Photonics / Fotonik
Permanent URI for this collectionhttps://hdl.handle.net/11147/2590
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Article Citation - WoS: 5Citation - Scopus: 5Thickness-Dependent Piezoelecticity of Black Arsenic From Few-Layer To Monolayer(Elsevier, 2023) Akgenç Hanedar, Berna; Ersan, Fatih; Altalhi, Tariq; Yağmurcukardeş, Mehmet; Yakobson, BorisUltra-thin forms of black phosphorus (b-P) have been widely investigated due to its unique properties arising from the in-plane anisotropy in its crystal structure. Recently, two-dimensional (2D) forms of black arsenic (b-As) have also been added to the 2D family. In this study, the thickness-dependent structural, electronic, and piezoelectric properties of layered b-As are investigated by means of ab-initio calculations. The structural optimizations confirm the van der Waals type layered structure for both these structures. In addition, increasing the thickness is shown to result in the decreasing of the band gap arising from the confinement of electrons in the layers. In contrast to the case of b-P, it is revealed that a transition from indirect-to-direct band gap behavior can be found in b-As which can be important for optically identifying the single-layer structure. Moreover, the piezoelectric properties are investigated as a function of the number of layers. It is shown that while a single-layer of b-As does not exhibit piezoelectric features, even in the case of bilayer structures the piezoelectricity is created. Our results revealed the strong in-plane anisotropy in piezoelectric coefficients for the three-layer and thicker structures. We have shown that the out-of-plane piezoelectric properties can be achieved by non-centrosymmetric features in the out-of-plane direction in thicker structures of b-As.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: 4Identification of a Magnetic Phase Via a Raman Spectrum in Single-Layer Mnse: an Ab Initio Study(Elsevier, 2022) Yayak, Yankı Öncü; Şahin, Hasan; Yağmurcukardeş, MehmetMotivated by the recent experimental realization of single-layer two-dimensional MnSe [ACS Nano2021, 15, 13794-13802], structural, magnetic, elastic, vibrational, and electronic properties of single-layer MnSe are investigated by using density functional theory-based calculations. Among four different magnetic phases, namely, ferromagnetic (FM) and Nẽel-, zigzag-, and stripy-antiferromagnetic (AFM) phases, the Nẽel-AFM structure is found to be the energetically most favorable phase. Structural optimizations show the formation of in-plane anisotropy within the structures of zigzag- and stripy-AFM phases in single-layer MnSe. For the dynamically stable four magnetic phases, predicted Raman spectra reveal that each phase exhibits distinctive vibrational features and can be distinguished from each other. In addition, the elastic constants indicate the mechanical stability of each magnetic phase in single-layer MnSe and reveal the soft nature of each phase. Moreover, electronic band dispersion calculations show the indirect band gap semiconducting nature with varying electronic band gap energies for all magnetic phases. Furthermore, the atomic orbital-based density of states reveals the existence of out-of-plane orbitals dominating the top valence states in zigzag- and stripy-AFM phases, giving rise to the localized states. The stability of different magnetic phases and their distinct vibrational and electronic properties make single-layer MnSe a promising candidate for nanoelectronic and spintronic applications.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: 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: 7Citation - Scopus: 8Stable janus TaSe2 single-layers via surface functionalization(Elsevier Ltd., 2021) Kahraman, Zeynep; Başkurt, Mehmet; Yağmurcukardeş, Nesli; Chaves, A.; Şahin, HasanFirst-principles calculations are performed in order to investigate the formation of Janus structures of single-layer TaSe2. The structural optimizations and phonon band dispersions reveal that the formation and stability of hydrogenated (HTaSe2), fluorinated (FTaSe2), and the one-side hydrogenated and one-side fluorinated (Janus-HTaSe2F) single-layers are feasible in terms of their phonon band dispersions. It is shown that bare metallic single-layer TaSe2 can be turned into a semiconductor as only one of its surface is functionalized while it remains as a metal via its two surfaces functionalization. In addition, the semiconducting nature of single-layers HTaSe2 and FTaSe2 and the metallic behavior of Janus TaSe2 are found to be robust under applied uniaxal strains. Further analysis on piezoelectric properties of the predicted single-layers reveal the enhanced in-plane and out-of-plane piezoelectricity via formed Janus-HTaSe2F. Our study indicates that single-layer TaSe2 is a suitable host material for surface functionalization via fluorination and hydrogenation which exhibit distinctive electronic and vibrational properties. © 2020 Elsevier B.V.Article Citation - WoS: 15Citation - Scopus: 16Parametrizing Nonbonded Interactions Between Silica and Water From First Principles(Elsevier, 2020) Özçelik, H. Gökberk; Sözen, Yiğit; Şahin, Hasan; Barışık, MuratSilica has been used in a vast number of micro/nano-fluidic technologies where interactions of water with silica at the molecular level play a key role. In such small systems, an understanding of mass and heat transport or surface wetting relies on accurate calculations of the water-silica interface coupling through atomic interactions. Molecular dynamics (MD) is a convenient tool for such use, but force field parameters for nonbonded interactions are required as an input, which are very limited in literature. These interaction parameters can be predicted by density functional theory, but dispersion forces are not calculated in standard models for electron correlations that additional correction models have been proposed at different levels of sophistications, and still under development. Accordingly, this work employs state of the art quantum chemistry to compute the binding energies. Force field parameters for silica/water van der Waals interactions were calculated, and later tested in MD simulations of water droplet on silica surface. While the standard dispersion corrections overestimated the binding energy, Becke-Johnson model yielded interactions parameters recovering experimentally measured wetting behavior of silica with a water contact angle of approximately 12.4 degrees on the flat and clean silica surface. Results will be useful for the current molecular modelling attempts by providing transferable parameters for simple silica/water van der Waals interactions as an alternative to existing complex surface interaction models.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.Article Citation - WoS: 6Citation - Scopus: 6Few-Layer Mos2 as Nitrogen Protective Barrier(IOP Publishing Ltd., 2017) Akbalı, Barış; Yanılmaz, Alper; Tomak, Aysel; Tongay, Sefaattin; Çelebi, Cem; Şahin, HasanWe report experimental and theoretical investigations of the observed barrier behavior of few-layer MoS2 against nitrogenation. Owing to its low-strength shearing, low friction coefficient, and high lubricity, MoS2 exhibits the demeanor of a natural N-resistant coating material. Raman spectroscopy is done to determine the coating capability of MoS2 on graphene. Surface morphology of our MoS2/graphene heterostructure is characterized by using optical microscopy, scanning electron microscopy, and atomic force microscopy. In addition, density functional theory-based calculations are performed to understand the energy barrier performance of MoS2 against nitrogenation. The penetration of nitrogen atoms through a defect-free MoS2 layer is prevented by a very high vertical diffusion barrier, indicating that MoS2 can serve as a protective layer for the nitrogenation of graphene. Our experimental and theoretical results show that MoS2 material can be used both as an efficient nanocoating material and as a nanoscale mask for selective nitrogenation of graphene layer.Article Citation - WoS: 3Citation - Scopus: 2?-Silicene as Oxidation-Resistant Ultra-Thin Coating Material(Beilstein-Institut Zur Forderung der Chemischen Wissenschaften, 2017) Kandemir, Ali; İyikanat, Fadıl; Bacaksız, Cihan; Şahin, HasanBy performing density functional theory (DFT)-based calculations, the performance of a-silicene as oxidation-resistant coating on Ag(111) surface is investigated. First of all, it is shown that the Ag(111) surface is quite reactive against O atoms and O2 molecules. It is known that when single-layer silicene is formed on the Ag(111) surface, the 3 × 3-reconstructed phase, a-silicene, is the ground state. Our investigation reveals that as a coating layer, a-silicene (i) strongly absorbs single O atoms and (ii) absorbs O2 molecules by breaking the strong O-O bond. (iii) Even the hollow sites, which are found to be most favorable penetration path for oxygens, serves as high-energy oxidation barrier, and (iv) α-silicene becomes more protective and less permeable in the presence of absorbed O atom. It appears that single-layer silicene is a quite promising material for ultra-thin oxidation-protective coating applications.