to 270 nm. The morphological properties of the nanoparticles have been adjusted by depositing a mass thickness of Ag ranging from 12 to 22 nm and then annealing from 190 - 300 C in nitrogen. A higher annealing temperature produced smoother nanoparticles exhibiting a sharper plasmon resonance. The plasmon response of the nanoparticle arrays can be further adjusted by depositing them on various underlying substrate materials including Si, SiO2, and Si3N4. By adjusting the nanoparticle morphology, we demonstrated enhanced absorption in c-Si substrates at ~ 500 nm and near the Si bandgap at ~1100 nm. The plasmon response of the nanoparticle assemblies was also investigated with respect to its local environment. To do this, identical nanoparticle assemblies were formed on c-Si substrates with different thicknesses of SiO2. This resulted in a series of samples where the nanoparticles were a known distance away from c-Si. Spectrometer measurements were used to map the optical response of the nanoparticle assemblies as their distance from the c-Si was increased. We found that a specific spacing between the nanoparticle assembly and c-Si is necessary to optimize the tradeoff of maintaining a large cross-sectional scattering area and coupling optical modes into the c-Si. If the nanoparticles are too close to the c-Si, we observe a reduction in scattering cross-section resulting from destructive interference between the incident and reflected driving fields [5]. If however the nanoparticles are too far away from the c-Si, a significant number of optical modes from the scattered light are not coupled into c-Si. These results, which are applicable to other metallic nanoparticle systems, provide a roadmap on design criteria that will lead to optimized plasmon-assisted photovoltaic cells.[1] H. R. Stuart et al, Appl. Phys. Lett. 73, 3815 (1998)[2] D. Derkacs, et al, Appl. Phys. Lett. 89, 093103 (2006)[3] S. Pillai et al, J. Appl. Phys. 101, 093105 (2007)[4] K. Nakayama et al, Appl. Phys. Lett. 93, 121904 (2008)[5] K. R. Catchpole et al, Appl. Phys. Lett. 93, 191113 (2008)
9:00 PM - D11.15
Proto-assembly of Gold Nanorods With Tunable Plasmon Coupling.
Dhriti Nepal 1 , Kyoungweon Park 1 , Christopher Tabor 1 , Jian Gao 2 , Jinsong Duan 1 , Qiwen Zhan 2 , Robert Nelson 1 , Ruth Pachter 1 , Michael Durstock 1 , Richard Vaia 1
1 , Wright Patterson Air Force Base, Wright Patterson , Ohio, United States, 2 Electro-Optics Graduate Program, University of Dayton, Dayton, Ohio, United States
Show AbstractThe coupling of optical excitation to the plasmon resonances of well-defined proto-assemblies of noble-metal nanoparticles, such as parallel rods, U- or Y- configurations, provide exciting opportunities to tailor local field intensities or generate an artificial permeability. In numerous applications, large-area, three-dimensional organization of these proto-assemblies is desired. As an alternative to top-down lithographic techniques and their inherent challenges limiting these goals, bottom-up approaches to fabricate the proto-assemblies provide a possible alternative commensurate with large-scale manufacturing. In this context, the different side and end chemistry of gold nanorods was utilized to control the orientation dependence of the particle-pair potential. This enabled assembly of rods into side-to-side, end-to-end, and pi-shape structures. The shape and number of rods within the proto-assembly was controlled by the compositional difference in end and side functionalization as well as the assembly (reaction) time, concentration of nanorods and solvent medium. The plasmon resonance of these assemblies was characterized by extinction spectroscopy and dark field scattering. The intensity and energy of the plasmon resonances depended on rod spacing and local arrangement, and were consistent with the plasmon hybridization model and electrodynamic calculations. Spectroscopic ellipsometry demonstrated tunability of the refractive index in the visible and near-infrared, demonstrating that these proto assemblies hold promise as optical metamaterials.
9:00 PM - D11.16
Synthesis, Single Particle Optical Characterization and Simulation of Plasmonic Janus Particles.
Robin Klupp Taylor 1 4 , Huixin Bao 1 , Wolfgang Peukert 1 4 , Oleksandr Zhuromskyy 2 4 , Frantisek Seifrt 3 4 , Guenter Leugering 3 4
1 Institute of Particle Technology, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen Germany, 4 Cluster of Excellence "Engineering of Advanced Materials", Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen Germany, 2 Institute of Optics, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen Germany, 3 Insititute of Applied Mathematics, Friedrich-Alexander-University of Erlangen-Nuremberg, Erlangen Germany
Show AbstractIn recent years, the investigation of plasmonic nanoparticles has taken a further step in complexity to include partial metal coatings on dielectric core particles. It has been shown theoretically and experimentally by various groups that such plasmonic Janus particles possess multiple resonances which are highly tunable by the coatings’ coverage and depend strongly on the orientation of the structure with respect to the incoming light. Such properties make the structures promising candidates for e.g. Raman sensing and communications applications. In this paper we will describe the synthesis of silver on silica sphere Janus particles using a modified colloid coating technique in which the thickness and coverage of the coatings can be controlled. The structures were analysed by UV-VIS-NIR spectrophotometry, transmission and scanning electron microscopy. The latter technique allowed the coordinates of particles with certain coating morphologies to be determined. The same particles were subsequently located in an optical system whereby a highly focussed beam was scanned over the region containing the particle of interest. Maps of back- and forward-scattered light were obtained and compared to the experimental results and were validated with t-matrix and finite element simulations. By tuning the wavelength of excitation and beam polarization profile we demonstrated the excitation of different electric and magnetic modes of the structures, further emphasizing the interest of such particles for optoelectronic and metamaterial applications.
9:00 PM - D11.18
Nonlinear Optical Switching Behavior of Au Nanocubes and Nanooctahedra Investigated by Femtosecond Laser Spectroscopy.
Yih Hong Lee 1 , Yongli Yan 1 , Lakshminarayana Polavarapu 1 , Qing-Hua Xu 1
1 Department of Chemistry, National University of Singapore, Singapore Singapore
Show AbstractTwo types of gold nanoparticles, nanocubes and nanooctahedra, were prepared and their nonlinear absorption properties were investigated by using femtosecond open aperture z-scan experiments. Various femtosecond laser spectroscopy techniques, including femtosecond z-scan, transient absorption and two-photon induced fluorescence, have been used to characterize these materials. Both nanocubes and nanooctahedra exhibited a shift from saturable absorption (SA) to reverse saturable absorption (RSA) at higher excitation intensities. The SA behaviour was ascribed to ground state plasmon band bleaching and RSA was ascribed to excited state absorption and two-photon absorption of these materials. The competition of different processes is responsible for the observed switching behaviour.
9:00 PM - D11.19
Microwave Absorption of Magnetic Antidot Arrays.
Leszek Malkinski 1 , Minghui Yu 1 , Seong-Gi Min 1
1 Advanced Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractThree antidot arrays with FeNi thickness of 20, 50 and 100 nm have been patterned using magnetron sputtering followed by the electron-beam lithography and lift-off technique. SQUID magnetometer Quantum Design) and ferromagnetic resonance technique (Bruker EPR) were used to study static and dynamic properties of the antidot arrays. These results were compared with the measurements of continuous films of Py with the same thickness. Two distinct resonant fields have been observed for the bias field aligned with the edges of the square holes. Resonance peaks shifted towards each other and eventually merged when the in-plane bias field was rotated towards diagonal of the squares. This dependence has been explained in terms of magnetostatic energy associated with the square holes. The magnitude of this effect was decreasing for the arrays with the reduced thickness. The perpendicular and lateral quantized standing spin wave modes were detected in the reference films and the antidot arrays due to the perpendicular and lateral dimensional confinements.
9:00 PM - D11.2
Plasmon Resonance in Diamond-like Carbon Films with Silver Nanoparticles.
Oleg Prikhodko 1 , Alexander Ryaguzov 1 , Suyumbika Maximova 1 , Yevgeniya Daineko 1 , Fawzy Mahmoud 2
1 Physical, Al-Faraby Kazakh National University, IETP, Almaty Kazakhstan, 2 Solid State physics , National research centre, Cairo Egypt
Show AbstractIt is known that incorporation in matrix of diamond-like carbon amorphous films (a-C:H) of high concentration metals, which do not form chemical compound with carbon, leads to formation of their nanoparticles. The investigation of that complex heterophase system is important for practical use. Such metals as, for example, aluminum, copper, silver and gold do not interact with carbon. The influence of silver impurity on structure and properties of a-C:H films does not investigated actually.In this report the results of structure and optical properties of silver nanoparticles embedded amorphous diamond-like carbon (a-C:H(Ag)) films investigation are presented and discussed.The films were prepared by method of magnetron sputtering of combined target, which consisted of polycrystalline graphite and silver. Argon-hydrogen gas mixture was used as a working gas. The substrate temperature was kept at 200°C. Silver concentration in a-C:H(Ag) films was changed by alteration of Ag area to that of graphite in total target. Silver content in the films was varied from 0 to 20 at. % and was determined by electron probe microanalyser Jeol Superprobe 733 with energydispersive Spectrometer JNCA ENERGY.By transition electron microscopy method (Philips-sm12 TEM) the spherical shape inclusions in a-C:H(Ag) films were revealed. The diameter of the inclusions increased, when Ag content rose in the films. In optical absorption spectra of the films one can see the absorption peaks at 420 nm, which are due to surface plasmon resonance on silver inclusions. The peaks intensity was larger in the films with greater Ag content. On the basis of the inclusions and resonance absorption peaks absence in pure a-C:H films it was concluded that C:H(Ag) films contained Ag clusters. The nanoparticles size was determined from micrographs and spectra of resonance optical absorption. It was changed from 2 to 8 nm when Ag content increased from 3 to 20 at. %.It was established that a-C:H(Ag) films optical gap Eg, which was determined from the transmission spectra, decreased quickly from 2.0 to 0.3 eV when Ag content increased from 0 to 3 at. %. Further optical gap changes were insignificant, and Eg was equal to 0.11 eV at 20 at. % Ag. The observed a-C:H(Ag) films optical gap changes were accompanied by significant increase of the films conductivity and by alternation of conductivity temperature dependence from semiconductor to metal-like behavior. The conductivity data analysis using percolation theory has been showed that percolation threshold occurred at Ag percentage in films xc = 5 at. %.Thus, in a-C:H(Ag) films prepared by ion-plasma sputtering of combined graphite-silver target the isolated spherical shape Ag nanoparticles were revealed. The nanoparticles size increased as Ag content in the films rose. It was accompanied by increase of surface plasmon resonance absorption, significant change of a-C:H(Ag) film optical and electrical parameters.
9:00 PM - D11.20
Effect of the Interface in Plasmon Enhanced Second Harmonic Generation from Nonlinear Optical Thin Films.
Hans Robinson 1 , Kai Chen 1 , Cemil Durak 1 , Akhilesh Garg 2 , Richey Davis 2 , James Heflin 1
1 Physics, Virginia Tech, Blacksburg, Virginia, United States, 2 Chemical Engineering, Virginia Tech, Blacksburg, Virginia, United States
Show AbstractThe second order nonlinear optical (NLO) properties of two different ionic self-assembled multilayer (ISAM) films combined with Ag nanoparticles have been investigated. The plasmon resonances in the Ag particles concentrate the incident light, markedly increasing in the NLO efficiencies of the films. We find that the efficiency enhancement is significantly larger in conventional ISAM films compared to films made using a hybrid covalent ISAM technique (HCISAM), even though the intrinsic bulk second order non-linear susceptibility (χ^(2)) is much larger for HCISAM films. We attribute this to the interfaces in HCISAM films being much easier to disrupt by external perturbations such as the metal deposition by which the nanoparticles are fabricated. We conclude that because the plasmon decay length is very short, the plasmonic enhancement of NLO effects primarily occurs at and near the film-particle interface. To discern the importance of the interfaces, we surrounded thin ISAM and HCISAM films with NLO-inactive buffer layers, which confirmed this hypothesis, particularly in the case of HCISAM films.
9:00 PM - D11.21
Plasmonic Couplings in Multi-Layered Nanohole and Nanoparticle Arrays.
Alp Artar 1 , Ahmet Ali Yanik 1 , Hatice Altug 1
1 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States
Show AbstractNanoplasmonics, the optical studies of metallic nanostructures, has emerged as a growing field due to the advances in nano-fabrication techniques and numerical modeling methods. This field found many applications in very diverse topics of optics such as biosensing, solar cells, LEDs etc. Studies built up so far is mainly focused on two-dimensional (2D) arrangements of these nanostructures, however expanding into the third dimension will provide higher degrees of freedom in the design space and will open new opportunities. Possible options of three-dimensional (3D) structures are coupled nanoholes, nanoparticles and also hybrid structures which are formed by alternating nanohole and nanoparticle layers. There are only a few examples of these 3D structures in the literature, such as the recent analysis of multi-layered nanoholes, which proved that these structures can result in metamaterials [1]. Most of the time expanding into the third dimension is avoided because of fabrication related issues and therefore novel approaches are required.We investigated the first-order of the hybrid multi-layered structures in a recent study [2]. These multi-layered structures has a straightforward single-lithography step fabrication scheme, which eliminates the need for focused ion-beam milling and lift-off. Resulting transmission spectra provided the conventional extraordinary optical transmission [3] peaks and also newly found modes. These newly found modes are observed due to the coupling of two physically separated metallic nanohole and nanoparticle layers. In this talk, we will present the effects of these plasmonic and photonic interactions between nanostructure layers both experimentally and theoretically. The newly found mode is explained as the fundamental Fabry-Perot mode of the nanocavity formed by two separated metallic layers. We will introduce a cavity model to explain the experimentally measured transmission spectra of the FP modes. We will also show that the transmission strength of the FP resonances are strongly affected by their spectral overlap with the EOT modes. Numerical analysis of this mode shows that the field pattern overlap in the dielectric is superior to any other mode, therefore making this resonance highly sensitive to refractive index changes. Also we will be presenting new results from another coupled 3D structure, multi-layered nanohole arrays.[1] J. Valentine et al., Nature (London) 455, 376 (2008)[2] A. Artar et al., Appl. Phys. Lett. 95, 051105 (2009)[3] T.W. Ebbesen et al., Nature (London) 391, 667 (1998)
9:00 PM - D11.22
Optical Control of Surface Plasmon Enhanced Transmission Through Metallic Nano-bump Arrays Fabricated by Nanosphere Lithography.
Yi Lou 1 , Leda Lunardi 1 , John Muth 1
1 Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractThe surface plasmon enhanced transmission of light through periodic arrays of sub-micron metallic structures provides a novel approach for building optical and electrical controlled light modulator. In the transmission spectrum, the light passing though these patterned metallic films is very sensitive to the surface environment since the excitation of the surface plasmon polariton modes is a resonance phenomena sensitive to the variations in the dielectric constant of the local environment. In this study, we use nanosphere lithography as a low cost method of fabricating large area, well patterned periodic structures on a 160nm thick gold film. Hexagonally packed colloidal spheres are lay down on the substrate by the directed self-assembly process. The samples undergo reactive ion etching process to reduce the sphere diameter to the desired size, subsequently a layer of metal is deposited to obtain the periodical nano-bump arrays surface structure. Nonlinear optical polymer (P3HT) in chlorobenzene solvent is deposited onto the metal film by spin coating. A 475 nm blue laser is used as control light to excite the polymer, while the transmission spectrum of the normal incident signal light is collected and studied. The result shows that the signal’s transmission rate in red and NIR wavelength is changed in response to the control light. The polymer active layer absorbs the control laser light and creating electron-hole pairs, so that the dielectric constant adjacent to the metal surface changed slightly. Due to the high sensitivity of surface plasmon polariton to the surface dielectric environment, we can achieve optical control of the signal light.
9:00 PM - D11.23
Reversible Fine-tuning of the Longitudinal Plasmon of Gold Nanorods.
Bishnu Khanal 1 , Jefferey Pietryga 1 , Victor Klimov 1 , Eugene Zubarev 2
1 Chemistry, Los Alamos National Laboratory, Los Alamos, New Mexico, United States, 2 Chemistry, Rice University, Houston, Texas, United States
Show AbstractPlasmonic metal nanoparticles are of increasing interest for use in next-generation optoelectronic devices. This is particularly true in solution-processed semiconductor nanocrystal-based devices, in which the strong, localized electric fields associated with plasmon resonance modes can enhance, e.g., the absorption of proximal nanocrystals in a solar cell, or the emission of nanocrystals in a light-emitting diode. Maximum enhancement is achieved when the plasmon mode of the metal nanoparticles is in resonance with the absorbing or emitting transition of the nanocrystals. Plasmon modes of spherical nanoparticles are somewhat tunable by controlling particle size, but the effective energy range achievable for any one metal is fairly limited. Thus, these effects are only relevant for a relatively small number of semiconductor nanocrystal materials and over a restricted range of sizes.Elongated nanorods, on the other hand, present independent radial and longitudinal modes (dependent on rod diameter and length, respectively) that offer increased tunability. The longitudinal plasmon of gold nanorods, for instance, can be tuned from the visible into the infrared, by changing the aspect ratio. Numerous attempts to increase the aspect ratio to values greater than 5, however, have met little success so far. This presentation will describe our new methods for synthesizing nanorods with any aspect ratio ranging from 1 to 350, and thereby tuning the longitudinal plasmon peak. Importantly, the position of this feature can be fine-tuned using a fully reversible growth/dissolution technique based on straight forward manipulation of reaction conditions. In this talk, we will describe the key redox processes that allow one to controllably elongate or shorten gold nanorods at will under mild conditions, and how modifying the reaction pH can allow the synthesis of extremely long gold nanowires, measuring up to ~25 µm. This new technique will enable us to probe plasmonic enhancement of semiconductor nanocrystals of a wide range of formulations and energies in a variety of potential device scenarios.
9:00 PM - D11.24
Photothermally Sensitive Plasmonic Poly(N-isopropylacrylamide) (PNIPAM) Droplet for Biomedical Applications.
Young Geun Park 1 2 3 , James Su 1 , Yeonho Choi 4 , Taewook Kang 3 , Kevin Healy 1 , Luke Lee 1 2
1 Bioengineering, UC Berkeley, Berkeley, California, United States, 2 Biomolecular Nanotechnology Center / Berkeley Sensor and Actuator Center , UC Berkeley, Berkeley, California, United States, 3 Chemical and Biomolecular Engineering, Sogang University, Seoul Korea (the Republic of), 4 Department of Biomedical Engineering, College of Health Science, Korea University, Seoul Korea (the Republic of)
Show AbstractWe report a direct synthesis of gold nano particle array in the ordered pore of mesoporous silica structure. The two dimensionally ordered mesoporous silica structure containing uniform sized gold nano particle are synthesized based on self assembly. The high surface area and ~ 10 nm size pore diameter with orderness enable to absorb and colorimetrically detect each liquid or gas selectively. By modification of tri-block copolymer in self assembly, the gold ions are selectively distributed the interface between hydrophilic and hydrophobic part of tri-block copolymer and form ordered polymer structure in liquid phase. This structure is still shown two dimensional hexagonal structure after SiO2 polymerization on hydrophilic part of triblock copolymer and following annealing process to form gold nano particle with removal of the organic part, triblock copolymer, in the thin film structure. This resulting highly ordered gold nano particle inside of the mesoporous stucture enables simple colorimetric detection.
9:00 PM - D11.26
Tailoring Surface Plasmon Resonance in Ag:ZrO2 Nanocomposite Thin Films.
Manish Kumar 1 2 , Gade Reddy 1 , Devesh Avasthi 2
1 Department of Physics, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, Delhi, India, 2 , Inter University Accelerator Center, New Delhi India
Show AbstractAg:ZrO2 nanocomposite thin films have been synthesized by a modified sol-gel technique. The effect of post deposition treatments i.e. thermal annealing and UV irradiation on the micro-structural, chemical and optical properties of nanocomposite thin films have been studied by high resolution transmission electron microscope, x-ray photoelectron spectrophotometer and UV-Vis spectrophotometer. Films deposited with a polymeric ZrO2 sol containing Ag+ ions when treated with either of thermal annealing or with UV-irradiation, exhibit formation of Ag:ZrO2 nanocomposite thin films via the decomposition of Ag2O3 into metallic Ag. Formed Ag nanoparticles are found predominantly in spherical shape and density of Ag nanoparticles increases with increasing the annealing duration for a particular concentration of Ag precursor. A protocol is provided to tailor the surface plasmon resonance induced absorption peak at wavelength from 454 nm to 586 nm. These nanocomposite thin films show saturable absorption and exhibits high value of non-linear absorption coefficient.
9:00 PM - D11.3
Assembly of Bimetallic Plasmonic Nanostructures as Active Raman Markers.
Ray Gunawidjaja 1 , Eugenia Kharlampieva 1 , Ikjun Choi 2 1 , Vladimir Tsukruk 1 2
1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 School of Polymer, Textile & Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Show AbstractThis work demonstrates a rational design of bimetallic silver-gold Raman markers by means of facile wet-assembly technique. Based on anionic-cationic interactions, various bimetallic silver-gold anisotropic nanostructures can be assembled from nanoparticle building blocks with well defined geometries as mediated by charged molecules. We employed three representative building blocks, one-dimensional (1D) silver nanowires, two-dimensional (2D) silver nanoplates, and zero-dimensional spherical gold nanoparticles. The gold nanoparticles are electrostatically bound onto the 1D silver nanowires and the 2D silver nanoplates to give silver-gold bimetallic nanostructures. The unique feature of the resulting nanostructures is the particle-to-particle interactions and plasmon coupling within the bimetallic silver-gold nanostructures that subjects absorbed analytes to an enhanced electromagnetic field with strong polarization dependence. Surface-enhanced Raman spectroscopy (SERS) micromapping of adsorbed Rh6G on individual nanostructures indicate that the bimetallic nanostructures exhibit highly anisotropic SERS properties when the 0D gold nanoparticles were assembled onto the 1D silver nanowire. UV/Vis measurement show that the bimetallic silver-gold nanostructures results in a combined, and thus broadened, plasmon absorption spectrum due to the distinct elements and geometrical shapes of the silver and gold nanoparticles. Furthermore, due to the multiple nanogaps and “hot spots”, the SERS capability of the individual bimetallic nanostructure is on par with the components in their aggregated state.
9:00 PM - D11.4
An Evolutionary Tree for Morphological Engineering of Gold Nanoparticles.
Kwonnam Sohn 1 , Franklin Kim 1 , Ken Pradel 1 , Jinsong Wu 1 , Yong Peng 2 , Feimeng Zhou 2 , Jiaxing Huang 1
1 Materials science and engineering, Northwestern university, Evanston, Illinois, United States, 2 Chemistry and Biochemistry, California State University, Los Angeles, California, United States
Show AbstractSince many properties of nanocrystals strongly depend on their size and shape, their chemistry includes not only chemical composition but also a structural factor like morphology. Here we demonstrate that gold nanoparticles can be morphologically engineered by constructing an evolutionary tree. This evolutionary tree consists of three independent growth pathways, namely the isotropic, anisotropic, and tip overgrowth. The differences in reaction conditions between the pathways are the pH and/or CTAB (Cetyltrimethylammonium bromide) concentration of growth solution. Each branch produces a string of continuously tunable morphologies from one reaction. The evolutionary tree can collectively constitute a library of nanoparticles’ morphologies with minimal changes of reaction parameters. Moreover, it can also give us opportunities to design new morphologies through crossing between different pathways.
9:00 PM - D11.5
Strong Polarization-dependent Plasmon-enhanced Fluorescence and Elliptically Polarized Dipoles of Single Gold Nanorods.
Ming Tian 1 , Zhao Lei 1 , Wang Jianfang 1
1 Department of Physics, The Chinese University of Hong Kong, Hong Kong China
Show AbstractNoble metal nanocrystals exhibit extraordinary plasmonic properties, owing to their localized surface plasmon resonances. Among variously shaped metal nanocrystals, gold nanorods have attracted tremendous attention, because they have smaller resonance linewidths, larger dephasing time constants, larger local electric field enhancements, and are easy to synthesize. The most distinguishing character of gold nanorods is the symmetry breaking-induced splitting of the plasmon resonance into the linearly polarized transverse and longitudinal plasmon modes. We have observed the strong polarization dependence of the plasmon-enhanced fluorescence on single gold nanorods (Nano Lett., 10.1021/nl902095q) and studied their light-bending properties.The fluorescence from the fluorophores that are embedded in a mesostructured silica shell around individual gold nanorods is observed to be enhanced by the longitudinal plasmon resonance of the nanorods. The polarization dependence of the plasmon-enhanced fluorescence is ascribed to the dependence of the averaged electric field intensity enhancement within the silica shell on the excitation polarization. The measured fluorescence enhancement factor is in very good agreement with that obtained from electrodynamic calculations. The fluorescence enhancement factor increases as the longitudinal plasmon wavelength is synthetically tuned towards the excitation wavelength.We have also carried out electrodynamic calculations on single gold nanorods under linearly polarized excitation. Under exactly resonant excitation, the electric field intensity enhancement contour around a nanorod is found to be circularly symmetrical around the length axis. In contrast, under off-resonance excitation, the electric field intensity enhancement contour tilts away from the length axis as the excitation polarization and wavelength are varied. The calculated far-field scattering patterns show that incident light beams can be bent by gold nanorods. The light-bending angle is controllable by the excitation wavelength and polarization. The light-bending property can be realized over the entire visible regime by making nanorods out of silver, gold, and their alloys. We have further employed Gans theory to analyze the electric dipole of single gold nanorods. The electric dipole is found to be elliptically polarized and highly dependent on the excitation polarization and direction relative to the length axis. We believe the light-bending properties of noble metal nanorods arising from the elliptically polarized dipole can have great potentials for a wide variety of optical applications.
9:00 PM - D11.6
A Comparison of Surface Plasmon Resonance Behaviour in Metal-metal and Metal-dielectric Bilayers.
Ghanashyam Krishna Mamidipudi 1 , Rajeeb Brahma 1
1 School of Physics, University of Hyderabad, Hyderabad India
Show AbstractSurface plasmon resonance behaviour in metal-metal and metal-dielectric bilayers is reported. The systems studied are bilayers of silver-Indium (SI), silver-titanium dioxide (ST) and silver-zirconium oxide (SZ). The surface plasmon resonance behaviour in these systems is compared with that observed in Ag nanostructures fabricated by ultra-low energy Ion beam sputtering at energies of the order of 100 to 200 eV. In the case of single layer Ag, the microstructure consists of almost spherically shaped particles of size 50 to 100 nm, separated by distances of similar order of magnitude. The particles organize themselves in to arrays over lengths of atleast 10 microns. As the thickness of the films increase, the main plasmon peaks can be tuned from 380 to 680 nm. The spheroidal shape of the particles induces additional peaks centered around 430 ±10 nm and 1100 nm due to localized surface plasmons. The SI bilayer thin films were fabricated by maintaining the Ag layer thickness constant at 5 nm while varying the In layer thickness between 3 to 30 nm. There is a red shift in the plasmon resonance from 372 to 522 nm in the case of the pure In layers whereas it was from 492 nm to 618 nm for the bilayer system. The Ag single layers exhibit a plasmon resonance at 540 nm. On coupling the In and Ag layers in the bilayers, additional resonances appear in the spectrum. The origin of the additional plasmon resonance peaks can be traced to the excitation of localized surface plasmons. ST and SZ bilayers were produced by first depositing the titania and zirconia layers on borosilicate glass substrates followed by ion beam sputtering of Ag on to these layers. In these cases it was observed that while the absorption spectrum was dominated by features from the oxide layers there was a strong surface plasmon resonance peak centered around 435 nm in the case of ST and 465 nm in the case of SZ bilayers. The observed behaviour can be explained within the framework of effective medium theories to distinguish the effects of shape and size on plasmon resonances.
9:00 PM - D11.7
Ag Nanoplates: Formation Mechanism, LSPR Properties and SERS Applications.
Jie Zeng 1 , Matthew Rycenga 1 , Weiyang Li 1 , Younan Xia 1
1 Department of Biomedical Engineering, Washington University in St Louis, St Louis, Missouri, United States
Show AbstractWe have presented the detailed comparison study of two kinds Ag nanoplates with different shapes – triangular shape with sharp corners and circular shape with round boundary – from the aspects of formation mechanism, local surface plasmon resonance (LSPR) properties, and surface enhanced Raman scattering (SERS) applications. A new possible nucleation mechanism involving the cluster attachment process was proposed during the synthesis of Ag nanoplates. Upon using the seed-mediated synthesis protocol, an effective strategy was demonstrated to methodologically tailor the shapes as well as the LSPR features of Ag nanoplates. As a result, the primary LSPR peak could be accurately tuned between 450 nm and 735 nm, and precisely harvest samples with desired shape and plasmon bands by controlling the quantity of seed. We also found that both the shape and the LSPR peaks of Ag nanoplates would affect the enhancement factor of SERS, which exhibited a plasmon band-dependent character. On the basis of the point that a strong polarization effect is necessary to get the remarkable SERS signals, it was revealed the SERS would be also sensitive to the type of polarization fields, showing an overwhelmingly intensive response on the in-plane polarization field relative to the in-plane quadrupole polarization field. As for the enhancement factor of SERS originated from the in-plane polarization field, triangular Ag nanoplates (excited at 785 nm) exhibited a better performance than circular Ag nanoplates (excited at 514 nm) did. This was consistent with the fact that the sharp shape would lead to the strong dipole polarization. The shape of Ag nanoplates might determine not only its intrinsic physical and chemical properties but also its relevance for biological and industrial applications.Key words: Ag, nanoplates, LSPR, SERS. References(1) Jin, R. C.; Cao, Y. W.; Mirkin, C. A.; Kelly, K. L.; Schatz, G. C.; Zheng, J. G. Science 2001, 294, 1901. (2) Li, W. Y.; Camargo, P. H. C.; Lu, X. M.; Xia, Y. N. Nano Lett. 2009, 9, 485.(3) Lu, X. M.; Rycenga, M.; Skrabalak, S. E.; Wiley, B.; Xia, Y. N. Annu. Rev. Phys. Chem. 2009, 60, 167.
9:00 PM - D11.8
Periodic Plasmonic Nanostructures as Efficient SERS Substrates for Biosensing.
Peng Jiang 1 , Nicholas Linn 1 , Tzung-Hua Lin 1 , Hongta Yang 1 , Bin Jiang 2
1 Department of Chemical Engineering, University of Florida, Gainesville, Florida, United States, 2 Department of Mathematics and Statistics, Portland State University, Portland, Oregon, United States
Show AbstractSurface-enhanced Raman scattering (SERS) is a non-invasive technique that enables the detection and characterization of both small organic and big biological molecules at very low concentrations. To overcome the reproducibility issue of stochastically aggregated colloidal nanoparticles in SERS, various periodic metallic nanostructures created by self-assembly have been exploited. Unfortunately, most of these bottom-up approaches are limited in creating centimeter-sized samples, and are not compatible with standard microfabrication, thereby impeding the cost-efficiency and scale-up of these unconventional methodologies. Here we show numerous scalable templating techniques for fabricating wafer-sized SERS substrates with high and reproducible enhancement factors. Non-closed-packed colloidal crystals prepared by a simple spin-coating technique are used as templates to create periodic arrays of nano-dimples, nano-pyramids, nano-nipples, nanoholes, and nanoflasks, as well as binary nanohole-nanoparticle assemblies. These nanostructures have high-density sharp features (e.g., circular edges and nanoscale tips) that function as “hot spots” to concentrate electromagnetic field. We have also developed a finite-element method (FEM) model to simulate the spatial distribution of the electromagnetic field and predict the corresponding SERS enhancement factor from the periodic metallic nanostructures.
9:00 PM - D11.9
Silver Nanoplates: Tailored Synthesis and Optical Properties.
Qiao Zhang 1 , Yadong Yin 1
1 Chemistry, University of California, Riverside, Riverside, California, United States
Show AbstractIn this presentation, we discuss the synthesis and applications of plate-like silver nanostructures. Using the strategy of “selective ligand protection”, we have developed a number of colloidal approaches for the synthesis of silver nanoplates with well-controlled size and shape, high stability, and tunable surface plasmon band from ~400 nm to IR. An unconventional backward growth approach has been used to precisely tune the aspect ratio of the silver nanoplates so that their plasmonic bands can be precisely tuned in the visible and near-IR spectrum. Conventional seeded growth method is also used to obtain nanoplates with extremely high aspect ratio which allows the extension of the plasmonic band to IR. We will also report the possibility of directed growth of silver nanoplates on solid substrates with a high degree of positional control. Finally, we will discuss the application of such functional nanostructures in areas such as biological and chemical sensing, Raman signal enhancement.
Symposium Organizers
Jennifer A. Dionne Stanford University
Luke A. Sweatlock Northrop Grumman Space Technology
Gennady Shvets University of Texas-Austin
Luke P. Lee University of California-Berkeley
D12: Super-resolution
Session Chairs
Friday AM, April 09, 2010
Room 2008 (Moscone West)
9:00 AM - **D12.1
Optical Metamaterials.
Xiang Zhang 1
1 , University of California at Berkeley, Berkeley, California, United States
Show AbstractMetamaterials 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 sub-wavelength plasmonic laser.
9:30 AM - **D12.2
Spectral Imaging Quality and Phase Effects in Near-field Imaging With an SiC Superlens.
Thomas Taubner 1 2 , Jon Schuller 2 , Mark Brongersma 2 , Chris Fietz 3 , Gennady Shvets 3 , Rainer Hillenbrand 4
1 1st Institute of Physics (IA), Aachen University, Aachen Germany, 2 Material Science and Engineering, Stanford University, Stanford, California, United States, 3 Department of Physics, University of Texas, Austin, Texas, United States, 4 Nanooptics Laboratory, CIC nanogune, San Sebastian Spain
Show AbstractHere we study the imaging process of a polariton-based SiC superlens with a near-field optical microscope (s-SNOM). A “superlens” is a planar device that allows for subwavelength imaging by employing coupled surface waves on a thin slab of a negative-permittivity material [1]. As opposed to previous intensity-only measurements [2,3] , we here perform amplitude and phase-measurements of the near-fields in the image plane of a superlens made from the polar crystal SiC [4]. Comparison of experimental data with full-field simulation explains the imaging process as a near-field mapping of complex-valued polariton fields [5]. A variation of the illumination wavelength allows us to examine image quality and phase effects when the superlensing condition is not exactly fulfilled. Particularly, we observe a sign change in the phase of the transmitted near-fields when tuning the illumination wavelength over the superlenses resonance wavelength.This observation can be explained by the dispersion relation of the superlens, in combination with a fundamental interference effect. When operating a superlens off-resonance, the interference of evanescent fields causes the intensity contrast to decrease. Such a decrease can be compensated for with phase-sensitive imaging to practically maintain the spectral range of high-resolution operation. Our results are important for the understanding and future spectroscopic applications of superlenses and other devices such as hyperlenses [6] or 2D plasmon lenses [7].[1] J. B. Pendry, Physical Review Letters 85, 3966 (2000).[2] N. Fang, H. Lee, C. Sun, X. Zhang, Science 308, 534 (2005).[3] D. O. S. Melville, R. J. Blaikie, Optics Express 13, 2127 (2005).[4] T. Taubner, D. Korobkin, Y. Urzhumov, G. Shvets, R. Hillenbrand, Science 313, 1595 (2006).[5] A. Huber, N. Ocelic, D. Kazantsev, R. Hillenbrand, Applied Physics Letters 87, 081103 (2005).[6] Z. Liu, H. Lee, Y. Xiong, C. Sun, X. Zhang, Science 315, 1686 (2007).[7] I. I. Smolyaninov, Y.-J. Hung, C. C. Davis, Science 315, 1699 (2007).
10:00 AM - D12.3
Realization of a Superlens for the Deep UV.
Joerg Schilling 1 2 , Alina Schilling 1 , Carsten Reinhardt 3 , Boris Chichkov 3
1 Dept. of Physics, Queen's University Belfast, Belfast United Kingdom, 2 ZIK "SiLi-nano", Martin-Luther-Universität Halle-Wittenberg, Halle Germany, 3 , Laser Zentrum Hannover, Hannover Germany
Show AbstractTo achieve a subwavelength imaging in the near field a superlens can be applied, which consists in its simplest case of a single metal layer. Since the illuminated objects are positioned in the near field of this metal layer, coupled surface plasmons are excited. The constructive interference of these surface plasmons forms then the near field images of the objects on the other side of the metal layer.Although the achievable near field resolution can be several times better than in traditional far field microscopy, it still depends on the wavelength of the surface plasmons. Using surface plasmons at deep UV frequencies having correspondingly short wavelengths will therefore result in the ultimate resolution necessary for near field lithography. Here we present an experimental realization of the near field imaging of a superlens based on a thin aluminium layer for an operating wavelength of 157nm. Aluminium is a very good plasmonic metal in the range 100nm < λ0 < 200nm since its absorption is relatively low (εim < 0.1 εr).MethodsTo determine first the theoretical possible near field resolution of an aluminium superlens we applied a finite element method (COMSOL) to simulate the near field imaging of single and double aluminium layers within a wavelength range from 130-200nm. Searching for the ultimate resolution, the wavelength of the light and the thickness of the layers was varied. To test the resolution experimentally, multilayer samples consisting of a CaF2 substrate (UV transparent), a tantalum mask layer, a spin on glass spacer layer, the aluminium lensing layer and a PMMA resist layer were fabricated. Double slit patterns with different separations were produced in the tantalum mask and the structure illuminated with a fluorine laser (λ0=157nm). The near field images on the upper side of the aluminium layer expose the PMMA and lead to grooves in the PMMA surface after development. These were observed using scanning electron microscopy (SEM) at low acceleration voltages and atomic force microscopy (AFM) scans.ResultsFrom the simulations it follows that for different wavelengths the best resolution is achieved at different aluminium thicknesses culminating in a possible ultimate near field resolution of 29nm for a single 10nm thick aluminium layer λ0=145nm. Experimentally a resolution of about 70nm (centre-to-centre distance of the slits) could be confirmed [1]. This deviates from the ultimate theoretical prediction mainly due to the difference in wavelength used and slightly different sample geometry.In conclusion 70nm resolution of an aluminium based superlens was demonstrated and a sub 40nm resolution appears feasible after sample optimization. These results confirm that aluminium is the material of choice for ultra short wavelength plasmonics in the deep UV.[1] A. Schilling, J. Schilling, C. Reinhardt, B. Chichkov, Applied Physics Letters 95, 121909 (2009)
10:15 AM - D12.4
High Throughput Plasmonic Nano-lithography for Nano-manufacturing.
Liang Pan 1 , Yongshik Park 1 , Yi Xiong 1 , Erick Ulin-Avila 1 , Li Zeng 1 , Cheng Sun 2 , David Bogy 1 , Xiang Zhang 1
1 Mechanical Engineering, University of California at Berkeley, Berkeley, California, United States, 2 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractSemiconductor business starts to be affected by the increasing cost of photolithography systems. Although state-of-the-art lithography system is expected to deliver 22 nm half pitch resolution, so far, there is still no cost effective solution to achieve smaller half pitch in mass production. At the meanwhile, the photo masks become more and more complex and prohibitively expensive as node size reduces. This trend opens up opportunities for high throughput mask less equipments to address IC manufacturing. However, most of mask-less lithography solutions are limited by their low throughput capabilities, making them never a credible option for manufacturing purposes. Here we report a new high-throughput mask-less nanolithography using plasmonic lens arrays flying using advance airbearing surfaces at 10 meter/second. The lens concentrates short wavelength surface plasmons into a sub-100 nm spot. However, the nano-scale focus only exists at the near field of the lens, typically 10-100 nm, making high-speed scanning of such arrays very difficult. We designed a unique air-bearing that flies the arrays 10 nm above the surface of a spinning disk with speeds of 4-12 meter/second. We experimentally demonstrated the capability of patterning with 20 nm features and theoretical simulation shows it can reach down to 5-10 nm. This low-cost nano-fabrication scheme has the potential of a few orders of magnitude higher throughput than current mask-less techniques, and promises a new route towards next generation nano-manufacturing. Besides its application in nanolithography, this technique may also lead optical and magnetic data storage to achieve two order higher capacities in the future.
D13: Plasmon Nanophotonics II
Session Chairs
Friday PM, April 09, 2010
Room 2008 (Moscone West)
11:00 AM - D13.0
Direct Photonic - Plasmonic Coupling and Routing in Single Nanowires.
Ruoxue Yan 1 , Peter Pausauskie 1 , Jiaxing Huang 1 , Peidong Yang 1
1 Chemistry, University of California, Berkeley, Berkeley, California, United States
Show AbstractMetallic nanoscale structures are capable of supporting surface plasmon polaritons (SPPs)–propagating collective electron oscillations with tight spatial confinement at the metal surface. SPPs represent one of the most promising structures to beat the diffraction limit imposed by conventional dielectric optics. However, the inherent metal loss makes it impractical to transfer digital data across the entire photonic IC chip solely with plasmonic waveguides. And it has become increasingly important to be able to integrate plasmonic modules with low-loss, dielectric optical interconnects. In order to achieve such hybrid plasmonic-photonic circuit, it is critical to develop nanoscale plasmonic waveguides with reduced losses and small mode volume, and equally important, to ensure the compatibility with conventional optical circuitry. In this context, chemically synthesized Ag nanowires have emerged as promising candidates for sub-wavelength plasmonic waveguides. Their high crystallinity and atomically smooth surface ensure two-dimensional sub-100nm mode confinement and much lower losses than fabricated metal structures. However, integrating the low-loss Ag nanowire waveguides into a plasmonic-photonic routing network requires a simple, efficient and versatile strategy to couple the light field in and out of the Ag nanowire which has yet to be achieved. Here, we demonstrate that SPPs can be excited simply by contacting a silver nanowire with a SnO2 nanoribbon that serves both as an unpolarized light source and a dielectric waveguide. The relative coupling efficiency (ηc), defined as the ratio between the total light input into the Ag nanowire and the total light output from the SnO2 at the Ag-SnO2 junction, depends on both the coupling angle and the photon frequency. ηc is higher for smaller coupling angle and lower excitation frequency due to better photonic-plasmonic mode matching, and can be as high as 56% at 20 degree coupling angle for 980nm input photons. The efficient coupling makes it possible to systematically measure the propagation-distance dependent waveguide spectra and frequency-dependent propagation length on a completely air-clad single Ag nanowire. The measurement shows that single-crystalline Ag nanowires have much lower propagation loss than its fabricated counterpart. For a 100nm Ag nanowire, the propagation length is 6.2μm for 532nm, 11.3μm for 650nm and 20.2μm for 980nm excitation. Furthermore, we have demonstrated prototypical photonic-plasmonic routing devices, which are essential for incorporating low-loss Ag nanowire waveguides as practical components into high capacity photonic circuits.
11:15 AM - D13.1
Long Range Surface Modes on Lossy Thin Films.
Christophe Arnold 1 2 , Yichen Zhang 1 2 , Jaime Gomez Rivas 1 2
1 Center for Nanophotonics, FOM institute AMOLF, Amsterdam Netherlands, 2 , Philips Research Laboratories, Eindhoven Netherlands
Show AbstractOptical losses generally reduce the performance of optical systems. However, there are exceptions. Long Range Surface Polaritons (LRSPs) supported by lossy thin films are a beautiful example of one of these exceptions: losses in the thin film help to support a guided mode. Moreover, the propagation length of this mode can be enhanced by increasing the losses. We present here experimental and theoretical results on LRSPs supported by thin films of chalcogenide glass and discuss their applicability as surface polariton sensors. The multilayer structure that we have investigated is composed of a Ge17Sb76Te7 (GeSbTe) thin film of 18nm deposited on a silica layer. To obtain a symmetric dielectric environment surrounding the thin film required to support LRSPs, we use a refractive index matching liquid in the other side of the thin film. We study the modes of this system in the visible by means of the attenuated total reflection method with a high refractive index prism. We show an important reduction of the total internal reflection on the prism-silica interface at the resonant angle revealing the efficient coupling of the LRSPs on the GeSbTe thin film. GeSbTe is a phase-change material with amorphous and crystalline phase. The possibility to change the phase allows us to change the refractive index of the thin film without changing other parameters in our system, such as the thickness of each layer or the refractive index of the surrounding media. Thus, we are able to investigate the dependence of LRSPs with the dielectric constant of the thin film. Our experiments and calculations reveal the insensitivity of the mode on the real part of the permittivity of the thin films as far as the imaginary component is larger.We also investigate the dependence of LRSPs on the surrounding dielectric demonstrating a large sensitivity of the LRSPs resonance at visible frequencies to overall changes in refractive index of the surrounding. Our results show that surface modes supported by absorbing media are able to improve the performance of surface plasmon resonance sensors, without the need of metal layers.
11:30 AM - **D13.2
Deep Subwavelenght Electrically Pumped Gap-plasmon Mode Laser Structures in the Near Infrared.
Martin Hill 1 , Milan Marell 1
1 , Technical University of Eindhoven, Eindhoven Netherlands
Show AbstractThe size of nano-lasers has dramatically decreased recently due to the use of metals to create optical cavities which can confine light below the diffraction limit. However, to be of significance for many applications, such devices will need to be electrically pumped, as this allows efficient energy transfer to just the nano-scale optical gain regions in the devices. Our work involves electrically pumped Metal-Insulator-Metal (MIM) waveguide laser devices. Such structures allow the concentration of both electrically injected carriers and the optical mode into a gain region of just a couple of tens of nanometers in size in two dimensions. We will show results from such waveguide devices. Another aspect in the application of metallic/plasmonic nano-lasers is the precise control of their lasing wavelength and the efficient emission of light or plasmons into conventional or plasmonic waveguides. A possible solution for this is the use of Bragg gratings in the MIM waveguide to form distributed feed-back lasers. Such structures allow good control over the lasing frequency, strongly confined optical modes with moderate quality factors, and efficient coupling of the light into waveguides. We will also show our progress in creating such Bragg grating devices and discuss some of the key issues in their design.
12:00 PM - **D13.3
Controlling Light Fields at the Nanoscale.
L. Kobus Kuipers 1
1 , AMOLF, Amsterdam Netherlands
Show AbstractNanostructures such as photonic crystals and plasmonic metallodielectrics can exert a huge control over light at the nanoscale. This control is of both academic and industrial interest. Nanoconfinement of light can miniaturize optical chips and the slow light achievable with Bragg structures leads to increased light-matter interactions with a potential for new (bio)sensors and ultrafast all-optical switches. Implicit in the control of light at the nanoscale is that the light field itself no longer conforms to our everyday intuition in terms of plane waves or rays. Close to a nanophotonic structure the light field itself becomes highly structured.In order to investigate light fields at the nanoscale in detail a subwavelength resolution is crucial. We have succeeded in measuring the structure of light in the near field of photonic crystal waveguides with phase-sensitive near-field microscopy. It turns out that the evanescent field of these waveguides is much richer than expected due to the Bloch nature of the eigenmodes. For example, it turns out that the light does not decay with a single or even multiple exponents away from the surface as might have naively been expected [1]. With a breakthrough in near-field microscopy we have succeeded to separate the two electric field components in to the plane above the waveguide structure and the phase difference between them. As a consequence we can reconstruct the polarization ellipse for every point above the nanophotonic structure. We find that the polarization above a photonics crystal structure is highly dependent on position to extent that the field even contains so-called polarization singularities [2]. The breakthrough has enabled the visualization of the effective excitation of nanowire plasmon modes through adiabatic mode transformation [3]. Building on our ability to distinguish different vector components, we used a ‘split’ nanoprobe to visualize the magnetic component of propagating light at optical frequencies [4]. This integral part of light is never observed as light-matter interactions are usually governed by the electric part rather than the magnetic part: when we see light, we perceive the electric field, we are ‘blind’ to the magnetic field.[1] R.J.P. Engelen, D. Mori, T. Baba, L. Kuipers, Subwavelength Structure of the Evanescent Field of an Optical Bloch Wave, Phys. Rev. Lett. 102, 023902 (2009).[2] M. Burresi, R.J.P. Engelen, A. Opheij, D. v. Oosten, D. Mori, T. Baba, L. Kuipers, Observation of polarization singularities at the nanoscale, Phys. Rev. Lett. 102, 033902 (2009).[3] E. Verhagen, M. Spasenovic, A. Polman, L. Kuipers, Observation of polarization singularities at the nanoscale, Phys. Rev. Lett. 102, 033902 (2009).[4] M. Burresi, D. van Oosten, T. Kampfrath, H. Schoenmaker, R. Heideman, A. Leinse and L. Kuipers, Probing the magnetic field of light at optical frequencies, Science 326, 550-553 (2009).
12:30 PM - D13.4
Hybrid Surface Plasmon/Dielectric Waveguides for VLSI-compatible Integrated Optics.
J. Bank 1 , T. Furtak 1 , P. Flammer 1 , C. Durfee 1 , R. Hollingsworth 2 , R. Collins 1
1 Physics, Colorado School of Mines, Golden, Colorado, United States, 2 , ITN Energy Systems, Inc., Littleton, Colorado, United States
Show AbstractIntegrating optical elements with silicon-based microelectronics is a topic of great interest. In particular, the ability to realize plasmonic components on chip to manipulate or process optical signals would improve the compactness, manufacturability and performance of optical devices while enabling entirely new classes of hybrid optical-electronic applications.We present a hybrid surface plasmon/dielectric single-mode, single-polarization waveguide using silicon-on-insulator wafers, which is designed for operation at telecommunications wavelengths. The device-silicon layer forms a dielectric waveguide in one transverse direction due to the bounding lower index buried oxide layer. In the other transverse direction, a surface plasmon at a metal/dielectric/device-silicon interface guides the mode along the metal line. Only transverse magnetic polarizations are guided because of the plasmonic nature of the waveguide. The structure can be fabricated using VLSI processing techniques. Its design naturally minimizes losses due to surface roughness and metallic absorption. Birefringent effects are eliminated, because only a single mode and single polarization can propagate. The metal/oxide/device-silicon structure naturally forms an MOS capacitor that can be used to integrate active devices, such as modulators based on electrically induced free carrier absorption or phase modulation within the guiding region of the mode.Both simulations and experimental verification of the modes are presented. The finite element simulations were performed as a function of waveguide parameters including metal line width, device-oxide thickness, device-silicon thickness, and the thickness of the buried oxide layer. Simulations show a trade off between mode confinement and propagation length, which can be tuned by changing the patterned metal line width or device-oxide thickness. For reasonable parameters, waveguides can be prepared with sub-wavelength confinement and propagation lengths greater than 100 microns or micron-scale confinement with ~10mm propagation lengths. Hybrid waveguides operating at λ = 1.5μm were fabricated on SOI wafers using standard optical lithography. Their modal characteristics including mode shape, polarization dependence, and dependence on dimensional parameters were in excellent agreement with model predictions. Electrical characteristics of the MOS structures were also determined and electrical modulation of the waveguides will be discussed.Support from AFOSR Award# FA9550-06-1-0548 and AFOSR Award# PO-09I-0451 is gratefully acknowledged.
12:45 PM - D13.5
Focusing and Electrical Detecting of Propagating Surface Plasmons Using Metallic Nanoparticles.
Mingxia Gu 1 , Ping Bai 1 , Er-Ping Li 1
1 Advanced Photonics and Plasmonics Group, Institute of High Performance Computing, A*STAR, Singapore, Singapore, Singapore
Show AbstractPlasmonic waveguide, with large bandwidth and subwavelength dimension, is considered as a potential candidate for data transmission in the next generation nano-opto-electronic systems. Various efforts have been made to realize the subwavelength waveguides towards matching the dimensions of optical devices with modern electronic ones. However, the dimensions of the devices to convert optical signals to electric ones remain very large due to low responsivity per unit volume. Consequently, efficient focusing of the optical power into a nanoscale volume becomes a critical challenge in the design of a nanoscale photodetector. We report a state of the art metallic nanoparticle structure to effectively focus the propagating surface plasmons from a plasmonic waveguide and to convert the focused optical power into electric current as a bridge between optical and electronic devices. To focus the propagating surface plasmons, we design a nanocavity located between two metallic nanoparticles that act as a dipole nanoantenna to receive the optical power. The received optical power is then localized in the nanocavity by exploiting the effect of the localized surface plasmon resonance of the nanoparticles. The dimensions, shapes and relative positions of the nanoparticles are studied to maximize the power transmission. The effects from environmental materials, such as substrate and cladding, which are important in real applications, are also investigated. Conversion of the localized surface plasmon polaritons into electric currents is realized by means of a metal-semiconductor-metal photodetector, by filling the nanocavity with absorption material while using the two nanoparticles as electrodes to apply bias voltages and to conduct the photocurrents. The effects of the bias voltages and photocurrent on the performance of the nanoantenna and nanocavity are analyzed. Possible leads of the detector are postulated and their effects are also investigated, including the type of the materials of the leads and the way to connect them to the nanoparticles. In addition, significant improvement of absorption rate can be achieved by carefully selecting the dimensions of the absorption material. With proposed configuration, the active volume of the detector can be as small as 50×50×50 nm3, which implies ultrasmall dimensions, compact structure, sub-picosecond transit time for drifting excited carriers to the electrodes, extremely low internal capacitance, high responsivity, and low power dispersion of the detector. Our theoretical studies show that 81% of the optical power from the plasmonic waveguide can be coupled to the detector and around 60% of it can be converted into photocurrent. Therefore, we would achieve the smallest optical detector ever reported along with the success of our ongoing experimental verification. We believe this work will advance a new step for the integration of nanophotonics with modern nanoelectronics.
D14: Nanoparticle Plasmonics II
Session Chairs
Friday PM, April 09, 2010
Room 2008 (Moscone West)
2:30 PM - D14.1
Gold Nanostars: Hot Tips for Field Enhancement.
Calin Hrelescu 1 , Tapan Sau 1 2 , Ludovic Douillard 3 , Fabrice Charra 3 , Severin Habisreutinger 1 , Andrey Rogach 1 4 , Frank Jaeckel 1 , Jochen Feldmann 1
1 Department of Physics and CeNS, Ludwig-Maximilians-University Munich, Munich Germany, 2 , International Institute of Information Technology-Hyderabad, Hyderabad, Gachibowli, India, 3 Service de Physique et Chimie des Surfaces et Interfaces, Institut Rayonnement Matière de Saclay, Gif sur Yvette France, 4 Department of Physics and Materials Science, City University of Hong Kong, Hong Kong China
Show AbstractFor an efficient coupling of light to nanoscale objects, such as molecules or nanocrystals, highly enhanced and highly localized electromagnetic fields, so-called hotspots, are of particular interest. Localized surface plasmons resonances on noble metal nanoparticle are an attractive possibility for the design of such hotspots. Single star-shaped gold nanoparticles have been shown to provide total Raman enhancement factors of 10^7 due to their highly anisotropic shape [1]. Here, we provide experimental evidence from photoelectron emission microscopy for the location of the hotspots at the tips of the nanostars and investigate the dependence of the SERS signal on the spectral position and polarization of the excitation light.[1] C. Hrelescu, T.K. Sau, A.L. Rogach, F. Jäckel, J. Feldmann, Appl. Phys. Lett. 94 (2009) 153113.
2:45 PM - D14.2
Fano Resonances and Directional Excitation in Plasmonic Heterodimers.
Lisa Brown 1 , Heidar Sobhani 2 , Britt Lassiter 2 , Peter Nordlander 2 3 , Naomi Halas 1 2 3
1 Chemistry, Rice University, Houston, Texas, United States, 2 Physics & Astronomy, Rice University, Houston, Texas, United States, 3 Electrical & Computer Engineering, Rice University, Houston, Texas, United States
Show AbstractPlasmonic heterodimers, which consist of two different metallic nanoparticles, possess simple geometries with fascinating optical properties. In this study, we explore two major characteristics of these structures: Fano resonances and directional excitation. All dimers were fabricated by a simple and versatile technique involving the migration of particles along the surface of a substrate due to a partial neutralization of their surface charge. Polarization-dependent measurements by dark field scattering microspectroscopy revealed optical properties of individual dimer structures. When a dimer is excited by light that is polarized parallel to the dimer axis, a Fano resonance originates from two hybridized energy modes involving the dipole and quadrupole resonances of the constituent particles. As the size of the gap between the particles changes, we observe an avoided crossing behavior in which there is an exchange of plasmon modes between higher and lower energy levels. Incident polarization that is perpendicular to the dimer axis gives rise to a directional excitation effect. When the light beam travels along the dimer axis, the overall scattering distribution and relative intensities of the hybridized modes change dramatically according to the direction of excitation, making this structure a nanophotonic diode. This property is most evident in heterodimers containing particles with differing plasmon energies, such as a solid gold nanoparticle and a gold nanoshell. The many interesting properties of these structures give a significant contribution to the fundamental knowledge of how plasmon resonances in neighboring spherical particles interact.
3:00 PM - D14.3
Broadband Tunability of Plasmonic Resonances for Sensing and Imaging.
Hanwei Gao 1 , Joel Henzie 2 , Min Hyung Lee 1 , Teri Odom 1
1 Department of Chemistry, Northwestern University, Evanston, Illinois, United States, 2 Department of Chemistry, University of California, Berkeley, California, United States
Show AbstractSurface plasmon polaritons (SPPs) are responsible for exotic optical phenomena including negative refraction, surface enhanced Raman scattering, and nanoscale focusing of light. Although many materials support SPPs, the choice of metal for most applications has been based on traditional plasmonic materials (Ag, Au) because there have been no side-by-side comparisons of the different materials on well-defined, nanostructured surfaces. We have developed a versatile platform to screen unconventional plasmonic materials and to tailor their resonances by tuning the refractive index environment, surface architecture, and excitation conditions. Plasmonic crystals based on nanopyramidal gratings were used not only to standardize plasmon dispersion diagrams for Al, Cu, Pd and Pt but also to identify the most appropriate materials combinations for sensing and imaging. Surprising findings included (i) high SPP coupling efficiencies in unconventional materials (Al, Cu); (ii) ultra-narrow resonances (< 7 meV FWHM) and ultra-high refractive index sensitivities; and (iii) tunable resonances in metallo-dielectric multilayer stacks, which behave like anisotropic metamaterials that can be used for subwavelength imaging.
3:15 PM - D14.4
Polarization Aspects of Localized Optical Spots Obtained Using Plasmonic Nano-antennas.
Erdem Ogut 1 , Kursat Sendur 1
1 , Sabanci University, Istanbul Turkey
Show AbstractPolarization is one of the fundamental aspects of light that plays a crucial role in the interaction of electromagnetic radiation with matter. Polarized electromagnetic radiation has therefore led to interesting technical applications and significant advancements at optical frequencies. With advances in nanoscience and nanotechnology, electromagnetic radiation beyond the diffraction limit with a particular polarization emerges as a need for plasmonic nano-applications. Among these applications, all-optical magnetic recording is a novel application, which requires circular polarization. In the literature, it has been demonstrated that the magnetization can be reversed in a reproducible manner by using a circularly polarized optical beam without any externally applied magnetic field. To advance the areal density of hard disk drives beyond 1 Tbit per inch square, magnetization reversal areas much smaller than 100 nm are required. To achieve sub-100 nm bits, a circularly polarized optical spot beyond the diffraction limit is required.In this study, a novel plasmonic nano-antenna is illuminated with diffraction-limited linearly polarized radiation. Plasmonic resonances of longitudinal and transverse components of the nano-antenna, and angle of incident polarization are adjusted to obtain optical spots at the nanoscale with linear, circular, and elliptical polarizations. Amplitude ratios and phase differences between the field components are presented for optical spots beyond the diffraction limit with various polarizations. Right-hand and left-hand circularly and elliptically polarized optical spots at nanoscale dimensions are achieved. Necessary conditions required for the longitudinal and transverse components of the nano-antenna, and angle of incident polarization are identified to obtain the state of polarization specific to a point that may be selected on the Poincare sphere. The Poincare sphere representation is utilized to visually present the calculated Stokes parameters for optical spots with linear, circular, and elliptical polarizations. Amplitudes and phase differences between the field components of the achieved polarizations are used to calculate the particular Stokes parameters.
D15: Metamaterials II
Session Chairs
Friday PM, April 09, 2010
Room 2008 (Moscone West)
4:00 PM - D15.1
Planar Chiral Metallic Nanostructures with Two Photon Lithography for Application in Metamaterials.
Shobha Shukla 1 2 , E. Furlani 2 , Paras Prasad 1 2 3
1 Department of Electrical Engineering, University at Buffalo, Buffalo, New York, United States, 2 Institute for Lasers, Photonics and Biophotonics, University at Buffalo, Buffalo, New York, United States, 3 Department of Chemistry, University at Buffalo, Buffalo, New York, United States
Show AbstractPlanar media consisting of chiral micro- or nano-structures can be used to rotate the polarization of a transmitted electromagnetic wave. Applications for such media are numerous, and research in this field has increased significantly in recent years. To date, most planar chiral media (PCM) have been fabricated using conventional top-down lithographic techniques. In this paper, we report the two photon assisted fabrication and simulation of a PCM consisting of metallic gammadion structures. Insitu photoreduction of a metal precursor and simultaneous polymerization of SU8 are used to achieve submicron metallic features. Upon writing the structures on the film, the unexposed part was removed by dipping the film in a solvent. This novel approach of insitu fabrication of metallic structures on a polymeric backbone enables the efficient fabrication of a variety of polymer-based metamaterials. As such, this method holds potential for the development of novel optically active media, which is a focus of our ongoing research.
4:15 PM - D15.2
Zero-effective Index PhoXonic(X=t,n) Meta-materials.
Cheong Yang Koh 1 2 , Edwin Thomas 1 2
1 Materials Science and Engineering, massachusetts institute of technology, Cambridge, Massachusetts, United States, 2 Institute for Soldier Nanotechnologies, Massachusetts institute of Technology, Cambridge, Massachusetts, United States
Show AbstractMeta-materials offer a novel route towards the manipulation of photons and phonons by tuning the material response at the correct length scales, essentially allowing us access to tailored novel “atomic-like” responses from these materials. Negative Index Materials (NIM) offer the potential to create non-intuitive propagation behavior in phoXons (X=t,n), such as left-handed behavior and reversed Doppler effects. In this work, we demonstrate unique behavior, brought about by combining both positive and negative “index” (i.e. dynamic impedance) materials to create an effective zero-index phononic material, in a certain frequency range where the negative index components are resonant. This leads to novel behavior such as the opening of a disorder insensitive "zero-index" gap (ZIG). By further judicious choice of the building blocks of components having positive and negative index, we show that we may combine the desired features of a disorder-tolerant ZIG, together with conventional band gaps that arise from the periodicity. We also investigate the differences between utilizing different kinds of "negative-index" materials, consisting of either phononic crystals or true meta-materials in combination with positive index materials. In particular, we investigate the behavior of the surface states at the interfaces for the two different types of effective index combinations. Brillouin light scattering measurements on these fabricated structures which support these theoretical designs are also presented.
4:30 PM - D15.3
Surface Plasmon Propagation and Light Polarization Conversion in Metal/Dielectric Swiss Rolls.
Marina Leite 1 , Eyal Feigenbaum 1 , Min Seok Jang 1 , Dennis Callahan 1 , Harry Atwater 1
1 , CALTECH, Pasadena, California, United States
Show AbstractLight polarization engineering is an important aspect of coupling unpolarized sunlight into thin film structures that support modes with specifically defined transverse electric (TE) and transverse magnetic (TM) polarizations. A microstructure that embodies this characteristic is a “Swiss roll”: a spiral that has cylindrical symmetry (coordinates r, φ, z), formed by a single metal layer or a metal/dielectric bilayer. “Swiss rolls” with 1-10 microns in inner diameter, up to 400 microns in length and between 3 to 20 layers were experimentally obtained by the self-rolling of thermally-stressed evaporated layers on a photolithographic pre-patterned substrate. Different metal (Au, Ag) and dielectric (Si, SiO2) materials, with 5 – 50 nm in thickness, and distinct coefficients of thermal expansion were used. By using an angled photolithographic pattern right-handed and left-handed chiral rolls were also achieved. Structure’s inner radius and number of layers depend on the pattern size and amount of material deposited. 3D Finite-Difference Time-Domain (FDTD) simulations showed that in a metal/dielectric “Swiss roll”, surface plasmon polaritons propagate differently than in a cylinder with similar dimensions and number of layers. Surface plasmons can be launched at the spiral entrance, and be propagated through the layers, both in radial and z (roll’s axis) directions, due to layer’s connection. FDTD simulations showed that light polarization can be reshaped throughout the 3D structure. A continuous plane wave (corresponding to visible and infrared wavelengths) with propagation direction tilted with respect to z direction was used as a linear polarized light source. We observed polarization conversion of light at the interface between the spiral ending and free-space in near and far fields. This result suggests that a Laguerre-Gaussian beam, with angular momentum, is generated by the “Swiss roll”, having helical power flow. Further investigation and modeling of the structure allows better control over the emerging beam’s characteristics. In conclusion, FDTD simulations were used to provide an understanding of how light can be polarized when traversing a “Swiss roll”. A beam with angular momentum can be used to concede torque to an illuminated system. Fabrication of microstructures with dimensions similar to the simulated structures that enable polarization conversion will be discussed.
4:45 PM - D15.4
Quasi-3D Plasmonic Crystals and Their Applications for Surface-enhanced Raman Spectroscopy.
Qiuming Yu 1 , Phillip Guan 1 , Jiri Homola 2
1 Chemical Engineering, University of Washington, Seattle, Washington, United States, 2 , Institute of Photonics and Electronics, Prague Czech Republic
Show Abstract Metallic nanoparticles and nanostructures have spurred great interesting recently because of the unique localized surface plasmon resonance (LSPR) excitations that, on one hand, pose challenges to fundamental solid state and optical physics while, on the other hand, offer great potential applications in many important areas such as novel optical devices, biosensors, surface-enhanced spectroscopy, solar cells, and solid-state lighting devices. Recently, we developed a unique quasi-3D plasmonic crystal composed of a thin metal film with nanoholes on top and metal disks at the bottom of each well. The plasmonic and optical properties of the quasi-3D plasmonic crystals were studied via the measurement of the normal transmission and dark field scattering spectroscopy. It was found that the plasmon resonance and the branching ratio of light absorption and scattering strongly depend on the materials (gold, silver or aluminum), the shape of holes (circle or triangle), the size of nanoholes (200-800 nm in diameter), the spacing (50-100 nm) between nanoholes and the separation (80-800 nm) between the top nanohole film and the bottom nanodisks. To further understand the plasmon excitation modes and the local electric field distribution, we conducted the three-dimensional finite-difference time-domain (3D-FDTD) calculations. The broad tenability of the plasmon resonances makes these quasi-3D plasmonic crystals good candidates for the application in surface-enhanced Raman spectroscopy (SERS). We found directly correlation between the enhancement factor of SERS and the plasmon resonances. The applications of SERS using these crystals as substrates in probing protein orientation on surfaces and in directly detecting cancer genes will be discussed.
5:00 PM - D15.5
Experimentally Realizing Negative Index of Refraction at Visible Frequencies.
Rene de Waele 1 , Stanley Burgos 2 , Harry Atwater 2 , Albert Polman 1
1 Photonic Materials, FOM Amolf, Amsterdam, Noord-Holland, Netherlands, 2 Applied Physics, California Institute of Technology, Pasadena, California, United States
Show AbstractIn the last decade remarkable progress has been made to miniaturize and redesign the scattering elements in negative-index metamaterials to enable operation at optical frequencies. However, operation in the visible is hampered by practical fabrication constraints limiting the size of sub-wavelength scatterers and the number of functional layers that can be made.
Here, we utilize a conceptually different method to realize negative-index metamaterials for the visible. Instead of relying on the collective response of sub-wavelength scatterers we design a single-layer metamaterial that consists of a two-dimensional array of coaxial waveguides with thin circular channels of Si surrounded by Ag that have a negative mode index in the blue. Using analytical calculations and simulations we show that this three-dimensional metamaterial exhibits a negative index of refraction n=-2 and figure-of-merit >8 in the blue-green spectral region. Coupling between the coaxial waveguides allows for negative refraction of energy in the layer in a direction antiparallel to the phase velocity in the slab.
To fabricate the metamaterial we use electron-beam lithography to define 25-nm-wide circular rings at a pitch of 165 nm in hydrogen silsesquioxane (HSQ) resist on 200-nm-thick silicon-on-insulator (SOI). The HSQ resist is used as an etch mask to form standing hollow cylinders of Si with a 30-nm-wide rim. Evaporation of ~100 nm-thick layer of Ag then yields the desired coaxial metamaterial. To remove any excess Ag we use a chemical-mechanical polishing process after deposition.
We will present preliminary experimental results of the optical behavior of the fabricated metamaterial and provide insights on the underlying principle and functionality of the negative-index metamaterial. Furthermore, we will give an outlook to possible applications in the visible.
5:15 PM - D15.6
A Three-dimensional Carpet Cloak in the Tera-Hertz Region.
Yongjun Bao 1 , Fan Zhou 1 , Cheng Sun 1
1 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States
Show AbstractRecently, invisible cloak has attracted many attentions but experimental demonstration of three-dimensional (3D) cloak still present many technical challenges. In a typical cloak design, the object is “hidden” successfully under a carpet cloak with curved reflecting surface and appears as if it is the original flat reflecting surface. This paper will introduce a three-dimensional (3D) carpet cloak in the tera-hertz (THz) region fabricated by the projection microstereolithography (PμSL) technique, which is unique for its capability of fabricating complex 3D structure in a layer-by-layer fashion. The invisibility will be demonstrated within 3D dielectrics, which provides possibility to make the cloak working in a broad frequency range. The cloak region is formed by varying the effective index of refraction (solid/air volume ratio). The index profiles are computed via Modified Liao’s function based mesh generation algorithm and realized by fabricating a series of high aspect ratio (~100:1) sub-wavelength channels with varying dimensions. The objective of the study is to provide comprehensive design strategies and experimental demonstration for effective implementation of the 3D carpet cloak in THz Region. The beam profiles of three configurations, a flat surface, a curved surface (without a cloak) and the same curved reflecting surface with a cloak, will be investigated to test the cloaking performance. Finite-element simulations shows that the reflected beam of curved surface (without cloak) is scattered by the bump into two distinct directions, while the reflected beam of the curved surface with a cloak propagates into the reflection direction similar to the case of the flat surface. In addition, the cloaking effect will be experimentally demonstrated on the time domain spectrometer (TDS) system. Finally, further steps toward achieving the 3D cloak design optimization and fabrication process is proposed.