Photonics / Fotonik
Permanent URI for this collectionhttps://hdl.handle.net/11147/2590
Browse
9 results
Search Results
Article Citation - WoS: 3Citation - Scopus: 4A Facile Method for Boosting the Graphitic Carbon Nitride's Photocatalytic Activity Based on 0d/2d S-Scheme Heterojunction Nanocomposite Architecture(Elsevier, 2024) Kahraman, Zeynep; Kartal, Uğur; Gent, Aziz; Alp, EmreGraphitic carbon nitride (g-C 3 N 4 ) has received significant interest as a metal -free photocatalyst. The S -scheme photocatalytic system has great potential to improve the charge separation in semiconductor photocatalysts. In this study, we have fabricated non-toxic and low-cost photocatalytic nanocomposites of 0D/2D S -scheme heterojunction composed of iron oxide and graphitic carbon nitride by a facile method. The developed facile method provides a sustainable way with a high atom economy to further enhance the photocatalytic performance of exfoliated g-C 3 N 4 . The 0D -iron oxide/2D-C 3 N 4 exhibited nearly 10 times better than bulk g-C 3 N 4 and almost 60 % better than exfoliated g-C 3 N 4 under simulated solar light irradiation. The experimental results demonstrated that the effective charge -carrier mechanism led to an improved generation of reactive oxygen species (ROSs), resulting in an impressive photocatalytic performance. A serial photocatalytic test was also conducted to understand photocatalytic reaction mechanisms with various scavengers.Article Citation - WoS: 3Citation - Scopus: 3Stable Single Layer Structures of Aluminum Oxide: Vibrational and Electronic Characterization of Magnetic Phases(Elsevier, 2022) Özyurt, A. Kutay; Molavali, Deniz; Şahin, HasanThe structural, magnetic, vibrational and electronic properties of single layer aluminum oxide (AlO2) are investigated by performing state-of-the-art first-principles calculations. Total energy optimization and phonon calculations reveal that aluminum oxide forms a distorted octahedral structure (1T′-AlO2) in its single layer limit. It is also shown that surfaces of 1T′-AlO2 display magnetic behavior originating from the O atoms. While the ferromagnetic (FM) state is the most favorable magnetic order for 1T′-AlO2, transformation to a dynamically stable antiferromagnetic (AFM) state upon a slight distortion in the crystal structure is also possible. It is also shown that Raman activities (350–400 cm−1) obtained from the vibrational spectrum can be utilized to distinguish the possible magnetic phases of the crystal structure. Electronically, both FM and the AFM phases are semiconductors with an indirect band gap and they can form a type-III vdW heterojunction with graphene-like ultra-thin materials. Moreover, it is predicted that presence of oxygen defects that inevitably occur during synthesis and production do not alter the magnetic state, even at high vacancy density. Apparently, ultra-thin 1T′-AlO2 with its stable crystal structure, semiconducting nature and robust magnetic state is a quite promising material for nanoscale device applications.Article Citation - WoS: 4Citation - Scopus: 4Light-Induced Modification of the Schottky Barrier Height in Graphene/Si Based Near-Infrared Photodiodes(Elsevier, 2022) Fidan, Mehmet; Dönmez, Gülçin; Yanılmaz, Alper; Ünverdi, Özhan; Çelebi, CemThe impact of light on the Schottky barrier height (SBH) in p-type graphene/n-type Si (p-Gr/n-Si) based near-infrared photodiodes is investigated. Hall effect and optoelectronic transport measurements carried out under illumination of 905 nm wavelength light showed that zero-bias SBH in such photodiodes can be effectively tuned in a range between 0.7 and 0.9 eV consistent with the variation in their open-circuit voltage. Shockley-Read-Hall model, which considers the charge recombination through mid-gap and interface states at the p-Gr/n-Si heterojunction, is used to explain the experimentally observed nonlinear dependence of SBH on the incident light. Light induced tunability of SBH at the graphene/semiconductor heterojunction is of great importance especially for the development of new generation optically driven devices in which graphene acts as a functioning element.Article Citation - WoS: 11Citation - Scopus: 13Electrical, Photodiode, and Dft Studies of Newly Synthesized Pi-Conjugated Bodipy Dye-Based Au/Bod-dim Device(Elsevier, 2021) Şahin, Muhammet Ferit; Taşcı, Enis; Emrullahoğlu, Mustafa; Gökçe, Halil; Tuğluoğlu, Nihat; Eymur, SerkanA pi-conjugated 4,4-difluoro-4- bora-3a,4a-diaza-s-indacene (BODIPY) dimer (BOD-Dim) compound has been synthesized and characterized. The optimized molecular structure, the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) simulations, and static isotropic polarizability of the isolated compound were computed via the Gaussian program. The simulated static dielectric constant value was calculated. The effect of the BOD-Dim interlayer on the diode characteristics of the Au/n-Si diode was investigated. The electrical and photovoltaic parameters of the Au/BOD-Dim/n-Si/In diode such as ideality factor (n), barrier height (phi B), open-circuit voltage (Voc), short-circuit current (Jsc), photosensitivity (S), and photoresponsivity (R) have been investigated by current-voltage measurements at dark and under various illumination intensities. The possible current conduction mechanism has been examined through the forward bias ln (IF)-ln(VF) and ln(IR)-VR1/2 characteristics. All obtained results confirmed that Au/BOD-Dim/n-Si/In diode exhibits a photovoltaic behavior and presents great potential as a photosensor for optoelectronic device applications.Article Citation - WoS: 8Citation - Scopus: 9Cesium Manganese Chloride: Stable Lead-Free Perovskite From Bulk To Single Layer(Elsevier, 2021) Sözen, Yiğit; Özen, Sercan; Şahin, HasanMotivated by the recent advances in perovskite-based solar cells, here we investigate stability, electronic properties and vibrational characteristics of lead-free perovskite, CsMnCl3, and its low dimensional forms by means of first-principles calculations. Structural optimizations reveal that, regardless of whether it is bulk or ultra-thin single layer cubic perovskite structure, CsMnCl3 crystal exhibit robust antiferromagnetism in its ground state due to oppositely aligned magnetic moments of Mn atoms. In addition to total energy calculations, phonon band dispersions indicate that CsMnCl3 structure sustains its dynamical stability down to its thinnest single layer crystal structures. The calculated Raman spectrums state that while the first-order Raman scattering is forbidden for bulk CsMnCl3 due to the cubic symmetry; dimensional-reduction-driven symmetry breaking leads to emergence of experimentally-observable distinctive Raman active modes in bilayer and single-layer crystal structures. Moreover, the electronic band dispersions reveal that from its bulk to ultra-thin single layer structures CsMnCl3 crystals are robust antiferromagnetic insulators. Multiple valid features like controllable dimensionality, robust antiferromagnetism and wide electronic band gap make cubic CsMnCl3 crystal as a potential candidate for nano-scale optoelectronic applications.Article Citation - WoS: 5Citation - Scopus: 6Contribution of O-2 Plasma Treatment and Amine Modified Gos on Film Properties of Conductive Pedot:pss: Application in Indium Tin Oxide Free Solution Processed Blue Oled(Elsevier, 2019) Diker, Halide; Yeşil, Fatih; Varlıklı, CananPrimary (n-propyl amine, n-PRYLA), secondary (dipropyl amine, DPRYLA) and alcohol (propanol amine, PRPOHA) amine derivatives were used as amine sources in graphene oxide (GO) modification and obtained samples were named as nPRYLA-GO, DPRYLA-GO and PRPOHA-GO, respectively. Modified graphene oxide (mGO) derivatives were doped in poly (3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PH1000) and O-2 plasma treatment (70W, 3 min) was applied on the spin casted films. PH1000:mGO films presented high optical transparency values (> 90%) and low resistivity (177-183 Q/sq). The roughness values were increased especially when the hydrophobic alkyl chain containing DPRYLA-GO and nPRYLA-GO were doped in PH1000. Prepared films were utilized as anode in solution processed blue organic light emitting diode. PH1000:PRPOHA-GO anode presented more than 30 nm of decrement in full with at half maximum and 1.6, 1.5 and 1.9 fold enhancements in current, power and external quantum efficiency values, compared to those of ITO anode, respectively.Article Citation - WoS: 1Citation - Scopus: 1Structural, Electronic and Vibrational Properties of Ultra-Thin Octahedrally Coordinated Structure of Euo2(Elsevier, 2020) Özcan, Mehmet; Özen, Sercan; Yağmurcukardeş, Mehmet; Şahin, HasanNovel stable ultra-thin phases of europium oxide are investigated by means of state-of-the-art first principles calculations. Total energy calculations show that single layers of EuO2 and Eu(OH)(2) can be stabilized in an octahedrally coordinated (1T) atomic structure. However, phonon calculations reveal that although both structures are energetically feasible, only the 1T-EuO2 phase has dynamical stability. The phonon spectrum of 1T-EuO2 displays three Raman active modes; a non-degenerate out-of-plane A(1g) mode at 353.5 cm(-1) and two doubly-degenerate in-plane E-g modes at 304.3 cm(-1). Furthermore, magnetic ground state and electronic band dispersion calculations show that the single layer EuO2 is a metal with net magnetic moment of 5(mu B) per unitcell resulting in a half-metallic ferrimagnetic behavior. Moreover, robustness of the half-metallic ferrimagnetic characteristics of EuO2 is confirmed by the application of electric field and charging. Single layer 1T-EuO2, with its stable ultra-thin structure and half-metallic ferrimagnetic feature, is a promising novel material for nanoscale electronic and spintronic applications.Article Citation - WoS: 10Citation - Scopus: 12The Effect of Dopa Hydroxyl Groups on Wet Adhesion To Polystyrene Surface: an Experimental and Theoretical Study(Elsevier, 2020) Yıldız, Remziye; Özen, Sercan; Şahin, Hasan; Akdoğan, YaşarMussels wet adhesive performance has been arousing curiosity for a long time. It is found that 3,4-dihydroxyphenylalanine (DOPA) is responsible for adhesive properties of mussels. Despite a large body of research characterizing the interactions DOPA with hydrophilic surfaces, relatively few works have addressed the mechanism of interactions with hydrophobic surfaces. The benzene ring of DOPA is the main attributor to the adhesion on hydrophobic polystyrene (PS) surface. However, here we showed that two hydroxyl groups of catechol have also effects on wet adhesion. We studied wet adhesive properties of DOPA, tyrosine and phenylalanine functionalized PEG polymers, PEG-(N-Boc-L-DOPA)(4), PEG-(N-Boc-L-Tyrosine)(4), PEG-(N-Boc-L-Phenylalanine)(4), on spin labeled PS nanobeads (SL-PS) by electron paramagnetic resonance (EPR) spectroscopy. Surface coverage ratio of SL-PS upon additions of PEG-(N-Boc-L-DOPA)(4), PEG-(N-Boc-L-Tyrosine)(4) and PEG-(N-Boc-L-Phenylalanine)(4) showed that SL-PS was covered with 70%, 50% and 0%, respectively. This showed that spontaneous wet adhesion on PS increases with the number of amino acids hydroxyl groups. This is also supported with the density functional theory (DFT) energy calculations and ab-initio molecular dynamics (AIMD) simulations. In water, interactions between water molecules and hydroxyl groups on the catechol induce catechol adhesion via 7C-7C stacking between the catechol and double styrene rings which were already tilted out with water.Article Citation - WoS: 13Citation - Scopus: 12Orthorhombic Cspbi3 Perovskites: Thickness-Dependent Structural, Optical and Vibrational Properties(Elsevier, 2020) Özen, Sercan; İyikanat, Fadıl; Özcan, Mehmet; Tekneci, Gülsüm Efsun; Eren, İsmail; Sözen, Yiğit; Şahin, HasanCesium lead halide perovskites have been subject to intense investigation, mostly because of their potential to be used in optoelectronic device applications. However, regarding the need for nanoscale materials in forthcoming nanotechnology applications, understanding of how the characteristic properties of these perovskite crystals are modified through dimensional crossover is essential. In this study, thickness-dependence of the structural, electronic and vibrational properties of orthorhombic CsPbI3, which is one of the most stable phase at room temperature, is investigated by means of state-of-the-art first-principles calculations. Our results show that (i) bilayers and monolayers of CsPbI3 can be stabilized in orthorhombic crystal symmetry, (ii) among; the possible ultra-thin perovskites only structures with CsI-terminated surface are dynamically stable (iii) electronic band gap increases with decrease in perovskite thickness due to quantum size effect and (iv) reflectivity and transmissivity of the orthorhombic CsPbI3 can be tuned by varying the thickness that modifies the electron confinement. (c) 2019 Elsevier B.V. All rights reserved.