Browsing by Author "Ayas, Sencer"

Now showing 1 - 6 of 6

Open Access
Applications of plasmon enhanced emission and absorption
(2009) Ayas, Sencer
The term plasmon-polariton is used to describe coupled modes of electromagnetic waves with electronic plasma oscillations in conductors. Surface plasmon resonances have found profound interest over the last few decades in multiple fields ranging from nanophotonics to biological sensing. In this thesis, we study enhancement of absorption and emission of radiation due to the presence of a modified local electromagnetic mode density within the vicinity of metallic surfaces supporting plasmon modes. Various coupling schemes of freespace electromagnetic modes to plasmon modes are investigated theoretically and experimentally. Local mode densities and field enhancements due to plasmon modes in planar structures, gratings and optical antennas have been studied in their relation to the absorption and emission enhancement of dipoles positioned in various orientations and locations with respect to structures displaying plasmonic effects. Particularly, grating coupled plasmon resonances were analysed using Rigorously Coupled Wave Analysis and Finite Difference Time domain methods. Experimental demonstrations of absorption and emission enhancement of dielectric layers containing Rhodamine 6G on various plasmonic structures are given. Confocal Raman microscopy was used in characterization of fabricated structures. It is seen that the experimental measurements are in good agreement with theoretical predictions. Direction dependent luminescence enhancement is observed with dye molecules on grating structures. Potential applications of plasmon enhanced absorption and emission include high sensitivity absorption spectroscopy, performance enhancement in thin film solar cells and luminescent concentrators.
Open Access
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.
Open Access
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.
Open Access
Interference coatings for infrared spectroscopy and colorimetric sensing
(OSA, 2018) Bakan, Gökhan; Ayas, Sencer; Özgür, Erol; Çelebi, Kemal; Dana, Aykutlu
Constructive interference and strong interference surfaces are created to sense ultrathin probe materials such as monolayer protein molecules using enhanced infrared absorption spectroscopy and colorimetric detection, respectively.
Open Access
Label-free nanometer-resolution imaging of biological architectures through surface enhanced raman scattering
(Nature Publishing Group, 2013) Ayas, Sencer; Çınar, Göksu; Özkan, Alper Devrim; Soran, Zeliha; Ekiz, Oner; Kocaay, Deniz; Tomak, A.; Toren, Pelin; Kaya, Yasin; Tunc, I.; Zareie, H.; Tekinay, T.; Tekinay, Ayse Begum; Güler, Mustafa O.; Dana, Aykutlu
Label free imaging of the chemical environment of biological specimens would readily bridge the supramolecular and the cellular scales, if a chemical fingerprint technique such as Raman scattering can be coupled with super resolution imaging. We demonstrate the possibility of label-free super-resolution Raman imaging, by applying stochastic reconstruction to temporal fluctuations of the surface enhanced Raman scattering (SERS) signal which originate from biomolecular layers on large-area plasmonic surfaces with a high and uniform hot-spot density (> 10(11)/cm(2), 20 to 35 nm spacing). A resolution of 20 nm is demonstrated in reconstructed images of self-assembled peptide network and fibrilated lamellipodia of cardiomyocytes. Blink rate density is observed to be proportional to the excitation intensity and at high excitation densities (> 10 kW/cm(2)) blinking is accompanied by molecular breakdown. However, at low powers, simultaneous Raman measurements show that SERS can provide sufficient blink rates required for image reconstruction without completely damaging the chemical structure.
Open Access
Reversible decryption of covert nanometer-thick patterns in modular metamaterials
(OSA - The Optical Society, 2019) Bakan, Gökhan; Ayas, Sencer; Serhatlıoğlu, Murat; Dana, Aykutlu; Elbüken, Çağlar
Continuous development of security features is mandatory for the fight against forgery of valuable documents and products, the most notable example being banknotes. Such features demonstrate specific properties under certain stimuli such as fluorescent patterns glowing under ultraviolet light. These security features should also be hard to copy by unlicensed people and be interrogated by anyone using easily accessible tools. To this end, this Letter demonstrates the development of an ideal security feature enabled by the realization of modular metamaterials based on metal–dielectric–metal cavities that consist of two separate parts: metal nanoparticles on an elastomeric substrate and a bottom mirror coated with a thin dielectric. Patterns generated by creating nanometer-thick changes in the dielectric layer are invisible (encrypted) and can only be detected (decrypted) by sticking the elastomeric patch on. The observed optical effects such as visibility and colors can only be produced with the correct combination of materials and film thicknesses, making the proposed structures a strong alternative to compromised security features.