Browsing by Subject "Substrate"

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    ItemOpen Access
    An array of surface-enhanced Raman scattering substrates based on plasmonic lenses
    (Wiley, 2012-10-01) Kahraman, M.; Cakmakyapan, S.; Özbay, Ekmel; Culha, M.
    An array of ring-shaped holes is prepared from silver thin films using electron beam lithography. The optimal conditions for high performance as a surface-enhanced Raman scattering (SERS) substrate are investigated. Either the diameter of the hole (0.5, 1.0, 2.0, 3.0 and 4.0 μm) or the slit width (200, 300, 400, 500 and 600 nm) is varied. 4-Aminothiophenol (ATP) adsorbed on the structures as a self-assembled monolayer (SAM) is used as probe to evaluate the SERS performance of the generated structures. It is found that there is an optimal configuration for ring-shaped holes with a 3.0-μm diameter and 200-nm slit width. The SERS activity on this optimal lens configuration is found to be 13 times greater than that of the activity on the silver thin film. An array of these structures at this optimal configuration can easily be constructed and used in a range of SERS-based sensing applications. An array of ring-shaped holes is prepared from silver thin films using electron beam lithography. The optimal conditions for high performance as a surface-enhanced Raman scattering (SERS) substrate are investigated. It is found that there is an optimal configuration for ring-shaped holes with a 3.0-μm diameter and 200-nm slit with. The SERS activity on this optimal lens configuration is found to be 13 times greater than that of the activity on the silver thin film.
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    ItemOpen Access
    Highly directive radiation from sources embedded inside photonic crystals
    (American Institute of Physics, 2003) Bulu, I.; Caglayan, H.; Özbay, Ekmel
    In this work, we have experimentally and theoretically studied the angular distribution of power emitted from a radiation source embedded inside a photonic crystal. Our results show that it is possible to obtain highly directive radiation sources operating at the band edge of the photonic crystal. Half power beam widths as small as 6degrees have been obtained. Our results also show that the angular distribution of power strongly depends on the frequency and on the size of the photonic crystal. (C) 2003 American Institute of Physics.
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    ItemOpen Access
    Microstructural defect properties of InGaN/GaN blue light emitting diode structures
    (Springer US, 2014-06-28) Bas, Y.; Demirel, P.; Akin, N.; Başköse, C.; Özen, Y.; Kınacı, B.; Öztürk, M. K.; Özcelik, S.; Özbay, Ekmel
    In this paper, we study structural and morphological properties of metal-organic chemical vapour deposition-grown InGaN/GaN light emitting diode (LED) structures with different indium (In) content by means of high-resolution X-ray diffraction, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and current-voltage characteristic (I-V). We have found out that the tilt and twist angles, lateral and vertical coherence lengths of mosaic blocks, grain size, screw and edge dislocation densities of GaN and InGaN layers, and surface roughness monotonically vary with In content. Mosaic defects obtained due to temperature using reciprocal lattice space map has revealed optimized growth temperature for active InGaN layer of MQW LED. It has been observed in this growth temperature that according to AFM result, LED structure has high crystal dimension, and is rough whereas according to PL and FTIR results, bandgap energy shifted to blue, and energy peak half-width decreased at high values. According to I-V measurements, it was observed that LED reacted against light at optimized temperature. In conclusion, we have seen that InGaN MQW structure's structural, optical and electrical results supported one another.
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    ItemOpen Access
    Ultrafast and sensitive bioassay using split ring resonator structures and microwave heating
    (American Institute of Physics, 2010-08-30) Caglayan, H.; Cakmakyapan, S.; Addae, S. A.; Pinard, M. A.; Caliskan, D.; Aslan, K.; Özbay, Ekmel
    In this paper, we have reported that split ring resonators (SRRs) structures can be used for bioassay applications in order to further improve the assay time and sensitivity. The proof-of-principle demonstration of the ultrafast bioassays was accomplished by using a model biotin-avidin bioassay. While the identical room temperature bioassay (without microwave heating) took 70 min to complete, the identical bioassay took less than 2 min to complete by using SRR structures (with microwave heating). A lower detection limit of 0.01 nM for biotinylated-bovine serum albumin (100-fold lower than the room temperature bioassay) was observed by using SRR structures.
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    ItemOpen Access
    XPS investigation of a Si-diode in operation
    (Royal Society of Chemistry, 2012) Süzer, Şefik
    X-ray photoelectron spectroscopy (XPS) is utilized to investigate a Si-diode during its operation under both forward and reverse bias. The technique traces chemical and location specified surface potential variations as shifts of the peak positions with respect to the magnitude as well as the polarity of the applied voltage bias, which enables one to separate the dopant dependent shifts from those of the chemical ones.