Physics / Fizik
Permanent URI for this collectionhttps://hdl.handle.net/11147/6
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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: 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: 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.Article Citation - WoS: 12Citation - Scopus: 17Junction Area Dependent Performance of Graphene/Silicon Based Self-Powered Schottky Photodiodes(Elsevier, 2021) Fidan, Mehmet; Ünverdi, Özhan; Çelebi, CemThis work reports the impact of junction area on the device performance parameters of Graphene/n-Silicon (Gr/n-Si) based Schottky photodiodes. Herein, three batches of Gr/n-Si photodiode samples were produced based on various sized CVD grown monolayer graphene layers transferred on individual n-Si substrates. The fabricated devices exhibited strong Schottky diode character and had high spectral sensi-tivity at 905 nm peak wavelength. The optoelectronic measurements showed that the spectral response of Gr/n-Si Schottky photodiodes has a linear dependence on the active junction area. The sample with 20 mm(2) junction area reached a spectral response of 0.76 AW(-1), which is the highest value reported in the literature for self-powered Gr/n-Si Schottky photodiodes without the modification of graphene electrode. In contrast to their spectral responsivities, the response speed of the samples were found to be lowered as a function of the junction area. The experimental results demonstrated that the device performance of Gr/n-Si Schottky photodiodes can be modified simply by changing the size of the graphene electrode on n-Si without need of external doping of graphene layer or engineering Gr/n-Si interface. This study may serve towards the standardization of junction area for the development of high performance Gr/Si based optoelectronic devices such as solar cells and photodetectors operating in between the ultraviolet and near-infrared spectral region. (C) 2021 Elsevier B.V. All rights reserved.Article Citation - WoS: 3Citation - Scopus: 4Lipid Bilayer on Wrinkled-Interfaced Graphene Field Effect Transistor(Elsevier Ltd., 2021) Özkendir İnanç, Dilce; Çelebi, Cem; Yıldız, Ümit HakanThis study describes lipid bilayer-based sensor interface on SiO2 encapsulated graphene field effect transistors (GFET). The SiO2 layer was utilized as a lipid compatible surface that drives bilayer formation. The two types of surface morphologies i) wrinkled morphology by thermal evaporation (TE) and ii) flat morphology by pulsed electron deposition (PED) were obtained. The sensing performance of wrinkled and flat interfaced-GFETs were investigated, pH sensitivity of wrinkled interfaced-GFETs were found to be ten fold larger than the flat ones. The enhanced sensitivity is attributed to thinning of the oxide layer by formation of wrinkles thereby facilitating electrostatic gating on graphene. We foresee that described wrinkled SiO2 interfaced-GFET holds promise as a cell membrane mimicking sensing platform for novel bioelectronic applications. © 2020