Browsing by Author "Balci, S."

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Open Access
Absorption enhancement of molecules in the weak plasmon-exciton coupling regime
(Optical Society of American (OSA), 2014) Balci, S.; Karademir, E.; Kocabas, C.; Aydınlı, Atilla
We report on the experimental and theoretical investigations of enhancing the optical absorption of organic molecules in the weak plasmon-exciton coupling regime. A metal-organic hybrid structure consisting of dye molecules embedded in the polymer matrix is placed in close vicinity to thin metal films. We have observed a transition from a weak coupling regime to a strong coupling one as the thickness of the metal layer increases. The results indicate that absorption of the self-assembled J-aggregate nanostructures can be increased in the weak plasmon-exciton coupling regime and strongly quenched in the strong coupling regime. A theoretical model based on the transfer-matrix method qualitatively confirms the experimental results obtained from polarization-dependent spectroscopic reflection measurements.
Open Access
Critical coupling in plasmonic resonator arrays
(Optical Society of America, 2011) Balci, S.; Kocabas, C.; Aydınlı, Atilla
We report critical coupling of electromagnetic waves to plasmonic cavity arrays fabricated on Moire surfaces. Dark field plasmon microscopy imaging and polarization dependent spectroscopic reflection measurements reveal the critical coupling conditions of the cavities. The critical coupling conditions depend on the superperiod of the Moire surface, which also defines the coupling between the cavities. Complete transfer of the incident power can be achieved for traveling wave plasmonic resonators, which have a relatively short superperiod. When the superperiod of the resonators increases, the coupled resonators become isolated standing wave resonators in which complete transfer of the incident power is not possible. Analytical and finite difference time domain calculations support the experimental observations. (C) 2011 Optical Society of America
Open Access
Dynamic tuning of plasmon resonance in the visible using graphene
(The Optical Society, 2016) Balci, S.; Balci, O.; Kakenov, N.; Atar, F. B.; Kocabas, C.
We report active electrical tuning of plasmon resonance of silver nanoprisms (Ag NPs) in the visible spectrum. Ag NPs are placed in close proximity to graphene which leads to additional tunable loss for the plasmon resonance. The ionic gating of graphene modifies its Fermi level from 0.2 to 1 eV, which then affects the absorption of graphene due to Pauli blocking. Plasmon resonance frequency and linewidth of Ag NPs can be reversibly shifted by 20 and 35 meV, respectively. The coupled graphene-Ag NPs system can be classically described by a damped harmonic oscillator model. Atomic layer deposition allows for controlling the graphene-Ag NP separation with atomic-level precision to optimize coupling between them.
Open Access
Electroless synthesis of 3nm wide alloy nanowires inside Tobacco mosaic virus
(2012) Balci, S.; Hahn, K.; Kopold P.; Kadri, A.; Wege, C.; Kern, K.; Bittner, A.M.
We show that 3nm wide cobaltiron alloy nanowires can be synthesized by simple wet chemical electroless deposition inside tubular Tobacco mosaic virus particles. The method is based on adsorption of Pd(II) ions, formation of a Pd catalyst, and autocatalytic deposition of the alloy from dissolved metal salts, reduced by a borane compound. Extensive energy-filtering TEM investigations at the nanoscale revealed that the synthesized wires are alloys of Co, Fe, and Ni. We confirmed by high-resolution TEM that our alloy nanowires are at least partially crystalline, which is compatible with typical Co-rich alloys. Ni traces bestow higher stability, presumably against corrosion, as also known from bulk CoFe. Alloy nanowires, as small as the ones presented here, might be used for a variety of applications including high density data storage, imaging, sensing, and even drug delivery. © 2012 IOP Publishing Ltd.
Open Access
Graphene as a Reversible and Spectrally Selective Fluorescence Quencher
(Nature Publishing Group, 2016) Salihoglu, O.; Kakenov, N.; Balci, O.; Balci, S.; Kocabas, C.
We report reversible and spectrally selective fluorescence quenching of quantum dots (QDs) placed in close proximity to graphene. Controlling interband electronic transitions of graphene via electrostatic gating greatly modifies the fluorescence lifetime and intensity of nearby QDs via blocking of the nonradiative energy transfer between QDs and graphene. Using ionic liquid (IL) based electrolyte gating, we are able to control Fermi energy of graphene in the order of 1 eV, which yields electrically controllable fluorescence quenching of QDs in the visible spectrum. Indeed, our technique enables us to perform voltage controllable spectral selectivity among quantum dots at different emission wavelengths. We anticipate that our technique will provide tunable light-matter interaction and energy transfer that could yield hybrid QDs-graphene based optoelectronic devices with novel functionalities, and additionally, may be useful as a spectroscopic ruler, for example, in bioimaging and biomolecular sensing. We propose that graphene can be used as an electrically tunable and wavelength selective fluorescence quencher. ï¿½ 2016 The Author(s).
Open Access
Graphene-Based Adaptive Thermal Camouflage
(American Chemical Society, 2018) Salihoğlu, Ömer; Uzlu, H. B.; Yakar, Ozan; Aas, Shahnaz; Balci, Osman; Kakenov, Nurbek; Balci, S.; Olcum, S.; Süzer, Şefik; Kocabas, Coşkun
In nature, adaptive coloration has been effectively utilized for concealment and signaling. Various biological mechanisms have evolved to tune the reflectivity for visible and ultraviolet light. These examples inspire many artificial systems for mimicking adaptive coloration to match the visual appearance to their surroundings. Thermal camouflage, however, has been an outstanding challenge which requires an ability to control the emitted thermal radiation from the surface. Here we report a new class of active thermal surfaces capable of efficient real-time electrical-control of thermal emission over the full infrared (IR) spectrum without changing the temperature of the surface. Our approach relies on electro-modulation of IR absorptivity and emissivity of multilayer graphene via reversible intercalation of nonvolatile ionic liquids. The demonstrated devices are light (30 g/m2), thin (<50 μm), and ultraflexible, which can conformably coat their environment. In addition, by combining active thermal surfaces with a feedback mechanism, we demonstrate realization of an adaptive thermal camouflage system which can reconfigure its thermal appearance and blend itself with the varying thermal background in a few seconds. Furthermore, we show that these devices can disguise hot objects as cold and cold ones as hot in a thermal imaging system. We anticipate that, the electrical control of thermal radiation would impact on a variety of new technologies ranging from adaptive IR optics to heat management for outer space applications.
Open Access
Graphene-quantum dot hybrid optoelectronics at visible wavelengths
(American Chemical Society, 2018) Salihoglu, O.; Kakenov, N.; Balci, O.; Balci, S.; Kocabas, C.
With exceptional electronic and gate-tunable optical properties, graphene provides new possibilities for active nanophotonic devices. Requirements of very large carrier density modulation, however, limit the operation of graphene based optical devices in the visible spectrum. Here, we report a unique approach that avoids these limitations and implements graphene into optoelectronic devices working in the visible spectrum. The approach relies on controlling nonradiative energy transfer between colloidal quantum-dots and graphene through gate-voltage induced tuning of the charge density of graphene. We demonstrate a new class of large area optoelectronic devices including fluorescent display and voltage-controlled color-variable devices working in the visible spectrum. We anticipate that the presented technique could provide new practical routes for active control of light-matter interaction at the nanometer scale, which could find new implications ranging from display technologies to quantum optics.
Open Access
Lasing in a Slow Plasmon Moiré Cavity
(American Chemical Society, 2015) Karademir, E.; Balci, S.; Kocabas, C.; Aydınlı, Atilla
We report on lasing from dye-based excitons coupled to slow plasmon states inside metallic Moiré cavities. Surface plasmon polaritons (SPPs) inside the cavity were slowed down to a maximum group velocity of 0.3c. Varying the modulation of the Moiré cavity, we tune the output wavelength of the plasmonic laser by varying the fast modulation period of the Moiré cavity. This work opens a new way to study SPP-matter interaction dynamics and plasmonic lasing with Bragg cavity confined slow plasmons.
Open Access
Lyotropic liquid-crystalline mesophase of lithium triflate-nonionic surfactant as gel electrolyte for graphene optical modulator
(American Chemical Society, 2023) Balci, F. M.; Balci, S.; Kocabas, C.; Dag, Ö.
Lithium salt (noncoordinating anions, such as lithium triflate (Ltf)) gel electrolytes may be key for the practical use of electrochemical devices. We introduce a new lyotropic liquid-crystalline (LLC) mesophase using Ltf, a small amount of water (as low as 1.3 water per Ltf), and nonionic surfactant (C18H37(OCH2CH2)10OH, C18E10). The LLC phase forms over a broad range of Ltf/C18E10 mole ratios, 2-18. The clear ethanol solution of the ingredients can be either directly spin-coated over a glass substrate to form a gel phase or it can be prepared as a gel by mixing Ltf, water, and C18E10. The mesophase leaches out surfactant molecules at low salt concentrations, but at a salt/surfactant mole ratio of above 8, the phase is homogeneous with a cubic mesostructure, fully transparent in the visible optical region, mechanically flexible, and an effective gel electrolyte. We have observed a large electrostatic doping on graphene with the Fermi energy level of ∼1.0 eV using Ltf-C18E10 gel electrolytes. The Ltf-based gels demonstrate better properties than commonly used ionic liquid electrolyte in graphene optical modulators. The stability of the new gel electrolytes and their superior performance make them suitable electrolytes for use in graphene-based optical modulators.
Open Access
Photosensitization of PVC dehydrochlorination by hydroquinone for improved optical and electrical properties
(Elsevier, 2004) Balci, S.; Birer, O.; Süzer, Şefik
Hydroquinone (HQ) is incorporated into the PVC films containing methyl violet or polyaniline (emeraldine base) for sensitizing the UV induced optical or electrical changes, respectively. It is observed that introduction of a small amount (less than 10% by weight) of HQ not only brings the dehydrochlorination onset down to 310 nm but also sensitizes the process by more than one order of magnitude as well as leading to strong polyene formation. UV-Vis-NIR spectroscopy is used to characterize the changes and investigate the mechanism. Accordingly, it is postulated that this HQ assisted photo-dehydrochlorination involves predominantly the formation of an excited triplet via an efficient intersystem crossing in HQ followed by abstraction of hydrogen from the poly(vinyl chloride) to initiate a zipping reaction in the PVC matrix. © 2004 Elsevier Ltd. All rights reserved.
Open Access
Plasmon-polaritons on graphene-metal surface and their use in biosensors
(A I P Publishing LLC, 2012) Salihoglu, O.; Balci, S.; Kocabas, C.
We studied excitation of surface plasmon-polaritons on graphene-metal surface. The metal surface is functionalized by transfer printing of graphene grown by chemical vapor deposition on copper foils. Surface plasmon resonance characteristics of monolayer and multilayer graphene on the metal surface are presented. We were able to obtain the dispersion relation of graphene-metal surface which reveals the essential feature of the plasmon-polaritons. As an application, we fabricated a surface plasmon resonance sensor integrated with a microfluidic device to study nonspecific physical interaction between graphene layer and proteins. © 2012 American Institute of Physics.
Open Access
Plasmonic band gap engineering of plasmon-exciton coupling
(Optical Society of American (OSA), 2014) Karademir, E.; Balci, S.; Kocabas, C.; Aydınlı, Atilla
Controlling plasmon-exciton coupling through band gap engineering of plasmonic crystals is demonstrated in the Kretschmann configuration. When the flat metal surface is textured with a sinusoidal grating only in one direction, using laser interference lithography, it exhibits a plasmonic band gap because of the Bragg scattering of surface plasmon polaritons on the plasmonic crystals. The contrast of the grating profile determines the observed width of the plasmonic band gap and hence allows engineering of the plasmonic band gap. In this work, resonant coupling between the molecular resonance of a J-aggregate dye and the plasmonic resonance of a textured metal film is extensively studied through plasmonic band gap engineering. Polarization dependent spectroscopic reflection measurements probe the spectral overlap occurring between the molecular resonance and the plasmonic resonance. The results indicate that plasmon-exciton interaction is attenuated in the band gap region along the grating direction. © 2014 Optical Society of America.
Open Access
Plexcitonic crystals: A tunable platform for light-matter interactions
(Optical Society of American (OSA), 2014) Karademir, E.; Balci, S.; Kocabas, C.; Aydınlı, Atilla
Coupled states of surface plasmon polaritons (SPPs) and excitons are collectively called plexcitons [Nano Lett. 8, 3481 (2008)]. Plexcitonics is an emerging field of research aiming to control light-matter interaction at the nanometer length scale using coupled pairs of surface-plasmons and excitons. Ability to control the interaction between localized excitons and propagating surface-plasmons is important for realization of new photonic devices. In this letter, we report plexcitonic crystals that yield direction-dependent plasmon-exciton coupling. We have fabricated one- and two-dimensional plexcitonic crystals on periodically corrugated silver surfaces, which are loaded with J-aggregate complexes. We show that plasmon-exciton coupling is blocked for some crystal directions when exciton energy falls inside the plasmonic band gap of the periodically corrugated metallic surface. ©2014 Optical Society of America.
Open Access
Probing molecular interactions on carbon nanotube surfaces using surface plasmon resonance sensors
(A I P Publishing LLC, 2012) Kakenov, N.; Balci, O.; Balci, S.; Kocabas, C.
In this work, we present a method to probe molecular interactions on single-walled carbon nanotube (SWNT) surfaces using a surface plasmon sensor. SWNT networks were synthesized by chemical vapor deposition and transfer-printed on gold surfaces. We studied the excitation of surface plasmon-polaritons on nanotube coated gold surfaces with sub-monolayer, monolayer, and multilayer surface coverage. Integrating the fabricated sensor with a microfluidic device, we were able to obtain binding dynamics of a bovine serum albumin (BSA) protein on SWNT networks with various tube densities. The results reveal the kinetic parameters for nonspecific binding of BSA on SWNT coated surfaces having various tube densities. © 2012 American Institute of Physics.
Open Access
Probing ultrafast energy transfer between excitons and plasmons in the ultrastrong coupling regime
(American Institute of Physics Inc., 2014) Balci, S.; Kocabas, C.; Küçüköz, B.; Karatay, A.; Akhüseyin, E.; Yaglioglu, H. G.; Elmali, A.
We investigate ultrafast energy transfer between excitons and plasmons in ensembles of core-shell type nanoparticles consisting of metal core covered with a concentric thin J-aggregate (JA) shell. The high electric field localization by the Ag nanoprisms and the high oscillator strength of the JAs allow us to probe this interaction in the ultrastrong plasmon-exciton coupling regime. Linear and nonlinear optical properties of the coupled system have been measured using transient absorption spectroscopy revealing that the hybrid system shows half-plasmonic and half-excitonic properties. The tunability of the nanoprism plasmon resonance provides a flexible platform to study the dynamics of the hybrid state in a broad range of wavelengths. © 2014 AIP Publishing LLC.
Open Access
Strong coupling between localized and propagating plasmon polaritons
(OSA - The Optical Society, 2015) Balci, S.; Karademir, E.; Kocabas, C.
We investigate plasmon-plasmon (PP) coupling in the strongly interacting regimes by using a tunable plasmonic platform consisting of triangular Ag nanoprisms placed nanometers away from Ag thin films. The nanoprisms are colloidally synthesized using a seed-mediated growth method and having size-tunable localized surface plasmon polariton (SPP) resonances immobilized on Si3N4 films. The PP coupling between the localized SPPs of metal nanoprisms and the propagating SPPs of the metal film is controlled by the nanoprism concentration and the plasmon damping in the metal film. Results reveal that Rabi splitting energy determining the strength of the coupling can reach up to several hundreds meV, thus demonstrating the ultrastrong coupling occurring between localized and propagating SPPs. The metal nanoparticle-metal thin film hybrid system over the square-centimeter areas presented here provides a unique configuration to study PP coupling all the way from the weak to ultrastrong coupling regimes in a broad range of wavelengths.
Open Access
Tunable plexcitonic nanoparticles: a model system for studying plasmon-exciton interaction from the weak to the ultrastrong coupling regime
(American Chemical Society, 2016) Balci, S.; Kucukoz, B.; Balci, O.; Karatay, A.; Kocabas, C.; Yaglioglu, G.
Controlling the number of dye molecules on metallic nanoparticles, which in turn affects the magnitude of Rabi splitting energy, is crucial for obtaining hybrid metal core–organic shell nanoparticles with tunable optical properties in the visible spectrum since the magnitude of the Rabi splitting energy directly determines the strength of the coupling between plasmonic nanoparticles and dye molecules. In this work, we present a new method for the synthesis of plexcitonic nanoparticles, and thus we are able to control the number of dye molecules self-assembled on Ag nanoprisms (Ag NPs) by adjusting the concentration of dye molecules used in the synthesis. Indeed, individual dye molecules self-assemble into J-aggregates on Ag NPs. Thus, in the finite-element simulations and experimental data of the hybrid metal organic nanoparticles, we observed a transition from weak coupling to the ultrastrong coupling regime. Besides, ultrafast energy transfer between plasmonic nanoparticles and excitonic aggregated dye molecules has been extensively studied as a function of Rabi splitting energy. We observe that the lifetime of the polariton states increases with the coupling strength and the upper polaritons are short-lived, whereas the lower polaritons are long-lived. Hybrid metal–organic nanoparticles presented in this study (i) have tunable Rabi splitting energies, (ii) are easy to prepare in large quantities in aqueous medium, (iii) can be uniformly assembled on solid substrates, (iv) have resonance frequencies in the visible spectrum, and (v) have small mode volume, thus making them an excellent model system for studying light–matter interaction at nanoscale dimensions from the weak to ultrastrong coupling regime.
Open Access
Tuning surface plasmon-exciton coupling via thickness dependent plasmon damping
(American Physical Society, 2012) Balci, S.; Kocabas, C.; Ates, S.; Karademir, E.; Salihoglu, O.; Aydınlı, Atilla
In this paper, we report experimental and theoretical investigations on tuning of the surface plasmon-exciton coupling by controlling the plasmonic mode damping, which is defined by the plasmonic layer thickness. The results reveal the formation of plasmon-exciton hybrid state characterized by a tunable Rabi splitting with energies ranging from 0 to 150 meV. Polarization-dependent spectroscopic reflection measurements were employed to probe the dispersion of the coupled system. The transfer matrix method and analytical calculations were used to model the self-assembled J-aggregate/metal multilayer structures in excellent agreement with experimental observations. © 2012 American Physical Society.
Open Access
Ultra hybrid plasmonics: Strong coupling of plexcitons with plasmon polaritons
(OSA - The Optical Society, 2015) Balci, S.; Kocabas, C.
We report a ternary-coupled plasmonic system consisting of excitons of J-aggregated dye, localized surface plasmon polaritons of Ag nanoparticles, and propagating surface plasmon polaritons of continuous Ag film. J-aggregate dyes are uniformly self-assembled on colloidally synthesized Ag nanoprisms forming plexcitonic nanoparticles, which are placed at a distance nanometers away from the Ag thin film. The reflection measurements, corroborated by theoretical predictions, reveal that the strong coupling of plasmon polaritons and plexcitons results in a newly formed plasmon-exciton-plasmon hybridized state that we call here, reportedly for the first time, a plexcimon state. The hybrid plasmonic system shows dispersion characteristics similar to a coupled resonator optical waveguide. The group velocity of the plexcimon state approaches zero at the band edges. The ultrahybrid plasmonic system presented here is promising for a variety of light-matter interaction studies, including polariton lasers, plasmonic devices, plasmonic waveguiding, and spectroscopy.
Open Access
Weighing graphene with QCM to monitor interfacial mass changes
(American Institute of Physics Inc., 2016) Kakenov, N.; Balci, O.; Salihoglu, O.; Hur, S. H.; Balci, S.; Kocabas, C.
In this Letter, we experimentally determined the mass density of graphene using quartz crystal microbalance (QCM) as a mechanical resonator. We developed a transfer printing technique to integrate large area single-layer graphene on QCM. By monitoring the resonant frequency of an oscillating quartz crystal loaded with graphene, we were able to measure the mass density of graphene as ∼118 ng/cm2, which is significantly larger than the ideal graphene (∼76 ng/cm2) mainly due to the presence of wrinkles and organic/inorganic residues on graphene sheets. High sensitivity of the quartz crystal resonator allowed us to determine the number of graphene layers in a particular sample. Additionally, we extended our technique to probe interfacial mass variation during adsorption of biomolecules on graphene surface and plasma-assisted oxidation of graphene.