Photonics / Fotonik
Permanent URI for this collectionhttps://hdl.handle.net/11147/2590
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Article Citation - WoS: 9Citation - Scopus: 11Electrospun Polyacrylonitrile (pan)/Polypyrrole (ppy) Nanofiber-Coated Quartz Crystal Microbalance for Sensing Volatile Organic Compounds(Springer, 2023) Yağmurcukardeş, Nesli; İnce Yardımcı, Atike; Yağmurcukardeş, Mehmet; Çapan, İnci; Erdoğan, Matem; Çapan, Rifat; Açıkbaş, YaserIn this study, electrospun polyacrylonitrile (PAN)/polypyrrole (PPy) nanofibers (NFs) coated quartz crystal microbalance (QCM) were investigated for their sensing characteristics against six different volatile organic compounds (VOCs): chloroform, dichloromethane, carbon tetrachloride, benzene, toluene and xylene. SEM, TEM, FT-IR and TGA analysis were carried out for the characterization of PAN/PPy nanofibers and characterization results of PAN/PPy NFs showed that these nanofibers were morphologically well-arranged and straightforward with a cylindrical shape with the average fiber diameter of 253.17 +/- 27 nm. Among all the gas measurement tests, dichloromethane displayed the highest response values for PAN/PPy coated QCM sensors. When the reproducibility of kinetic studies for PAN/PPy NFs coated QCM sensors were examined, the most repetitive results were obtained by this QCM sensor during dichloromethane investigation and the diffusion coefficients of VOCs for the first and second regions increased with the order of xylene < toluene < benzene < carbontetrachloride < chloroform < dichloromethane. The sensitivities of the PAN/PPy nanofibers-coated QCM sensor against organic vapors are determined between 4.71 and 6.17 (Hz ppm(-1)) x 10(-4). As a result, PAN/PPy nanofibers exhibited high sensitivity and selectivity for VOCs sensor applications, especially for dichloromethane.Article Citation - WoS: 2Citation - Scopus: 2High-Throughput Analysis of Tetragonal Transition Metal Xenes(Royal Society of Chemistry, 2022) Šabani, Denis; Milošević, Milorad V.; Yorulmaz, Uğur; Yağmurcukardeş, Mehmet; Sevik, CemWe report a high-throughput first-principles characterization of the structural, mechanical, electronic, and vibrational properties of tetragonal single-layer transition metal Xenes (t-TMXs). Our calculations revealed 22 dynamically, mechanically and chemically stable structures among the 96 possible free-standing layers present in the t-TMX family. As a fingerprint for their structural identification, we identified four characteristic Raman active phonon modes, namely three in-plane and one out-of-plane optical branches, with various intensities and frequencies depending on the material in question. Spin-polarized electronic calculations demonstrated that anti-ferromagnetic (AFM) metals, ferromagnetic (FM) metals, AFM semiconductors, and non-magnetic semiconductor materials exist within this family, evidencing the potential of t-TMXs for further use in multifunctional heterostructures.Article Citation - WoS: 17Citation - Scopus: 20Electrospun Polyacrylonitrile (pan) Nanofiber: Preparation, Experimental Characterization, Organic Vapor Sensing Ability and Theoretical Simulations of Binding Energies(Springer, 2022) İnce Yardımcı, Atike; Yağmurcukardeş, Nesli; Yağmurcukardeş, Mehmet; Çapan, İnci; Erdoğan, Matem; Çapan, Rıfat; Tarhan, Özgür; Açıkbaş, YaserIn this study, polyacrilonitrile (PAN) nanofibers obtained by electrospinning were directly coated on the surface of a quartz crystal microbalance (QCM) and were investigated for their sensing characteristics against chloroform, dichloromethane and carbon tetrachloride as volatile organic compounds (VOCs). PAN nanofibers were characterized by SEM, DSC, Raman Spectroscopy, and FT-IR and the results indicated that beadless and regular nanofibers with the average diameter of 182.7 ± 32 nm were obtained. Kinetic measurements indicated that electrospun PAN nanofibers were sensitive to the VOCs and they were appropriate for sensing applications of chlorine compounds. The reproducibility of PAN nanofiber sensor was also shown in this study. The results revealed that the diffusion coefficients of VOCs increased with the order carbontetrachloride < dichloromethane < chloroform which was supported by the density functional theory (DFT) simulations that revealed the highest binding energy for chloroform.Article Citation - WoS: 13Citation - Scopus: 15Electronic and Magnetic Properties of Single-Layer Fecl2 With Defects(Amer Physical Soc, 2021) Ceyhan, Eray; Yağmurcukardeş, Mehmet; Peeters, François M.; Şahin, HasanThe formation of lattice defects and their effect on the electronic properties of single-layer FeCl2 are investigated by means of first-principles calculations. Among the vacancy defects, namely mono-, di-, and three-Cl vacancies and mono-Fe vacancy, the formation of mono-Cl vacancy is the most preferable. Comparison of two different antisite defects reveals that the formation of the Fe-antisite defect is energetically preferable to the Cl-antisite defect. While a single Cl vacancy leads to a 1 mu(B) decrease in the total magnetic moment of the host lattice, each Fe vacant site reduces the magnetic moment by 4 mu(B). However, adsorption of an excess Cl atom on the surface changes the electronic structure to a ferromagnetic metal or to a ferromagnetic semiconductor depending on the adsorption site without changing the ferromagnetic state of the host lattice. Both Cl-antisite and Fe-antisite defected domains change the magnetic moment of the host lattice by -1 mu(B) and +3 mu(B), respectively. The electronic ground state of defected structures reveals that (i) single-layer FeCl2 exhibits half-metallicity under the formation of vacancy and Cl-antisite defects; (ii) ferromagnetic metallicity is obtained when a single Cl atom is adsorbed on upper-Cl and Fe sites, respectively; and (iii) ferromagnetic semiconducting behavior is found when a Cl atom is adsorbed on a lower-Cl site or a Fe-antisite defect is formed. Simulated scanning electron microscope images show that atomic-scale identification of defect types is possible from their electronic charge density. Further investigation of the periodically Fe-defected structures reveals that the formation of the single-layer FeCl3 phase, which is a dynamically stable antiferromagnetic semiconductor, is possible. Our comprehensive analysis on defects in single-layer FeCl2 will complement forthcoming experimental observations.Article Citation - WoS: 10Citation - Scopus: 10Vibrational and Optical Identification of Geo2 and Geo Single Layers: a First-Principles Study(Royal Society of Chemistry, 2021) Sözen, Yiğit; Yağmurcukardeş, Mehmet; Şahin, HasanIn the present work, the identification of two hexagonal phases of germanium oxides (namely GeO2 and GeO) through the vibrational and optical properties is reported using density functional theory calculations. While structural optimizations show that single-layer GeO2 and GeO crystallize in 1T and buckled phases, phonon band dispersions reveal the dynamical stability of each structure. First-order off-resonant Raman spectral predictions demonstrate that each free-standing single-layer possesses characteristic peaks that are representative for the identification of the germanium oxide phase. On the other hand, electronic band dispersion analysis shows the insulating and large-gap semiconducting nature of single-layer GeO2 and GeO, respectively. Moreover, optical absorption, reflectance, and transmittance spectra obtained by means of G(0)W(0)-BSE calculations reveal the existence of tightly bound excitons in each phase, displaying strong optical absorption. Furthermore, the excitonic gaps are found to be at deep UV and visible portions of the spectrum, for GeO2 and GeO crystals, with energies of 6.24 and 3.10 eV, respectively. In addition, at the prominent excitonic resonances, single-layers display high reflectivity with a zero transmittance, which is another indication of the strong light-matter interaction inside the crystal medium.Article Citation - WoS: 24Citation - Scopus: 86A Dirac-Semimetal Two-Dimensional Ben4: Thickness-Dependent Electronic and Optical Properties(AIP Publishing LLC, 2021) Bafekry, A.; Stampfl, C.; Faraji, M.; Yağmurcukardeş, Mehmet; Fadlallah, M. M.; Jappor, H. R.; Ghergherehchi, M.Motivated by the recent experimental realization of a two-dimensional (2D) BeN4 monolayer, in this study we investigate the structural, dynamical, electronic, and optical properties of a monolayer and few-layer BeN4 using first-principles calculations. The calculated phonon band dispersion reveals the dynamical stability of a free-standing BeN4 layer, while the cohesive energy indicates the energetic feasibility of the material. Electronic band dispersions show that monolayer BeN4 is a semi-metal whose conduction and valence bands touch each other at the Sigma point. Our results reveal that increasing the layer number from single to six-layers tunes the electronic nature of BeN4. While monolayer and bilayer structures display a semi-metallic behavior, structures thicker than that of three-layers exhibit a metallic nature. Moreover, the optical parameters calculated for monolayer and bilayer structures reveal that the bilayer can absorb visible light in the ultraviolet and visible regions better than the monolayer structure. Our study investigates the electronic properties of Dirac-semimetal BeN4 that can be an important candidate for applications in nanoelectronic and optoelectronic. Published under an exclusive license by AIP Publishing.Article Citation - WoS: 21Citation - Scopus: 21Prediction of Monoclinic Single-Layer Janus Ga2tex (x = S and Se): Strong In-Plane Anisotropy(American Physical Society, 2021) Yağmurcukardeş, Mehmet; Moğulkoç, Yeşim; Akgenç, Berna; Moğulkoç Aybey; Peeters, François M.By using density functional theory (DFT) based first-principles calculations, electronic, vibrational, piezo-electric, and optical properties of monoclinic Janus single-layer Ga2TeX (X = S or Se) are investigated. The dynamical, mechanical, and thermal stability of the proposed Janus single layers are verified by means of phonon bands, stiffness tensor, and quantum molecular dynamics simulations. The calculated vibrational spectrum reveals the either pure or coupled optical phonon branches arising from Ga-Te and Ga-X atoms. In addition to the in-plane anisotropy, single-layer Janus Ga2TeX exhibits additional out-of-plane asymmetry, which leads to important consequences for its electronic and optical properties. Electronic band dispersions indicate the direct band-gap semiconducting nature of the constructed Janus structures with energy band gaps falling into visible spectrum. Moreover, while orientation-dependent linear-elastic properties of Janus single layers indicate their strong anisotropy, the calculated in-plane stiffness values reveal the ultrasoft nature of the structures. In addition, predicted piezoelectric coefficients show that while there is a strong in-plane anisotropy between piezoelectric constants along armchair (AC) and zigzag (ZZ) directions, there exists a tiny polarization along the out-of-plane direction as a result of the formation of Janus structure. The optical response to electromagnetic radiation has been also analyzed through density functional theory by considering the independent-particle approximation. Finally, the optical spectra of Janus Ga2TeX structures is investigated and it showed a shift from the ultraviolet region to the visible region. The fact that the spectrum is between these regions will allow it to be used in solar energy and many nanoelectronics applications. The predicted monoclinic single-layer Janus Ga2TeX are relevant for promising applications in optoelectronics, optical dichroism, and anisotropic nanoelasticity.Article Citation - WoS: 119Citation - Scopus: 119Janus Two-Dimensional Transition Metal Dichalcogenide Oxides: First-Principles Investigation of Wxo Monolayers With X = S, Se, and Te(American Physical Society, 2021) Varjovi, M. Jahangirzadeh; Yağmurcukardeş, Mehmet; Peeters, François M.; Durgun, EnginStructural symmetry breaking in two-dimensional materials can lead to superior physical properties and introduce an additional degree of piezoelectricity. In the present paper, we propose three structural phases (1H, 1T, and 1T') of Janus WXO (X = S, Se, and Te) monolayers and investigate their vibrational, thermal, elastic, piezoelectric, and electronic properties by using first-principles methods. Phonon spectra analysis reveals that while the 1H phase is dynamically stable, the 1T phase exhibits imaginary frequencies and transforms to the distorted 1T' phase. Ab initio molecular dynamics simulations confirm that 1H- and 1T'-WXO monolayers are thermally stable even at high temperatures without any significant structural deformations. Different from binary systems, additional Raman active modes appear upon the formation of Janus monolayers. Although the mechanical properties of 1H-WXO are found to be isotropic, they are orientation dependent for 1T'-WXO. It is also shown that 1H-WXO monolayers are indirect band-gap semiconductors and the band gap narrows down the chalcogen group. Except 1T'-WSO, 1T'-WXO monolayers have a narrow band gap correlated with the Peierls distortion. The effect of spin-orbit coupling on the band structure is also examined for both phases and the alteration in the band gap is estimated. The versatile mechanical and electronic properties of Janus WXO monolayers together with their large piezoelectric response imply that these systems are interesting for several nanoelectronic applications.Article Citation - WoS: 7Citation - Scopus: 8Optoelectronic Properties of Confined Water in Angstrom-Scale Slits(American Physical Society, 2020) Shekarforoush, S.; Jalali, H.; Yağmurcukardeş, Mehmet; Miloševic, M.V.; Neek-Amal, M.The optoelectronic properties of confined water form one of the most active research areas in the past few years. Here we present the multiscale methodology to discern the out-of-plane electronic and dipolar dielectric constants (el and dip) of strongly confined water. We reveal that el and dip become comparable for water confined in angstrom-scale channels (with a height of less than 15Å) within graphene (GE) and hexagonal boron nitride (hBN) bilayers. Channel height (h) associated with a minimum in both el and dip is linked to the formation of the ordered structure of ice for h?(7-7.5)Å. The recently measured total dielectric constant T of nanoconfined water [L. Fumagalli et al., Science 360, 1339 (2018)10.1126/science.aat4191] is corroborated by our results. Furthermore, we evaluate the contribution from the encapsulating membranes to the dielectric properties, as a function of the interlayer spacing, i.e., the height of the confining channel for water. Finally, we conduct analysis of the optical properties of both confined water and GE membranes, and show that the electron energy loss function of confined water strongly differs from that of bulk water. © 2020 American Physical Society.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.