Browsing by Author "Habib, M."

Now showing 1 - 4 of 4

Open Access
Graphene-based tunable plasmon induced transparency in gold strips
(Optical Society of America, 2018) Habib, M.; Rashed, A. R.; Özbay, Ekmel; Caglayan, H.
Plasmon induced transparency (PIT) has been numerically investigated and experimentally realized by two parallel gold strips on graphene for the mid-infrared (MIR) range. The PIT response is realized by the weak hybridization of two bright modes of the gold strips. The response of the device is adjusted with the lengths of two strips and tuned electrically in real time by changing the Fermi level (Ef) of the graphene. Ef is changed to tune the resonance frequency of the transparency window. A top gating is used to achieve high tunability and a 263 nm shift is obtained by changing the gate voltage from -0.6 V to 2.4 V. The spectral contrast ratio of our devices is up to 82%.
Open Access
Highly-sensitive refractive index sensing by near-infrared metatronic nanocircuits
(Nature Publishing Group, 2018) Rashed, A. R.; Gudulluoglu, B.; Yun, H. W.; Habib, M.; Boyaci, I. H.; Hong, S. H.; Özbay, Ekmel; Caglayan, H.
In this work, we present a highly-sensitive refractive index sensor based on metatronic nanocircuits operating at near-infrared spectral range. The structure is designed based on simple nanorod geometry and fabricated by nanopatterning of transparent conducting oxides. The functionality of these polarization dependent metatronic nanocircuits is enhanced by applying tunable response. This feature is investigated by depositing NH2 (Amine) groups via plasma polymerization technique on top of indium-tin-oxide nanorods. The dielectric constant of Amine groups is a function of their thickness, which can be controlled by the RF power and the time duration of the applied plasma polymerization process. The resonance wavelengths of nanocircuits shift to higher wavelength, as the dielectric constant of the deposited material increases. An excellent agreement between the design and experimental results are obtained. Our metatronic based nanosensor offers a high-sensitive performance of 1587 nm/RIU with a satisfactory figure of merit for this class of sensors.
Open Access
Plasmon-modulated photoluminescence enhancement in hybrid plasmonic nano-antennas
(IOP Publishing, 2020) Rashed, A. R.; Habib, M.; Das, N.; Özbay, Ekmel; Çağlayan, H.
In this work, we performed a systematic study on a hybrid plasmonic system to elucidate a new insight into the mechanisms governing the fluorescent enhancement process. Our lithographically defined plasmonic nanodisks with various diameters act as receiver and transmitter nano-antennas to outcouple efficiently the photoluminescence of the coupled dye molecules. We show that the enhancement of the spontaneous emission rate arises from the superposition of three principal phenomena: (i) metal enhanced fluorescence, (ii) metal enhanced excitation and (iii) plasmon-modulated photoluminescence of the photoexcited nanostructures. Overall, the observed enhanced emission is attributed to the bi-directional near-field coupling of the fluorescent dye molecules to the localized plasmonic field of nano-antennas. We identify the role of exciton–plasmon coupling in the recombination rate of the sp-band electrons with d-band holes, resulting in the generation of particle plasmons. According to our comprehensive experimental analyses, the mismatch between the enhanced emission and the emission spectrum of the uncoupled dye molecules is attributed to the plasmon-modulated photoluminescence of the photoexcited hybrid plasmonic system.
Open Access
Tuning plasmon induced reflectance with hybrid metasurfaces
(MDPI AG, 2019-03) Habib, M.; Özbay, Ekmel; Çağlayan, Hümeyra
Electrically tunable metasurfaces with graphene offer design flexibility to efficiently manipulate and control light. These metasurfaces can be used to generate plasmon-induced reflectance (PIR), which can be tuned by electrostatic doping of the graphene layer. We numerically investigated two designs for tunable PIR devices using the finite difference time-domain (FDTD) method. The first design is based on two rectangular antennas of the same size and a disk; in the second design, two parallel rectangular antennas with different dimensions are used. The PIR-effect was achieved by weak hybridization of two bright modes in both devices and tuned by changing the Fermi level of graphene. A total shift of ∼362 nm was observed in the design with the modulation depth of 53% and a spectral contrast ratio of 76%. These tunable PIR devices can be used for tunable enhanced biosensing and switchable systems.