Photonics / Fotonik
Permanent URI for this collectionhttps://hdl.handle.net/11147/2590
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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; Yayak, Yankı Öncü; Yağmurcukardeş, Mehmet; Şahin, Hasan; 04.04. Department of Photonics; 01. Izmir Institute of Technology; 04. Faculty of ScienceMotivated 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: 6Citation - Scopus: 7Interface-Dependent Phononic and Optical Properties of Geo/Moso Heterostructures(Royal Society of Chemistry, 2022) Yağmurcukardeş, Mehmet; Sözen, Yiğit; Sözen, Yiğit; Peeters, François M.; Şahin, Hasan; Şahin, Hasan; Yağmurcukardeş, Mehmet; 04.04. Department of Photonics; 01. Izmir Institute of Technology; 04. Faculty of ScienceThe interface-dependent electronic, vibrational, piezoelectric, and optical properties of van der Waals heterobilayers, formed by buckled GeO (b-GeO) and Janus MoSO structures, are investigated by means of first-principles calculations. The electronic band dispersions show that O/Ge and S/O interface formations result in a type-II band alignment with direct and indirect band gaps, respectively. In contrast, O/O and S/Ge interfaces give rise to the formation of a type-I band alignment with an indirect band gap. By considering the Bethe-Salpeter equation (BSE) on top of G0W0 approximation, it is shown that different interfaces can be distinguished from each other by means of the optical absorption spectra as a consequence of the band alignments. Additionally, the low-and high-frequency regimes of the Raman spectra are also different for each interface type. The alignment of the individual dipoles, which is interface-dependent, either weakens or strengthens the net dipole of the heterobilayers and results in tunable piezoelectric coefficients. The results indicate that the possible heterobilayers of b-GeO/MoSO asymmetric structures possess various electronic, optical, and piezoelectric properties arising from the different interface formations and can be distinguished by means of various spectroscopic techniques.Article Citation - WoS: 13Citation - Scopus: 15Electronic and Magnetic Properties of Single-Layer Fecl2 With Defects(Amer Physical Soc, 2021) Ceyhan, Eray; Şahin, Hasan; Yağmurcukardeş, Mehmet; Yağmurcukardeş, Mehmet; Peeters, François M.; Şahin, Hasan; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe 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: 93Citation - Scopus: 95Single-Layer Janus-Type Platinum Dichalcogenides and Their Heterostructures(American Chemical Society, 2019) Kahraman, Zeynep; Kandemir, Ali; Yağmurcukardeş, Mehmet; Şahin, Hasan; Şahin, Hasan; Kahraman, Zeynep; 04.04. Department of Photonics; 04. Faculty of Science; 01. Izmir Institute of TechnologyUltrathin two-dimensional Janus-type platinum dichalcogenide crystals formed by two different atoms at opposite surfaces are investigated by performing state-of-the-art density functional theory calculations. First, it is shown that single-layer PtX2 structures (where X = S, Se, or Te) crystallize into the dynamically stable IT phase and are indirect band gap semiconductors. It is also found that the substitutional chalcogen doping in all PtX2 structures is favorable via replacement of surface atoms with a smaller chalcogen atom, and such a process leads to the formation of Janus-type platinum dichalcogenides (XPtY, where X and Y stand for S, Se, or Te) which are novel single-layer crystals. While all Janus structures are indirect band gap semiconductors as their binary analogues, their Raman spectra show distinctive features that stem from the broken out-of-plane symmetry. In addition, it is revealed that the construction of Janus crystals enhances the piezoelectric constants of PtX2 crystals significantly both in the in plane and in the out-of-plane directions. Moreover, it is shown that vertically stacked van der Waals heterostructures of binary and ternary (Janus) platinum dichalcogenides offer a wide range of electronic features by forming bilayer heterojunctions of type-I, type-II, and type-III, respectively. Our findings reveal that Janus-type ultrathin platinum dichalcogenide crystals are quite promising materials for optoelectronic device applications.Article Citation - WoS: 46Citation - Scopus: 49Tuning Electronic and Magnetic Properties of Monolayer ?-Rucl3 by In-Plane Strain(Royal Society of Chemistry, 2018) İyikanat, Fadıl; Yağmurcukardeş, Mehmet; Senger, Ramazan Tuğrul; Şahin, Hasan; Yağmurcukardeş, Mehmet; Şahin, Hasan; 04.04. Department of Photonics; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyBy employing density functional theory-based methods, the structural, vibrational, electronic, and magnetic properties of monolayer α-RuCl3 were investigated. It was demonstrated that ferromagnetic (FM) and zigzag-antiferromagnetic (ZZ-AFM) spin orders in the material have very close total energies with the latter being the ground state. We found that each Ru atom possesses a magnetic moment of 0.9 μB and the material exhibits strong magnetic anisotropy. While both phases exhibit indirect gaps, the FM phase is a magnetic semiconductor and the ZZ-AFM phase is a non-magnetic semiconductor. The structural stability of the material was confirmed by phonon calculations. Moreover, dynamical analysis revealed that the magnetic order in the material can be monitored via Raman measurements of the crystal structure. In addition, the magnetic ground state of the material changes from ZZ-AFM to FM upon certain applied strains. Valence and conduction band-edges of the material vary considerably under in-plane strains. Owing to the stable lattice structure and unique and controllable magnetic properties, monolayer α-RuCl3 is a promising material in nanoscale device applications.Article Citation - WoS: 31Citation - Scopus: 31Hydrogen-Induced Structural Transition in Single Layer Res2(IOP Publishing Ltd., 2017) Yağmurcukardeş, Mehmet; Bacaksız, Cihan; Şahin, Hasan; Şahin, Hasan; Senger, Ramazan Tuğrul; Yağmurcukardeş, Mehmet; 04.04. Department of Photonics; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyBy performing density functional theory-based calculations, we investigate how structural, electronic and mechanical properties of single layer ReS2 can be tuned upon hydrogenation of its surfaces. It is found that a stable, fully hydrogenated structure can be obtained by formation of strong S-H bonds. The optimized atomic structure of ReS2H2 is considerably different than that of the monolayer ReS2 which has a distorted-1T phase. By performing phonon dispersion calculations, we also predict that the Re2-dimerized 1T structure (called 1TRe2) of the ReS2H2 is dynamically stable. Unlike the bare ReS2 the 1TRe2–ReS2H2 structure which is formed by breaking the Re4 clusters into separated Re2 dimers, is an indirect-gap semiconductor. Furthermore, mechanical properties of the 1TRe2 phase in terms of elastic constants, in-plane stiffness (C) and Poisson ratio (ν) are investigated. It is found that full hydrogenation not only enhances the flexibility of the single layer ReS2 crystal but also increases anisotropy of the elastic constantsArticle Citation - WoS: 2Citation - Scopus: 2Atomic-scale understanding of dichlorobenzene-assisted poly 3-hexylthiophene-2,5-diyl nanowire formation mechanism(Elsevier Ltd., 2017) Yağmurcukardeş, Mehmet; Kıymaz, D.; Senger, Ramazan Tuğrul; Senger, Ramazan Tuğrul; Yağmurcukardeş, Mehmet; Şahin, Hasan; 04.04. Department of Photonics; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyLow-dimensional Poly 3-hexylthiophene-2,5-diyl (P3HT) structures that serve efficient exciton dissociation in organic solar cells, play a major role in increasing the charge collection, and hence, the efficiency of organic devices. In this study, we theoretically and experimentally investigate the Dichlorobenzene (DCB)-assisted formation of P3HT nanowires. Our experiments show that the solution of DCB molecules drive randomly oriented P3HT polymers to form well-stacked nanowires by stabilizing tail-tail and π−π interactions. Here the question is how DCB molecules migrate into the P3HT layers while forming the nanowire structure. Our density functional theory-based calculations reveal that the vertical migration of the DCB molecules between P3HT layers is forbidden due to a high energy barrier that stems from strong alkyl chain-DCB interaction. In contrast to vertical diffusion, lateral diffusion of DCB molecules in between P3HT layers is much more likely. Our results show that migration of a DCB molecule occurs through the alkyl groups with a low energy barrier. Therefore, laterally diffused DCB molecules assist nucleation of top-to-top stacking of P3HT polymers and formation of well-ordered nanowires.Article Citation - WoS: 45Citation - Scopus: 45Mg(OH)2-WS2 van der Waals heterobilayer: Electric field tunable band-gap crossover(American Physical Society, 2016) Yağmurcukardeş, Mehmet; Torun, Engin; Yağmurcukardeş, Mehmet; Peeters, François M.; Senger, Ramazan Tuğrul; Şahin, Hasan; 04.04. Department of Photonics; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyMagnesium hydroxide [Mg(OH)2] has a layered brucitelike structure in its bulk form and was recently isolated as a new member of two-dimensional monolayer materials. We investigated the electronic and optical properties of monolayer crystals of Mg(OH)2 and WS2 and their possible heterobilayer structure by means of first-principles calculations. It was found that both monolayers of Mg(OH)2 and WS2 are direct-gap semiconductors and these two monolayers form a typical van der Waals heterostructure with a weak interlayer interaction and a type-II band alignment with a staggered gap that spatially separates electrons and holes. We also showed that an out-of-plane electric field induces a transition from a staggered to a straddling-type heterojunction. Moreover, by solving the Bethe-Salpeter equation on top of single-shot G0W0 calculations, we show that the low-energy spectrum of the heterobilayer is dominated by the intralyer excitons of the WS2 monolayer. Because of the staggered interfacial gap and the field-tunable energy-band structure, the Mg(OH)2-WS2 heterobilayer can become an important candidate for various optoelectronic device applications in nanoscale.Article Citation - WoS: 166Citation - Scopus: 170Mechanical Properties of Monolayer Gas and Gase Crystals(American Physical Society, 2016) Yağmurcukardeş, Mehmet; Senger, Ramazan Tuğrul; Senger, Ramazan Tuğrul; Şahin, Hasan; Yağmurcukardeş, Mehmet; Şahin, Hasan; 04.04. Department of Photonics; 04.05. Department of Pyhsics; 04. Faculty of Science; 01. Izmir Institute of TechnologyThe mechanical properties of monolayer GaS and GaSe crystals are investigated in terms of their elastic constants: in-plane stiffness (C), Poisson ratio (ν), and ultimate strength (σU) by means of first-principles calculations. The calculated elastic constants are compared with those of graphene and monolayer MoS2. Our results indicate that monolayer GaS is a stiffer material than monolayer GaSe crystals due to the more ionic character of the Ga-S bonds than the Ga-Se bonds. Although their Poisson ratio values are very close to each other, 0.26 and 0.25 for GaS and GaSe, respectively, monolayer GaS is a stronger material than monolayer GaSe due to its slightly higher σU value. However, GaS and GaSe crystals are found to be more ductile and flexible materials than graphene and MoS2. We have also analyzed the band-gap response of GaS and GaSe monolayers to biaxial tensile strain and predicted a semiconductor-metal crossover after 17% and 14% applied strain, respectively, for monolayer GaS and GaSe. In addition, we investigated how the mechanical properties are affected by charging. We found that the flexibility of single layer GaS and GaSe displays a sharp increase under 0.1e/cell charging due to the repulsive interactions between extra charges located on chalcogen atoms. These charging-controllable mechanical properties of single layers of GaS and GaSe can be of potential use for electromechanical applications. © 2016 American Physical Society.