Physics / Fizik
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Article Anisotropic Tunability of Vibrational Modes in Black Phosphorus Under Uniaxial Compressive/Tensile Strain(Wiley, 2023) Li, Hao; Kutlu, Tayfun; Carrascoso, Felix; Şahin, Hasan; Munuera, Carmen; Castellanos Gomez, AndresStrain engineering is a powerful strategy for tuning the optical, electrical, vibrational properties of 2D nanomaterials. In this work, a four-point bending apparatus is constructed to apply both compressive and tensile strain on 2D anisotropic black phosphorus flake. Further polarized Raman spectroscopy is used to study the vibrational modes of black phosphorus flakes under uniaxial strain applied along various crystalline orientations. Here, a strong anisotropic blue/redshift of A1g, B2g, and A2g modes is found under compressive/tensile strain, respectively. Interestingly, mode A1g exhibits the maximum/minimum shift while mode B2g and mode A2g present the minimum/maximum shift when the strain is applied along armchair/zigzag direction. Density functional theory calculations are carried out to investigate the anisotropic strain response mechanism, finding that the strain-induced regulation of the PP bond angle, bond length, and especially interlayer interaction has a giant influence on the Raman shift. A four-point bending apparatus is constructed to study the effect of uniaxial strain on the vibrational property of anisotropic black phosphorus. Particularly, strong anisotropy on the Raman blueshift/redshift rate upon compressive/tensile strain can be observed, which results from the strain-induced regulation of the bond angle, bond length, and interlayer interactions according to density functional theory calculation analysis.imageArticle Single Layer Res2h2: Stability, Raman Activity and Electronic Properties(Eskişehir Teknik Üniversitesi, 2018) Ünsal, Elif; Şahin, HasanIn this study, the structural, vibrational and electronic properties of the hydrogenated single layer of ReS2 are investigated byperforming the first principle calculations based on density functional theory. We found that the characteristic properties ofthe monolayer ReS2 can be manipulated upon the hydrogen functionalization. As the monolayer ReS2, the ReS2H2 hasdistorted 1T phase; however, the bonding in Re slab significantly varies with the hydrogenation. Our results demonstrate thatthe full-surface hydrogenation leads to an expansion in lattice and the Re4 tetramer-chains in the monolayer ReS2 areseparated into two dimers in the hydrogenated monolayer. It is calculated that the dynamically stable monolayer of ReS2H2has 26 Raman-active vibrational modes. Constant volume specific heat calculations are also performed and the resultsindicate that at high temperature, the monolayer ReS2 approaches to limit of 3R before the monolayer ReS2H2. By performingthe electronic band structure calculations, it is shown that when the ReS2 surface is fully hydrogenated, there occurs a directto indirect band gap transition and the semiconducting hydrogen-induced monolayer has a band gap of 0.74 eV.Article Citation - WoS: 15Citation - Scopus: 15Ag and Au Atoms Intercalated in Bilayer Heterostructures of Transition Metal Dichalcogenides and Graphene(American Institute of Physics, 2014) İyikanat, Fadıl; Şahin, Hasan; Senger, Ramazan Tuğrul; Peeters, François M.The diffusive motion of metal nanoparticles Au and Ag on monolayer and between bilayer heterostructures of transition metal dichalcogenides and graphene are investigated in the framework of density functional theory. We found that the minimum energy barriers for diffusion and the possibility of cluster formation depend strongly on both the type of nanoparticle and the type of monolayers and bilayers. Moreover, the tendency to form clusters of Ag and Au can be tuned by creating various bilayers. Tunability of the diffusion characteristics of adatoms in van der Waals heterostructures holds promise for controllable growth of nanostructures. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.Article Citation - WoS: 24Citation - Scopus: 24Defect Tolerant and Dimension Dependent Ferromagnetism in Mnse2(Royal Society of Chemistry, 2019) Eren, İsmail; İyikanat, Fadıl; Şahin, HasanBy performing density functional theory-based calculations, we investigate the structural, vibrational, electronic and magnetic properties of 2D monolayers, nanoribbons and quantum dots of MnSe2. Vibrational spectrum analysis reveals the dynamical stability of not only ferromagnetic but also antiferromagnetic phases of single layer MnSe2 crystal structures. Electronically, calculations show that 1T-MnSe2 is a ferromagnetic structure displaying metallic behavior. It is also found that the structure preserves its dynamical stability and metallic behavior even under the presence of high density Se vacancies. Moreover, it was predicted that, differing from the 2D MnSe2, metal-metal interaction driven reconstructions result in ferromagnetic-to-antiferromagnetic crossover in the ground state of nanoribbons and quantum dots. With its robust ferromagnetic metallic character in the 2D ultra-thin limit and dimension-dependent magnetic properties, MnSe2 is an important candidate for spintronic device applications.Article Citation - WoS: 30Citation - Scopus: 29Stacking-Dependent Excitonic Properties of Bilayer Blue Phosphorene(American Physical Society, 2019) İyikanat, Fadıl; Torun, Engin; Senger, Ramazan Tuğrul; Şahin, HasanAb initio calculations in the framework of many-body perturbation theory (MBPT) are performed to calculate the electronic and optical properties of monolayer and bilayer blue phosphorene with different stacking configurations. It is found that the stacking configuration of bilayer blue phosphorene strongly affects the electronic band gap of the material. By solving the Bethe-Salpeter equation (BSE) on top of the G(0)W(0) calculation, the binding energies, spectral positions, and band decomposition of excitons of monolayer and bilayer configurations are investigated. The most prominent two excitonic peaks of bilayers are examined in detail. Our calculations show that different stacking configurations lead to distinct interlayer interaction characteristics which lead to substantial change in the optical spectrum of bilayer blue phosphorene. Mostly intralayer and mixed interlayer excitons with quite high binding energies are obtained in bilayer blue phosphorene. Our results show that excitonic properties of ultrathin materials play an important role in tuning and improving the optoelectronic performance of two-dimensional materials.Article Citation - WoS: 3Citation - Scopus: 3Hydrogenated Derivatives of Hexacoordinated Metallic Cu2si Monolayer(Royal Society of Chemistry, 2018) Ünsal, Elif; İyikanat, Fadıl; Şahin, Hasan; Senger, Ramazan TuğrulHerein, we carried out first-principles calculations based on density functional theory to investigate the effects of surface functionalization with hydrogen atoms on structural, dynamical and electronic properties of Cu2Si monolayer. Pristine Cu2Si, a metallic monolayer, has a planar hexacoordinate structure. Calculations revealed that the most favorable position of a single H atom on the Cu2Si monolayer is at the top of a Si site. Derivatives of Cu2Si monolayer with various H concentrations were investigated, and by performing phonon calculations, it was found that there are three stable hydrogenated structures. Specific heat of these monolayers was found to increase with the hydrogen concentration at temperatures higher than 100 K. Electronically, the hydrogenated derivatives of Cu2Si monolayer preserve the metallic character.Article Citation - WoS: 36Citation - Scopus: 34Raman Fingerprint of Stacking Order in Hfs2-Ca(oh)(2) Heterobilayer(American Physical Society, 2019) Yağmurcukardeş, Mehmet; Özen, Sercan; İyikanat, Fadıl; Peeters, François M.; Şahin, HasanUsing density functional theory-based first-principles calculations, we investigate the stacking order dependence of the electronic and vibrational properties of HfS2-Ca(OH)(2) heterobilayer structures. It is shown that while the different stacking types exhibit similar electronic and optical properties, they are distinguishable from each other in terms of their vibrational properties. Our findings on the vibrational properties are the following: (i) from the interlayer shear (SM) and layer breathing (LBM) modes we are able to deduce the AB' stacking order, (ii) in addition, the AB' stacking type can also be identified via the phonon softening of E-g(I) and A(g)(III) modes which harden in the other two stacking types, and (iii) importantly, the ultrahigh frequency regime possesses distinctive properties from which we can distinguish between all stacking types. Moreover, the differences in optical and vibrational properties of various stacking types are driven by two physical effects, induced biaxial strain on the layers and the layer-layer interaction. Our results reveal that with both the phonon frequencies and corresponding activities, the Raman spectrum possesses distinctive properties for monitoring the stacking type in novel vertical heterostructures constructed by alkaline-earth-metal hydroxides.Article Citation - WoS: 15Citation - Scopus: 15Vertical van der waals heterostructure of single layer InSe and SiGe(American Chemical Society, 2019) Eren, İsmail; Özen, Sercan; Sözen, Yiğit; Yağmurcukardeş, Mehmet; Şahin, HasanWe present a first-principles investigation on the stability, electronic structure, and mechanical response of ultrathin heterostructures composed of single layers of InSe and SiGe. First, by performing total energy optimization and phonon calculations, we show that single layers of InSe and SiGe can form dynamically stable heterostructures in 12 different stacking types. Valence and conduction band edges of the heterobilayers form a type-I heterojunction having a tiny band gap ranging between 0.09 and 0.48 eV. Calculations on elastic-stiffness tensor reveal that two mechanically soft single layers form a heterostructure which is stiffer than the constituent layers because of relatively strong interlayer interaction. Moreover, phonon analysis shows that the bilayer heterostructure has highly Raman active modes at 205.3 and 43.7 cm(-1), stemming from the out-of-plane interlayer mode and layer breathing mode, respectively. Our results show that, as a stable type-I heterojunction, ultrathin heterobilayer of InSe/SiGe holds promise for nanoscale device applications.Article Citation - WoS: 1Interaction of Ge With Single Layer Gaas: From Ge-Island Nucleation To Formation of Novel Stable Monolayers(Elsevier, 2020) Sözen, Yiğit; Eren, İsmail; Özen, Sercan; Yağmurcukardeş, Mehmet; Şahin, HasanIn this study, reactivity of single-layer GaAs against Ge atoms is studied by means of ab initio density functional theory calculations. Firstly, it is shown that Ge atoms interact quite strongly with the GaAs layer which allows the formation of Ge islands while it hinders the growth of detached germanene monolayers. It is also predicted that adsorption of Ge atoms on GaAs single-layer lead to formation of two novel stable single-layer crystal structures, namely 1H-GaGeAs and 1H(A)-GaGeAs. Both the total energy optimizations and the calculated vibrational spectra indicate the dynamical stability of both single layer structures. Moreover, although both structures crystallize in 1H phase, 1H-GaGeAs and 1H(A)-GaGeAs exhibit distinctive vibrational features in their Raman spectra which is quite important for distinguishing the structures. In contrast to the semiconducting nature of single-layer GaAs, both polytypes of GaGeAs exhibit metallic behavior confirmed by the electronic band dispersions. Furthermore, the linear-elastic constants, in-plane stiffness and Poisson ratio, reveal the ultrasoft nature of the GaAs and GaGeAs structures and the rigidity of GaAs is found to be slightly enhanced via Ge adsorption. With their stable, ultra-thin and metallic properties, predicted single-layer GaGeAs structures can be promising candidates for nanoscale electronic and mechanical applications.Article Citation - WoS: 30Citation - Scopus: 32Vanadium Dopant- and Strain-Dependent Magnetic Properties of Single-Layer Vi3(Elsevier, 2020) Başkurt, Mehmet; Eren, İsmail; Yağmurcukardeş, Mehmet; Şahin, HasanMotivated by the recent synthesis of two-dimensional VI3 [Kong et al. Adv. Mater. 31, 1808074 (2019)], we investigate the effect of V doping on the magnetic and electronic properties of monolayer VI3 by means of first-principles calculations. The dynamically stable semiconducting ferromagnetic (FM) and antiferromagnetic (AFM) phases of monolayer VI3 are found to display distinctive vibrational features that the magnetic state can be distinguished by Raman spectroscopy. In order to clarify the effect of experimentally observed excessive V atoms, the magnetic and electronic properties of the V-doped VI3 structures are analyzed. Our findings indicate that partially doped VI3 structures display FM ground state while the fully-doped structure exhibits AFM ground state. The fully-doped monolayer VI3 is found to be a semiconductor with a relatively larger band gap than its pristine structure. In addition, strain-dependent electronic and magnetic properties of fully- and partially-doped VI3 structures reveal that pristine monolayer displays a FM-to-AFM phase transition with robust semiconducting nature for 5% of compressive strain, while fully-doped monolayer VI3 structure possesses AFM-to-FM semiconducting transition at tensile strains larger than 4%. In contrast, the partially-doped VI3 monolayers are found to display robust FM ground state under biaxial strain. Its dopant and strain tunable electronic and magnetic nature makes monolayer VI3 a promising material for applications in nanoscale spintronic devices.