Browsing by Author "Dirisaglik, F."

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Open Access
Extracting the temperature distribution on a phase-change memory cell during crystallization
(American Institute of Physics Inc., 2016-10) Bakan, G.; Gerislioglu, B.; Dirisaglik, F.; Jurado, Z.; Sullivan, L.; Dana, A.; Lam, C.; Gokirmak A.; Silva, H.
Phase-change memory (PCM) devices are enabled by amorphization- and crystallization-induced changes in the devices' electrical resistances. Amorphization is achieved by melting and quenching the active volume using short duration electrical pulses (∼ns). The crystallization (set) pulse duration, however, is much longer and depends on the cell temperature reached during the pulse. Hence, the temperature-dependent crystallization process of the phase-change materials at the device level has to be well characterized to achieve fast PCM operations. A main challenge is determining the cell temperature during crystallization. Here, we report extraction of the temperature distribution on a lateral PCM cell during a set pulse using measured voltage-current characteristics and thermal modelling. The effect of the thermal properties of materials on the extracted cell temperature is also studied, and a better cell design is proposed for more accurate temperature extraction. The demonstrated study provides promising results for characterization of the temperature-dependent crystallization process within a cell.
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.