WoS İndeksli Yayınlar Koleksiyonu / WoS Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7150
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Article Citation - WoS: 1Citation - Scopus: 1A Multi-Layered Graphene Based Gas Sensor Platform for Discrimination of Volatile Organic Compounds Via Differential Intercalation(Royal Society of Chemistry, 2023) Özkendir İnanç, Dilce; Ng, Zhi Kai; Başkurt, Mehmet; Keleş, Berfin; Vardar, Gökay; Şahin, Hasan; Tsang, Siu Hon; Palaniappan, Alagappan; Yıldız, Ümit Hakan; Teo, EhtSelective and sensitive detection of volatile organic compounds (VOCs) is of critical importance for environmental monitoring, disease diagnosis and industrial applications. Among VOCs, assay development for primary alcohols has captured significant research attention since their toxicity causes adverse effects on gastrointestinal and central nerve systems, resulting in irreversible blindness, and coma, and can be even fatal at high exposure levels. However, selective detection of primary alcohols is extremely challenging owing to the similarity in their molecular structure and characteristic groups. Herein, we have attempted to investigate the differential methanol (MeOH)-ethanol (EtOH) discriminative properties of single-layer, bi-layer, and multi-layer graphene morphologies. Chemiresistors fabricated using the three morphologies of graphene illustrate discriminative MeOH-EtOH responses, which is attributed to the phenomenon of differential intercalation of MeOH within layered graphene morphologies as compared to that of EtOH. This hypothesis is verified by density functional theory calculations, which revealed that the adsorption of EtOH molecules on the graphene surface is more energetically favorable as compared to that of MeOH molecules, thereby inhibiting their intercalation within the layered graphene morphologies. It is further evaluated that the degree of MeOH intercalation increases with increasing layers of graphene for obtaining differential MeOH-EtOH responses. Experimental results suggest possibilities to develop selective and sensitive MeOH assays fabricated using various graphene morphologies in a combinatorial sensor array format.Article Citation - WoS: 2Citation - Scopus: 2Magnetic Single-Layer Nanoribbons of Manganese Oxide: Edge- and Width-Dependent Electronic Properties(Royal Society of Chemistry, 2022) Sözen, Yiğit; Topkıran, Uğur; Şahin, HasanIn the present work, the structural, magnetic, and electronic properties of the two- and one-dimensional honeycomb structures of recently synthesized MnO [Zhang et al., Hexagonal metal oxide monolayers derived from the metal-gas interface, Nat. Mater., 2021, 20, 1073-1078] are investigated by using first-principles calculations. Our calculations show that the single-layer 2D MnO crystal has a degenerate antiferromagnetic (AFM) ground state and a relatively less favorable ferromagnetic (FM) state. In addition, the magnetic anisotropy calculations unveil that the easy-axis direction for magnetism originating from unpaired electron states in manganese atoms is normal to the crystal plane. Electronically, while the FM MnO is a direct semiconductor with a narrow bandgap, AFM phases display large indirect bandgap semiconducting behavior. Moreover, the calculations on nanoribbons of MnO reveal that zigzag-edged ribbons display metallic behaviors, whereas armchair-edged nanoribbons are semiconductors. Magnetically, for both zigzag- or armchair-edged nanoribbons, the AFM order perpendicular to the nanoribbon growth direction is found to be favorable over the other AFM and FM orders. Moreover, depending on the edge symmetry and ribbon width, forbidden bandgap values of nanoribbons display distinct family behaviors.Article Citation - WoS: 6Citation - Scopus: 7Interface-Dependent Phononic and Optical Properties of Geo/Moso Heterostructures(Royal Society of Chemistry, 2022) Yağmurcukardeş, Mehmet; Sözen, Yiğit; Başkurt, Mehmet; Peeters, François M.; Şahin, HasanThe 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: 6Citation - Scopus: 6Novel Ultra-Thin Two-Dimensional Structures of Strontium Chloride(Royal Society of Chemistry, 2020) Akyol, Cansu; Başkurt, Mehmet; Şahin, HasanBy performing density functional theory-based calculations, possible stable ultra-thin crystal structures of SrCl(2)are investigated. Phonon calculations reveal that, among the possible crystal structures, three different phases; namely 1H, 1T, and square, are dynamically stable. In addition,ab initiomolecular dynamics calculations show that these three phases are thermally stable up to well above room temperature. Another important stability factor of crystals, the chemical inertness against abundant molecules in the atmosphere, such as N-2, O-2, H2O, and CO2, is also investigated. The analysis shows that SrCl(2)single-layers are chemically stable against these molecules. Moreover, it is determined that in contact with H2O and CO2, ultra-thin SrCl(2)sheets display unique electronic features, allowing them to be used in sensing applications. It is also shown that single layers of SrCl(2)crystals, all having a wide electronic band gap, can form type-I and type-II vertical van der Waals heterostructures with well-known 2D materials such as MoS2, WSe2, and h-BN.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: 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: 15Citation - Scopus: 16Monitoring the Crystal Orientation of Black-Arsenic Via Vibrational Spectra(Royal Society of Chemistry, 2019) Kandemir, Ali; İyikanat, Fadıl; Şahin, HasanIn this study, the structural, mechanical, and vibrational properties of a recently discovered anisotropic ultra-thin material, black-arsenic (b-As), are investigated by using density functional theory. Direction dependent elastic constants such as in-plane stiffness, Young's modulus and Poisson's ratio of single-layer b-As are calculated and compared with those of the structural cousin black-phosphorus (b-P). The calculated Poisson's ratio of b-As for the zigzag direction is nearly 1, which is quite higher than that of b-P, 0.65. Besides, it is found that all the three elastic constants are highly anisotropic and their values in the zigzag direction are almost three times higher than that of the armchair direction. The mechanical strength of the material is also calculated and high-toughness is seen in both armchair and zigzag directions. It is revealed that the material is quite stiff against straining along the zigzag direction; in contrast, it is quite flexible along the armchair direction. Vibrational stability analysis shows that the material is stable up to 9% biaxially applied strain, and 12% and 45% uniaxially applied strain in the zigzag and armchair directions, respectively. Furthermore, the prominent Raman active peaks of the b-As structure show strong anisotropy in the strain dependent vibrational spectra and they can also be used for easy-determination of the crystal orientation of b-As from Raman measurements.Article Citation - WoS: 67Citation - Scopus: 66Bilayers of Janus Wsse: Monitoring the Stacking Type: Via the Vibrational Spectrum(Royal Society of Chemistry, 2018) Kandemir, Ali; Şahin, HasanMotivated by the recent successful synthesis of Janus type single layers of transition metal dichalcogenides, we investigate the stability, vibrational and electronic properties of the Janus single layer structure of WSSe and its bilayers by means of density functional theory. The structural and vibrational analysis show that the Janus single layer of WSSe forms a dynamically stable structure in the 2H phase. Owing to its non-centrosymmetric structure, the Janus WSSe single layer has two in-plane (E) and two out-of-plane (A) Raman active phonon modes. The eigen-frequencies of the prominent Raman active modes are calculated to be 277 (A) and 322 (E) cm-1. Similar to single layer WS2 and WSe2, Janus WSSe is a direct band gap semiconductor that has two electronically different faces. In addition, the possible bilayer stacking orders of the Janus WSSe single layers are investigated. It is found that there are 3 stacking types of bilayer Janus WSSe and each stacking type has distinctive Raman characteristics in its vibrational spectrum. Our results show that thanks to the vibrational characteristics, which stem from the distinctive interlayer interactions at different sides, the stability and stacking types of the bilayer of WSSe Janus structure can be monitored.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, HasanBy 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: 11Citation - Scopus: 11Stable Monolayer ?-Phase of Cdte: Strain-Dependent Properties(Royal Society of Chemistry, 2017) Ünsal, Elif; Senger, Ramazan Tuğrul; Şahin, HasanCdTe is a well known and widely used binary compound for optoelectronic applications. In this study, we propose the thinnest, free standing monolayer of CdTe which has a tetragonal-PbO (α-PbO) symmetry. The structural, electronic, vibrational and strain dependent properties are investigated by means of first principles calculations based on density functional theory. Our results demonstrate that monolayer α-CdTe is a dynamically stable and mechanically flexible material. It is found that the thinnest monolayer crystal of CdTe is a semiconductor with a direct band gap of 1.95 eV, which corresponds to red light in the visible spectrum. Moreover, it is found that the band gap can be tunable under biaxial strain. With its strain-controllable direct band gap within the visible spectrum, the stable α-phase of monolayer CdTe is a suitable candidate for optoelectronic device applications.