Browsing by Subject "Surface plasmons"

Now showing 1 - 18 of 18

Open Access
Broadband absorption enhancement in an uncooled microbolometer infrared detector
(SPIE, 2014) Kebapcı, B.; Dervişoğlu, Ö.; Battal, Enes; Okyay, Ali Kemal; Akın, T.
This paper introduces a method for a broadband absorption enhancement in the LWIR range (8-12 μm), in single layer microbolometer pixels with 35 μm pitch. For the first time in the literature, this study introduces a very simple and low cost approach to enhance the absorption by embedding plasmonic structures at the same level as the already existing metallic layer of a microbolometer pixel. The metal layer comprises the electrode and the arm structures on the body. Even though the periodicity of the plasmonic structures is slightly disturbed by the placement of the electrodes and the connecting metal, the metal arms and the electrodes compensate for the lack of the periodicity contributing to the resonance by their coupling with the individual plasmonic resonators. Various plasmonic structures are designed with FDTD simulations. Individual, plasmonically modified microbolometer pixels are fabricated, and an increase in the average absorption due to surface plasmon excitation at Au/Si3N4 interfaces is observed. Plasmonic structures increase the average absorption from 78% to 82% and result in an overall enhancement of 5.1%. A good agreement between the simulation and the FTIR measurement results are obtained within the LWIR range. This work paves the way for integration of the plasmonic structures within conventional microbolometer devices for performance enhancement without introducing additional costs.
Open Access
Concentric ring structures as efficient SERS substrates
(Institute of Electrical and Electronics Engineers, 2013) Cinel, N. A.; Cakmakyapan, S.; Ertas, G.; Özbay, Ekmel
Plasmonic nanopatterned structures that can work as highly efficient surface-enhanced Raman scattering (SERS) substrates are presented in this study. A 'coupled' concentric ring structure has been designed, fabricated, tuned, and compared to an 'etched' concentric ring structure and plain gold film via SERS experiments. The proposed design gives Raman signal intensity 630 times larger than plain gold film and 8 times larger than an 'etched' concentric ring structure. The surface plasmons were imaged with the fluorescence imaging technique and supporting numerical simulations were done.
Open Access
Coupled plasmonic structures for sensing, energy and spectroscopy applications
(2015-08) Ayas, Sencer
Recent advances in nanofabrication and characterization methods have enabled the study of novel optical phenomena, thus boosting the research in nanophotonics and plasmonics. Metal nanostructures offer a route for the excitation of surface plasmons by confining the light in sub-wavelength dimensions, yielding extremely high electromagnetic field intensities. Moreover, coupling different plasmon modes offers a rich optical dispersion which cannot be obtained inherently by using single plasmonic resonator. In this thesis, we first present a detailed study of simple coupled plasmonic structures based on metal-insulator-metal structure. Then, we use similar structures to devise novel optical platforms in various applications such as surface enhanced Raman spectroscopy (SERS), surface enhanced infrared absorption spectroscopy (SEIRA) and plasmon enhanced hot-electron devices. The first part of this thesis concentrates on coupled plasmonic structures and their spectroscopy and photodetector applications. Firstly, we study these structures numerically and analytically and show surface enhanced Raman spectroscopy (SERS) as a possible application with uniform signal intensities over large areas. Then, fabricating these plasmonic surfaces with sub-10nm gaps over large areas lead to development of single molecule Raman spectroscopy platforms. As an energy related application, a contact free characterization method is developed to probe hot electrons where similar coupled plasmonic surfaces are employed as hot electron devices. Finally, using aluminum and its native aluminum oxide hierarchical plasmonic surfaces are fabricated and its spectroscopy applications are demonstrated. In the second part of, we develop interference-coating-based sensing platforms in the visible and infrared wavelengths. Despite large field enhancements, plasmonic structures suffer from low signal intensities due to low mode volumes. To overcome this issue we propose another strategy, namely using interference coatings with small and uniform electric field enhancements over large mode volumes. These surfaces outperform the conventional plasmonic surfaces when they are used as infrared absorption spectroscopy platforms. Finally, similar surfaces are employed as colorimetric sensor platforms to sense monolayer and bilayer proteins simply by change in the surface color.
Open Access
Enhanced optical characteristics of light emitting diodes by surface plasmon of Ag nanostructures
(SPIE, 2011) Jang L.-W.; Ju J.-W.; Jeon J.-W.; Jeon, D.-W.; Choi J.-H.; Lee, S.-J.; Jeon, S.-R.; Baek J.-H.; Sarı, Emre; Demir, Hilmi Volkan; Yoon H.-D.; Hwang, S.-M.; Lee I.-H.
We investigated the surface plasmon coupling behavior in InGaN/GaN multiple quantum wells at 460 nm by employing Ag nanostructures on the top of a roughened p-type GaN. After the growth of a blue light emitting diode structure, the p-GaN layer was roughened by inductive coupled plasma etching and the Ag nanostructures were formed on it. This structure showed a drastic enhancement in photoluminescence and electroluminescence intensity and the degree of enhancement was found to depend on the morphology of Ag nanostructures. From the time-resolved photoluminescence measurement a faster decay rate for the Ag-coated structure was observed. The calculated Purcell enhancement factor indicated that the improved luminescence intensity was attributed to the energy transfer from electron-hole pair recombination in the quantum well to electron vibrations of surface plasmon at the Ag-coated surface of the roughened p-GaN. © 2011 SPIE.
Open Access
Experimental validation of strong directional selectivity in nonsymmetric metallic gratings with a subwavelength slit
(American Institute of Physics, 2011-02-02) Cakmakyapan, S.; Caglayan, H.; Serebryannikov, A. E.; Özbay, Ekmel
Strong directional selectivity is theoretically predicted and experimentally validated at the microwave frequencies in the beaming regime for a single subwavelength slit in nonsymmetric metallic gratings with double-side corrugations. The operation regime can be realized at a fixed angle of incidence when the surface-plasmon assisted transmission is significant within a narrow range of observation angles, if illuminating one of the grating interfaces, and tends to vanish for all observation angles, if illuminating the opposite interface. The studied effect is connected with asymmetry (nonreciprocity) in the beaming that occurs if the surface plasmon properties are substantially different for the two interfaces being well isolated from each other.
Open Access
Guided plasmon modes of a graphene-coated kerr slab
(Springer New York LLC, 2016) Hajian, H.; Rukhlenko, I. D.; Leung, P. T.; Caglayan, H.; Özbay, Ekmel
We study analytically propagating surface plasmon modes of a Kerr slab sandwiched between two graphene layers. We show that some of the modes that propagate forward at low field intensities start propagating with negative slope of dispersion and positive flux of energy (fast-light surface plasmons) when the field intensity becomes high. We also discover that our structure supports an additional branch of low-intensity fast-light guided modes. The possibility of dynamically switching between the forward and the fast-light plasmon modes by changing the intensity of the excitation light or the chemical potential of the graphene layers opens up wide opportunities for controlling light with light and electrical signals on the nanoscale.
Open Access
Hybridization of fano and vibrational resonances in surface-enhanced infrared absorption spectroscopy of streptavidin monolayers on metamaterial substrates
(2014) Alici, K. B.
We present spectral hybridization of organic and inorganic resonant materials and related bio-sensing mechanism. We utilized a bound protein (streptavidin) and a Fano-resonant metasurface to illustrate the concept. The technique allows us to investigate the vibrational modes of the streptavidin and how they couple to the underlying metasurface. This optical, label-free, nonperturbative technique is supported by a coupled mode-theory analysis that provides information on the structure and orientation of bound proteins. We can also simultaneously monitor the binding of analytes to the surface through monitoring the shift of the metasurface resonance. All of this data opens up interesting opportunities for applications in biosensing, molecular electronics and proteomics. © 2014 IEEE.
Open Access
Long-range tamm surface plasmons supported by graphene-dielectric metamaterials
(American Institute of Physics Inc., 2017) Hajian, H.; Caglayan, H.; Özbay, Ekmel
Considering the Ohmic losses of graphene in the calculations and by obtaining exact dispersion relations of the modes, we theoretically study propagation and localization characteristics of Tamm surface plasmons supported by terminated graphene metamaterials. The metamaterials are composed of alternating layers of graphene and dielectric with subwavelength periods. We also examine the Tamm modes within the framework of long-wavelength approximation. It is shown that, in case the Ohmic losses of the graphene layers are taken into account, surface plasmons are not supported in a long-wavelength region, in which the graphene-dielectric multilayer structure behaves as a hyperbolic metamaterial. We prove that, when the metamaterial is truncated with air, by choosing sufficiently thick but still subwavelength dielectric layers, i.e., d = 300 nm, these surface waves will have a moderate propagation (localization) length that is comparable with those of a single layer of graphene. On the other hand, in case a miniaturized graphene metamaterial (10 < d(nm) < 100) is truncated by a thick cap layer (dcap = 5d) with εcap > εdielectric, it is possible to considerably improve the propagation and localization characteristics of the Tamm modes supported by the system within the 5.5-50 THz range of frequency, as compared to a single layer of graphene.
Open Access
Metal-semiconductor-metal UV photodetector based on Ga doped ZnO/graphene interface
(Pergamon Press, 2015) Kumar, M.; Noh, Y.; Polat, K.; Okyay, Ali Kemal; Lee, D.
Fabrication and characterization of metal-semiconductor-metal (MSM) ultraviolet (UV) photodetector (PD) based on Ga doped ZnO (ZnO:Ga)/graphene is presented in this work. A low dark current of 8.68 nA was demonstrated at a bias of 1 V and a large photo to dark contrast ratio of more than four orders of magnitude was observed. MSM PD exhibited a room temperature responsivity of 48.37 A/W at wavelength of 350 nm and UV-to-visible rejection ratio of about three orders of magnitude. A large photo-to-dark contrast and UV-to-visible rejection ratio suggests the enhancement in the PD performance which is attributed to the existence of a surface plasmon effect at the interface of the ZnO:Ga and underlying graphene layer.
Open Access
Nearly perfect resonant absorption and coherent thermal emission by hBN-based photonic crystals
(Optical Society of America, 2017) Hajian, H.; Ghobadi, A.; Butun, B.; Özbay, Ekmel
In this paper, we numerically demonstrate mid-IR nearly perfect resonant absorption and coherent thermal emission for both polarizations and wide angular region using multilayer designs of unpatterned films of hexagonal boron nitride (hBN). In these optimized structures, the films of hBN are transferred onto a Ge spacer layer on top of a one-dimensional photonic crystal (1D PC) composed of alternating layers of KBr and Ge. According to the perfect agreements between our analytical and numerical results, we discover that the mentioned optical characteristic of the hBN-based 1D PCs is due to a strong coupling between localized photonic modes supported by the PC and the phononic modes of hBN films. These coupled modes are referred as Tamm phonons. Moreover, our findings prove that the resonant absorptions can be red- or blue-shifted by changing the thickness of hBN and the spacer layer. The obtained results in this paper are beneficial for designing coherent thermal sources, light absorbers, and sensors operating within 6.2 μm to 7.3 μm in a wide angular range and both polarizations. The planar and lithography free nature of this multilayer design is a prominent factor that makes it a large scale compatible design. © 2017 Optical Society of America.
Open Access
One-way transmission through the subwavelength slit in nonsymmetric metallic gratings
(Optical Society of America, 2010-07-27) Cakmakyapan, S.; Serebryannikov, A. E.; Caglayan, H.; Özbay, Ekmel
An approach for obtaining one-way transmission in the beaming regime is suggested that is based on the directional radiation of surface plasmons in nonsymmetric metallic gratings with a single slit. In contrast to the various nonsymmetric one-way diffraction gratings that have recently been proposed, the possibility of obtaining of narrow beams is demonstrated. Strong directional selectivity can appear a wide range of the observation angles, while the angle of incidence is retained.
Open Access
A plasmonically enhanced pixel structure for uncooled microbolometer detectors
(SPIE, 2013) Erturk O.; Battal, Enes; Kucuk, S.E.; Okyay, Ali Kemal; Akin, T.
This paper introduces a method of broadband absorption enhancement that can be integrated with the conventional suspended microbolometer process with no significant additional cost. The premise of this study is that electric field can be enhanced throughout the structural layer of the microbolometer, resulting in an increase in the absorption of the infrared radiation in the long wave infrared window. A concentric double C-shaped plasmonic geometry is simulated using the FDTD method, and this geometry is fabricated on suspended pixel arrays. Simulation results and FTIR measurements are in good agreement indicating a broadband absorption enhancement in the 8 μm - 12 μm range for LWIR applications. The enhancement is attained using metallic geometries embedded in the structural layer of the suspended microbridge, where the metallic-dielectric interface increases the average absorption of a 35 μm pixel from 67.6% to 80.1%. © 2013 SPIE.
Open Access
Semiconductor-less photovoltaic device
(IEEE, 2013) Atar, Fatih B.; Battal, Enes; Aygun, Levent E.; Dağlar, Bihter; Bayındır, Mehmet; Okyay, Ali Kemal
We demonstrate a novel semiconductor-less photovoltaic device and investigate the plasmonic effects on this device structure. The device is made of metal and dielectric layers and the operation is based on hot carrier collection. We present the use of surface plasmons to improve energy conversion efficiency. The field localization provided by surface plasmons confine the incident light in the metal layer, increasing the optical absorption and hot electron generation rate inside the metal layer. The device consists of two tandem MIM (metal-insulator-metal) junctions. Bottom MIM junction acts as a rectifying diode and top MIM junction is used to excite surface plasmons. The device operation principle as well as the topology will be discussed in detail. © 2013 IEEE.
Open Access
Slowing down surface plasmons on a Moiré surface
(The American Physical Society, 2009-02) Kocabaş, Aşkın; Şenlik, S. Seçkin; Aydınlı, Atilla
We have demonstrated slow propagation of surface plasmons on metallic Moiré surfaces. The phase shift at the node of the Moiré surface localizes the propagating surface plasmons and adjacent nodes form weakly coupled plasmonic cavities. Group velocities around vg=0.44c at the center of the coupled cavity band and almost a zero group velocity at the band edges are observed. A tight binding model is used to understand the coupling behavior. Furthermore, the sinusoidally modified amplitude about the node suppresses the radiation losses and reveals a relatively high quality factor (Q=103).
Open Access
Spoof-plasmon relevant one-way collimation and multiplexing at beaming from a slit in metallic grating
(Optical Society of America, 2012) Çakmakyapan, Semih; Serebryannikov, A.E.; Caglayan H.; Özbay, Ekmel
Diode and collimator/multiplexer functions are suggested to be combined in one device that is based on a thin metallic grating with a single subwavelength slit. A proper choice of the structural (a)symmetry of the grating can result in obtaining one-way collimation and multiplexing with a single on-axis or off-axis, or two off-axis narrow outgoing beams. It is possible due to freedom in utilizing different combinations of the excitation conditions of the spoof surface plasmons at the four grating parts - right and left front-side and right and left back-side ones. Such a combining provides one with an efficient tool to engineer one-way collimators and multiplexers with the desired characteristics. Strong asymmetry in transmission with respect to the incidence direction (forward vs backward case) can be obtained within a wide range of variation of the incident beam parameters, i.e., angle of incidence and frequency, while the outgoing radiation is concentrated within a narrow range of the observation angle variation. Most of the observed asymmetric transmission features can be qualitatively explained using the concept of the equivalent source placed inside the slit. © 2012 Optical Society of America.
Open Access
Tunable graphene plasmonic structures with different gating schemes
(2016-08) Aygar, Ayşe Melis
The aim of this thesis is to examine graphene plasmonic structures which yields actively tunable spectral resonances and compare two different ways to gate graphene. Plasmonic structures that consist of periodic fractal gold squares on graphene are used to increase light-graphene interaction. We show by simulations and experiments that higher degree fractal structures result in higher spectral tunability of resonance wavelength. This is explained by more plasmonic localization of light for higher degree fractal structures. Furthermore, spectral tunability of a plasmonic structure integrated with graphene is investigated comparing two different schemes for electrostatic gating. The fabrication methods and fabrication steps of the devices with different gating schemes is explained in detail. Comparison of back-gating and top-gating schemes confirms that top-gating using ionic liquid is a more efficient gating method. Top-gating yields the same amount of spectral tunability while requiring smaller gate voltages compared to that of back-gating experiments.
Open Access
Tuning optical discs for plasmonic applications
(Springer New York, 2009) Kaplan, B.; Guner, H.; Senlik, O.; Gurel, K.; Bayındır, Mehmet; Dana, A.
We present simple physical and chemical procedures that allow tuning and modification of the topography of gratings present in optical storage discs into geometries optimal for grating coupled plasmon resonance excitation. After proper metal coating, the tuned surfaces exhibit sharp plasmon resonances that can be excited at wavelengths ranging from 260 nm to over 2.7 μm with relatively high quality factors. As an immediate exemplary application, use of such optimized gratings in aqueous medium for refractive index measurement is demonstrated.
Open Access
Ultrahigh contrast one-way optical transmission through a subwavelength slit
(Springer, 2013) Battal, E.; Yogurt, T. A.; Okyay, Ali Kemal
We computationally demonstrate one-way optical transmission characteristics of a subwavelength slit. We comparatively study the effect in single layer and double layer metallic corrugations. We also investigate the effect of a dielectric spacer layer between double corrugations to control the volumetric coupling of plasmon and optical modes. We computationally show unidirectional transmission behavior with an ultrahigh contrast ratio of 53.4 dB at λ = 1.56 μm. Volumetric coupling efficiency through the nanoslit strongly depends on the efficient excitation of both the surface plasmon resonance and metal–insulator–metal waveguide modes. We show that the behavior is tunable in a wide spectral range.