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: 14Citation - Scopus: 12Photocatalytic Hydrogen Energy Evolution From Sugar Beet Wastewater(Wiley-VCH Verlag, 2021) Orak, Ceren; Yüksel, AslıHydrogen is a clean, environmentally friendly, storable, and sustainable green energy source as well as a potential fuel. It could be produced from various biomass, wastewater, or other sources by different processes. In this study, hydrogen was evolved from sucrose model solution and real sugar beet wastewater by photocatalytic oxidation using a perovskite catalyst under solar light irradiation. In this context, firstly, the graphene supported LaFeO3 (GLFO) was synthesized and then, a characterization study shows that GLFO is successfully synthesized. To optimize the reaction parameters (pH, catalyst loading, and initial hydrogen peroxide concentration), an experimental matrix was created using the Box Behnken model. Whereas the highest hydrogen evolution from sucrose model solution was observed as 3520 μmol/gcat, the highest hydrogen evolution from sugar beet wastewater was obtained as 7035 μmol/gcat. The highest TOC removal (99.73 %) from sugar beet wastewater was also achieved at the same reaction conditions.Article Citation - WoS: 8Citation - Scopus: 10Microstructures and Mechanical Properties of Graphene Platelets-Reinforced Spark Plasma Sintered Tantalum Diboride-Silicon Carbide Composites(IOP Publishing, 2019) Gürcan, Kübra; İnci, Ezgi; Saçkan, İbrahim; Ayaş, Erhan; Gasan, HakanGraphene nanoplates reinforcement (GNPs) TaB2-SiC composites were fabricated with Spark Plazma sintering (SPS) at 1850 degrees C with a-uniaxial pressure of 50 MPa and 10 min dwell time. Systematic investigation on the effect of GNP amount of densification, microstructural and mechanical properties (microhardness and fracture toughness) of the composites were presented. Density and hardness of composites decreased with the addition of GNP, while similar to 35% increase of fracture toughness value was obtained with GNP addition. The microstructural evaluation indicated that overlapped and agglomerated GNPs increased with an increasing amount of GNP in the composites and caused to decrease of density and hardness. On the other hand, GNP was retained in the composite form even with high process temperature (1850 degrees C) and cause toughening of composites with changing the fracture mode from transgranular to transgranular/intergranular fracture. GNP pull out, crack branching, crack bridging and crack deflection were observed as main toughening mechanisms.Article Citation - WoS: 5Citation - Scopus: 5Defect Induced Anderson Localization and Magnetization in Graphene Quantum Dots(Elsevier, 2018) Altıntaş, Abdulmenaf; Güçlü, Alev DevrimWe theoretically investigate the effects of atomic defect related short-range disorders and electron-electron interactions on Anderson type localization and the magnetic properties of hexagonal armchair graphene quantum dots using an extended mean-field Hubbard model and wave packet dynamics for the calculation of localization lengths. We observe that randomly distributed defects with concentrations between 1 and 5% of the total number of atoms leads to localization alongside magnetic puddle-like structures. Although the localization lengths are not affected by interactions, staggered magnetism and localization are found to be enhanced if the defects are distributed unevenly between the sublattices of the honeycomb lattice.Article Citation - WoS: 4Citation - Scopus: 4Effect of Aromatic Sams Molecules on Graphene/Silicon Schottky Diode Performance(Electrochemical Society, Inc., 2016) Yağmurcukardeş, Nesli; Aydın, Hasan; Can, Mustafa; Yanılmaz, Alper; Mermer, Ömer; Okur, Salih; Selamet, YusufAu/n-Si/Graphene/Au Schottky diodes were fabricated by transferring atmospheric pressure chemical vapor deposited (APCVD) graphene on silicon substrates. Graphene/n-Si interface properties were improved by using 5-[(3-methylphenyl)(phenyl) amino]isophthalic acid (MePIFA) and 5-(diphenyl)amino]isophthalic acid (DPIFA) aromatic self-assembled monolayer (SAM) molecules. The surface morphologies of modified and non-modified films were investigated by atomic force microscopy and scanning electron microscopy. The surface potential characteristics were obtained by Kelvin-probe force microscopy and found as 0.158 V, 0.188 V and 0,383 V as a result of SAMs modification. The ideality factors of n-Si/Graphene, n-Si/MePIFA/Graphene and n-Si/DPIFA/Graphene diodes were found as 1.07, 1.13 and 1.15, respectively. Due to the chain length of aromatic organic MePIFA and DPIFA molecules, also the barrier height φB values of the devices were decreased. While the barrier height of n-Si/Graphene diode was obtained as 0.931 eV, n-Si/MePIFA/Graphene and n-Si/DPIFA/Graphene diodes have barrier height of 0.820 and 0.720 eV, respectively.Article Citation - WoS: 26Citation - Scopus: 26Theory of Optical Properties of Graphene Quantum Dots(John Wiley and Sons Inc., 2016) Özfidan, Işıl; Güçlü, Alev Devrim; Korkusinski, Marek; Hawrylak, PawelWe present here a theory of the optical properties of graphene quantum dots (GQDs) with tunable band gaps by lateral size confinement, from UV to THz. Starting from the Hartree-Fock ground state, we construct the correlated many-body ground and excited states of GQDs as a linear combination of a finite number of electron-hole pair excitations. We discuss the evolution of the band gap with size and its renormalization by self-energy and excitonic effects. We calculate and analyze the dipole moments of graphene quantum dots that possess a degenerate valence and conduction band edge, and construct a characteristic exciton and biexciton spectrum. We find an exciton band consisting of a pair of robust, spin singlet bright exciton states and a band of dark, spin singlet and spin triplet, exciton states at lower energies. We predict a characteristic band of biexciton levels at the band edge, discuss the Auger processes and identify a biexciton-exciton cascade. Our theoretical results are compared with experimental linear absorption and non-linear transient absorption spectra of colloidal GQDs. We next discuss the optical properties of triangular GQDs with zigzag edges whose magnetic moment can be controlled by gates. The control over the magnetic moment through carrier density manipulation results in optical spin blockade and gate tunable optical properties over a wide range of photon energies.Article Citation - WoS: 8Citation - Scopus: 9Sublattice Engineering and Voltage Control of Magnetism in Triangular Single and Bi-Layer Graphene Quantum Dots(John Wiley and Sons Inc., 2016) Güçlü, Alev Devrim; Potasz, P.; Hawrylak, PawelWhen a Dirac electron is confined to a triangular graphene quantum dot with zigzag edges, its low-energy spectrum collapses to a shell of degenerate states at the Fermi level leading to a magnetized edge. The shell degeneracy and the total magnetization are proportional to the edge size and can be made macroscopic. In this review, we start with a general discussion of magnetic properties of graphene structures and its relation to broken sublattice symmetry. Then, we discuss single electronic properties of single and bilayer triangular graphene quantum dots, focusing on the nature of edge states. Finally, we investigate the role of electronic correlations in determining the nature of ground state and excitation spectra of triangular graphene quantum dots as a function of dot size and filling fraction of the shell of zero-energy states. The interactions are treated by a combination of tight-binding, Hartree-Fock and configuration interaction methods. We show that the spin polarization of the triangular graphene quantum dots can be controlled through gating, i.e., by adding or removing electrons. In bilayer graphene dots, the relative filling of edge states in each layer and the magnetization can be tuned down to single localized spin using an external vertical electrical field.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.