Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 54Citation - Scopus: 53Nitrogen Doping for Facile and Effective Modification of Graphene Surfaces(Royal Society of Chemistry, 2017) Yanılmaz, Alper; Tomak, Aysel; Akbalı, Barış; Bacaksız, Cihan; Özçeri, Elif; Arı, Ozan; Senger, Ramazan Tuğrul; Selamet, Yusuf; Zareie, Hadi M.We report experimental and theoretical investigations of nitrogen doped graphene. A low-pressure Chemical Vapor Deposition (CVD) system was used to grow large-area graphene on copper foil, using ethylene as the carbon source. Nitrogen-doped graphene (N-graphene) was prepared by exposing the graphene transferred to different substrates to atomic nitrogen plasma. The effect of varying nitrogen flow rates on doping of graphene was investigated while keeping the power and time constant during the process. The N-graphene was characterized via Raman Spectroscopy, X-ray Photoelectron Spectroscopy (XPS), Scanning Tunneling Microscopy and Spectroscopy (STM and STS), and Fourier Transform Infrared spectroscopy (FTIR). Raman mapping of N-graphene was also performed to show homogeneity of nitrogen on the graphitic lattice. XPS results have revealed the presence of different nitrogen configurations in the graphitic lattice with similar doping concentrations. Density functional theory (DFT) based calculations showed that the periodic adsorption of N atoms predominantly occurs on top of the C atoms rather than through substitution of C in our N-graphene samples. Our results indicate a feasible procedure for producing N-graphene with homogenous and effective doping which would be valuable in electronic and optical applications.Article Citation - WoS: 58Citation - Scopus: 60Layer- and Strain-Dependent Optoelectronic Properties of Hexagonal Aln(American Physical Society, 2015) Keçik, Deniz; Bacaksız, Cihan; Senger, Ramazan Tuğrul; Durgun, EnginMotivated by the recent synthesis of layered hexagonal aluminum nitride (h-AlN), we investigate its layer- and strain-dependent electronic and optical properties by using first-principles methods. Monolayer h-AlN is a wide-gap semiconductor, which makes it interesting especially for usage in optoelectronic applications. The optical spectra of 1-, 2-, 3-, and 4-layered h-AlN indicate that the prominent absorption takes place outside the visible-light regime. Within the ultraviolet range, absorption intensities increase with the number of layers, approaching the bulk case. On the other hand, the applied tensile strain gradually redshifts the optical spectra. The many-body effects lead to a blueshift of the optical spectra, while exciton binding is also observed for 2D h-AlN. The possibility of tuning the optoelectronic properties via thickness and/or strain opens doors to novel technological applications of this promising material.Article Citation - WoS: 40Citation - Scopus: 40Nitrogenated, Phosphorated and Arsenicated Monolayer Holey Graphenes(Royal Society of Chemistry, 2015) Yağmurcukardeş, Mehmet; Horzum, Şeyda; Torun, Engin; Peeters, François M.; Senger, Ramazan TuğrulMotivated by a recent experiment that reported the synthesis of a new 2D material nitrogenated holey graphene (C2N) [Mahmood et al., Nat. Commun., 2015, 6, 6486], the electronic, magnetic, and mechanical properties of nitrogenated (C2N), phosphorated (C2P) and arsenicated (C2As) monolayer holey graphene structures are investigated using first-principles calculations. Our total energy calculations indicate that, similar to the C2N monolayer, the formation of the other two holey structures are also energetically feasible. Calculated cohesive energies for each monolayer show a decreasing trend going from the C2N to C2As structure. Remarkably, all the holey monolayers considered are direct band gap semiconductors. Regarding the mechanical properties (in-plane stiffness and Poisson ratio), we find that C2N has the highest in-plane stiffness and the largest Poisson ratio among the three monolayers. In addition, our calculations reveal that for the C2N, C2P and C2As monolayers, creation of N and P defects changes the semiconducting behavior to a metallic ground state while the inclusion of double H impurities in all holey structures results in magnetic ground states. As an alternative to the experimentally synthesized C2N, C2P and C2As are mechanically stable and flexible semiconductors which are important for potential applications in optoelectronics.Article Citation - WoS: 166Citation - Scopus: 170Mechanical Properties of Monolayer Gas and Gase Crystals(American Physical Society, 2016) Yağmurcukardeş, Mehmet; Senger, Ramazan Tuğrul; Peeters, François M.; Şahin, HasanThe 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.Article Citation - WoS: 105Citation - Scopus: 105Pentagonal Monolayer Crystals of Carbon, Boron Nitride, and Silver Azide(American Institute of Physics, 2015) Yağmurcukardeş, Mehmet; Şahin, Hasan; Kang, J.; Torun, E.; Peeters, François M.; Senger, Ramazan TuğrulIn this study, we present a theoretical investigation of structural, electronic, and mechanical properties of pentagonal monolayers of carbon (p-graphene), boron nitride (p-B2N4 and p-B4N2), and silver azide (p-AgN3) by performing state-of-the-art first principles calculations. Our total energy calculations suggest feasible formation of monolayer crystal structures composed entirely of pentagons. In addition, electronic band dispersion calculations indicate that while p-graphene and p-AgN3 are semiconductors with indirect bandgaps, p-BN structures display metallic behavior. We also investigate the mechanical properties (in-plane stiffness and the Poisson's ratio) of four different pentagonal structures under uniaxial strain. p-graphene is found to have the highest stiffness value and the corresponding Poisson's ratio is found to be negative. Similarly, p-B2N4 and p-B4N2 have negative Poisson's ratio values. On the other hand, the p-AgN3 has a large and positive Poisson's ratio. In dynamical stability tests based on calculated phonon spectra of these pentagonal monolayers, we find that only p-graphene and p-B2N4 are stable, but p-AgN3 and p-B4N2 are vulnerable against vibrational excitations.