Browsing by Subject "Spectral tunability"

Now showing 1 - 3 of 3

Open Access
Alloyed heterostructures of CdSexS1-x nanoplatelets with highly tunable optical gain performance
(American Chemical Society, 2017) Kelestemur Y.; Dede, D.; Gungor K.; Usanmaz, C. F.; Erdem, O.; Demir, Hilmi Volkan
Here, we designed and synthesized alloyed heterostructures of CdSexS1-x nanoplatelets (NPLs) using CdS coating in the lateral and vertical directions for the achievement of highly tunable optical gain performance. By using homogeneously alloyed CdSexS1-x core NPLs as a seed, we prepared CdSexS1-x/CdS core/crown NPLs, where CdS crown region is extended only in the lateral direction. With the sidewall passivation around inner CdSexS1-x cores, we achieved enhanced photoluminescence quantum yield (PL-QY) (reaching 60%), together with increased absorption cross-section and improved stability without changing the emission spectrum of CdSexS1-x alloyed core NPLs. In addition, we further extended the spectral tunability of these solution-processed NPLs with the synthesis of CdSexS1-x/CdS core/shell NPLs. Depending on the sulfur composition of the CdSexS1-x core and thickness of the CdS shell, CdSexS1-x/CdS core/shell NPLs possessed highly tunable emission characteristics within the spectral range of 560-650 nm. Finally, we studied the optical gain performances of different heterostructures of CdSexS1-x alloyed NPLs offering great advantages, including reduced reabsorption and spectrally tunable optical gain range. Despite their decreased PL-QY and reduced absorption cross-section upon increasing the sulfur composition, CdSexS1-x based NPLs exhibit highly tunable amplified spontaneous emission performance together with low gain thresholds down to ∼53 μJ/cm2.
Open Access
Comparison of back and top gating schemes with tunable graphene fractal metasurfaces
(American Chemical Society, 2016) Aygar, A. M.; Balci, O.; Cakmakyapan, S.; Kocabas, C.; Caglayan, H.; Özbay, Ekmel
In this work, fractal metasurfaces that consist of periodic gold squares on graphene are used to increase light-graphene interaction. We show by simulations and experiments that higher level fractal structures result in higher spectral tunability of resonance wavelength. This is explained by higher field localization for higher level fractal structures. Furthermore, spectral tunability of fractal metasurfaces integrated with graphene is investigated comparing two different schemes for electrostatic gating. Experiment results show that a top-gated device yields more spectral tunability (8% of resonance wavelength) while requiring much smaller gate voltages compared to the back-gated device. © 2016 American Chemical Society.
Open Access
Tunable graphene plasmonic structures with different gating schemes
(2016-08) Aygar, Ayşe Melis
The aim of this thesis is to examine graphene plasmonic structures which yields actively tunable spectral resonances and compare two different ways to gate graphene. Plasmonic structures that consist of periodic fractal gold squares on graphene are used to increase light-graphene interaction. We show by simulations and experiments that higher degree fractal structures result in higher spectral tunability of resonance wavelength. This is explained by more plasmonic localization of light for higher degree fractal structures. Furthermore, spectral tunability of a plasmonic structure integrated with graphene is investigated comparing two different schemes for electrostatic gating. The fabrication methods and fabrication steps of the devices with different gating schemes is explained in detail. Comparison of back-gating and top-gating schemes confirms that top-gating using ionic liquid is a more efficient gating method. Top-gating yields the same amount of spectral tunability while requiring smaller gate voltages compared to that of back-gating experiments.