Browsing by Subject "Interference coatings"

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    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.
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    Infrared absorption spectroscopy of monolayers with thin film interference coatings
    (Optical Society of America, 2017) Ayas, Sencer; Bakan, Gökhan; Ozgur, E.; Celebi, Kemal; Dana, Aykutlu
    We report high performance Infrared spectroscopy platforms based on interference coatings on metal using CaF2 dielectric films and Ge2Sb2Te5 (GST) phase-change films. IR vibrational bands of proteins and organic monolayers are also detected.
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    Perfectly absorbing ultra thin interference coatings for hydrogen sensing
    (OSA - The Optical Society, 2016) Serhatlioglu, M.; Ayas S.; Bıyıklı, Necmi; Dana, A.; Solmaz, M. E.
    Here we numerically demonstrate a straightforward method for optical detection of hydrogen gas by means of absorption reduction and colorimetric indication. A perfectly absorbing metal-insulator-metal (MIM) thin film interference structure is constructed using a silver metal back reflector, silicon dioxide insulator, and palladium as the upper metal layer and hydrogen catalyst. The thickness of silicon dioxide allows the maximizing of the electric field intensity at the Air/SiO2 interface at the quarter wavelengths and enabling perfect absorption with the help of highly absorptive palladium thin film (∼7 nm). While the exposure of the MIM structure to H2 moderately increases reflection, the relative intensity contrast due to formation of metal hydride is extensive. By modifying the insulator film thickness and hence the spectral absorption, the color is tuned and eye-visible results are obtained.
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    Thermally tunable ultrasensitive infrared absorption spectroscopy platforms based on thin phase-change films
    (American Chemical Society, 2016-11) Bakan, G.; Ayas S.; Ozgur E.; Celebi, K.; Dana, A.
    The thermal tunability of the optical and electrical properties of phase-change materials has enabled the decades-old rewritable optical data storage and the recently commercialized phase-change memory devices. Recently, phase-change materials, in particular, Ge2Sb2Te5 (GST), have been considered for other thermally configurable photonics applications, such as active plasmonic surfaces. Here, we focus on nonplasmonic field enhancement and demonstrate the use of the phase-change materials in ultrasensitive infrared absorption spectroscopy platforms employing interference-based uniform field enhancement. The studied structures consist of patternless thin GST and metal films, enabling simple and large-area fabrication on rigid and flexible substrates. Crystallization of the as-fabricated amorphous GST layer by annealing tunes (redshifts) the field-enhancement wavelength range. The surfaces are tested with ultrathin chemical and biological probe materials. The measured absorption signals are found to be comparable or superior to the values reported for the ultrasensitive infrared absorption spectroscopy platforms based on plasmonic field-enhancement.