Browsing by Subject "J-aggregates"

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Open Access
Hybrid J-Aggregate–graphene phototransistor
(American Chemical Society, 2020) Balcı, Osman; Uzlu, Burkay; Yakar, Ozan; Polat, Nahit; Ari, O.; Tunç, İlknur; Kocabaş, Coşkun; Balcı, Sinan
J-aggregates are fantastic self-assembled chromophores with a very narrow and extremely sharp absorbance band in the visible and near-infrared spectrum, and hence they have found many exciting applications in nonlinear optics, sensing, optical devices, photography, and lasing. In silver halide photography, for example, they have enormously improved the spectral sensitivity of photographic process due to their fast and coherent energy migration ability. On the other hand, graphene, consisting of single layer of carbon atoms forming a hexagonal lattice, has a very low absorption coefficient. Inspired by the fact that J-aggregates have carried the role to sense the incident light in silver halide photography, we would like to use Jaggregates to increase spectral sensitivity of graphene in the visible spectrum. Nevertheless, it has been an outstanding challenge to place isolated J-aggregate films on graphene to extensively study interaction between them. We herein noncovalently fabricate isolated J-aggregate thin films on graphene by using a thin film fabrication technique we termed here membrane casting (MC). MC significantly simplifies thin film formation of water-soluble substances on any surface via porous polymer membrane. Therefore, we reversibly modulate the Dirac point of graphene in the J-aggregate/graphene van der Waals (vdW) heterostructure and demonstrate an all-carbon phototransistor gated by visible light. Owing to the hole transfer from excited excitonic thin film to graphene layer, graphene is hole-doped. In addition, spectral and power responses of the all-carbon phototransistor have been measured by using a tunable laser in the visible spectrum. The first integration of J-aggregates with graphene in a transistor structure enables one to reversibly write and erase charge doping in graphene with visible light that paves the way for using J-aggregate/graphene vdW heterostructures in optoelectronic applications.
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 the exciton-plasmon coupling
(2012) Ateş, Simge
Exciton-plasmon coupling has recently drawn much interest. In this work, FDTD simulations of exciton-plasmon coupling in plasmonic cavity structures with corrugation patterns are investigated. Excitonic modes are obtained from a Lorentz absorber modeling of a J-aggregate organic dye. The coupling of these excitonic and plasmonic modes on Ag thin films is demonstrated. Rabi splitting due to coupling was clearly observed. Flat metallic surfaces, uniform gratings and Moiré surfaces are used in simulations as corrugation patterns. Metal film thickness and dye concentration dependence of Rabi splitting via exciton-plasmon coupling was also observed on thin flat Ag films. We show that Rabi splitting occurs even at low dye concentrations, and the magnitude of splitting increases as dye concentration increases. A new state in the band gap is observed when the total oscillator strength is increased. Large Rabi splitting is observed when plasmon damping is modulated. Exciton-plasmon coupling on uniform gratings is studied as a function of cavity size, corrugation periodicity and depth. Q factor and Rabi splitting behavior of excitonplasmon coupling on Moiré cavities are investigated as a function of cavity size. Strong anti-crossing is observed when the excitonic absorption matches with the cavity state.