Browsing by Author "Güner, H."
Now showing 1 - 4 of 4
Results Per Page
Sort Options
Item Open Access Electrochemically tunable ultrafast optical response of graphene oxide(A I P Publishing LLC, 2011) Kürüm, U.; Ekiz, O. Ö.; Yaglioglu, H. G.; Elmali, A.; Ürel, M.; Güner, H.; Mızrak, A. K.; Ortaç, B.; Dâna, A.We demonstrate reversible and irreversible changes in the ultrafast optical response of multilayer graphene oxide thin films upon electrical and optical stimulus. The reversible effects are due to electrochemical modification of graphene oxide, which allows tuning of the optical response by externally applied bias. Increasing the degree of reduction in graphene oxide causes excited state absorption to gradually switch to saturable absorption for shorter probe wavelengths. Spectral and temporal properties as well as the sign of the ultrafast response can be tuned either by changing the applied bias or exposing to high intensity femtosecond pulses. © 2011 American Institute of Physics.Item Open Access Exploiting native Al2O3 for multispectral aluminum plasmonics(American Chemical Society, 2014) Ayas S.; Topal, A. E.; Cupallari, A.; Güner, H.; Bakan, G.; Dana, A.Aluminum, despite its abundance and low cost, is usually avoided for plasmonic applications due to losses in visible/infrared regimes and its interband absorption at 800 nm. Yet, it is compatible with silicon CMOS processes, making it a promising alternative for integrated plasmonic applications. It is also well known that a thin layer of native Al2O3 is formed on aluminum when exposed to air, which must be taken into account properly while designing plasmonic structures. Here, for the first time we report exploitation of the native Al2O3 layer for fabrication of periodic metal-insulator-metal (MIM) plasmonic structures that exhibit resonances spanning a wide spectral range, from the near-ultraviolet to mid-infrared region of the spectrum. Through fabrication of silver nanoislands on aluminum surfaces and MIM plasmonic surfaces with a thin native Al2O3 layer, hierarchical plasmonic structures are formed and used in surface-enhanced infrared spectroscopy (SEIRA) and surface-enhanced Raman spectrocopy (SERS) for detection of self-assembled monolayers of dodecanethiol. (Chemical Equation Presented). © 2014 American Chemical Society.Item Open Access Raman enhancement on a broadband meta-surface(American Chemical Society, 2012-07-30) Ayas S.; Güner, H.; Türker, B.; Ekiz, O. O.; Dirisaglik, F.; Okyay, Ali Kemal; Dâna, A.Plasmonic metamaterials allow confinement of light to deep subwavelength dimensions, while allowing for the tailoring of dispersion and electromagnetic mode density to enhance specific photonic properties. Optical resonances of plasmonic molecules have been extensively investigated; however, benefits of strong coupling of dimers have been overlooked. Here, we construct a plasmonic meta-surface through coupling of diatomic plasmonic molecules which contain a heavy and light meta-atom. Presence and coupling of two distinct types of localized modes in the plasmonic molecule allow formation and engineering of a rich band structure in a seemingly simple and common geometry, resulting in a broadband and quasi-omni-directional meta-surface. Surface-enhanced Raman scattering benefits from the simultaneous presence of plasmonic resonances at the excitation and scattering frequencies, and by proper design of the band structure to satisfy this condition, highly repeatable and spatially uniform Raman enhancement is demonstrated. On the basis of calculations of the field enhancement distribution within a unit cell, spatial uniformity of the enhancement at the nanoscale is discussed. Raman scattering constitutes an example of nonlinear optical processes, where the wavelength conversion during scattering may be viewed as a photonic transition between the bands of the meta-material.Item Open Access Reversible electrical reduction and oxidation of graphene oxide(American Chemical Society, 2011) Ekiz, O. O.; Ürel, M.; Güner, H.; Mizrak, A. K.; Dâna, A.We demonstrate that graphene oxide can be reversibly reduced and oxidized using electrical stimulus. Controlled reduction and oxidation in two-terminal devices containing multilayer graphene oxide films are shown to result in switching between partially reduced graphene oxide and graphene, a process which modifies the electronic and optical properties. High-resolution tunneling current and electrostatic force imaging reveal that graphene oxide islands are formed on multilayer graphene, turning graphene into a self-assembled heterostructure random nanomesh. Charge storage and resistive switching behavior is observed in two-terminal devices made of multilayer graphene oxide films, correlated with electrochromic effects. Tip-induced reduction and oxidation are also demonstrated. Results are discussed in terms of thermodynamics of oxidation and reduction reactions. © 2011 American Chemical Society.