Advanced Research Laboratories (ARL)

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Browsing Advanced Research Laboratories (ARL) by Author "Aydınlı, Atilla"

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    Comparison of electron and hole charge-discharge dynamics in germanium nanocrystal flash memories
    (AIP Publishing, 2008-02) Akça, İmran B.; Dâna, Aykutlu; Aydınlı, Atilla; Turan, R.
    Electron and hole charge and discharge dynamics are studied on plasma enhanced chemical vapor deposition grown metal-oxide-silicon germanium nanocrystal flash memory devices. Electron and hole charge and discharge currents are observed to differ significantly and depend on annealing conditions chosen for the formation of nanocrystals. At low annealing temperatures, holes are seen to charge slower but to escape faster than electrons. They discharge slower than electrons when annealing temperatures are raised. The results suggest that discharge currents are dominated by the interface layer acting as a quantum well for holes and by direct tunneling for elec-trons.
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    Coupled plasmonic cavities on moire surfaces
    (Springer, 2010-08) Balcı, Sinan; Karabıyık, Mustafa; Kocabaş, Aşkın; Kocabaş, Coşkun; Aydınlı, Atilla
    Surface plasmon polariton (SPP) waveguides formed by coupled plasmonic cavities on metallic Moire surfaces have been investigated both experimentally and numerically. The Moire surface, fabricated by interference lithography, contains periodic arrays of one-dimensional cavities. The coupling strength between the cavities has been controlled by changing the periodicities of the Moire surface. The ability to control the coupling strength allows us to tune the dispersion and the group velocity of the plasmonic coupled cavity mode. Reflection measurements and numerical simulation of the array of SPP cavities have shown a coupled resonator type plasmonic waveguide band formation within the band gap. Coupling coefficients of cavities and group velocities of SPPs are calculated for a range of cavity sizes from weakly coupled regime to strongly coupled regime.
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    Direct imaging of localized surface plasmon polaritons
    (Optical Society of America, 2011-08) Balcı, Sinan; Karademir, Ertuğrul; Kocabaş, Coşkun; Aydınlı, Atilla
    In this Letter, we report on dark field imaging of localized surface plasmon polaritons (SPPs) in plasmonic waveguiding bands formed by plasmonic coupled cavities. We image the light scattered from SPPs in the plasmonic cavities excited by a tunable light source. Tuning the excitation wavelength, we measure the localization and dispersion of the plasmonic cavity mode. Dark field imaging has been achieved in the Kretschmann configuration using a supercontinuum white-light laser equipped with an acoustooptic tunable filter. Polarization dependent spectroscopic reflection and dark field imaging measurements are correlated and found to be in agreement with finite-difference time-domain calculations.
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    Electro-optic and electro-absorption characterization of InAs quantum dot waveguides
    (Optical Society of America, 2008-03) Akça, İmran B.; Dana, Aykutlu; Aydınlı, Atilla; Rossetti, M.; Li, L.; Fiore, A.; Dağlı, N.
    Abstract Optical properties of multilayer InAs quantum dot waveguides, grown by molecular beam epitaxy, have been studied under applied electric field. Fabry-Perot measurements at 1515 nm on InAs/GaAs quantum dot structures yield a significantly enhanced linear electro-optic efficiency compared to bulk GaAs. Electro-absorption measurements at 1300 nm showed increased absorption with applied field accompanied with red shift of the spectra. Spectral shifts of up to 21% under 18 Volt bias was observed at 1320 nm. (C) 2008 Optical Society of America.
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    Grating based plasmonic band gap cavities
    (Optical Society of American (OSA), 2009-08) Şenlik, S. Seçkin; Kocabaş, Aşkın; Aydınlı, Atilla
    We report on a comparative study of grating based plasmonic band gap cavities. Numerically, we calculate the quality factors of the cavities based on three types of grating surfaces; uniform, biharmonic and Moiré surfaces. We show that for biharmonic band gap cavities, the radiation loss can be suppressed by removing the additional grating component in the cavity region. Due to the gradual change of the surface profile in the cavity region, Moiré type surfaces support cavity modes with higher quality factors. Experimentally, we demonstrate the existence of plasmonic cavities based on uniform gratings. Effective index perturbation and cavity geometries are obtained by additional dielectric loading. Quality factor of 85 is obtained from the measured band structure of the cavity. © 2009 Optical Society of America.
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    Localization of surface plasmon polaritons in hexagonal arrays of Moiré cavities
    (AIP Publishing, 2011-01) Balcı, Sinan; Kocabaş, Aşkın; Kocabaş, Coşkun; Aydınlı, Atilla
    In view of the progress on the confinement of light, we report on the dispersion characteristics of surface plasmon polaritons (SPPs) on two-dimensional Moire surfaces in the visible part of the electromagnetic spectrum. Polarization dependent spectroscopic reflection measurements show omnidirectional confinement of SPPs. The resonance wavelength of SPP cavity modes can be adjusted by tuning the propagation direction of SPPs. The results may have an impact on the control of spontaneous emission and absorption with applications in light emitting diodes and solar cells, as well as in quantum electrodynamics experiments.
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    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).
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    Slowing surface plasmon polaritons on plasmonic coupled cavities by tuning grating grooves
    (American Institute of Physics, 2010-09) Balcı, Sinan; Kocabaş, Aşkın; Kocabaş, Coşkun; Aydınlı, Atilla
    We investigate slow surface plasmon polaritons (SPPs) in plasmonic waveguiding bands formed by coupled plasmonic cavities on Moiŕ surfaces. We demonstrate controlling the group velocity and dispersion of the SPPs by varying the depth of the plasmonic Bragg grating groove. Changing the grating depth results in modification of coupling coefficients between the cavities and hence the SPPs group velocity is altered. Variation in the group velocity and dispersion of SPPs can be measured with polarization dependent spectroscopic reflection measurements. Dispersion of SPPs has been calculated by finite-difference time-domain method in agreement with the experimental data.
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    Spectroscopic ellipsometric study of Ge nanocrystals embedded in SiO 2 using parametric models
    (Wiley, 2008-05) Basa, P.; Petrik, P.; Fried, M.; Dâna, Aykutlu; Aydınlı, Atilla; Foss, S.; Finstad, T. G.
    Ge-rich SiO2 layers on top of Si substrates were deposited using plasma enhanced chemical vapour deposition. Ge nanocrystals embedded in the SiO2 layers were formed by high temperature annealing. The samples were measured and evaluated by spectroscopic ellipsometry. Effective medium theory (EMT) and parametric semiconductor models have been used to model the dielectric function of the layers. Systematic dependences of the layer thickness and the oscillator parameters have been found on the annealing temperature (nanocrystal size).
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    Tunable surface plasmon resonance on an elastomeric substrate
    (Optical Society of American (OSA), 2009-05) Olcum, Selim; Kocabaş, Aşkın; Ertaş, Gülay; Atalar, Abdullah; Aydınlı, Atilla
    In this study, we demonstrate that periods of metallic gratings on elastomeric substrates can be tuned with external strain and hence are found to control the resonance condition of surface plasmon polaritons. We have excited the plasmon resonance on the elastomeric grating coated with gold and silver. The grating period is increased up to 25% by applying an external mechanical strain. The tunability of the elastomeric substrate provides the opportunity to use such gratings as efficient surface enhanced Raman spectroscopy substrates. It's been demonstrated that the Raman signal can be maximized by applying an external mechanical strain to the elastomeric grating. © 2009 Optical Society of America.