Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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Article A Quantitative Description of Barite Thermodynamics, Nucleation and Growth for Reactive Transport Modelling(Elsevier, 2024) Dideriksen,K.; Zhen-Wu,B.Y.; Dobberschütz,S.; Rodríguez-Blanco,J.D.; Raahauge,P.J.; Ataman, Evren; Stipp,S.L.S.The regression of available thermodynamic data in the BaSO4–NaCl–H2O system yielded Pitzer ion interaction parameters that accurately describe the activities of aqueous species and mineral solubilities in this system. This thermodynamics description is compared with published Pitzer parameter sets, and combined with a model for the kinetics of barite nucleation and growth, based on classical nucleation theory. Both the thermodynamic and nucleation/growth models have been incorporated into the PHREEQC computer code to facilitate calculation of the extent and consequences of barite formation in natural and engineered systems. Results of geochemical modelling calculations agree adequately with the amount of barite scale thicknesses derived from calliper measurements from an oil well if the effective surface free energy of barite nuclei is assumed to be ∼50 mJ m−2. Better results, however, are achieved using a temperature dependent effective surface free energy. In contrast, calculations performed by ignoring the effects of barite nucleation lead to a substantial overestimation of the amount of scale formed in our modelled systems. The success of our mineral nucleation and growth model to describe scaling in our modelled system suggests this description of precipitation rates can be applied to many other mineral-aqueous fluid systems, in particular where supersaturation is slight and the solids forming have substantial surface free energy. © 2024 Elsevier LtdArticle Citation - WoS: 9Citation - Scopus: 9High Voltage Response of Graphene/4h-sic Uv Photodetector With Low Level Detection(Elsevier, 2023) Jehad, Ala K.; Ünverdi, Özhan; Çelebi, CemA self-powered graphene/silicon carbide (G/4H-SiC) ultraviolet photodetector of a p-i-n like-structure with high voltage response has been fabricated to detect and measure low intensity ultraviolet (UV) radiation. Bilayer graphene sheet grown by chemical vapor deposition (CVD) method was transferred on the top of an epilayer structure of n-/n+ 4 H-SiC. In this structure, two Schottky contacts were formed: one at G/ n- 4H-SiC interface and the other at bulk-4 H-SiC/Cr/Au interface. The photodetector's characteristic measurements revealed low dark current of - 0.58 nA and spectral voltage responsivity of - 0.75 V/W at 300 nm wavelength. Under low level UV illumination of 300 nm wavelength, the photodetector exhibited a leakage current and a photogenerated response voltage of 1.1 nA and 10 mV, respectively. The time-dependent photovoltage measurements displayed a rapid photovoltage response with rise and decay times of -74 ns and - 580 ns, respectively. This novel device holds promise for applications requiring sensitive and self-powered UV detection.Article Citation - WoS: 3Citation - Scopus: 3Amperometric Detection of Nh3 by Aromatic Sam-Modified Graphene(IEEE, 2023) Yağmurcukardeş, Nesli; Bayram, Abdullah; Aydın, Hasan; Can, Mustafa; Demiç, Şerafettin; Açıkbaş, Yaşar; Çelebi, CemAmmonia (NH3) is a toxic substance resulting in various acute and chronic effects on individuals. NH3 detection, monitoring methods, and detection tools are desperately needed. In this work, we improved the NH3 sensing capabilities of grapheme (GP) films deposited by chemical vapor deposition (CVD) by modifying aromatic self-assembled monolayer (SAM) molecules such as 5-[(3-methylphenyl) (phenyl) amino] isophthalic acid (MeIPA) and 5-(diphenyl)amino] isophthalic acid (PhIPA) on amperometric detection method. Morphological investigations of the films were carried out by optical and scanning electron microscopy (SEM). Surface potential was characterized with Kelvin probe force microscopy (KPFM), and vibrational properties were characterized with Raman spectroscopy. MeIPA modification increased NH3 uptake by two times compared to unmodified GP. The results indicated that the SAM modification enhanced NH3 molecule adsorption and improved its periodic reversible and reproducible response using the amperometric detection system, indicating that SAM molecules might be a feasible probe for NH3. © 2001-2012 IEEE.Article Citation - WoS: 35Citation - Scopus: 35Cvd Graphene/Sic Uv Photodetector With Enhanced Spectral Responsivity and Response Speed(Elsevier, 2023) Jehad, Ala K.; Fidan, Mehmet; Ünverdi, Özhan; Çelebi, CemA self-powered, high-performance graphene/Silicon Carbide (G/4H-SiC) ultraviolet Schottky junction photodetector has been fabricated, and the effect of using monolayer and bilayer graphene on the device performance parameters was investigated. P-type graphene sheets were grown by the chemical vapor deposition (CVD) method, while 4H-SiC material consists of an epilayer structure of n-/n+ on bulk n-SiC. Two photodetector devices have been studied, one with monolayer graphene (MLG) and the other with bilayer graphene (BLG). The proposed photodetector structure reveals the highest spectral responsivity known of a G/4H-SiC UV photodetector so far. Electronic and optoelectronic characterizations were done under an ultraviolet wavelength range from 240 to 350 nm. The results show two spectral responsivity maxima (Rmax) at 285 nm and 300 nm wavelengths. Exhibiting two maxima in spectral responsivity and detectivity is caused by the constructive and destructive interference effects of multiple reflections at the SiC epilayer's interfaces. The photodetector devices exhibit high spectral responsivity (R ? 0.09 AW?1), maximum detectivity (D* ? 2.9 × 1012 Jones), and minimum noise equivalent power (NEP ? 0.17 pWHz-1/2) in both devices. Using bilayer graphene instead of monolayer showed no significant change in both the photogenerated current and the spectral responsivity due to the higher absorption coefficient of bilayer graphene, however, it exhibited a significant improvement in the response speed. The response speed was found to increase by 50 % when bilayer graphene was used as a hole collecting electrode in the G/4H-SiC junction. This is because bilayer graphene creates a narrower depletion layer and higher electric field, which promotes efficient charge separation and recombination. © 2023 Elsevier B.V.Article Citation - WoS: 3Citation - Scopus: 4Terahertz Wavefront Engineering Using a Hard-Coded Metasurface(Springer, 2023) Noori, Aileen; Akyürek, Bora; Demirhan, Yasemin; Özyüzer, Lütfi; Güven, Kaan; Altan, Hakan; Aygün, GülnurDuring the past few years, coding metamaterials (MM) drew significant attention, where the far-field scattering/transmission pattern of the electromagnetic wave (particularly in the THz regime) can be encoded into a single or few-bit digitized phase-response of the metasurface, thereby enabling a full digital control. Single-bit MMs contain two types of unit cells where the phase becomes 0 and 1 (in units of ?), respectively. By arranging these unit cells into a 2D surface pattern, the THz wavefront can be shaped. In this work, a novel hard-coded metasurface was designed, fabricated, and experimentally investigated for multi-beam reflection of incident THz beam. The design employs stripe and checkerboard patterns of bilayer MM unit cells consisting of square gold patches with a polymer spacing layer from a gold backplane. Experimental and simulation results show that the incident wave in the 0.500–0.750 THz range can be reflected with > 95% efficiency in uniform amplitude and 1-bit coded phase. For the checkerboard metasurface pattern, the measured and analytically calculated reflection angle shows good agreement. The metasurface design is suitable for large-scale fabrication and can potentially be used as a template in the development of actively coded metasurfaces. © 2023, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.Article Citation - WoS: 22Citation - Scopus: 26Flexible Metal/Semiconductor Type Photodetectors Based on Manganese Doped Zno Nanorods(Elsevier, 2023) Karagöz, Emine; Altaf, Çiğdem Tuç; Yaman, Ecenaz; Yıldırım, İpek Deniz; Erdem, Emre; Çelebi, Cem; Fidan, Mehmet; Sankir, Mehmet; Demirci Sankir, NurdanHigh-performance flexible photodetectors are one of the most interesting research areas due to their great possibilities for a variety of applications such as portable and wearable optoelectronics. This study verifies the performance of flexible metal/semiconductor/metal-type photodetector based on pristine and manganese doped ZnO nanorods (ZnO-NRs) prepared in two different concentrations of zinc precursors and manganese dopant at low temperatures. The photodetectors having ZnO-NRs with high aspect ratios were investigated by various material characterization techniques such as electron paramagnetic resonance and photoluminescence spectroscopy to confirm the relationship between defect concentrations and photodetector performance parameters. It has been calculated that the detectivity (D*) and responsivity (R) of the ZnO nanorod-based photodetectors increased 20 and 18 folds, respectively by increasing the concentration of zinc precursor. Besides the D* and R values of the photodetectors, prepared by the 16.5 mM zinc precursor, increased 18 and 4.5-fold, respectively, after manganese doping. We confirmed that even a very low concentration of zinc precursor could produce a photodetector with high performance in photo-response characteristics, flexibility, and stability against 10,000 cycles of convex/concave bending.(c) 2023 Elsevier B.V. All rights reserved.Article Citation - WoS: 5Citation - Scopus: 5Self-Powered Photodetector Array Based on Individual Graphene Electrode and Silicon-On Integration(Elsevier, 2023) Yanılmaz, Alper; Ünverdi, Özhan; Çelebi, CemOne of the key limitations for the device performance of the silicon (Si) based photodetector arrays is the optical crosstalk effect encountered between photoactive elements as well. The scope of this work is to reduce optical crosstalk and thus increasing the device performances with graphene and Si integration. This paper presents the design, fabrication process, and performance evaluation of self-powered individual Graphene/Silicon on Insulator (GSOI) based Schottky barrier photodiode array (PDA) devices. A 4-element GSOI Schottky barrier PDA with separate graphene electrodes is fabricated to examine possible optical crosstalk encountered between each diode in the array structure. Here, monolayer graphene is utilized as hole collecting separate electrode on individually arrayed n-type Si on SOI substrate by photolithography technique. Each diode in the array exhibited a clear rectifying Schottky character. Photoresponse characterizations revealed that all diodes had excellent device performance even in self-powered mode in terms of an Ilight/Idark ratio up to 104, a responsivity of ∼0.12 A/W, a specific detectivity of around 1.6 × 1012 Jones, and a response speed of ∼1.32 μs at 660 nm wavelength. As revealed by optical crosstalk measurement, the device with pixel pitch of 1.5 mm had a total crosstalk of about 0.10% (−60 dB) per array. These results showed that the optical crosstalk between neighboring n-Si elements can be greatly minimized when graphene is used as separated electrode on arrayed Si on SOI substrate. Our study is expected give an insight into the performance characteristics of GSOI PDA devices which have great potential to be used in many technological applications such as multi-wavelength light measurement, level metering, high-speed photometry and position/motion detection. © 2023 Elsevier B.V.Article Citation - WoS: 20Citation - Scopus: 23Surface Free Energy and Wettability Properties of Transparent Conducting Oxide-Based Films With Ag Interlayer(Elsevier, 2021) Özbay, Salih; Erdoğan, Nursev; Erden, Fuat; Ekmekçioğlu, Merve; Rakop, Büşra; Özdemir, Mehtap; Aygün, Gülnur; Özyüzer, LütfiITO, ZTO, AZO and Ag are commonly used in transparent conducting oxide (TCO)/metal/TCO electrodes to form multilayered thin films on a suitable substrate. A detailed surface free energy (SFE) knowledge of these films is critical to design desirable TCO-based sandwich structures. In this study, TCO/Ag/TCO multilayer thin films were coated onto glass substrates using ITO, ZTO, AZO and Ag targets by magnetron sputtering. The wettability properties of TCO, Ag interlayer and TCO/Ag/TCO were evaluated by contact angle measurements of seven different liquids having various surface tension values. The dispersive and polar components of SFE were calculated using geometric and harmonic mean approaches. The acidic and basic components of SFE were calculated using van Oss-Chaudhury-Good method. Following this, the work of adhesion values between TCO films and Ag interlayer were estimated using SFE values of the films. The results show that the SFE components of the surfaces differ depending on the TCO type, the total SFE values of TCO/Ag/TCO films were lower than that of TCO films, and AZO/Ag adhesion is stronger than the other TCO/Ag structures. The reasons behind these differences were discussed by evaluating the SFE, XRD, AFM and SEM analysis simultaneously.Article Citation - WoS: 17Citation - Scopus: 19Bacterial Surface, Biofilm and Virulence Properties of Listeriamonocytogenes Strains Isolated From Smoked Salmon and Fish Food Contact Surfaces(Elsevier, 2021) Sudağıdan, Mert; Özalp, Veli Cengiz; Öztürk, Orhan; Yurt, Mediha Nur Zafer; Yavuz, Orhan; Taşbaşı, Behiye Busra; Uçak, Samet; Mavili, Zehra Seda; Çoban, AyşenBiofilm formation is one of the defense mechanisms of bacteria against disinfectants and antimicrobials. The aim of this study was to determine biofilm-forming L.monocytogenes from fish processing and salmon surfaces. Biofilm formation at 15, 25, 37, and 40 degrees C from 1 to 6-days period, adhesion to glass, polypropylene and stainless-steel surfaces, bacterial surface charge and hydrophobicity was determined. Adhesion behavior of the strains was evaluated using Surface Plasmon Resonance (SPR) technique. Totally 32 L.monocytogenes strains belonging to serogroups IIa (n:17), IIc(n:14) and IVb(n:1) were detected from 1320 swabs and 16 smoked salmons. Biofilm formation tests revealed that 21 strains form biofilm on microplate by increasing time and temperature. Although all strains strongly formed biofilm on glass surfaces, two strains slightly adhered polypropylene surfaces. High surface roughness of stainless-steel FeCrNi alloy (Ra = 4.15 nm) and CoCrMo alloy (Ra = 10.75 nm) increased biofilm formation of L.monocytogenes on stainless-steel surfaces. Zeta potential results showed that non-biofilm formers were more negatively charged after 6-days and hydrophobicity couldn't give a distinct distribution among biofilm formers and non-formers. SPR analysis method was evaluated to distinguish biofilm formers to adhere SPR gold chip surfaces. PCR results revealed that all strains were positive for hylA, iap, actA, plcA, plcB, fri, flaA, inlA, inlB, inlC, inlJ, and lmo1386 genes. Additionally, all strains were susceptible to penicillin, ampicillin, meropenem, erythromycin and trimethoprim-sulfamethoxazole. Biofilm-forming, virulence properties of L. monocytogenes strains isolated from fish processing surfaces and smoked salmons were evaluated and SPR was used to differentiate biofilm formers as a sensitive technique for biofilm studies.Article Citation - WoS: 4Citation - Scopus: 5The Role of Charge Distribution on the Friction Coefficients of Epitaxial Graphene Grown on the Si-Terminated and C-Terminated Faces of Sic(Pergamon-Elsevier Science Ltd, 2021) Keskin, Yasemin; Ünverdi, Özhan; Erbahar, Doğan; Kaya, İsmet İnönü; Çelebi, CemThe friction coefficients of single-layer epitaxial graphene grown on the Si-terminated and C-terminated faces of Silicon Carbide (SiC) substrate were measured under ambient conditions using Friction Force Microscope (FFM). The lateral friction force measurements acquired in the applied normal force range between 4.0 and 16.0 nN showed that the friction coefficient of graphene on the C-terminated face of SiC is about two times smaller than the one grown on its Si-terminated face. The lateral friction was found to be decreased as the average of root mean square roughness increases suggesting the observed difference in the friction coefficients cannot be related to the roughness of the graphene layers. DFT calculations demonstrated that the altered periodicity of charge distribution on graphene due to the specific interactions with two distinct polar faces of SiC substrate might explain the observed difference in the friction coefficients. (C) 2021 Elsevier Ltd. All rights reserved.