Browsing by Author "Turan, S."

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    Current-Transport mechanisms in the AlInN/AlN/GaN single-channel and AlInN/AlN/GaN/AlN/GaN double-channel heterostructures
    (Elsevier, 2013) Arslan, E.; Turan, S.; Gökden, S.; Teke, A.; Özbay, Ekmel
    Current-transport mechanisms were investigated in Schottky contacts on AlInN/AlN/GaN single channel (SC) and AlInN/AlN/GaN/AlN/GaN double channel (DC) heterostructures. A simple model was adapted to the current-transport mechanisms in DC heterostructure. In this model, two Schottky diodes are in series: one is a metal-semiconductor barrier layer (AIInN) Schottky diode and the other is an equivalent Schottky diode, which is due to the heterojunction between the AlN and GaN layer. Capacitance-voltage studies show the formation of a two-dimensional electron gas at the AlN/GaN interface in the SC and the first AlN/GaN interface from the substrate direction in the DC. In order to determine the current mechanisms for SC and DC heterostructures, we fit the analytical expressions given for the tunneling current to the experimental current-voltage data over a wide range of applied biases as well as at different temperatures. We observed a weak temperature dependence of the saturation current and a fairly small dependence on the temperature of the tunneling parameters in this temperature range. At both a low and medium forward-bias voltage values for Schottky contacts on AlInN/AlN/GaN/AlN/GaN DC and AlInN/AlN/GaN SC heterostructures, the data are consistent with electron tunneling to deep levels in the vicinity of mixed/screw dislocations in the temperature range of 80-420 K.
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    Enhancing the properties of yttria-stabilized zirconia composites with zeolitic imidazolate framework-derived nanocarbons
    (American Chemical Society, 2023-12-09) Cakan, N.; Issa, A. A.; Alsalman, H.; Aliyev, Emin; Duden, E. I.; Gurcan Bayrak, K.; Caglar, M.; Turan, S.; Erkartal, M.
    Ceramicmatrixcomposites(CMCs)reinforcedwithnanocarbonhaveattractedsignificantinterestdue to theirpotentialto enhancemechanical,thermal,andelectricalproperties.Althoughthe investigationof carbon-basedmaterialssuchas grapheneandcarbonnanotubesas additivesfor advancedceramicshasbeenwidespread,theutilizationof metal−organicframework(MOF)-derivednanocarbonsin CMCsremainslargelyunexplored.We extendedour previousproof-of-conceptinvestigationsby demonstratingthe effectivenessofa differenttypeof MOF-derivedcarbonas a reinforcingphasein an alternativeceramicmatrix.We employedsparkplasmasintering(SPS)to consolidateyttria-stabilizedzirconia(YSZ)andzeoliticimidazolateframework(ZIF-67)powderblendsat 1300°C and a uniaxialpressureof 50 MPa.YSZservesas the ceramicmatrix,whereasZIF-67servesas the nanocarbonsource.Thecompositeexhibitsa highlysignificantimprovementin fracturetoughnesswithan increaseof up to13%comparedto thatof the YSZmonolith.Theformationof ZIF-derivednanocarboninterlayersis responsiblefor the observedenhancementin ductility,whichcan be attributedto theirabilityto facilitateenergydissipationduringcrackpropagationand inhibitgraingrowth.Furthermore,the room-temperatureelectricalconductivityof the sinteredsamplesdemonstratesa substantialimprovement,primarilydue to the in situ formationof nanocarbon-basedfillers,reachingan impressive27 S/mwith10 wt % ZIF-67content.Basedon the results,it can be inferredthatthe incorporationof in situ MOF-derivednanocarbonsintoCMCsleadsto asubstantialimprovementin boththe mechanicaland electricalproperties.
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    An experimental and theoretical examination of the effect of sulfur on the pyrolytically grown carbon nanotubes from sucrose-based solid state precursors
    (Elsevier, 2011) Kucukayan, G.; Ovali, R.; Ilday, S.; Baykal, B.; Yurdakul, H.; Turan, S.; Gulseren, O.; Bengu, E.
    Multi-walled carbon nanotubes (MWCNTs) were synthesized through pyrolysis of the sulfuric acid-carbonized byproduct of sucrose. While the presence of sulfur in the reaction media has a key role in the formation and population density of MWCNTs, we have not observed the formation of Y-junctions or encountered other novel carbon nanotube formations. Results indicate the presence of sulfur in catalyst particles trapped inside nanotubes, but failed to find sulfur in the side-walls of the CNTs. In order to verify and explain these findings, we analyzed the behavior of sulfur and its possible effects on the side-wall structure of CNTs by using density functional theory-based calculations on various atomic models depicting sulfur inclusion in the side-walls. The results of the computational study were in line with the experimental results and also provided a new perspective by suggesting that the defects such as pentagons may act as nucleation sites for the Y-branches. The results indicated that sulfur prefers to adsorb on these defective regions, but it is not responsible for the formation of these structures or defects.
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    Mitochondrial carrier homolog 1 (Mtch1) antibodies in neuro-Behçet's disease
    (Elsevier, 2013) Vural, B.; Şehitoğlu, E.; Çavuş, F.; Yalçınkaya, N.; Haytural, H.; Küçükerden, M.; Ulusoy, C.; Uğurel, E.; Turan, S.; Bulut, L.; Türkoğlu, R.; Shugaiv, E.; Kürtüncü, M.; Atakan, S.; Güre, A. O.; Gül, A.; Eraksoy, M.; Demir, G. A.; Tüzün, E.
    Efforts for the identification of diagnostic autoantibodies for neuro-Behcet's disease (NBD) have failed. Screening of NBD patients' sera with protein macroarray identified mitochondrial carrier homolog 1 (Mtch1), an apoptosis-related protein, as a potential autoantigen. ELISA studies showed serum Mtch1 antibodies in 68 of 144 BD patients with or without neurological involvement and in 4 of 168 controls corresponding to a sensitivity of 47.2% and specificity of 97.6%. Mtch1 antibody positive NBD patients had more attacks, increased disability and lower serum nucleosome levels. Mtch1 antibody might be involved in pathogenic mechanisms of NBD rather than being a coincidental byproduct of autoinflammation. © 2013 Elsevier B.V.
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    Synthesis of Phosporus included multiwalled carbon nanotubes by pyrolysis of sucrose
    (American Chemical Society, 2013) Dogu, G. k.; Sen, H. S.; Yurdakul, H.; Turan, S.; Gulseren, O.; Bengu, E.
    Multiwalled carbon nanotubes (MWCNT) were synthesized by a pyrolysis route which involves a dehydration step using phosphoric acid. The resultants were found to be mostly containing amorphous carbon with scattered MWCNTs using scanning electron and transmission electron microscopy techniques. These MWCNTs were smaller in size and limited in quantity compared to the ones synthesized using other common precursors. Energy dispersive X-ray and electron energy loss spectroscopy analysis indicated the presence of phosphorus both at the MWCNT sidewalls and in the catalyst particles encapsulated inside the MWCNTs. In addition, a comparative investigation for sulfur and phosphorus inclusion to the sidewalls of MWCNTs was carried out using density functional theory calculations. The results of the computational study showed that both phosphorus and sulfur atoms prefer to bind among themselves rather than adsorbing directly on carbon nanotubes (CNT). Furthermore, cluster calculations revealed that phosphorus atoms more likely form carbonaceous clusters which result in a decrease in the number of free carbon atoms that can be used for CNT formation. Therefore, we concluded that MWCNT growth might be hindered (promoted) in a phosphorus (sulfur) rich environment which results in needle like phosphorus containing MWCNTs.