Browsing by Subject "MoS2"
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Item Open Access CVD grown 2D MoS2 layers: a photoluminescence and fluorescence lifetime imaging study(Wiley-VCH Verlag, 2016) Özden, A.; Şar, H.; Yeltik A.; Madenoğlu, B.; Sevik, C.; Ay, F.; Perkgöz, N. K.In this letter, we report on the fluorescence lifetime imaging and accompanying photoluminescence properties of a chemical vapour deposition (CVD) grown atomically thin material, MoS2. µ-Raman, µ-photoluminescence (PL) and fluorescence lifetime imaging microscopy (FLIM) are utilized to probe the fluorescence lifetime and photoluminescence properties of individual flakes of MoS2 films. Usage of these three techniques allows identification of the grown layers, grain boundaries, structural defects and their relative effects on the PL and fluorescence lifetime spectra. Our investigation on individual monolayer flakes reveals a clear increase of the fluorescence lifetime from 0.3 ns to 0.45 ns at the edges with respect to interior region. On the other hand, investigation of the film layer reveals quenching of PL intensity and lifetime at the grain boundaries. These results could be important for applications where the activity of edges is important such as in photocatalytic water splitting. Finally, it has been demonstrated that PL mapping and FLIM are viable techniques for the investigation of the grain-boundaries. (Figure presented.). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, WeinheimItem Open Access High-figure-of-merit biosensing and enhanced excitonic absorption in an mos2-integrated dielectric metasurface(MDPI, 2023-02-01) Hajian, H.; Rukhlenko, I. D.; Bradley, A. L.; Özbay, EkmelAmong the transitional metal dichalcogenides (TMDCs), molybdenum disulfide (MoS2) is considered an outstanding candidate for biosensing applications due to its high absorptivity and amenability to ionic current measurements. Dielectric metasurfaces have also emerged as a powerful platform for novel optical biosensing due to their low optical losses and strong near-field enhancements. Once functionalized with TMDCs, dielectric metasurfaces can also provide strong photon–exciton interactions. Here, we theoretically integrated a single layer of MoS2 into a CMOS-compatible asymmetric dielectric metasurface composed of TiO2 meta-atoms with a broken in-plane inversion symmetry on an SiO2 substrate. We numerically show that the designed MoS2-integrated metasurface can function as a high-figure-of-merit ((Formula presented.)) van der Waals-based biosensor due to the support of quasi-bound states in the continuum. Moreover, owing to the critical coupling of the magnetic dipole resonances of the metasurface and the A exciton of the single layer of MoS2, one can achieve a (Formula presented.) enhanced excitonic absorption by this two-port system. Therefore, the proposed design can function as an effective biosensor and is also practical for enhanced excitonic absorption and emission applications. © 2023 by the authors.Item Open Access In pursuit of barrierless transition metal dichalcogenides lateral heterojunctions(Institute of Physics Publishing, 2018) Aierken, Y.; Sevik, C.; Gülseren, Oğuz; Peeters, F. M.; Çakir, D.There is an increasing need to understand interfaces between two-dimensional materials to realize an energy efficient boundary with low contact resistance and small heat dissipation. In this respect, we investigated the impact of charge and substitutional atom doping on the electronic transport properties of the hybrid metallic-semiconducting lateral junctions, formed between metallic (1T and 1Td) and semiconducting (1H) phases of MoS2 by means of first-principles and non-equilibrium Green function formalism based calculations. Our results clearly revealed the strong influence of the type of interface and crystallographic orientation of the metallic phase on the transport properties of these systems. The Schottky barrier height, which is the dominant mechanism for contact resistance, was found to be as large as 0.63 eV and 1.19 eV for holes and electrons, respectively. We found that armchair interfaces are more conductive as compared to zigzag termination due to the presence of the metallic Mo zigzag chains that are directed along the transport direction. In order to manipulate these barrier heights we investigated the influence of electron doping of the metallic part (i.e. 1Td-MoS2). We observed that the Fermi level of the hybrid system moves towards the conduction band of semiconducting 1H-MoS2 due to filling of 4d-orbital of metallic MoS2, and thus the Schottky barrier for electrons decreases considerably. Besides electron doping, we also investigated the effect of substitutional doping of metallic MoS2 by replacing Mo atoms with either Re or Ta. Due to its valency, Re (Ta) behaves as a donor (acceptor) and reduces the Schottky barrier for electrons (holes). Since Re and Ta based transition metal dichalcogenides crystallize in either the 1Td or 1T phase, substitutional doping with these atom favors the stabilization of the 1Td phase of MoS2. Co-doping of hybrid structure results in an electronic structure, which facilities easy dissociation of excitons created in the 1H part.Item Open Access Nanoscience for sustainable energy production(2011) Ataca, CanHydrogen economy towards the utilization of hydrogen as a clean and sustainable energy source has three ingredients. These are (i) hydrogen production; (ii) hydrogen storage; and (iii) fuel cells. Optimization of fuel cells for desired applications is a challenging engineering problem. The subject matter of my thesis is to develop nanostructures and to reveal physical and chemical mechanisms for the production of free hydrogen and its high capacity storage. The predictions of this study are obtained from rst-principles density functional theory and nite temperature molecular dynamics calculations, phonon calculations and transition state analyses. Recent studies have revealed that single layer transition metal oxides and dichalcogenides (MX2; M:Transition metal, X:Chalcogen atom) may o er properties, which can be superior to those of graphene. Synthesis of single layer free standing MoS2 and its nanoribbons, fabrication of transistor using this nanostructure, active edges of akes of MoS2 taking a part in hydrogen evolution reaction (HER) boost the interest in these materials. The electronic, magnetic, mechanical, elastic and vibrational properties of three-, two- and quasi one-dimensional MoS2 are investigated. Dimensionality e ects such as indirect to direct band gap transition, shift of phonon modes upon three- to two- dimensional transition, half metallic nanoribbons are revealed. Functionalization of single layer MoS2 and its nanoribbons are achieved by creating vacancy defects and adatom adsorption. Moreover, out of 88 di erent combinations of MX2 compounds (transition metal dichalcogenides) it is also predicted that more than 50 single layer, free standing MX2 can be stable in honeycomb like structures and o er novel physical and chemical properties relevant for hydrogen economy. It is predicted that H2O can be split spontaneously into its constituents O and H at speci c vacancy defects of single layer MoS2 honeycomb structure. Interacting with the photons of visible light, H atoms adsorbed to two folded S atoms surrounding the vacancy start to migrate and eventually form free H2 molecules, which in turn, are released from the surface. Not only taking a part in HER, but also it is shown that MoS2 as a catalyst can release H2 molecule from water. Also other possible candidates among the manifold of stable MX2 compounds, which are capable of presenting similar catalytic activities are deduced. In an e ort to obtain a high capacity hydrogen storage medium, the functionalization of graphene with adatoms is investigated. It is found that Li-graphene complex can serve as a high capacity hydrogen storage medium. A gravimetric storage capacity of 12.8 wt % is attained, whereby each Li atom donates the significant part of its charge to graphene and eventually attracts up to four H2 through a weak interaction. Similarly Ca adatoms can hold H2 molecule on graphene up to 8.4 wt % through an interesting mechanism involving charge exchange among Ca, graphene and H2.