June 4 - The 7th International Conference on Surface Plasmon

SPP7 Conference
Poster Presentations
Part II
June 4, 2015
1
Linearly Dichroic Plasmonic Lens and Hetero-Chiral Structures
Grisha Spektor, Asaf David, Bergin Gjonaj, Guy Bartal, Lior Gal,
Meir Orenstein
Electrical Engineering, Technion-Israel Institute of Technology, Haifa, Israel
It is well known that chiral structures, lacking in-plane mirror symmetry, exhibit circular dichroism.
Namely, they can discriminate the handedness of circularly polarized light. The field of Plasmonic
Lenses is concerned with structures on metal layers that can couple impinging light into surface
plasmons-polaritons (SPPs) and combine them into a focal spot. With the main goal being the
focusing of the out-of-plane SPP field components. Archimedes‟ spiral Plasmonic Lenses (ASPLs),
which are chiral by definition, are used as circularly dichroic lenses – focusing circular polarization
with proper handedness and resulting in a dark focal spot for the opposite handedness.
In contrast, much lesser emphasis had been made on linearly dichroic devices – namely devices
focusing electromagnetic waves with a specific linear polarization – while blocking (not focusing)
the orthogonally polarized wave.
We demonstrate that a combination of two ASPLs with opposite handedness (chirality) and unity
geometrical charge results in a Hetero-Chiral plasmonic lens (HC lens) with a linearly dichroic
focal spot. In the process of their merging, the chiral symmetry of the constituents is broken,
however the mirror symmetry is not completely restored implying that the combined structure
should distinguish between horizontal and vertical excitations leading to linear dichroism. Fig. 1a.
gives the schematics and Fig. 1d,e the experimental results of the actual HC lens.
A further simplification of the 2 engaged spirals can be gained by removing the central part of the
structure (Fig. 1b) obtaining a structure resembling a distorted circle. Intriguingly, this slight
deformation results in a rather strong linear dichroism of the focal spot (Fig. 1f,g). Different
selective erasure procedure can be also applied to result in the Half-circles structure (Fig. 1c,h-i).
We study, experimentally verify and quantitatively compare several members of the HC family,
deriving necessary conditions for linear dichroism and several comparative engineering parameters.
The HC structures were fabricated by FIB in gold. The samples were illuminated by relevant
polarizations and the transmitted near field pattern was collected using aperture-less NSOM
exhibiting excellent match to the simulation results.
[email protected]
2
Theoretical Designation of All-Optical Modulator Consisting of Subwavelength Metal Slits
Huai-Yu Wang, Yu Liu
Department of Physics, Tsinghua University, Beijing, China
We have designed by simulation computation an all-optical modulator with simple structure. It
consists of subwavelength metal slits, and its structure mimics that of an electronic transistor,
having one input (Port 1), one base (Port 2) and one output (Port 3), see
Fig. 1. The parameters of the structure in Fig. 1 are h1 = 0.5 μm, h2 = 0.51 μm, l = 1.18 μm, w = 0.1
μm.
The light wavelength in vacuum is l0 = 0.8 mm and correspondingly the wavelength of in-slit SPP
mode lS = 0.653 mm. The mechanism of the in-slits SPP interference is utilized. The light entering
the Port 2 is invariant, and the input signal interferes with it, which determines the output. As a
primary study, the static response is simulated. That is to say, the input signal is a plane wave
continuously emitted from the launch field 1 without the variation of its profile. When the phases of
the input and base are the same, the output shows a function of amplification, while when their
phases are contrary, the output shows a diminishing function. Figure 2 shows the results. Therefore,
the device acts as either an amplifier or a diminishing one. This all-optical modulator does not
require any auxiliary equipment, and its response time is of the order of magnitude of 0.1
picoseconds. (a) Dj = 0, (b) Dj = π. The inset in (b) shows the
When the widths of the slits are
in sub-micrometers,
results around Iin=1. The lines are to guide eyes. The device is of nanoscaled structure.
Fig. 1. Model structure of the optical modulator.
This work was supported by the Natural Science Foundation of China (No. 61275028).
[email protected]
3
Non-Invasive Near-Field Photocurrent Nanoscopy Enables Graphene Device Quality Control
Achim Woessner1, Pablo Alonso-González2, Mark B. Lundeberg1,
Gabriele Navickaite1, Yuanda Gao3, Qiong Ma4, Davide Janner1,
Kenji Watanabe5, Takashi Taniguchi5, Valerio Pruneri1, Pablo Jarillo-Herrero4,
James Hone3, Rainer Hillenbrand6,7, Frank Koppens1
1
., ICFO - Institut de Ciencies Fotoniques, Barcelona, Spain
2
., CIC nanoGUNE, San Sebastian, Spain
3
Department of Mechanical Engineering, Columbia University, New York,
NY, USA
4
Department of Physics, Massachusetts Institute of Technology, Cambridge,
MA, USA
5
National Institute for Materials Science, Tsukuba, Japan
6
CIC nanoGUNE and UPV/EHU, San Sebastian, Spain
7
IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
Graphene is a promising material for optoelectronic applications as its lack of a bandgap leads to a
broad band absorption that spans the visible, near-infrared, mid-infrared and THz regime.[1,2] For
applications it is of great importance to know the exact optoelectronic properties of the devices
used. With common far-field methods the large size of the laser spot after focusing prevents a
spatial resolution below the diffraction limit. This leads to smearing of the spatial photocurrent
maps, which can mask important details. Here we introduce a photocurrent measurement technique
which is not limited by the diffraction limit. Using a scattering-type scanning near-field optical
microscope (s-SNOM) [3,4] with a mid-infared laser source we excite a strong near-field at the
apex of a metallized atomic force microscope probe tip, which acts as a local heat source,
generating a temperature gradient in the graphene. This temperature gradient together with a change
in Seebeck coefficient leads to a photothermoelectric photocurrent that can be measured spatially.
[5] Here we show how near-field photocurrent measurements with extremely high spatial resolution
can be used for characterizing optoelectronic devices made of graphene and graphene
heterostructures.[6] We show photocurrent measurements at grain boundaries intrinsic to graphene
grown by chemical vapor deposition [7] and extract their polarity. Furthermore we use this unique
tool to measure photocurrent from charge puddles [8] of exfoliated graphene on silicon dioxide and
show a photocurrent resolution of sub-30 nm. This proofs the extremely high spatial resolution
which can be obtained, which ultimately is only limited by the radius of the tip apex. Finally we use
the near-field photocurrent technique to confirm the spatial uniformity of the charge neutrality point
of graphene encapsulated in hexagon boron nitride.[9] In summary, in this talk we introduce the
novel near-field photocurrent mapping technique and show its potential applications in device
characterization and quality control.
References
[1] F.H.L. Koppens et al., Nature Nanotechnology, 9 (2014) 780-793.
[2] M. Badioli et al., Nano Letters, 14 (2014) 6374-6381.
[3] J. Chen et al., Nature, 487 (2012) 77–81.
[4] Z. Fei et al., Nature, 487 (2012) 82-85.
[5] N. Gabor et al., Science, 334 (2011) 648-652.
[6] A.K. Geim et al., Nature, 499 (2013) 419-425.
[7] A.W. Cummings et al., Advanced Materials, 30 (2014) 5079-5094.
[8] J. Martin et al., Nature Physics, 4 (2008) 144-148.
[9] L. Wang et al., Science, 342 (2013) 614-617.
[email protected]
4
Collective Light Scattering on Gold Nano-Spheres in Micro-Droplets of Suspension
Maciej Kolwas, Maciej Kolwas, Krystyna Kolwas, Daniel Jakubczyk,
Genadij Derkachow
Optics & Spectroscopy, Institute of Physics, Polish Academy of Sciences,
Warszawa, Poland
We study scattering of light on evaporating single microdroplet of suspension of gold inclusions
(125nm radius) in glycol (DEG). The optical diagnostics of a single droplet levitating in the
electrodynamic trap was based on the analysis of the spatial interference pattern and temporal
distributions of the scattered light intensity
Fig.1 Outline of experimental set-up (let) and (right)the evolution of intensities IVV (red), IHH
(green), IVH (blue) and IHV (dark yellow). Cross polarized intensities IVH, and IHV are small but
substantial. Fast oscillations of intensities IVV and IHH are due to the droplet WGM, magnified in
the inset.
The intensity of scattered depolarized light was used to determine effective index of refrac-ion of
the medium surrounding inclusions. The resonant increase of scattered light intensity was observed
in the region of overlap inclusions mean distance and light wavelength (on Fig 1 near t=500s).
Observed resonances were interpreted as collective scattering (CS) of plasmons induced in different
inclusions showing importance of influence of nonlocal fields on local field scattered by given
inclusion. More than double increase of scattered light intensity was observed for “high”
preliminary density of inclusions (ca.1500 inclusions) at resonance. The oscillatory shape of CS
resonances showed constructive (in phase) and partly destructive interference of plasmons in
separate inclusions on collective oscillations . Observed CS resonances were modulated by
whispering gallery modes (cavity modes of droplet acting as a spherical resonator[1]) showing ultra
narrow structure of CS resonance connected with droplet cavity modes (WGM). The property of
very narrow and relatively strong resonances giving possibility to tune scattering in very precise
manner seems to be extremely interesting feature for future studies and possible applications.
[1] Kolwas, M.; Jakubczyk, D.; Derkachov, G. and Kolwas, K. J.Q.S.R.T. 2013, 131(0), 138 – 145
[email protected]
5
Sub-Diffraction Limitted Imaging with a Spatially Dispersive Slab
Avner Yanai, Uriel Levy
Applied Physics, The Hebrew University of Jerusalem, Jerusalem, Israel
In 2000, it was suggested that a thin planar metallic slab can perform as a lens capable of producing
an image with sub-diffraction limited (SDL) resolution [1]. In this seminal paper, Pendry showed
that by using a thin metallic slab, only few tens of nanometers thick, which is excited with light near
its surface plasmon (SP) resonance frequency, an image with SDL size can be obtained, due to the
high momentum frequency components of the SP modes that are supported by the interfaces
between the metallic slab and the dielectric medium surrounding it. This imaging concept was
coined as the “poor man‟s lens” and was the subject of debate in the scientific community over the
years. Here, we propose a different physical concept for achieving SDL imaging, taking advantage
of the longitudinal modes within a thin metallic slab that is described by the hydrodynamic model.
The SDL imaging occurs for discrete frequencies satisfying ωω­p. This frequency regime is
different from the original proposal of the “poor man‟s lens”, in which the incident illumination
frequency is in the vicinity of the SP resonance frequency ω­p/√2. Furthermore, the underlying
physical mechanism of the two approaches is different. In the original proposal, the high-k
components of the source are reconstructed at the image plane due to that the SP resonance surface
modes which support high spatial frequency components. In contrast, our approach is not based on
surface modes. Instead, the high-k components are transferred to the image plane by the
longitudinal modes, which typically have propagation constants more than an order of magnitude
larger than the vacuum propagation constant k0=2π/λ0. The permittivity of the slab is described by
the hydrodynamic model [2,3].
[1] J. B. Pendry, Phys. Rev. Lett. 85, 3966 (2000).
[2] C. David, N.A. Mortensen, and J. Christensen, Sci. Rep. 3, 2526 (2013).
[3] P. J. Feibelman, Prog. Surf. Sci. 12, 287–408 (1982).
[email protected]
6
Magnetic Field Enhancement in Graphene Diabolo Nanoantenna with and without Nonlocal
Effect
Zenghong Ma, Wei Cai, Lei Wang, Weiwei Luo, Xinzheng Zhang, Jingjun Xu
The Key Laboratory of Weak-Light Nonlinear Photonics, Ministry of Education,
School of Physics and TEDA Applied Physics School, Nankai University, Tianjin,
China
Graphene is made of carbon atoms arranged on a hexagons honeycomb structure [1], whose pristine
form is a semimetal, but with appropriate doping it is emerging as a promising plasmonic material
as well. Compared with surface plasmons in metal, graphene plasmons provide a conveniently
tunable platform for strong light-matter interactions, much due to their enormous confinement and
relatively long propagation length [2]. In this work, we study the plasmonic properties of graphene
diabolo nanoantennas (GDAs) [3], the complemental structures of bowtie aperture antenna
according to Babinet‟s principle. We discuss the enhancement and localization of magnetic field of
GDA in mid-infrared frequency range by using the finite element method. Simulation results
indicate that a smaller gap induces larger magnetic field enhancement. Specifically, a positive
correlation between the polarization current density of the electric field and magnetic field intensity
is obtained in local approximation, which agrees well with Ampere‟s rule. In further, the magnetic
field enhancement effect is calculated and compared with the nonlocal effect of graphene. What is
worth mentioning is that our results present another efficient way, compare to using traditional
ferromagnetic materials, to concentrate and enhance magnetic fields.
[1] Novoselov, K. S. et al. Science306,666–-669(2004).
[2] Koppens, F. H. L. et al. Nano Lett. 11, 3370 (2011)
[3] Grosjean, T. et al. Nano Lett. 11, 1009 (2011)
[email protected]
7
Nanoplasmonic Directional Light Sensor and Color Filter
Matthew Davis, Henri Lezec, Amit Agrawal
National Institute of Standards and Technology,
Center for Nanoscale Science and Technology, Gaithersburg, Maryland, USA
Surface plasmon polaritons (SPPs) are surface waves that exist at the interface between a metal and
a dielectric resulting from coupling of electromagnetic radiation to surface charge oscillations. The
study of SPPs, though easily understood with classical electromagnetics, offers a richness of
phenomena that have led to a diverse range of applications in sensing, imaging, and nonlinear
optics. Advances in theoretical understanding and fabrication methods have resulted in an
unprecedented ability to control light through plasmonic nanostructures. For instance, enhanced
transmission of light through subwavelength apertures is achieved by surrounding the aperture with
nanopatterned grooves. Furthermore, periodic arrangements of the grooves results in a highly
wavelength sensitive device response. Such spectral response has proven to be a useful property for
color filtering in sensing, display, and imaging devices. More recently, we have demonstrated that
an aperiodic slit-grooved-array (SGA) can act as a wavelength-dependent plasmonic directional
light filter. This behavior is achieved through careful selection of individual groove widths, depths,
and placements between the slit and the grooves. Typically, selection of groove parameters for the
SGA device is achieved through time-consuming FDTD calculations. This is feasible on current
desktop computers for 1D devices such as the SGA, however extending this approach to 3D
plasmonic filters would benefit from a less computationally-intensive design method. In this talk,
we will first present the design methodology using a 1st-order SPP interference model that is used
for the filter design, a process that is free of FDTD calculations. This model is based on optimizing
the phase-shift accrued by light coupling/scattering from multiple grooves surrounding a single
deep-subwavelength slit. Finally, we will discuss the nanofabrication and experimental
characterization of the designed nanoplasmonic filter; and demonstrate the immense time saving
factor of this approach. It is expected that a passive plasmonic device sensitive to the direction of
incident white light may represent a simpler approach over existing light trackers.
[email protected]
8
Enhanced Magneto-Optical Activity in Photonic Crystals with Plasmonic Patterns
Olga Borovkova1, Nikolai Khokhlov1, Mikhail Kozhaev1,2, Anatoliy Prokopov3,
Alexander Shaposhnikov3, Vladimir Berzhansky3, Ajith Ravishankar4,
Venu Gopal Achanta4, Anatoly Zvezdin2, Vladimir Belotelov1,2,5
1
Magneto-Optics, Plasmonics and Nanophotonics Group,
Russian Quantum Center, Moscow, Russia
2
Department of Theoretical physics, Prokhorov General Physics Institute Russian
Academy of Sciences, Moscow, Russia
3
Faculty of Physics and Computer Science,
Crimean Federal University, Simpheropol, Russia
4
Department of Condensed Matter Physics and Materials Science,
Tata Institute of Fundamental Research, Mumbai, India
5
Faculty of Physics, Lomonosov Moscow State University, Moscow, Russia
Multilayer structure consisting of a magnetophotonic crystal with rare-earth iron garnet
microresonator layer and plasmonic grating deposited on it was fabricated and studied in order to
combine functionalities of photonic and plasmonic crystals. The plasmonic pattern allows excitation
of the hybrid plasmonic-waveguide modes localized in dielectric Bragg mirrors of the
magnetophotonic crystal or waveguide modes inside its microresonator layer. These modes give
rise to the additional resonances in the optical spectra and optical field localization within the
structure. It leads to the higher light – magnetic materials interaction and results in the enhancement
of the magneto-optical effects. The Faraday effect increases by about 50% at the microresonator
modes while the transverse magneto-optical Kerr effect demonstrates pronounced peculiarities at
both hybrid waveguide modes and microresonator modes and increases by several times with
respect to the case of the bare magnetophotonic crystal without the metal grating. The shape of the
TMOKE resonance depends on the type of the waveguide mode that gives rise to the resonance. In
some cases, the magnetization mostly influences on the reflectance minima related to the
resonances. However, in some other cases the magnetization mostly shifts the spectral position of
the waveguide mode resonance.
The studied novel type of heterostructures may find applications in optical signal modulators via
external magnetic field or high-sensitive biosensors and magnetic field detectors. Here the
advantages of the magnetophotonic crystals with plasmonic gratings are spectral narrowness of
optical and magneto-optical resonances and the possibility for their observation in transmission.
The work is supported by the Russian Foundation for Basic Research (projects No 13-0291334, 1402-01012) and the Russian Presidential Grant MD-5763.2015.2.
[email protected]
9
Pari-Time Symmetry Breaking in Ddouble-Slab Surface-Plasmon Waveguides
Seok Ho Song1, Youngsun Choi1, Seok Song1, Choloong Han1,
Jong-Kyun Hong2
1
Physics, Hanyang University, Seoul, South Korea
2
Electrical Engineering, Hanyang University, Seoul, South Korea
Asymmetric propagation behaviors of light in Parity-Time (PT) symmetric complex-index media
are evaluated.[1] Dould-slab surface-plasmon polariton (DS-SPP) waveguide couplers,[2]
consisting of metal slabs with loss and gain, are considered as the PT-symmeric media. So far, in
demonstrations of the symmetry breaking in optical systems, the main difficulty has been to control
gain and loss with a high reliability. The coupled DS-SPP waveguides proposed here allow us to
separately and systematically control the parity and time symmetries, appealing that they would be
an useful tool for investigating underlying physics on PT-symmetry breaking phenomena in nonHermitian Hamiltonian systems.
(Double-slab SPP coulers) (Mode propagation behaviors before and after PR-symmetry breaking)
[1] C. M. Bender and S. Boettcher, Physical Review Letters 80, 5243 (1998).
[2] Jaewoong Yoon, Seok Ho Song, and Suntak Park, Optics express, 15, 17151-17162. (2007).
[email protected]
10
Narrow Bandwidth Metal-Insulator-Metal-Insulator-Metal Filters for Hyperspectral Imaging
Applications
Dagny Fleischman1, Luke Sweatlock1,2, Hirotaka Murakami1,3,
Sozo Yokogawa1,3, Harry A. Atwater1
1
Materials Science, California Institute of Technology, Pasadena, California, USA
2
N/A, Northrop Grumman, Redondo Beach, California, USA
3
N/A, Sony Corporation, Tokyo, Japan
Plasmonic structures have shown promise for applications as color filters in the visible and near IR
parts of the spectrum. Due to their subwavelength mode volumes, plasmonic filters are well
matched to the small size of state-of-the-art active pixels for dense integration in CMOS image
sensor arrays. However, typical plasmonic filters possess a tradeoff between relatively broad
transmission bandwidths and multiple resonances. If it were possible to dramatically reduce the
FWHM of the transmission spectra while retaining a single peak, CMOS hyperspectral imaging
arrays could be realized. We have designed and optimized metal-insulator-metal-insulator-metal
(MIMIM) structures that possess a single transmission peak with FWHM as small as 17 nm. Using
finite difference time domain calculations and a boundary value solution method for multilayer
plasmonic structures, we have calculated MIMIM dispersion relations to identify the nanophotonic
parameters responsible for narrowband filter transmittance.
The transmission element of MIMIM filters is an array of parallel sub-wavelength slits perforating
the MIMIM stack, which acts as a narrowband transmission resonator. The in-plane periodicity of
the slit array dictates the filter transmission wavelength, so the same MIMIM architecture can be
densely integrated in adjacent filter elements for multiple wavelength intervals by simply adjusting
the spacing between the slits. Additionally, the MIMIM structure itself is highly tunable. Along
with changing the periodicity of the slits in the filter, the active plasmon mode can be manipulated
by controlling the thickness of the insulating layers, by changing the indices of the constituent
materials or by adjusting the thickness of the middle metal layer that couples together the two
individual MIM structures of the device.
We have developed an amorphous silicon facilitated lift-off process to fabricate the MIMIM filter
structures, because transmission behavior is highly dependent on the straightness of the sidewalls of
the slits that perforate the stacked films. The results of the transmission measurements of these
filters and prospective ways for integration with CMOS image sensors will also be discussed.
[email protected]
11
Active THz Plasmonic Structures and Circuits on Flat Semiconductor Layers
Giorgos Georgiou1, Arkabrata Bhattacharya1, Jaime Gomez-Rivas1,2
Center for Nanophotonics, FOM Institute AMOLF, Amsterdam, Netherlands
2
COBRA Research Institute, Eindhoven University of Technology, Eindhoven,
Netherlands
1
Optical illumination of semiconductors leads to photoinduced doping. When the illumination is
local and intense, the semiconductor transits from a dielectric to a metallic behavior at THz
frequencies only at the illuminated area. We have used this concept to demonstrate experimentally
the photo-excitation of THz localized surface plasmon polaritons (LSPPs) in flat semiconductor
layers [1]. This is realized by a patterned optical excitation of free charge carriers in thin films of
GaAs using a spatial light modulator, which enables full spatial and temporal control of resonances
without the need of physically structuring the sample. This approach is also used to excite
capacitively and inductively coupled LSPPs in loaded plasmonic antennas. We also propose the
spatially structured photoinduced doping of semiconductors to dynamically generate plasmonic
waveguides and circuits [2].
[1] G. Georgiou, H.K. Tyagi, P. Mulder, G. Bauhuis, J. Schermer and J. Gómez Rivas,
Photo-generated THz antennas, Sci. Rep. 4, 3584 1-5 (2014)
[2] H.K. Tyagi and J. Gómez Rivas, Photo-generated THz plasmonic waveguides, J. Opt. 16,
094011 1-7 (2014)
[email protected]
12
Fabrication of Scanning Probe Tips made of Epitaxial Germanium with Plasma Frequency in
the Mid-Infrared
Valeria Giliberti1, Emilie Sakat2, Leonetta Baldassarre3, Jacopo Frigerio4,
Giovanni Isella4, Mauro Melli5, Alexander Weber-Bargioni5, Stefano Cabrini5,
Marco Finazzi2, Michele Celebrano2, Paolo Biagioni2, Michele Ortolani1,
Monica Bollani4,6
1
Department of Physics, Sapienza University of Rome, Rome, Italy
2
Department of Physics, Politecnico di Milano, Italy, Milano, Italy
3
Center for Life and Nano Sciences, Italian Institute of Technology, Rome, Italy
4
LNESS, Laboratory for Nanostructure Epitaxy and Spintronics on Silicon, Como,
Italy
5
Lawrence Berkeley National Labs, Molecular Foundry, Berkeley, USA
6
Institute for Photonics and Nanotechnologies, National Research Council of Italy,
Milano, Italy
We target the nanofabrication of scanning probe tips made of high-crystal-quality epitaxial
semiconductor material layers with high heterostructure complexity for optical applications at the
nanoscale. Here the fabrication method for epitaxial germanium grown on a silicon substrate is
demonstrated but the same approach can be extended to any heterostructure material.
The first step of the process is the fabrication of nanostructures out of planar epitaxial wafers in the
form of pillars with arbitrary section and high aspect ratio by electron-beam lithography and deep
reactive-ion etching. Electron-beam induced deposition is used to weld the cut tip of an Atomic
Force Microscopy (AFM) cantilever to the top of one pillar, whose base is then cut by focused ionbeam (FIB) milling (figure 1a). Finally, the epitaxial germanium nanostructure is shaped into a
pyramid tip by FIB milling (figure 1b and 1c).
Micro-photoluminescence and transmission electron microscopy analysis performed on the
germanium scanning probe tips confirm that the high crystal quality typical of epitaxial layers
grown on a large-area substrate is preserved throughout the different fabrication steps. First
prototypes of the tips obtained from heavily-electron-doped germanium with plasma frequency in
the mid-infrared have been successfully applied to perform scattering scanning near-field infrared
microscopy on nanostructured samples.
Work at the Molecular Foundry was performed under User Proposal # 1773. The research leading
to these results has received funding from the European Union‟s Seventh Framework Programme
under grant agreement n°613055.
[email protected]
13
Second Harmonic Generation from Uniaxial Plasmonic Metamaterials: from Elliptical to
Hyperbolic Dispersion Regimes
Giuseppe Marino, Paulina Segovia, Alexey V. Krasavin, Pavel Ginzburg,
Mahzar E. Nasir, Wayne Dickson, Nicolas Olivier, Grégory Wurtz,
Anatoly Zayats
Department of Physics, King's College London, London, UK
Second Harmonic Generation (SHG) was the first nonlinear optical effect to be observed once
lasers became available [1]. Since, SHG has been studied in various materials and geometries
including noble metal surfaces and films. In the latter surface plasmon polaritons have primarily
been used to enhance SHG. Recently, SHG in noble metal nanostructures has seen increased
scrutiny [2,3] due to the unique optical properties offered by both localized surface plasmons and
their hybridization in complex nanostructured systems. However, the rational study of complex
structures requires the development of suitable theoretical approaches and numerical tools [4].
We have developed a numerical model to study SHG at the nanoscale and applied it to study gold
nanorod-based plasmonic metamaterials. The metamaterial shows an Epsilon Near Zero (ENZ)
frequency tunable across the visible and near-IR frequency range, responsible for the emergence of
a set of resonances in its vicinity, enabling a multi-resonant coherent response both at the
fundamental (FF) and harmonic frequencies (HF). This property allow the achievement of high
SHG conversion efficiency and tailored SHG emission. The SHG response of the metamaterial is
investigated and discussed based on the modal properties with a particular focus made on the
relationship between their near and far-field response, spatial field overlap between FF and HF, and
geometry-allowed SH emission.
[1] P.A. Franken, A.E. Hill, C.W. Peters, and G. Weinreich, Phys Rev. Lett. 7, 118 (1961)
[2] G. A. Wurtz, R. Pollard, W. Hendren, G.P. Wiederrecht, D.J. Gosztola, V.A. Podolskiy, and
A.V. Zayats, Nature Nanotech. 6, 107-111 (2011)
[3] P. Gingzburg, A. Krasavin, Y. Sonnefraud, A. Murphy, R.J. Pollard, S.A. Maier, and
A.V.Zayats, Phys Rev. B, 86, 085422 (2012)
[4] P. Ginzburg, A. V. Krasavin, Gregory A.Wurtz, and A.V. Zayats, arXiv preprint
arXiv:1405.4903 (2014).
[email protected]
14
Alloy Nanoplasmonics: PdAu Alloy Nanoparticles for Hysteresis-Free Plasmonic Hydrogen
Sensing
Ferry Anggoro Ardy Nugroho, Carl Wadell, Emil Lidström,
Christoph Langhammer
Department of Applied Physics, Chalmers University of Technology, Gothenburg,
Sweden
The notion of a hydrogen economy has catalyzed the development of various fields, like the use of
nanostructured metal-hydride systems as signal transducer in plasmonic hydrogen sensors. [1] For
this application, to date, Pd has been the transducer material of choice since it readily absorbs and
releases hydrogen at room temperature and, more importantly, also exhibits localized surface
plasmon resonance. However, the usage of pure Pd for hydrogen sensing purpose in real devices is
not ideal. It exhibits wide hysteresis upon hydrogen sorption, which creates the problem of
ambiguous readout depending on the sensor‟s history. Alloying Pd with another metal (e.g. Au, Ag)
is one possible solution to reduce the hysteresis and thus eliminate this problem. [2]
In this work we present a generic means to fabricate arrays of well-defined alloy plasmonic
nanoparticles. Specifically, we fabricate quasi-random PdAu alloy nanodisks using Hole-mask
Colloidal Lithography[3], in combination with alternating deposition of layers of Pd and Au
followed by annealing at 500oC to promote alloy formation. For the application as hysteresis-free
signal transducer in hydrogen sensors we find that increasing the Au content in the alloy
nanoparticles significantly lowers the width of the hysteresis. Moreover, the sensitivity towards
hydrogen at low H2 concentrations in the sensor environment increases up to eight times compared
to pure Pd. Notably, this improved performance is obtained without compromising the signal-tonoise ratio of the sensor.
As we have shown before, plasmonic hydrogen sensing is also very useful to scrutinize more
fundamental aspects of metal-hydrogen interactions at the nanoscale. Therefore we also utilize our
PdAu nanoparticle arrays to shed light on the thermodynamics and kinetics of metal hydride
formation as a function of alloy composition, and report on the most important findings.
References
[1] C. Wadell, et al., ACS Nano, Article ASAP DOI: 10.1021/nn505804f
[2] R. C. Hughes, et al. J. Appl Phys. 62, 1074 (1987).
[3] H. Fredriksson, et al., Adv. Mater. 19 4297 (2007).
[email protected]
15
Optical and Electrical Properties of Silver-Titanium Dioxide Layered Nanocomposites
Piotr Nyga1, Sylwester Chmiel1, Marzena Szczurek1, Malwina Liszewska1,
Marek Stefaniak1, Jozef Firak1, Bartłomiej Jankiewicz1, Malgorzata Norek2,
Jadwiga Mierczyk1
1
Institute of Optoelectronics, Military University of Technology, Warsaw, Poland
2
Department of Advanced Materials and Technologies,
Military University of Technology, Warsaw, Poland
There is great interest in nanoscale metal-dielectric and metal-semiconductor structures and
composites for their potential in many science and engineering fields. Various types of such
nanostructures are studied for applications in sunlight harvesting processes like photovoltaics,
photocatalysis, heat generation, but also for substrates for surface enhanced Raman and Infrared
spectroscopies and many more. Most of the fabrication methods of nanostructures are relatively
expensive considering cost per area, for example electron beam lithography. Physical vapor
deposition (PVD) is one of the inexpensive methods of production of plasmonic metal
nanostructures on surface or embedded in dielectric or semiconductor. When thin metal layer is
deposited using PVD technique randomly arranged nanostructured semicontinuous metal film can
be obtained. Size, shape and optical properties of these nanostructures can be controlled by
choosing specific deposition process conditions. [1,2]
Here we present the details of optical and electrical properties of silver-titanium dioxide (Ag-TiO2)
layered nanocomposites fabricated using electron beam (EB) PVD technique. We varied several
parameters of the fabricated structures and EB PVD process including silver and TiO2 layer
thickness, number of layers, deposition temperature, oxygen dosage and post fabrication annealing.
Utilizing the semicontinuous nature of silver films we achieved structures with broadband
absorption. The level and spectral width of absorption can be tuned by design. Through number of
silver layers and their thickness the absorption level of composite can be adjusted from about 10%
to above 90% in the visible and/or infrared range. We have also achieved control over composite
sheet resistance, which will be reported along with its thermo-electric properties.
[1] P. Nyga, V.P. Drachev, M.D. Thoreson and V.M. Shalaev, “Mid-IR plasmonics and
photomodification with Ag films,” Applied Physics B 93, 59-68 (2008).
[2] M.D. Thoreson, J. Fang, A.V. Kildishev, L.J. Prokopeva, P. Nyga, U.K. Chettiar, V.M. Shalaev
and V.P. Drachev,” Fabrication and Realistic Modeling of 3D Metal-Dielectric Composites”,
Journal of Nanophotonics 5, 051513-051513-17 (2011).
The research was financed by the Polish National Centre for Research and Development grant no
LIDER/23/22/L-3/11/NCBR/2012.
[email protected]
16
Linear and Non-linear Optical Properties of Plasmonic Quasi Crystals
Ajith Padyana Ravishankar1, Venkata Jayasurya Yallapragada1,
Sachin Kasture2, Arvind Nagarajan1, Gajendra Mulay1, Venu Gopal Achanta1
1
Department of Condensed Matter Physics and Material Science,
Tata Institute of Fundamental Research, Mumbai, Maharashtra, India
2
Centre for Quantum Dynamics, Griffith University, Brisbane, Queensland,
Australia
Plasmonic quasicrystals (PlQCs) offer several advantages over plasmonic crystals [1]. Some of the
properties like broadband transmission enhancement and designable spectral response are recently
demonstrated showing their potential for light harvesting applications [2]. Here we report linear and
nonlinear optical properties of plasmonic quasicrystals. Especially, we demonstrate two orders of
magnitude enhancement in the transmission through surface roughened pattern compared to
unpatterned metal. We also show that, though the gold second order nonlinear susceptibility is
weak, second harmonic generation (SHG) is possible over a broadband and is directly related to the
transmission enhancement of the fundamental. Another interesting question to address is the role of
the metal thickness on the observed properties.
We have realized PlQCs over 1mm2 area in the form of air holes in gold film by electron beam
lithography. We prepared and studied samples with peak responses at about 600nm and 800nm. By
combining quasicrystal hole array pattern with surface roughness, two orders of magnitude
enhancement in broadband transmission through sample was observed compared to unpatterned
metal of 100nm thickness.
Plasmon mediated local field is strong and was shown to result in SHG from metal patterned with
hole arrays [3]. We studied SHG from PlQCs and find it to be over broadband. Also we studied
SHG for different angle and launch polarization. From the measured fundamental and SHG, we
estimate the second order susceptibility of gold film in the 740nm to 840nm wavelength range.
Though, PlQC with roughness showed large linear transmission enhancement, it did not show
correspondingly high SHG indicating that the increased linear transmission due to roughness is not
related to plasmon excitation.
17
Fig: Broad band response of SHG output at normal incidence of Fundamental for different
wavelengths. (Inset) Quadratic Dependence of SHG output power with Fundamental at 800nm.
References:
[1] V. G. Achanta, Prog. Quant. Electron. 39, 1-23 (2015)
[2] Sachin Kasture et al., Scientific Reports, 4, 5257, (2014)
[3] M Airola et al., J. Opt. A: Pure Appl. Opt. 7, S118–S123 (2005)
[email protected]
18
Gate-Tunable Conducting Oxide Metasurfaces
Yao-Wei Huang1,2,3, Ho Wai Lee2,3, Ruzan Sokhoyan2, Krishnan Thyagarajan2,3,
Georgia Papadakis2, Seunghoon Han2,4, Din Ping Tsai1,5, Harry A. Atwater2,3
1
Department of Physics, National Taiwan University, Taipei, Taiwan
2
Thomas J. Watson Laboratories of Applied Physics, California Institute of
Technology, Pasadena, California, USA
3
Kavli Nanoscience Institute, California Institute of Technology, Pasadena,
California, USA
4
Samsung Advanced Institute of Technology, Samsung, Suwon, Gyeonggi-do,
South Korea
5
Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan
In the past decade, metasurfaces composed of sub-wavelength artificial ultrathin structures show the
promises to exhibit extraordinary light-manipulation and to overcome the limitations of
conventional optical components such as lens, wave plates, orbital angular detection, and holograms
in any electromagnetic wavelength region. Recent developments in metasurface employs the
flexible and reconfigurable optical responses in light manipulation that promises to achieve tunable
metasurface devices. Electrical tuning methods based on carrier-induced index changes in
transparent conducting oxide provide a capability for potential technology in dynamic response and
compatibility with silicon technology to mass-produce.
We report an original approach to create electrically tunable metasurfaces with amplitude and phase
modulation based on the voltage applied on conducting oxide active region. The electrically tunable
metasurface consists of connected gold nanoantenna array patterned on a 5 nm thin Al 2O3 and
indium tin oxide (ITO) layers on a gold mirror. By increasing the bias voltage on the nanoantenna,
the carrier concentration of the conducting oxide material increases and forms an accumulation
layer at the Al2O3-ITO interface, resulting in the higher plasma frequency of active ITO and the
modification of its complex permittivity. The real part of permittivity of active ITO approaches near
zero region (epsilon-near-zero, ENZ) at wavelength 0.5 – 3 μm corresponding to carrier
concentration about 1×1022 – 2×1020 cm-3, which occurs a large electric field enhancement in this
region. Using the electrical modulation on the active ITO layer, we show that coupling ENZ region
of ITO with plasmonic resonance of gold nanoantenna can generate two resonances, which can be
used in amplitude-modulated metasurface. In contrast, the wavelength region between these two
resonances shows capable of obtaining large phase modulation of 2π versus carrier concentration in
active ITO, leading to a phase-modulated metasurface. These results have potential applications in
performing dynamic beam shaping, reconfigurable imaging, and high capacity data storage based
on electrically tunable metasurfaces.
[1] N. Yu et al., Science 334, 333-337 (2011).
[2] S. Sun et al., Nano Lett. 12, 6223-6229 (2012).
[3] H. W. Lee et al., Nano Lett. 14, 6463-6468 (2014).
[email protected]
19
Optical Properties and Applications of Multilayer Systems of Thin Metal Films with
Nanometer Hole Arrays on Porous Alumina - Aluminum Substrate
Juris Prikulis, Tomas Tamulevičius, Raimonds Poplausks, Gatis Bergs,
Indra Apsite, Uldis Malinovskis, Donats Erts
Institute of Chemical Physics, University of Latvia, Riga, Latvia
Recently metal coated porous anodized aluminum oxide (AAO) layers have attracted interest for
potential optical filtering or sensor applications. The colorful appearance of these coatings is mainly
governed by interference effects between the semitransparent thin metal film and reflection from
aluminum surface. This simplified interference model largely neglects the role of holes in metal
layers, which however, can significantly change the spectral properties [1] and are of great
importance e.g. for surface enhanced Raman spectroscopy [2].
We addresses the optical properties of 10-35 nm thin metal films with 18-25 nm diameter holes
obtained by deposition of gold or silver on 75-280 nm layers of AAO supported by bulk aluminum
substrate. We show a comprehensive study of these multilayer systems including spectroscopic
ellipsometry measurements and demonstrate how various system parameters influence the optical
response. Apart from interference related minima and maxima, which shift with change of AAO
thickness we observe optical attenuation components which fall out of regular pattern and are metal
material dependent.
We also demonstrate several applications of these multilayer systems where simple optical
measurements can be used to extract e.g. information about metallurgical structure of aluminum or
refractive index sensing.
Support from the ESF project 1DP/1.1.1.2.0/13/APIA/VIAA/054 is gratefully acknowledged.
References
[1] Masuda, H., & Fukuda, K. (1995). Ordered metal nanohole arrays made by a two-step
replication of honeycomb structures of anodic alumina. Science, 268(5216), 1466–8.
doi:10.1126/science.268.5216.1466
[2] Choi, D., Choi, Y., Hong, S., Kang, T., & Lee, L. P. (2010). Self-organized hexagonal-nanopore
SERS array. Small, 6(16), 1741–4. doi:10.1002/smll.200901937
[email protected]
20
Coupling in Plasmonic Systems and their Interaction with Moleucles
Adam Weissman, Elad Segal, Lihi Efremushkin, Hannah Aharon,
Adi Salomon
Chemistry, BINA, Nano Center, Bar-Ilan University, Ramat-Gan, Israel
Herein we demonstrate long range interaction between plasmonic modes of metallic nanocavities
(holes). Upon coupling a strong nonlinearly response of the medium is observed and the signal is
enhanced or suppressed and is dependent on the polarization of the incoming beam.
We further study the optical properties of molecules deposited on such metallic nanostructures with
respect to the free molecules. We show experimentally and theorticallicy that molecular excited
states can be strongly coupled to plasmonic modes. By tuning the plasmonic modes to be on/off
resonance with respect to molecular excited state, one can modify the photophysical and even the
chemical properties of these molecules.
Fig1. Polarization properties of triangular nano cavities upon coupling.
Left: SEM image of the structures right: Scanning of the nonlinear response (SHG) of the structures
when the polarization of the incoming beam is along the x-axis.
Salomon, A. Genet, C. and Ebbesen, TW. Angewandte-Chemie, 48, 8749-8751,2009
Salomon, A.; Gordon R.J.; Prior, Y.; Seideman, T.; Sukharev, PRL 109, 073002, 2012
Salomon A.Wang, S. Hutchison, J.A., Genet, C. Ebbesen, T.W. Vol 14, pp. 1882-1886,
ChemPhysChem 2013
Salomon, A.;Zielinski, M.; Kolkowski, R.; Zyss,J. and Prior, Y.; J. Phys.Chem C.
10.1021/jp403010q 2013
Salomon, A. et al. 2014 J. Opt. 16 114012
[email protected]
21
Tunable Plasmonic Properties of Rounded Object-Arrays Achievable Via Interferometric
Illumination of Colloid Sphere Monolayers
Áron Sipos, Anikó Somogyi, Gábor Szabó, Mária Csete
Department of Optics and Quantum Electronics, University of Szeged, Szeged,
Hungary
Interferometric illumination of colloid sphere monolayers (IICSM) by circularly polarized beams
makes possible to fabricate complex patterns consisting of wavelength-scaled arrays of rounded
nano-objects. By applying the IICSM method to illuminate metal colloid sphere monolayers
rectangular patterns of mini-arrays consisting of various rounded nano-objects can be generated.
The IICSM method requires the perfect synchronization of a desired intensity modulation with
respect to preselected colloid sphere arrays inside hexagonally close packed monolayers [1]. It was
demonstrated that via IICSM method complex patterns with six independently tunable geometrical
parameters can be fabricated. The spectral and near-field effects of three complex patterns, which
can be generated via illumination (i) by perpendicularly and (ii) oblique incident homogeneous
beam and (iii) in IICSM-configuration were studied by finite element method. The azimuthal
orientation dependent spectra of hexagonal arrays of (i) nano-rings and (ii) nano-crescents, as well
as of (iii) rectangular pattern of mini-arrays is presented. It is demonstrated that the (iii) rectangular
pattern of mini-arrays consisting of a central nano-ring and satellite nano-crescents have unique
capabilities in spectral tunability, and in tight near-field confinement. The near-field and charge
distribution on these structures were inspected at several azimuthal orientations, and were compared
to calculations made previously on hole-doublets achievable via illumination by linearly polarized
light [2, 3].
(a) Presentation of the IICSM method and of the six independently tunable geometric parameters;
(b) hexagonal arrays of (i) nano-rings and (ii) nano-crescents, and (iii) rectangular pattern of miniarrays. (c) Azimuthal angle (γ) and wavelength (λ) dependent transmittance spectra with each unit
cell used for calculation, (d) 3D near-field and charge distribution on rounded objects achievable
via homogeneous illumination and IICSM at transmittance maxima arising at γ=90° azimuthal
orientation of rectangular patterns of mini-arrays in a gold film.
[1] Á. Sipos, A. Szalai, M. Csete, Proc. SPIE 8323, 83232E (2012)
[2] M. Csete, Á. Sipos, A. Szalai, G. Szabó, IEEE Photonics Journal 4, 1909 (2012)
[3] Á. Sipos, A. Somogyi, G. Szabó, M. Csete, Plasmonics 9, 1207 (2014)
[email protected]
22
Nanoantenna-Enhanced Light-Matter Interaction in Atomically thin WS2
Andreas Trügler1, Johannes Kern2, Iris Niehues2, Johannes Ewering2,
Robert Schmidt2, Robert Schneider2, Sina Najmaei3, Antony George3,
Jing Zhang3, Jun Lou3, Ulrich Hohenester1, Steffen Michaelis de Vasconcellos2,
Rudolf Bratschitsch2
1
Institute of Physics, Karl-Franzens-University, Graz, Austria
2
Institute of Physics and Center for Nanotechnology, University of Münster,
Münster, Germany
3
Department of Mechanical Engineering and Material Science, Rice University,
Houston, USA
Atomically thin transition metal dichalcogenides (TMDCs) are promising two-dimensional
materials for optical and opto-electronic devices [1], because they exhibit an optical band gap in the
visible regime. Monolayers absorb more than 10% of the light at their excitonic resonance and show
photoluminescence [2]. However, the absorption length of TMDC monolayers is extremely short
and the photoluminescence quantum yield is low. Therefore, strategies are needed to optimize lightmatter interaction.
In this paper we present a combined experimental and theoretical study of a novel hybrid system,
consisting of a plasmonic nanoantenna and an atomically thin tungsten disulphide (WS 2) layer. We
use gold nanorods as antennas, which are dropcast onto the WS2 monolayer. Due to the plasmon
resonance of the nanoparticles, strongly enhanced optical near-fields are generated within the WS2.
We observe an increase in photoluminescence intensity by more than one order of magnitude,
resulting from a combined absorption and emission enhancement of the WS2 exciton. We further
investigate the antenna-monolayer coupling with respect to the spectral position of the plasmon
resonance, which is tuned across the exciton resonance at 618 nm wavelength by varying the
lengths of the nanorods. The plasmon resonance shifts to longer wavelengths with increasing
antenna length and a prominent, narrow minimum is present in the broad plasmon spectrum.
Additional simulations performed with the MNPBEM toolbox [3] allow us to attribute this
minimum to the coupling of exciton and plasmon and are in excellent agreement with the
experimental findings.
Fig. 1: (a) Calculated near-field intensity of the hybrid system. (b) Emission-polarization resolved
photoluminescence spectra (coloured lines) compared to scattering spectra (black lines) for different
rod lengths.
The tailored hybrid nanoantenna-monolayer system lights the way to efficient photodetectors, solar
cells, light emitting and conceptually new valleytronic devices based on two-dimensional materials.
[1] Q. H. Wang et al., Nat. Nanotechnol. 7, 699–712 (2012).
[2] P. Tonndorf et al., Opt. Express 21, 4908–4916 (2013).
[3] U. Hohenester and A. Trügler, Comp. Phys. Commun. 183, 370 (2012).
[email protected]
23
Low-Loss Polycrystalline Copper Films for CMOS Plasmonic Applications
Dmitry Yakubovsky, Aleksey Arsenin, Dmitry Fedyanin
Laboratory of Nanooptics and Plasmonics, Moscow Institute of Physics and
Technology (State University), Dolgoprudny, Russia
The size of photonic components is fundamentally limited by diffraction and it is a great challenge
to design sub-wavelength devices using only dielectric materials. On the other hand, at optical
frequencies, noble metals demonstrate a highly negative dielectric constant and the penetration
depth of the electromagnetic field into them does not exceed a few tens of nanometers.
Furthermore, plasmonic modes can be excited at metal-dielectric interfaces, which allows to break
down the conventional diffraction limit. However, reducing the mode size in the metal structure,
one increases the portion of the electromagnetic field in the metal, which results in high ohmic
losses and consequently low quality factors and short propagation lengths. This process is governed
by the imaginary part of the dielectric function, which can be represented through the Drude
damping rate Γ given by the sum of three different processes: electron-phonon scattering, electronelectron scattering and electron scattering on structural defects. Gold and silver are known to have
small Γ, but, being inert metals, they are hardly compatible with conventional microelectronic
fabrication techniques, such as CMOS processes.
Here we present low loss polycrystalline copper films and a theoretical model, which brings
together their optical, electrical and structural properties. Thin Cu layers were deposited on the
silicon substrate by an electron-beam evaporator and their optical properties were obtained with a
spectroscopic ellipsometer. At the same time, we used an atomic force microscope and a four-point
probe system to measure structural and electrical properties, respectively. Fig. 1 shows that the
imaginary part of the dielectric function of Cu is as low as 1.5 for thick films at λ=800 nm, which is
in a good agreement with the theory. Moreover, the theory predicts that absorption losses can be
further reduced by controlling the structural parameters of copper films.
Figure 1. (a) Imaginary part of the dielectric function of Cu measured by ellipsometry and
calculated theoretically. (b-c) AFM images of 30 nm (b) and 170 nm (c) thick copper films.
[email protected]
24
Enhancement of Goos-Hänchen Shifts in Dielectric Gratings on a Metal Surface
Venkata Jayasurya Yallapragada, Arvind Nagarajan, Ajith Padyana
Ravishankar, Gajendra Mulay, Venu Gopal Achanta
Department of Condensed Matter Physics and Materials Science,
Tata Institute of Fundamental Research, Mumbai, India
The Goos-Hänchen (GH) shift is a displacement of the centroid of a beam of finite spatial extent,
when reflected at the surface of an absorbing medium, or during total internal reflection. This
displacement lies in the plane of incidence, and is known to be amplified by excitation of surface
modes at the reflecting interface, for example, at Surface Plasmon Resonance (SPR) [1,2]. The
sensitivity of this enhanced GH shift, makes it a good candidate for sensor applications, as has been
demonstrated using the Kretschmann - Raether configuration [2].
Plasmonic gratings, offer improved portability and scope for miniaturization of such sensors.
Dielectric gratings on metal [3], have SPR conditions, and therefore reflection spectra which can be
conveniently tailored. Here, we present a method to design such gratings and calculate the GH shift,
and proceed to determine the shift experimentally.
We have simulated the reflected field amplitudes using Rigourous Coupled Wave Analysis, from
which GH shift is computed using a calculation scheme outlined previously [4]. The grating
resonances, can be tailored by optimizing grating parameters, for example, to obtain the resonance
at a certain angle of incidence, depending on the requirement for a particular application.
We have designed a grating consisting of stripes of 120 nm thick Poly Methyl Methacrylate
(PMMA) on an opticaly thick Gold film on Silicon, which exhibits SPR at an angle of incidence of
about 11.5 degrees, using p-polarized light of wavelength 785 nm. Close to this point, a large GH
shift is expected. Experiments have been performed using light from a 785 nm diode laser, and a
quadrant photodiode for position measurements. These measurements show the presence of a large
relative GH shift difference between s and p polarization of 45 micrometres, as is expected from
calculations. Such gratings can be used for sensors based on the GH shift.
[1] X. Yin, and L. Hesselink, Applied Physics Letters 89, 261108 (2006).
[2] C. Bonnet et al., Optics Letters 26, 666 (2001).
[3] J. Yoon, et al., Journal of Applied Physics 94, 123 (2003).
[4] VJ Yallapragada, AV Gopal, and GS Agarwal, Optics Express 21, 10878 (2013).
[email protected]
25
Plasmonic Metasurfaces Based on Phase Bifurcation
Chen Yan, Thottungal Valapu Raziman, Kuang-Yu Yang, Olivier J.F. Martin
Nanophotonics and Metrology Laboratory, Swiss Federal Institute of Technology
Lausanne (EPFL), Lausanne, Switzerland
The field of plasmonics has been largely concerned about controlling both the near-field and farfield responses of plasmonic nanostructures that enables various practical applications in wave-front
engineering with metasurfaces [1]. It is well known that harmonic oscillators can model the related
physical quantities, including scattering, absorption and extinction, to describe not only the
individual plasmonic resonances but also coupled responses such as the plasmonic analogue of
electromagnetically induced transparency [2]. Although the intensity extracted from these models
explains very well the experimental results, we discuss in this work the advantages of using phase
information to provide deeper insights into the physics of the system.
We experimentally design and demonstrate a phase gradient metasurface for shaping the wave-front
at a specific wavelength. Sufficient phase variation is achieved by tuning the geometric parameters
of a Fano-resonant structure on a metallic backplane. A dual-color routing metasurface with high
directionality is realized as a proof-of-concept. In order to explain the design rule, we construct a
simple model for extracting the phase information from plasmonic resonances including the effect
of substrates utilizing the classical oscillator model and the transfer matrix method. Analyzing the
time-independent complex field on an Argand diagram allows a more comprehensive understanding
and effective design of the structures. Based on the same principle, we show that the asymmetric
spectral feature of reflected field from a Fano-resonant metasurface is more pronounced with
incidence from a high index glass substrate. Furthermore, the spectrum can contain phase
dislocation and bifurcation in the frequency domain with properly tuned coupling strength. The
resulting 2π phase jump at this range of frequencies will be instrumental for increasing the
sensitivity of phase-based measurements such as ellipsometric detection [3].
[1] N. Yu and F. Capasso, “Flat Optics with Designer Metasurfaces”, Nat. Mater. 13 (2014) 139150
[2] Y. S Joe et al., “Classical Analogy of Fano Resonances”, Phys. Scr. 74 (2006) 259-266
[3] F. Abelès, “Surface Electromagnetic Waves Ellipsometry”, Surf. Sci. 56 (1976) 237-251
[email protected]
26
Light Driven Nonlinear Plasmonic Optomechanical Metamaterials
Jun-Yu Ou1, Eric Plum1, Nikolay Zheludev1,2
Optoelectronics Research Centre and Centre for Photonic Metamaterials,
University of Southampton, Southampton, UK
2
Centre for Disruptive Photonic Technologies, Nanyang Technological University,
Singapore, Singapore
1
The realization of integrated optical system on a chip requires extreme miniaturization functional
elements. To reach this objective, novel approach must be developed to manipulate light with light
in small areas and interaction lengths. Here we experimentally demonstrate optically driven
mechanically reconfigurable photonic metamaterial exhibiting an extraordinarily large optical
nonlinarity(β~0.8 cm/W) which is 7 orders of magnitude larger than nonlinearity of a conventional
nonlinear material, GaAs at optical frequencies.
Fig. 1(a) shows a nonlinear reconfigurable array of Π-shaped plasmonic resonators sitting on double
clamped silicon nitride bridges fabricated by focused ion beam milling from a 50 nm thick gold
layer covering a 50 nm thick silicon nitride membrane. In order to manipulate the metamaterial`s
optical properties by light, a modulated laser beam was pumped at 1550 nm, where simulations
predict significant relative optical forces on the bridges. The modulation of the metamaterial`s
transmission was probed at 1310 nm and detected using a photoreciver and a lock-in amplifier. At
modulation frequencies of 10s of kHz, the optical pump leads to pronounced modulation of the
structure‟s transmission characteristics at the probe wavelength, see Fig. 1(b). For a pump power of
2 mW (peak intensity I =206 W/cm2) a modulation amplitude on the order of 1% is detected at 25
kHz modulation. As the modulation frequency increases, the out-of-plane and in-plane mechanical
resonances are observed optically. While optically induced differential thermal expansion
contributes to the mechanical nonlinearity at low frequencies, the in-plane mechanical modes (1.2
MHz and 1.4 MHz) cannot be directly excited by thermal effects but can be explained by near field
optical forces.
In summary, optically actuated plasmonic optomechanical metamaterials offer an opportunity to
achieve precise control of metamaterial properties through optically induced mechanical
deformation of nanoscale metamaterial structures by electromagnetic near-field interaction and
thermo-optical effects. With light intensity of few μW/μm2, metamaterial arrays can be sufficiently
actuated leading to light-by-light modulation with MHz bandwidth.
[email protected]
27
Quantum Levitation in Metamaterial Plate Configurations
Dentcho Genov, Caylin VanHook, Venkatesh Pappakrishnan
Center for Applied Physics Studies, Louisiana Tech University, Ruston, Louisiana,
USA
The Casimir force repulsion between a dielectric and magneto-dielectric thick parallel plates
separated by air or vacuum is investigated for arbitrary temperatures. The Casimir force between
purely dielectric materials is generally attractive that can lead to increased friction and stiction
effects in nanoscale devices. Here, we consider a parallel plates design based on artificial
electromagnetic metamaterials. A simple analytical treatment of the problem is provided through
the introduction of an upper bound of the force. Explicit necessary and sufficient conditions for the
manifestation of Casimir force repulsion are derived in terms of the plate`s material parameters and
temperature. The sufficient condition can be used as a tool in designing levitating systems with air
as the intermediate medium, which is the natural environment for practical microscopic devices.
[email protected]
28
Controlling Quantum Dot Emission by Plasmonic Nanoarrays
Rui Guo1, Stéphane Derom1, Relinde J.A. van Dijk-Moes2, Tommi Hakala1,
Peter Liljeroth3, Daniël Vanmaekelbergh2, Päivi Törmä1
1
COMP Centre of Excellence, Department of Applied Physics, Aalto University,
Espoo, Finland
2
Condensed Matter and Interfaces, Debye Institute for Nanomaterials Science,
Utrecht, Netherlands
3
Department of Applied Physics, Aalto University, Espoo, Finland
We investigate control of the emission of quantum dots (QDs) coupled with silver nanoparticle
arrays. Plasmonic nanoparticle arrays support collective Surface Lattice Resonances (SLRs) which
are an ideal platform for tailoring the emission profiles of nanoscale emitters [1]. Furthermore, the
coupling between excitons and the collective modes of nanoarrays also offers an approach to
exploring quantum and coherence phenomena if the strong coupling regime is achieved [2-4].
In this work we fabricate silver nanoparticle arrays supporting SLRs modes. Colloidal QDs are then
positioned on top of nanoparticles, ensuring a deterministic coupling between the emitters and
plasmonic particles. Using a Fourier-space (k-space) measurement setup [3], we excite the sample
with a laser and then collect the emitted light. We observe that the emission remarkably well
follows the dispersion of the SLR modes (see Fig. 1). Thus by placing QDs in the near-field regions
of nanoparticles, the collective modes of nanoarrays are coupled efficiently with the emission of
QDs; the emitted light becomes directional, with an increased level of coherence. We will present a
detailed analysis of the emission properties and decay rate measurements of the hybrid structures.
Fig 1. Observed emission of QDs coupled with plasmonic nanoarrays follows closely the SLR
dispersions. The lattice periods are 400nm (left) and 365nm (right).
References:
[1] S. R. K. Rodriguez, G. Lozano, M. A. Verschuuren, R. Gomes, K. Lambert, B. De Geyter, A.
Hassinen, D. Van Thourhout, Z. Hens, and J. Gómez Rivas, Appl. Phys. Lett. 100, 111103 (2012).
[2] A. I. Väkeväinen, R. J. Moerland, H. T. Rekola, A.-P. Eskelinen, J.-P. Martikainen, D.-H. Kim,
and P. Törmä, NanoLett., 14, 1721 (2014).
[3] L. Shi, T. K. Hakala, H. T. Rekola, J.-P. Martikainen, R. J. Moerland, and P. Törmä, Phys. Rev.
Lett. 112, 153002 (2014).
[4] T. Schwartz, J. A. Hutchison, C. Genet, and T. W. Ebbesen, Phys. Rev. Lett. 106, 196405
(2011).
[email protected]
29
Spatial Coherence Properties of Organic Molecules Coupled to Plasmonic Surface Lattice
Resonances in the Weak and Strong Coupling Regimes
Tommi Hakala1, Rekola Heikki Tapani1, Lei Shi1, Jani-Petri Martikainen1,
Robert Jan Moerland1,2, Päivi Törmä1
1
COMP Centre of Excellence, Department of Applied Physics, Aalto University,
Espoo, Finland
2
Department of Imaging Physics, Faculty of Applied Sciences, Delft University of
Technology, Delft, Netherlands
We study the spatial coherence properties of a system composed of periodic silver nanoparticle
arrays covered with fluorescent organic molecule film [1]. The evolution of spatial coherence of
this composite structure is investigated both in weak and strong coupling regimes by systematically
varying the coupling strength between the localized molecular excitons and the collective,
delocalized modes of the nanoparticle array known as surface lattice resonances (SLRs). We show
that the high degree of spatial coherence is maintained in the strong coupling regime, even when the
mode is very exciton-like (80 %). This is in stark contrast to pure localized excitons, which do not
display long range coherence. By appropriately tuning the nanoparticle size, their spacing and the
dye molecule concentration, we demonstrate that the hybrid mode properties, such as the dispersion,
spatial coherence length and the relative weights of the exciton-SLR superposition, can be tailored
with high precision.
[1] Spatial Coherence Properties of Organic Molecules Coupled to Plasmonic Surface Lattice
Resonances in the Weak and Strong Coupling Regimes, L. Shi, T. K. Hakala, H. T. Rekola, J.-P.
Martikainen, R. J. Moerland, and P. Törmä, Phys. Rev. Lett. 112, 153002, 2014. DOI:
http://dx.doi.org/10.1103/PhysRevLett.112.153002
[email protected]
30
Quantum Conductance Effects in Charge Transfer Plasmons
Alejandro Manjavacas, Vikram Kulkarni, Peter Nordlander
Department of Physics and Astronomy, Rice University, Houston, Texas, USA
Localized surface plasmon resonances (LSPR) are a subject of intense experimental and theoretical
research interest. Thanks to their exceptional light capturing and focusing capabilities, LSPR have
found applications in catalysis, solar energy, cancer therapy, or surface enhanced Raman
spectroscopy (SERS). An LSPR of particular interest is the charge transfer plasmon (CTP). This
mode appears when two plasmonic nanoparticles are bridged by a conductive junction. Due its
origin, the CTP is extraordinarily sensitive to the conductive properties of the junction. Here [1] we
perform a first-principles investigation of the properties of the CTP of a system composed of two
gold nanospheres bridged by a quantum dot, using the time dependent density functional theory
(TDDFT). By modulating the electronic structure of the quantum dot we are able to effectively turn
the CTP on and off. Specifically, the CTP emerges only when a quantum dot energy level is
resonant with the Fermi energy of the plasmonic nanoparticles. This behavior is analogous to DC
transport theory, where the conductance through the junction is given by the number of conducting
channels multiplied by the quantum unit of conductance. Interestingly, we find that the conductance
through the junction is on the order of the quantum unit of conductance. This work is of great
interest to the future design of plasmonic and molecular electronic systems.
[1] V. Kulkarni, A. Manjavacas, and P. Nordlander, in preparation (2015).
[email protected]
31
On the Rabi Model and its Generalizations
Alexander Moroz
Wavescattering, Wavescattering, Berlin, Germany
The Rabi model is shown to be only a particular case of a generic class R of models characterized
by the following properties:
(i) wave function Ψ(E,x) is the generating function for orthogonal polynomials φn(E) of a discrete
energy variable E;
(ii) any model of R has nondegenerate purely point spectrum that corresponds to infinite discrete
support of measure dν in the orthogonality relation of the polynomials φn;
(iii) the support is determined exclusively by the points of discontinuity of dν(E);
(iv) the spectrum can be numerically determined as fixed points of monotonic flows of the zeros of
orthogonal polynomials φn(E);
(v) one can compute practically an unlimited number of energy levels;
(vi) the spectrum of exactly solvable models from R can only assume one of four qualitatively
different types.
[1] A. Moroz, Europhys. Lett.100, 60010 (2012); Ann. Phys. (N.Y.) 338, 319 (2013); ibid. 340, 252
(2014); ibid. 351, 960 (2014); J. Phys. A: Math. Theor. 47, 495204 (2014).
[email protected]
32
Probing of Propagating Plasmons wth Two Near-Field Tips
Roy Kaner1, Yaara Bondy1, Guy Shalem2, Yehiam Prior1
Chemical Physics, Weizmann Institute of Science, Rehovot, Israel
2
Mechanical Engineering, Technion-Israel Institute of Technology, Haifa, Israel
1
Unlike the case of coupled nanoparticles, surface propagating plasmons in thin metal films give rise
to a much longer-range coupling between metallic nanocavities[1]. Localized surface plasmons
from a cavity couple to propagating surface plasmons polaritons (SPP), which in turn excite
localized plasmons in a neighboring cavity. Here we characterize this coupling by measurements
and calculations of electric field distribution near the cavities.
We study circular nanocavities pairs (~200nm) in thin gold films at distances of 40-2000 nm. First,
the sample is far-field illuminated (632.8nm, polarized along or perpendicular to the cavities axis)
from below, and the electric field above is near-field mapped with spatial resolution of ~100nm by
a gold coated NSOM tip (Nanonics MV4000). At large distances (part a, bottom) we observe
patterns of interfering propagating SPPs which is modelled very well (a, top) by classical dipoles
located at the cavities center. For small gaps (b), the „capacitor‟ effect between the two dipoles
occurs for parallel polariza---tion.
Next, we used two tips, one illuminating and scanning above one cavity, while the collecting tip is
located up to a few microns away. The propagating field is measured as a function of height above
the surface. Fig c depicts a typical rapid decay when the tip is raised above the surface.
Last, we observed the transmission spectrum for a range of cavity separation (d). The spectra were
calculated by solving FDTD equations, and measured (not shown here). A discrete set of modes of
plasmon propagation between the coup---led cavities is clearly visible, and its origin and potential
applications will be discussed.
[1] Adi Salomon et al. Plasmonic coupling between metallic nanocavities, Journal of Optics, 16,
114012 (2014)
[email protected]
33
Near Infra-Red Spectrum Regional Color Filter Development using a Single Metal Layer of
Nanohole Arrays
Se Min Kim1,5, Sang Hyun Jung2, Keun Woo Lee2, Woong Sun Lim2,
Hong Min Yoon2, Hee Jung Hong3, Hyoung Koo Lee3, Jae Hong Noh4,
Min Soo Lee5, Sung Moon5
1
Department of physics, Inha University, Incheon, South Korea
2
Convergence Technology Division, Korea Advanced Nano Fab Center, Suwon,
Gyeonggi-do, South Korea
3
Deparment of research & development, Clairpixel Co.,Ltd, Sungnam,
Gyeonggi-do, South Korea
4
Advanced Analysis Center, Korea Institute of Science and Technology, Seoul,
South Korea
5
Nano & Quantum Information Research Center, Korea Institute of Science and
Technology, Suwon, Gyeonggi-do, South Korea
Many research about nano hole array typed color filter using extraordinary optical
transmission(EOT) phenomenon has been performed for the recent years. We introduce three
channels filter for the near infra-red spectrum region. Each center peak of the filter specturm is
950nm, 850nm, and 750nm respectively, These regional filter also can be applied to CMOS image
sensor for the night vision.
Numerous Finite Difference Time Domain (FDTD) calculations were performed by automated
performance to search proper structural dimension conditions (i.e a layer material, hole shape,
depth, diameter, period, existence of the adhesion & cover layer) which are satisfied with not only
the best filter property but also easiness of the fabrication process. Through these FDTD simulation
results, we choosed cylinderical nanohole arrays in a single silver metal layer.
Designed arrays were fabricated by Electron Beam Lithography (EBL) mainly, also etching and
descum process. One of the distinguished differences from the conventional fabrication methods is
not to use the adhesion layer between substrate and silver metal layer, because existence of
adhesion layer has negative effect on the filter property.
In conclusion, this result shows that evaluated transmission properties of this fabricated filter are
well-matched to expected FDTD simulation results. We present how to find successful fabrication
variables (i.e. E-beam dose current, kind of resist etching gas, gas, etcing time, pressure,
temperature, descum methods and so on) through numerous attempts and failures, especially
mension removing Electron beam Resist(ER). And also present how to evaluate the transmissition
property of fabricated filter samples using CMOS image sensor and monochromator.
Fig1. The silver metal surface of cylinderical nano hole array structure after etching process, prior
to the deposition of SiO2 cover layer (Designed for NIR filter whose resonance wavelengh is
850nm)
[email protected]
34
Floating Thin Plasmonic Graded-Index Lens
Sun-Je Kim, Kyookeun Lee, Seung-Yeol Lee, Byoungho Lee
Electrical Engineering, Seoul National University, Seoul, South Korea
Manipulation of optical information using surface plasmon polaritons (SPPs) has been rigorously
studied by utilizing subwavelength nature of SPPs. Specifically, the intensity and launching
direction of SPPs can be efficiently controlled when the geometry of metallic structure and the
shape of dielectric material are designed [1]. There exist many types of in-plane plasmonic lenses
based on principles of Fourier optics [2]. But thickness of the floating lens in previous study is
about 5 µm and it is quite long for applying in plasmonic devices. Therefore, we propose a novel
floating thin lens based on the graded-index method. Figures 1(a) and 1(b) show the top and front
view of the lens structure. By changing the gap between floating silicon-dioxide and silver
substrate, it is possible to make gradual variation of effective index of SPPs. Planar SPP waves,
after passing through the thin flat lens region, are focused to the focal point on the central axis.
Figure 1(c) shows simulation result of transverse H-field distribution at the boundary of silver
substrate and air. The lens is designed to impose parabolic phase and numerically analyzed by fullwave simulation based on finite difference time domain method (FDTD) while the operating
wavelength is designed to 633 nm. Lateral width and thickness of the lens is 1.1 µm and 100 nm,
respectively. The floating gap thickness varies from 20 nm to 500 nm in 11 symmetrically separated
lens sectors in order to form a discrete parabolic phase. We expect that the proposed method can be
used to design various compact plasmonic devices that may help avoid loss problem by reduction of
device size.
[1] S.-Y. Lee et al., "Role of magnetic induction currents in nanoslit excitation of surface plasmon
polaritons," Physical Review Letters, 108, 213907 (2012).
[2] H. Kim, J. Hahn, and B. Lee, "Focusing properties of surface plasmon polariton floating
dielectric lenses," Optics Express, 16, 3049-3057 (2008).
[email protected]
35
Characteristics of Local Electric Field Excitation in the Asymmetric Nanostructure
Illuminated by Ultrafast Laser Pulse
Boyu Ji, Zuoqiang Hao, Jingquan Lin
Department of Physics, Changchun University of Science and Technology,
Changchun, China
Localized surface plasmon resonances has been widely used in the field of chemosensing，surface
enhanced Raman scattering, biomedicine and near-field control[[1]]. Nanoscale symmetric structure
is an ideal for obtaining local surface plasmon resonance while illuminated with ultrafast linear
polarization laser pulse. In many applications, especially for the cases of illumination source are
white light, or femtosecond laser that has a wide spectral bandwidth, a significant drawback of the
symmetric geometric nanostructure is their narrowband response, the narrow structure with dual or
multiple bands are desirable for a number of promising applications[2]. Adoption of the asymmetric
nanostructure can result in multiple resonant peaks and greatly enhance the spectral absorption,
which may find applications in such as selective optical fibers, multiple detector array. In this paper,
to the best of our knowledge, systematical research of excitation and dynamic response of the
plamon resonance of asymmetric structure under ultrafast laser excitation will be firstly presented.
Extinction spectrum, local electric field intensity, current density distribution and temporal response
of the local electric field for the asymmetric nanocross are simulated using FDTD method. It is
found that, in addition to arms that are parallel with the laser polarization occur strong local
plasmonic resonance, perpendicular arms (vertical to laser polarization) can get large local electric
field enhancement as symmetry of the nanocross is broken. For the asymmetric nanocross
extinction spectra show red-shift as arm length increases and simultaneous multiple resonant
wavelength peaks appear. Current density distribution of the nanocross further supports the result of
the local electric field enhancement. Temporal response of electric field in arms of the asymmetric
nanocross shows that the parallel arms start to oscillation under the ultrafast laser illumination,
followed by oscillation of local electric field of the perpendicular arms. Underneath physics of the
perpendicular arm excitation is given. The results obtained in this paper are important to the field
that using plasmon effect as perfect absorber and also to the field of optical near-field coherent
control.
F. J. Rodriguez-Fortuno, M. Martínez-Marco, B. Tomas-Navarro, et al., Applied Physics
Letters 98(13), 133118-133118-3 (2011)
J. Homola, Chemical reviews, 2008, 108(2): 462-493
[email protected]
36
Design and Integration of Plasmonic Lenses Dedicated to Near Infrared Detection (1.064 μm)
for CMOS Image Sensors
Thomas Lopez1, Sébastien Massenot1, Magali Estribeau1, Pierre Magnan1,
Jean-Luc Pelouard2
1
DEOS, ISAE-SUPAERO Université de Toulouse, Toulouse, France
2
MiNaO, LPN-CNRS, Marcoussis, France
The interest of the near infrared spectral band in imaging applications is well established, the fact
that these waves are less scattered than visible light provide them a great potential of applications in
the field of security and defense (vision through fog, for example). Image sensors for laser active
imaging in this spectral band are mostly based on III-V materials [1]. However, there is a strong
interest in using silicon-based detectors to reduce manufacturing cost. Unfortunately, silicon
absorptivity and quantum efficiency are not high enough at this wavelength to compete with
conventional NIR detection technology. One potential solution is to integrate light collection
functions at the level of each pixel. Due to their exceptional confinement properties, plasmonic
structures will be involved. They have already been studied to enhance silicon based
photodetetectors performances. For instance, plasmonic color filters for CMOS image sensor
applications and improving light absorption in solar cells using metal nanoparticules have been
investigated. This contribution deals with the design of plasmonic lenses in order to enhance the
collection of near-infrared photons in the photosensitive area for a standard CMOS imager. In order
to cause the least possible disruption to the CMOS fabrication process, such structures will be
deposited at the top of passivation layers (post-process integration). The first design explored is the
Plasmonic Lens [2]. Nevertheless, the complex combination of nanoscale high aspect ratio slits is
hardly achievable. This design can be greatly simplified releasing technological constraints: the
simplified system is called Huygens Lens [3]. Numerical simulations have been performed through
finite-difference time domain to optimize the structures both integrated into a pixel. Performances
of both lenses are compared.
[1] J. Bentell et al., “Flip chipped INGaAs photodiode arrays for gated imaging with eye-safe
lasers", Solid-State Sensors, Actuators and Microsystems Conference, 2007.
[2] P. B. Catrysse et al., “Nanoscale slit arrays as planar far-field lenses", SPIE NanoScience
Engineering, International Society for Optics and Photonics, 2009.
[3] Q. Levesque et al., “Compact planar lenses based on a pinhole and an array of single mode
metallic slits", Journal of the European Optical Society - Rapid publications;Oct. 2013.
[email protected]
37
Evidence of Random Surface Plasmon Modes in Fractal Metal Films
Arthur Losquin1,2, Sophie Camelio3, David Rossouw4, Mondher Besbes5,
Frédéric Pailloux3, David Babonneau3, Gianluigi A. Botton4,
Jean-Jacques Greffet5, Odile Stéphan1, Mathieu Kociak1
1
Laboratoire de Physique des Solides, CNRS - Université Paris Sud, Orsay, France
2
Department of Physics, Lund University, Lund, Sweden
3
Institut P’, Département Physique et Mécanique des Matériaux,
CNRS - Université de Poitiers, Futuroscope Chasseneuil, France
4
Department of Materials Science and Engineering, McMaster University,
Hamilton, Canada
5
Laboratoire Charles Fabry,
Institut d'Optique - Université Paris-Sud - CNRS, Palaiseau, France
Surface Plasmon (SP) modes dictate the optical properties of metal nanoparticles. In simple
nanoobjects, they depend on both the size and shape through simple trends. However, the situation
becomes complex in disordered systems. Strong broadband absorption properties have been
measured in percolating metal films [1], and are commonly attributed to a strong localization of
light at the nanoscale [2]. This strong localization suggests an extraordinary character of the SP
modes of percolating films [3]. However, despite the great deal of work in the past 15 years, a
comprehensive experimental evidence of the unusual features of these SP modes was missing until
recently, due to a lack of studies combining high spatial resolution, broad spectral range of
excitation and simultaneous access to the local sample morphology. On the other hand, Electron
Energy Loss Spectroscopy (EELS) in Scanning Transmission Electron Microscopes (STEM) has
emerged as an essential tool to map the SP modes of simple nanoobjects with nanometer spatial
resolution. We have recently performed STEM EELS measurements on different samples to
investigate the SP modes of disordered metallic systems [4]. This work demonstrates that
percolating metal films sustain numerous strongly confined random SP modes induced by the
fractal geometry of the medium.
a. STEM image of a percolating silver film. b. Local (colored) and mean (gray) EELS spectra
recorded in the area shown in a. The large spectral variations imply a complex set of SP modes. c.
Spatial variations of the EELS signal at constant energies (1.0 and 1.4 eV). The numerous local
intensity maxima are due to strongly confined random modes showing no obvious correlation with
the substrate local geometry.
[1] P. Gadenne et al., J. Appl. Phys. 66, 3019 (1989)
[2] S. Grésillon et al., Phys. Rev. Lett. 82, 4520 (1999)
[3] M. I. Stockman et al., Phys. Rev. Lett. 87,167401 (2001)
[4] A. Losquin et al., Phys. Rev. B 88, 115427 (2013)
[email protected]
38
Realization of Fano Resonance in Graphene Ribbons on a Hetergeneous Substrate
Weiwei Luo, Wei Cai, Lei Wang, Zenghong Ma, Xinzheng Zhang, Jingjun Xu
The Key Laboratory of Weak Light Nonlinear Photonics, Ministry of Education,
TEDA Applied Physics Institute and School of Physics, Nankai University, Tianjin,
China
The excitation of collective electron oscillations in plasmonic nanostructures have been realized in
different structures[1]. The creation of sharp spectral features such as Fano resonances[2] presents
important potential applications such as biosensing and plasmonic nanolasing. Fano resonances
arise from the coherent interference of a narrow discrete resonance with a broad spectral line or
continuum.
Here we show that for graphene ribbons where plasmons can be excited by a perpendicular incident
light beam[3], if the substrate is heterogeneous and configured properly, apparent Fano resonances
could arise. In further, the Fano resonance can be explained by the interference between plasmons
in graphene ribbons and substrate cavity modes. Our structure is very simple and easily achievable,
which is very promising for sensing application.
In fig. 1, we analyze a simple situation where graphene ribbons are separated from a semi-infinite
substrate with a layer of dielectric. The plasmon resonance of graphene ribbons is at 18.3 THz,
which has a Lorentz shape. However, multi-reflection will occur when the incident light passes
through the heterogeneous substrate. Therefore a series of peaks and valleys in the reflection
spectrum will appear, whose frequencies and periods are determined by the dielectric constant and
the thickness of the dielectric layer. As the modes of the dielectric layer are spectrally broad and the
plasmon mode is much narrower, their coherent interferences result in the asymmetric resonance
shape. As shown in fig.1(c) and (d), by changing the thickness of the layer and the Femi energy of
graphene, the asymmetry line shape can be tuned effectively.
References
[1] Anker, J. N. et al. Nat Mater. 7, 442–453(2008)
[2] Verellen, N. et al. Nano Lett. 9, 1663–1667 (2009)
[3] Ju, L. et al Nat Nanotechnol. 6, 630-634(2010)
[email protected]
39
Light-Tunable Plasmonic Nanoarchitectures Using Photosensitive Gold-Surfactant
Complexes
Liudmila Lysyakova1,2, Nino Lomadze1, Alexey Kopyshev1,
Ksenia Maximova3, Andrei Kabashin3, Dieter Neher2, Svetlana Santer1
1
Department of Experimental Physics, Institute of Physics and Astronomy,
University of Potsdam, Potsdam, Germany
2
Department of Soft Matter Physics, Institute of Physics and Astronomy, University
of Potsdam, Potsdam, Germany
3
LP3 UMR 7341, Aix Marseille University, CNRS, Marseille, France
Surfactant molecules carrying photosensitive azobenzene units have attracted considerable interest
due to their versatile applications in the field of light controlled shape and functionality of soft
nano-objects.1,2 Azobenzenes are known to undergo trans-cis isomerization under irradiation with
light, serving therefore a photo-trigger for the hydrophobicity of the surfactant. In this work we
demonstrate how azobenzenes offer controllable plasmonic response in "hard" nano-objects.
Here, we present the results of a comprehensive study of the optical and structural properties of
complexes formed between gold nanoparticles (10 nm average diameter) and azobenzenecontaining cationic surfactant molecules, employing UV-Vis absorption spectroscopy, dynamic
light scattering and electron microscopy. Depending on gold-surfactant molar ratios, three different
constitutions of the nanoparticle-surfactant complexes were identified, where nanoparticles are
represented either by negatively (region I) or positively (region III) charged single specimens, or by
clusters in the intermittent region II.
We show that UV light illumination enables nanoaggregation into spherical gold nanoclusters of
around 100nm in diameter, exhibiting visible change in solution color from red to blue. We also
find that the presence of gold nanoparticles accelerates the cis-trans isomerization rate of the
adsorbed azobenzenes, probably due to electron transfer. Finally, decorated with azobenzenecontaining molecules gold nanoparticles from region III are applied to form plasmonic nanowires.
[1] Zakrevskyy, Y.; Cywinski, P.; Cywinska, M.; Paasche, J.; Lomadze, N.; Reich, O.;
Löhmannsröben, H.-G.; Santer, S. The Journal of Chemical Physics, 140 (2014), 044907.
[2] Zakrevskyy, Y.; Kopyshev, A.; Lomadze, N.; Morozova, E.; Lysyakova, L.; Kasyanenko, N.;
Santer, S. Phys Rev E, 84 (2011), 021909.
[email protected]
40
On-Demand Positioning of Various Active Nanoparticles in Plasmonic Antennae Structures
will be Discussed and Complemented by Thorough Numerical Modelling
Niko Nikolay, Oliver Benson
Department of Physics, Humboldt University, Berlin, Germany
The concentration of the electromagnetic field in plasmonic antennae allows for significant
improvement of nanophotonic devices. The Purcell effect increases the emission rate of single
photon sources [1], and the large field enhancement supports non-linear effects such as frequency
up-conversion [2]. The advantage of plasmonic compared to resonant dielectric structures is a
smaller size and larger bandwidth. Furthermore, the electrical conductivity of plasmonic materials
automatically provides electrodes or electric wires, which are essential parts of almost any
integrated electro-optic device.
Nanoemitters like molecules [3], quantum dots [4] or defect centers in diamond [1] have been used
as active material at the fundamental limit of active plasmonic antennae.
In this contribution we will introduce our approach of local functionalization of an antenna using
atomic force microscope (AFM) manipulation [5]. On-demand positioning of various nanoparticles,
such as single nanodiamonds, colloidal quantum dots, organic molecules and rare-earth-doped
particles will be discussed. The experimental results will be complemented by full numerical
calculations.
[1] Schietinger, S., Barth, M., Aichele, T., & Benson, O. (2009). Plasmon-enhanced single photon
emission from a nanoassembled metal− diamond hybrid structure at room temperature. Nano
letters, 9(4), 1694-1698.
[2] Schietinger, S., Aichele, T., Wang, H. Q., Nann, T., & Benson, O. (2009). Plasmon-enhanced
upconversion in single NaYF4: Yb3+/Er3+ codoped nanocrystals. Nano letters, 10(1), 134-138.
[3] Kinkhabwala, A., Yu, Z., Fan, S., Avlasevich, Y., Müllen, K., & Moerner, W. E. (2009). Large
single-molecule fluorescence enhancements produced by a bowtie nanoantenna. Nature Photonics,
3(11), 654-657.
[4] Harats, M. G., Livneh, N., Zaiats, G., Yochelis, S., Paltiel, Y., Lifshitz, E., & Rapaport, R.
(2014). Full spectral and angular characterization of highly directional emission from nanocrystal
quantum dots positioned on circular plasmonic lenses. Nano letters, 14(10), 5766-5771.
[5] Schell, A. W., Kewes, G., Schröder, T., Wolters, J., Aichele, T., & Benson, O. (2011). A
scanning probe-based pick-and-place procedure for assembly of integrated quantum optical hybrid
devices. Review of Scientific Instruments, 82(7), 073709.
[email protected]
41
Room Temperature GaN Film Growth by UV Surface Plasmon-Mediated N2H4
Decomposition
Siying Peng1, Matthew Sheldon1, Wei-Guang Liu2, Andres Jaramillo-Botero2,
William Goddard III2, Harry A. Atwater1
1
Thomas J. Watson Laboratories of Applied Physics,
California Institute of Technology, Pasadena, California, USA
2
Materials and Process Simulation Center, California Institute of Technology,
Pasadena, California, USA
We report growth of GaN films at room temperature facilitated by UV surface plasmon-mediated
N2H4 decomposition to generate reactive nitride growth precursors. Conventional growth methods
for GaN include CVD and MBE, which both require high temperatures ( 500 K) to create atomic
nitrogen by thermally decomposing nitride precursor molecules. Alternatively, magnetron
sputtering can be used to grow GaN at room temperature but the high ion kinetic energy limits the
crystalline quality of the growing film. Our study is motivated by the fact that UV radiation can
resonantly dissociate nitrogen bonds, through a pathway that neither produces species with high
kinetic energy nor requires high temperatures. Ultraviolet surface plasmons are generated at a
nanostructured aluminum surface where nitrogen precursors are adsorbed, and the resonantly
excited surface plasmons generate dissociated nitrogen species that lead to GaN film growth.
Additionally, because film growth can occur at lower temperatures, our method may open doors for
new semiconductor materials such as indium-rich InGaN, which is normally hindered due to phase
separation into InN and GaN at elevated growth temperatures.
For UV surface plasmon-mediated GaN growth, we identified N2H4 as a promising nitrogen
precursor molecule. We have performed full wave simulation to design periodic aluminum
nanostructure arrays, yielding a surface field enhancement of 25x at 248 nm which corresponds to
the maximum absorption cross section for hydrogen abstraction from N2H4. We fabricated large
area (3 mm x 9 mm) Al UV plasmonic nanostructures using nanoimprint lithography printing from
a master stamp generated by e-beam lithography. Reflection spectroscopy characterization of these
aluminum nanostructures showed enhanced absorption at 248 nm. In high vacuum ambient
conditions at cryogenic temperatures, mass spectrometry indicated that UV surface plasmons
enhance N2H4 dissociation by an overall factor of 6.2x. The calibrated gallium flux and surface
plasmon generated nitrogen flux were introduced sequentially to enable layer by layer growth of
GaN on gold. XPS of nitrogen 1s electrons confirms the Ga-N bond formation based similar
binding energy distribution compared to that of a bulk GaN crystal. XRD characterization confirms
nanocrystalline quality of the GaN film. EDS indicates partial oxidation of the Ga-N bond during
film growth. Strategies to improve crystalline quality of the film as well as suppressing oxidation
will be discussed.
[email protected]
42
Tunable Gold-Graphene Metasurface for Beamsteering
Michelle Sherrott1, Victor Brar1, Philip Hon2, Luke Sweatlock1,2,
Harry A. Atwater1
1
Materials Science and Applied Physics, California Institute of Technology,
Pasadena, California, USA
2
Metamaterials and Nanophotonics Lab, Northrop Grumman Aerospace
Corportation, Los Angeles, California, USA
Reconfigurable flat optical components in the mid-infrared (mid-IR) have been a longstanding goal
for civil and military applications including holographic displays, beam shaping, and spatial light
modulation. However, despite progress in the field, existing approaches are typically limited in
speed, efficiency, and size. Graphene-modulated metasurfaces offer the opportunity to overcome
these limitations.
Here we will experimentally demonstrate an actively modulated beamsteering device using a
metasurface comprised of 2um long gold bowtie antennas on a continuous graphene sheet with a
gold back-reflector separated by a 170nm thick SiO2 layer (see schematic below). We treat the
graphene as a controllable dielectric environment which we can actively modulate via electrostatic
gating. By electrostatically doping the graphene from its charge neutral point (CNP, EF=0eV) to
EF=0.55eV, a tunability of reflection phase over 240° is demonstrated at a wavelength of 8um. This
allows us a calculated range of beamsteering over an angular range of +/-50° from the normal with
a signal:noise exceeding 2:1. We explain this large range of tunability by the widely variable optical
conductivity of graphene with charge carrier concentration. In addition, our design exploits the gap
between the gold antennas to serve as a Fabry-Perot cavity, confining a graphene plasmon and
increasing the local field intensity, resulting in a stronger interaction with the antennae. By
individually gating each element in an array of these gold antennas, we create a tunable reflectarray
and show that the reflection angle of an incident beam can be modified in real time, with the
potential for ultrafast switching times.
Schematic illustration of tunable gold/graphene element
[email protected]
43
Mid-IR Plasmonic Antennas Fabricated by FIB and EBL: Does an Ultrathin Silicon Oxide
Layer Matter?
Lukáš Břínek1,2, Tomáš Šamořil1,2, Ondřej Tomanec1,2, Michal Kvapil1,2,
Radek Kalousek1,2, Martin Hrtoň1,2, Jan Čechal1,2, Petr Dub1,2, Jiří Spousta1,2,
Peter Varga1,2, Tomáš Šikola1,2
1
Institute of Physical Engineering, Brno University of Technology, Brno,
Czech Republic
2
CEITEC BUT, Brno University of Technology, Brno, Czech Republic
One of the most straightforward applications of FIB technology is fabrication of plasmonic
nanoantennas by milling their shapes out of metallic thin films. However, we have found that the
Mid-IR Au rectangular antennas show different behaviour according to their fabrication origin.
These antennas prepared by EBL on transparent samples (e.g. Si) possessed linear scaling of
resonance frequency with their arm length. Contrary to that, those prepared by Ga (Xe) FIB milling
of the Au layer (60 nm) revealed more complex behaviour. In principle, the resonant peak of
relative reflectance of antennas (measured by FTIR) was split into two sub-peaks separated by a dip
at λ ≈ 8.2 μm. The short-wavelength sub-peak was moving with the antenna arm length towards
higher wavelengths until its motion almost stopped at higher arm lengths. However, the longwavelength sub-peak almost did not move with the antenna arm length for shorter arm lengths and
then started to move towards higher wavelengths.
In the presentation such an unexpected effect will be explained and the proofs for it given. Our
previous work [1] indicated that this complex behaviour can be related to a strong coupling of
antenna plasmons to the absorbing substrate modified by ions. X-ray Photoelectron Spectroscopy
revealed the presence of a silicon-oxide layer having an enhanced thickness (6 nm) with respect to
the native oxide (≈ 2 nm) at the silicon surface in the vicinity of antennas fabricated by Ga or Xe
ions. FDTD simulations (Lumerical) proved that such an ultrathin oxide layer absorbing in Mid-IR
was able to cause the splitting of the resonant peak. Finally, removing the oxide layer by HF
etching the dip in the MID-IR resonant peaks disappeared and the antennas started permanently to
show up the same spectra like in case of the EBL antennas. The mechanism of the formation of
such an oxide layer will be explained as well.
[1] T. Šikola, R. D. Kekatpure, E. S. Barnard, J. S. White, P. Van Dorpe , L. Břínek, O.
Tomanec, J. Zlámal, D. Lei, Y. Sonnefraud, S. A. Maier, J. Humlíček, M. L. Brongersma: Appl.
Phys. Lett. 95 (2009), 253109.
[email protected]
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Multifunctional Snoptical Gradient Metasurfaces
Dekel Veksler, Elhanan Maguid, Dror Ozeri, Nir Shitrit, Vladimir Kleiner,
Erez Hasman
Nanotechnology and Nanoscience, Technion-Israel Institute of Technology, Haifa,
Israel
Photonic gradient metasurfaces are ultrathin electromagnetic wave-molding metamaterials that
provide a route for realizing flat optics. However, the up-to-date metasurface design, manifested by
imprinting the required phase profile for a single, on-demand light manipulation functionality, is not
compatible with the desired goal of multifunctional flat optics. We present a generic concept to
control multifunctional optics by disordered (random) gradient metasurfaces with a custom-tailored
geometric phase. This approach combines the peculiar ability of random patterns to support
extraordinary information capacity, and the polarization helicity control in the geometric phase
mechanism, simply implemented in a two-dimensional structured matter by imprinting optical
antenna patterns. By manipulating the local orientations of the nanoantennas, we generate multiple
wavefronts with different functionalities via mixed random antenna groups, where each group
controls a different phase function.
[email protected]
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Proposal for Plasmonically-Enhanced Optical Spin Readout of Nitrogen-Vacancy Centers in
Diamond
Sigal Wolf1, Itamar Rosenberg1, Ronen Rapaport1, Nir Bar-Gill1,2
1
The Racah Institute of Physics, The Center for Nanoscience and Nanotechnology,
The Hebrew University of Jerusalem, Jerusalem, Israel
2
Dept. of Applied Physics, Rachel and Selim School of Engineering,
The Hebrew University of Jerusalem, Jerusalem, Israel
Nitrogen-Vacancy (NV) color centers in diamond have emerged as promising quantum solid-state
systems, with applications ranging from quantum information processing to magnetic sensing. One
of the most useful properties of NVs is the ability to read their ground-state spin projection optically
at room temperature. In our work we study theoretically plasmonic enhancement of the NV optical
coupling, and find parameters for optimal Signal to Noise Ratio (SNR) of optical spin-state readout.
We find that a combined increase in spontaneous emission (through plasmon-induced Purcell
enhancement) and in optical excitation could significantly increase the readout SNR.
Based on the dynamics of the system‟s rate equations we find that there is an optimal radiative
decay rate which maximizes the SNR for given excitation rate and measuring-pulse duration, as
well as an optimal pulse duration for given excitation and radiative decay rates (as expected from
experimental results). However, by increasing the radiative decay rate and excitation rate
simultaneously, the SNR can be increased indefinitely. For example, by reaching a Purcell factor
(PF) of only 10 and adjusting the excitation rate and pulse duration respectively, the SNR can be
increased by a factor of 5. These results can improve significantly the ability to read out the spin
state of NV centers, which is essential for many NV applications.
The figure shows the saturated readout SNR as a function of the Purcell factor. The red star shows
the saturated SNR with PF = 1. By increasing the PF and the excitation rate and adjusting the pulse
duration to its optimal value can increase the SNR significantly.
[email protected]
46
Optical Mode Control of Anisotropic Quasicrystal Metasurface
Igor Yulevich, Elhanan Maguid, Nir Shitrit, Dekel Veksler, Vladimir Kleiner,
Erez Hasman
Mechanical Enginnering, Technion-Israel Institute of Technology, Haifa, Israel
The excitation of unique thermal radiative collective modes from a quasicrystalline metasurface
consisting of anisotropic nanoantennas is presented. These discrete states appear as a result of the
geometric phase induced by aperiodic orientations of the antennas. The observed modes manifest
significantly different dispersion in comparison to a similar metasurface composed of isotropic
nanoantennas, where only their positions determine the reciprocal space. Consideration of the
geometric phase may be implemented in crystallographic analysis of complex systems as it provides
extra information about the local anisotropy of material building-blocks.
[email protected]
47
Chiral Liquid Crystal Assisted SPR Sensor of Physical Fields
Katerina Zhelyazkova1, Minko Petrov2, Boyko Katranchev2, Georgi Dyankov1
1
Faculty of Physics, Plovdiv University "Paisii Hilendarski", Plovdiv, Bulgaria
2
Institute of Solid State Physics, Bulgarian Academy of Sciences, Sofia, Bulgaria
Surface plasmon resonance (SPR) – based sensors are one of the most advanced real time detection
technologies. Usually Kretschmann configuration is used for effective plasmon excitation. In this
paper we consider the influence of chiral liquid crystal layer, adjacent to the metal, on SPR. Bearing
in mind that the alignment of liquid crystal is easily controlled by different physical fields, such as
electric field or temperature, we have studied how helical pitch, tilt angle and number of periods
influence SPR. The pitch length considerably changes resonance position with more than 30 nm,
shifting the resonance towards red wavelengths. So, factors causing self-assembling helical
structures can be sharply detected. Moreover, we have found that waveguide modes strongly
depend on the parameters of chiral liquid crystal layer. At optimal conditions for pitch length/ liquid
crystal thickness/ tilt angle the waveguide mode appears exactly at the plasmon resonance, causing
its splitting as shown in the figure. This effect, together with SPR shift, increases considerably the
accuracy of measurement. The influence of large birefringence of liquid crystal on the sensitivity
has been studied as well. Our theoretical study is performed by Maxwell equations solver based on
4x4 method.
[email protected]
48
Plasmonic Graded Gratings for Hyperspectral Near-field Infrared Sensing and Imaging
Arthur O. Montazeri1,2, Michael Fang1,4, Hoi-Ying Holman3,
Roya Maboudian1, Carlo Carraro1, Nazir Kherani2
1
Chemical and Biomolecular Engineering, University of California - Berkeley,
Berkeley, California, USA
2
Electrical and Computer Engineering, University of Toronto, Toronto,
Ontario, Canada
3
Berkeley Synchrotron Infrared Structural Biology,
Lawrence Berkeley National Laboratory, Toronto, California, USA
4
Physics, University of California - Berkeley, Berkeley, California, USA
Patterning a metal-dielectric surface with properly arranged subwavelength features provides the
means for light to excite surface plasmon polaritons (SPPs) [1]. However, these creases, or other
indentations of the surface can become more than just a means for SPP excitation. Indeed, these
features could become resonant cavities, waveguides, or a combination thereof, extending in one,
two or three dimensions. They can be functionally graded through spatial tapering of their pertinent
geometrical parameters. (See Fig. 1 (a)) E.g. these subwavelength grooves can act as resonant
waveguides with no cut-off for certain cavity modes and polarizations [2]. As a result, even in the
spectral ranges where SPPs do not form on flat metallo-dielectric boundaries (λ mid-IR), these
subwavelength features can give rise to SPP-like behavior, known as “spoof SPPs” [3].
One aspect of these subwavelength grooves (See Fig. 1 (b) or (c)), is that when the groove-width is
comparable to the evanescent tail of the SPP, it can result in SPP-coupling. The narrower the groove
becomes, the stronger this coupling. We show that a far more practical approach is to use this
property alone to create frequency selective surfaces without changing the groove-depth.
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Fig. 1: (a.) Illustrates the emergent “rainbow-trapping” on a system of weakly-coupled grooves
each housing strongly-coupled SPPs (b.) The E-field simulation of a graded-grating trapping
localized infrared wavelength at λ = 6 µm (c.) An application example: utilizing this substrate as a
platform for low-phototoxicity infrared spectroscopy in biological tissue.
This approach is a powerful tool for facile design of hyperspectral surfaces without the need for full
wave simulation.
References:
[1] J. B. Pendry, et al., Science, vol. 305, no. 5685, pp. 847–848 (2004).
[2] J. Le Perchec, et al., Physical Review Letters 100, (2008).
[3] A.O. Montazeri, M. Fang, P. Sarrafi, and N.P. Kherani, arXiv 1406.3083v2 (2015)
[email protected]
50
Molecular Sensing with Tunable Graphene Plasmons
1
Andrea Marini1, Iván Silveiro1, Javier Garcia de Abajo1,2
Nanophotonics Theory Group, ICFO-Institut de Ciencies Fotoniques, Barcelona,
Spain
2
., ICREA-Institució Catalana de Recerca i Estudis Avançats, Barcelona, Spain
Infrared spectroscopy is an important field of research as it enables sensing of molecules through
the measurement of their resonances, acting as molecular fingerprints. Nanophotonics is tightly
bound to this field of research as the engineering of nano-scaled plasmonic structures is crucial for
enhancing the local electromagnetic field. The high local field is mainly responsible for the giant
surface-induced enhancement of infrared absorption (SEIRA) and Raman scattering (SERS) by
molecules in close proximity of metallic nanoparticles. These techniques have brought a number of
viable, cheap and efficient commercial applications, e.g., pregnancy tests based on metal colloids
[1], and promise further revolutionary applications in plasmonic sensing, although they suffer from
some drawbacks. Indeed, plasmon resonances in metal-based nanoparticles are fixed by the
underpinning geometric details of the plasmonic structure and lack of efficient external tunability.
Besides, their spectral width can not cover the whole broad spectrum of roto-vibrational infrared
transitions, and thus they enhance only few molecular resonances. Multi-frequency sensors based
on subwavelength hole arrays and optical antennas have been proposed for overcoming this
limitation and for achieving broadband surface-enhanced spectroscopy [2, 3]. In the last years,
doped graphene has emerged as an attractive alternative to noble metals for the exploitation of
surface plasmons at infrared (IR) and terahertz (THz) frequencies. Here, we develop a theoretical
framework accounting for SEIRA and SERS by molecules adsorbed on graphene nano-disks. We
evaluate the efficiency of these graphene-based infrared sensors finding that, thanks to the
outstanding tunability of graphene through externally applied gate voltage, broadband SEIRA and
SERS can be achieved. The calculated enhancement factors with respect to molecular cross-sections
in the gas-phase (in the absence of graphene), are of the order of 103 for SEIRA and 104 for SERS,
thus making these techniques highly appealing for sensing devices.
[1] M. I. Stockman, Phys. Today 64, 39 (2011).
[2] O. Limaj et al., J. Phys. Chem. C 117, 19119 (2013).
[3] H. Aouani et al., ACS Nano 7, 669 (2013).
[email protected]
51
The Broadband Surface Plasmon
Michael Chasnitsky, Michael Golosovsky, Dan Davidov
Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem, Israel
A very high sensitivity of the surface-plasmon based sensors stems from the fact that the surface
plasmon is a resonance phenomenon. In the Kretchmann‟s geometry, optical reflectivity as a
function of incident angle exhibits a very sharp dip associated with the excitation of the surface
plasmon wave at the metal-dielectric interface. The position and depth of this dip is very sensitive
to the properties of dielectric in contact with metal (analyte). In this work we explore a rare scheme
of the excitation of the surface plasmon resonance- a wavelength scanning. We demonstrate that the
reflectivity may be close to zero in a broad wavelength range while the high sensitivity to the
properties of the analyte is retained through the whole wavelength range. The reason behind this is
the resonance condition of phase- matching: the phase velocity of the surface plasmon wave VSP
shall be equal to the lateral component of the phase velocity of the incident light,. Here, Θ is the
incident angle and n is the refractive index of the incident medium. This condition does not involve
wavelength (explicitly) and can be satisfied in a wide range of wavelengths.
The broadband surface plasmon can be achieved by dispersion engineering, namely, by the
modification of the interface where surface plasmon propagates, or by broadband coupling through
dispersion compensation.
We explore these two methods using computer simulation and show how the broadband surface
plasmon may be achieved at the Au-water or Au-air interface across the near-infrared range λ=1-3
µm. We demonstrate experimentally the broadband surface plasmon in the Kretschmann
configuration at the Au-air interface using a 900 sapphire prism coated with 18 nm thick Au layer
and test samples: 5-100 nm thick water and ethanol films. We show the advantages of the
broadband plasmon for thin films sensing: spectroscopic measurements in the regime of the surface
plasmon resonance and discrimination between continuous and island films. The broadband surface
plasmon can be also useful for creation of surface plasmon pulses and for broadband absorbers.
[email protected]
52
Gain-Enhanced Propagation of Surface Plasmons in V-Groove Metallic Waveguides
Oren Lotan1, Cameron Smith2, Jonathan Bar-David1, Anders Kristensen2,
Uriel Levy1
1
Department of Applied Physics, The Hebrew University of Jerusalem, Jerusalem,
Israel
2
Department of Micro- and Nanotechnology, Technical University of Denmark,
Denmark
Surface Plasmon Polaritons (SPP‟s) are electromagnetic waves coupled to surface charge density
oscillations which propagate on metallic interfaces. Due to their unique dispersive relation and
strong light confinement, Plasmonic based devices are showing promise in the attempt to
manipulate light at the nano-scale. This can be of importance in the fields of optical
communications, optical computing, sensing and more [1].
However, Plasmonic devices suffer from high losses which limit the propagation length and
therefore present an obstacle for integrating plasmonic devices into photonic circuits or lab-on-Chip
devices. A proposed solution to this problem is introducing a gain medium into plasmonic devices,
thus amplifying the plasmonic signal and compensating for the high losses [2].
In this work, we shall examine a plasmonic waveguide, which is a V-shaped groove made of gold
(Au) layer deposited on a Silicon substrate [3]. Above the gold layer we fabricate a flow cell and
stream through a dye solution which will act as the gain medium, interacting evanescently with the
plasmonic mode.
Our device is designed to support a probe beam around the wavelength of . This beam is coupled
into the waveguide through a nano-mirror on one end of the device and coupled out of the
waveguide in a similar fashion. At the same time, a second beam ( is directed to the center of the
waveguide serving as a pump for the gain medium excitation. By measuring the output signal
versus the input signal for waveguides of various lengths, with different types of gain media and
varying pump beam intensities, we should be able to obtain the gain efficiency and the propagation
loss in these structures.
[1] “Ozbay, Ekmel. 2006. “Plasmonics: Merging Photonics and Electronics at Nanoscale
Dimensions.” Science 311 (5758): 189–93. doi:10.1126/science.1114849.
[2] Nezhad, Maziar P., Kevin Tetz, and Yeshaiahu Fainman. 2004. “Gain Assisted Propagation of
Surface Plasmon Polaritons on Planar Metallic Waveguides.” Optics Express 12 (17): 4072.
doi:10.1364/OPEX.12.004072.
[3] Smith, Cameron L. C., Anil H. Thilsted, Cesar E. Garcia-Ortiz, Ilya P. Radko, Rodolphe Marie,
Claus Jeppesen, Christoph Vannahme, Sergey I. Bozhevolnyi, and Anders Kristensen. 2014.
“Efficient Excitation of Channel Plasmons in Tailored, UV-Lithography-Defined V-Grooves.”
Nano Letters, February. doi:10.1021/nl5002058.
[email protected]
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