WoS İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/394
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Article Citation - WoS: 12Citation - Scopus: 11Trans-Cis Isomerization Assisted Synthesis of Solution-Processable Yellow Fluorescent Maleic Anhydrides for White-Light Generation(Elsevier Science SA, 2015-12) Ozdemir, Mehmet; Genc, Sinan; Ozdemir, Resul; Altintas, Yemliha; Citir, Murat; Sen, Unal; Usta, HakanHeterocyclic maleic anhydride derivatives have been extensively studied in natural products chemistry over the past few decades. However, their incorporation into optoelectronic devices has lagged behind that of other pi-conjugated systems, and they have never been studied in white light emitting diodes (WLEDs). The development of emissive pi-conjugated materials for (WLEDs) has been an emerging scientific and technological research area to replace phosphors used in LED-based solid-state lighting. Here, we demonstrate the design, synthesis and characterization of two new highly emissive alkyl-substituted bis(thienyl)maleic anhydrides (C6-Th2MA and C12-Th2MA) with favorable photophysical properties. The new core is synthesized via a novel trans-to-cis isomerization-assisted one-pot reaction, which is demonstrated for the first time in the literature for the synthesis of a bis(heteroaryl)maleic anhydride. Due to its favorable absorption and fluorescence properties in the blue and yellow region of the visible spectrum, respectively, C12-Th2MA is studied as a potential wavelength-upconverting material. A WLED fabricated by drop-casting a polymeric solution of C12-Th2MA on a blue LED (InGaN, 455 nm) yields promising CIE coordinates and color-rendering index (CRI) values of (0.24, 0.20) and 65.0, respectively. Considering the simplicity of the current molecular structure and facile synthesis, alkyl-substituted bis(thienyl)maleic anhydrides stand as ideal phosphor alternatives. Therefore, the current findings may open new perspectives for the development of maleic anhydride-based small molecules for low-cost, energy-efficient, and solution-processed lighting technologies. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 15Citation - Scopus: 14The Effect of Ligand Chain Length on the Optical Properties of Alloyed Core-Shell InPZnS/ZnS Quantum Dots(Elsevier Science SA, 2017-07) Altintas, Yemliha; Talpur, Mohammad Younis; Mutlugun, EvrenIn this work, we demonstrate the effect of organic ligands on the optical properties of alloyed core-shell InPZnS/ZnS quantum dots (QDs). We have systematically studied the synthesis and characterization of InPZnS/ZnS QDs using short and long chain length ligands i.e., butyric (C4), hexanoic (C6), octanoic (C8), dodecanoic (C12), myristic (C14), palmitic (C16) and stearic acids (C18), respectively. This study achieved more than 85% quantum yield with 43 nm full-width-half maximum value, using dodecanoic acid as the capping ligand. The properties of the QDs with short and long chain length ligands have been analyzed using UV Vis absorption spectrophotometer, steady state and time resolved photoluminescence spectrometer, X-ray diffraction, Zeta sizer, transmission electron microscopy and energy dispersive X-ray spectroscopy. (C) 2017 Published by Elsevier B.V.Article Citation - WoS: 9Citation - Scopus: 11Size, Material Type, and Concentration Estimation for Micro-Particles in Liquid Samples(Elsevier Science SA, 2024-05) Genc, Sinan; Erdem, Talha; Icoz, KutayThe on -site examination and characterization of microparticles are becoming crucial due to the significant rise in plastic pollution in natural resources. Hence, identifying the specific microplastic composition and quantity would enable the implementation of preventive measures. This paper presents a cost-effective setup that utilizes the Random Forest algorithm to detect the size and refractive index of micro particles, hence facilitating the identification of the material type. The system utilizes the scattering patterns of laser light from the dispersion of microparticles, namely within the concentration range of 0.05 fM to 3.00 fM. The refractive indices and particle sizes of melamine (Me8) spheres with a size of 8 mu m, as well as polystyrene (PS8) spheres with a size of 8 mu m and (PS10) 10 mu m, were estimated using the Random Forest algorithm and recorded scattering patterns. The proposed method may deliver findings with an average deviation of 0.23 mu m for particle size and 0.015 for particle refractive index. The statistical analysis indicated that there was no notable disparity between the experimental findings and the predictions derived from the machine learning system. The existing configuration can be readily converted into a point -of -use system that can be employed on -site for the purpose of monitoring and identifying microplastic contamination.Article Citation - WoS: 18Citation - Scopus: 20Respiration Monitoring Using a Paper-Based Wearable Humidity Sensor, a Step Forward to Clinical Tests(Elsevier Science SA, 2023-06) Solak, Irfan; Gencer, Serife; Yildirim, Beyza; Oznur, Emine; Hah, Dooyoung; Icoz, KutayMonitoring respiratory variables can provide valuable information for clinical applications and sport activities. Paper-based wearable respiration monitoring systems have great advantages and potential, they are low-cost, easily disposable, non-invasive and can provide real-time, reliable data. Despite some examples presented for exhaled breath analysis using paper-based sensors exist, none of them have been validated yet in a study involving many patients. In this work, we present a novel paper-based platform for exhaled breath sensors and validate it on 101 subjects including 41 patients to demonstrate its clinical applicability. By using the paperbased wearable capacitive sensors, we collected respiration data from different groups of people, namely, smokers, non-smokers and patients diagnosed with pneumonia, or chronic obstructive pulmonary disease (COPD). The change in humidity during inhale and exhale was converted to capacitance change and thus an electrical signal was obtained. The electrical signal was transmitted to a nearby computer and capacitance versus time data was post-processed. Four ratio parameters were defined on the recorded data; area, rate, maximum amplitude, and average maximum-minimum difference, all of which were compared between deep breathing and normal breathing. The collected data was statistically analyzed, and the humidity changes were compared among different groups. The results show that the developed sensor and the proposed analysis method can be used to detect the humidity changes in breathing, and to differentiate between smokers and non-smokers, and between non-smokers and patients with pulmonary disease.Article Citation - WoS: 29Citation - Scopus: 31Pressure-Induced Amorphization, Mechanical and Electronic Properties of Zeolitic Imidazolate Framework (ZIF-8)(Elsevier Science SA, 2020-01) Erkartal, Mustafa; Durandurdu, MuratAb initio molecular dynamics (AIMD) simulations are carried out to probe the high-pressure behavior of ZIF-8 over wide pressure-range. Under compression, the enormous distortions in the ZnN4 tetrahedral units lead to a crystal-to-amorphous phase transition at around 3 GPa. During the amorphization process, the Zn-N coordination is retained. No other phase change but a possible fracture of the system is proposed above 10 GPa. Depending on released pressures, amorphous states with different densities are recovered. Yet when the applied pressure is released just before the amorphization, the rotations of imidazolate linkers (swing effect) cause an isostructural crystal-to-crystal phase transition, in agreement with experiments. In the tensile regime, no phase transition is perceived up to -2.75 GPa at which point the structural failure is observed. The crystal-amorphous phase transitions are also discovered at around 4 GPa under uniaxial compressions. The amorphous structures formed under uniaxial stress are about 20% denser than the one formed under the hydrostatic pressure. The average Young's modulus and Poisson's ratio of ZIF-8 are estimated to be around 5.6 GPa and 0.4, respectively. Interestingly, the tensile strength of ZIF-8 is found to be about 50% greater than its compressive strength. This paper shows that the experimentally observed phase transitions can be successfully reproduced with a clear explanation about the transition mechanism(s) at the atomistic level and all mechanical properties can be accurately calculated for a given ZIF structure by using AIMD simulations.Article Citation - WoS: 23Citation - Scopus: 25Preparation of Highly Emissive and Reproducible Cu-In-S/ZnS Core/Shell Quantum Dots With a Mid-Gap Emission Character(Elsevier Science SA, 2020-05) Jawhar, Nawzad Nadhim; Soheyli, Ehsan; Yazici, Ahmet Faruk; Mutlugun, Evren; Sahraei, RezaCopper indium sulfide (CIS) quantum dots (QDs) are one of the newest types of luminescent semiconductors with low-toxicity and earth-abundant features. The present work reports the successful aqueous synthesis of CIS/ZnS core/shell QDs using dual-stabilizing agents of N-acetyl-L-cysteine and trisodium citrate. Off-stoichiometric QDs with In-rich compositions were found to be very small and highly emissive after coating by a shell of wide bandgap ZnS. The effect of various experimental parameters was evaluated to achieve highly reproducible QDs with bright reddish emission. Results showed a significant contribution of mid-gap defect states in the recombination processes (based on the gradual increase in absorbance recorded for samples, relatively high Urbach energy, large Stokes shift, large FWHM value in PL spectra, as well as the long-lived PL decay time). In addition, the chemical stability of samples was investigated using highly oxidant H2O2 agent and results demonstrate their superior stability. The combination of low-toxicity, intense and stable emission, along with synthetic advantages demonstrates that the present aqueous-soluble and emissive QDs can be considered as an excellent bio-photonic structure suitable for different fields of biological imaging and diagnostics. (C) 2020 Elsevier B.V. All rights reserved.Article Citation - WoS: 51Citation - Scopus: 51Multiplexed Patterning of Cesium Lead Halide Perovskite Nanocrystals by Additive Jet Printing for Efficient White Light Generation(Elsevier Science SA, 2020-01) Altintas, Yemliha; Torun, Ilker; Yazici, Ahmet Faruk; Beskazak, Emre; Erdem, Talha; Onses, M. Serdar; Mutlugun, Evren; Serdar Onses, M.Inorganic perovskite nanocrystals (PNCs) offer the ability to precisely but also flexibly control the peak emission wavelength while also possessing narrow-band emission spectra and high quantum yields. Owing to these features, PNCs have been already employed as color converters on LEDs. Nevertheless, the anion exchange reactions that prevent the blending of perovskites of different colors remain as an important bottleneck. As a remedy to this issue, here we employ additive jet printing to form separated stripes of these nanocrystals. Within this framework, we first present the synthesis of CsPbBr3 and CsPbBrxI3-x nanocrystals spanning the whole visible regime and optimize the cleaning procedure to obtain PNCs possessing photoluminescence quantum yields as high as 91% and emission linewidths as narrow as 15 nm, making them suitable for high quality white light generation. Next, we employ electrohydrodynamic jet printing to form closely spaced stripes of PNCs of various colors and integrated these films with a blue LED to create a white LED. Our proof-of-concept LED achieves high photometric performance as it possesses a color rendering index of 91.3, luminous efficacy of optical radiation > 300 lm/W-opt, and correlated color temperature of ca. 7000 K. We believe that additive jet printing technique will pave the way for a ubiquitous use of these PNCs in light-emitting devices in the near future.Article Citation - WoS: 22Citation - Scopus: 26Microstructure and Mechanical Properties of Dense Si3N4 Ceramics Prepared by Direct Coagulation Casting and Cold Isostatic Pressing(Elsevier Science SA, 2022-09) Marulcuoglu, Hande; Kara, FerhatComplex shaped dense Si3N4 ceramics were produced by using direct coagulation casting technique via dispersant reaction method of Si3N4 suspension, followed by gas pressure sintering. The effects of solid content of the suspension, additional cold isostatic pressing of the cast parts, and sintering behaviour and on the mechanical reliability of silicon nitride ceramics were investigated. It was observed that all slurries exhibited rheological properties suitable for casting in the range of 44-50 vol.% solid concentrations. Nevertheless, higher solid concentration suspensions resulted in smaller floc size and thus better green microstructures. Parts shaped by direct coagulation casting at all the solid loadings had relatively low strength and reliability after sintering. However, application of additional cold isostatic pressing to the cast parts increased the strength and, particularly, reliability. Dense Si3N4 ceramics with relative density above 99.5%, average bending strength 760 +/- 39 MPa and Weibull module 23.5 had been obtained with 50 vol.% solids content after DCC + CIP process.Article Citation - WoS: 11Citation - Scopus: 11Logarithmic Organic Photodetectors(Elsevier Science SA, 2015-12) Elgazzar, Elsayed; Ozdemir, Mehmet; Usta, Hakan; Al-Ghamdi, Ahmed A.; Dere, A.; El-Tantawy, Farid; Yakuphanoglu, F.A novel photodetector of Al/GO:C8-BTBT/n-Si/Au with various graphene oxide (GO) contents has been investigated. The electrical properties of the diodes were characterized by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The values of barrier height, ideality factor, and series resistance of the diodes were determined from I-V characteristic curves by using Norde's equations. The photocurrent properties of the diode were studied under various illumination intensities. The photoconducting mechanism of the diodes is controlled by the traps. The photoresponse properties of the diodes are increased with GO contents. The obtained results indicate that graphene oxide doped 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene/n-Si heterojunctions can be used as a photodetector for optoelectronic applications. (C) 2015 Elsevier B.V. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 3Key Role of High-Tc Twinned Martensitic Materials to Gain a Magnetic Actuation Higher Than 15%(Elsevier Science SA, 2021-12) Sarli, Numan; Paran, Nejdet; Ablay, Gunyaz; Ocak, Hamza Y.; Yildiz, Yasin G.; Yildiz, Gokcen D.; Yagci, Nermin K.Twinning angle outcomes of the twinned martensitic (TM) and detwinned martensitic (DTM) structural transformations on the magnetic features of the austenite (A) parent phase are researched by using the effective field theory established by Kaneyoshi. The implementation of the effective field theory verifies that the shape memory mechanism occurs with phase transformations, A -> TM -> DTM -> A. It also shows that the austenite parent phase has two types of actuations: one-dimensional actuation (in only y-axis) for TM, and two-dimensional actuation (in x and y-axes) for DTM. Magnetic field-induced actuation (strain) in the range of 5-15% at twinning angle theta >= 120.816 degrees of TM and DTM is reported for some materials in the literature. On the other hand, in this work, it is estimated that a twinning angle lower than this twinning angle (i.e., theta < 120.816 degrees) must be achieved to have a strain higher than 15%. We also suggest that materials with higher magnetization, Curie temperature, coercive field and remanence magnetization should be taken into account to get a strain higher than 15%, since all these features are directly affected by the twinning angle (theta). Our results on Curie temperature (T-c) match with the experimental results of Ni49.8Mn28.5Ga21.7 (achieved 6% strain) with T-c = 95 degrees C (368 K) by Murray et al., and Ni46Mn24Ga22Co4Cu4 with T-c = 393 K (achieved 12% strain) by Sozinov et al. (C) 2021 Elsevier B.V. All rights reserved.