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Öğe 13 Atomlu Cu-Au-Pt Üçlü Metal Nanoalaşımların Yapısal Özellikleri(2019) Taran, SongülBu çalışmada, 13 atomlu Cu-Au-Pt üçlü metal nanoalaşımların yapısal özellikleri, üç farklı kompozisyon sistemiele alınarak incelenmiştir. Cu1AunPt12-n, Au1CunPt12-n ve Pt1CunAu12-n üçlü metal kompozisyonların en kararlıyapıları Basin-Hopping algoritması kullanılarak elde edilmiştir. Tüm kompozisyonlarda ikosahedral yapıgözlenmiştir. Bu ikosahedral yapıların merkezini Cu ve Au atomuna göre daha yüksek yüzey ve bağlanmaenerjisi olan Pt atomu oluşturmuştur.Öğe Alloying Effect on the Local Atomic Pressures of Nanoclusters(2020) Taran, SongülIn this study, simulations were performed to investigate local atomic pressures of icosahedral nanoclusters with 55 atoms. Before analyzing the local atomic pressures, the best chemical ordering structures were obtained using Monte Carlo Basin-Hopping algorithm within Gupta potential. Binary and ternary alloying effect on the local atomic pressures of mono, binary and ternary nanoclusters formed by Cu, Ag and Pt atoms was investigated in detail. It was obtained that adding one atom of second alloying metal in pure nanoclusters and also third alloying metal in binary nanoalloys can change the local atomic pressure due to locating tendency in the icosahedral structure. Also, it was observed that adding a smaller atom at the central site of the icosahedral structure exhibits decreasing of core stress.Keywords: nanocluster, alloying, simulation, atomic pressureÖğe Composition effect on melting behaviors of Cu-Au-Pt trimetallic nanoalloys(Elsevier, 2019) Taran, SongülIn this study, molecular dynamics simulations were performed on 55-atom icosahedral Cu13AunPt42-n, Au13CunPt42-n and Pt13AunCu42-n (n = 1-41) nanoalloys. In order to present the composition effect on the melting behaviors in detail, three different icosahedral compositions corresponding to Cu13Au13Pt29, Au13Cu29Pt13 and Pt13Au29Cu13 were selected from Cu13AunPt42-n, Au13CunPt42-n and Pt13AunCu42-n, nanoalloy systems. The temperature dependence of the caloric curve, Lindemann index, heat capacity and root mean square displacement methods was analyzed thoroughly to clarify the simulation results. The simulation results showed that the melting temperature is closely associated with the composition and also atomic distribution of the nanoalloys. It was observed that Au atoms are generally more movable than Cu and Pt atoms in Cu-Au-Pt trimetallic nanoalloys with increasing temperature. Moreover, the Lindemann index variations of second and third layers showed that pre-melting of shell occurs especially for Au13Cu29Pt13 and Pt13Au29Cu13 nanoalloys in these three compositions.Öğe ConPdm ve ConAum (nm100) Nanoalaşımlarının MgO(001) Yüzeyi Üzerindeki Yapısal Özelliklerinin İncelenmesi(2018) Taran, Songül; Arslan, HaydarBu çalışmada, MgO(001) yüzeyi üzerinde desteklenen ConAum(nm100) ve ConPdm(nm100) ikili metalnanoalaşımlarda Co atom oranının %10 ile %90 arasında değiştirilmesi sonucu her bir kompozisyonun yapısalözellikleri incelenmiştir. İkili metal nanoalaşımların global minimum(GM) yapıları Basin-Hopping optimizasyonyöntemi ile elde edilmiştir. Atomlar arası etkileşmeleri inceleyebilmek için Gupta çok cisim potansiyel enerjifonksiyonu kullanılmıştır. Optimizasyonu yapılan ConAum ve ConPdm ikili metal nanoalaşımların MgO(001)yüzeyi üzerindeki yapısal özelliklerinde Au ve Pd atomlarının sebep olduğu benzerlik ve farklılıklar incelenmiştir.Ayrıca, nanoalaşımların yüzey üzerindeki epitaksiyel yerleşimleri de ele alınmıştır.Öğe Double parallel barrier height behavior of Au/Poly (linoleic acid)-g-poly (methyl methacrylate) (PLiMMA)/n-Si structure(Pergamon-Elsevier Science Ltd, 2019) Gökçen, Muharrem; Taran, SongülThe main electrical parameters and current conduction mechanisms of Au/Poly (linoleic acid)-g-poly (methyl methacrylate)/n-Si diode were carried out in the range of 300 K-400 K with a temperature increment of 10 K. Two distinct linear regions were observed in semi-logarithmic current-voltage (I-V) plots for each investigated temperature. For each linear region, leakage currents, barrier heights and ideality factors which are main electrical parameters of the diode were extracted from the experimental I-V measurements. Also, interface state density was derived by Card and Rhoderick's function. To obtain effective current conduction mechanisms, lnI versus lnV plots were obtained by taking into account of double linear region of current-voltage plots and abnormal increasing of barrier height and ideality factor at above the room temperature.Öğe The effect of Co substitution on the stability and magnetic behavior of FeAg nanoalloys(Elsevier, 2022) Taran, Songül; Arslan, HaydarIn this research the structural and magnetic properties of 19-atom Fe-Co-Ag trimetallic nanoalloys have been investigated systematically. In the study, both empirical potentials (EP) and DFT approaches on Fe2ConAg17-n nanoalloys have been performed. For this reason, the global minimum structures and a few low-energy isomers optimized by EP are subjected to DFT reoptimization. It has been found that the double icosahedron structure is the lowest energy configuration for trimetallic Fe2ConAg17-n nanoalloys and fixed two Fe atoms are preferentially located in the inner sites of the nanoalloys. It has also been found that total magnetic moment increases in general and a wide range of magnetic moment values can be obtained by alloying with Co atoms. It is also clear that the local magnetic moments and the local charges of the constituent atoms are well correlated with the composition and the local coordination of the Co atoms.Öğe MgO(001) Yüzeyi Üzerinde Desteklenen AuN, PdN ve 1:1 Oranına Sahip (AuPd)N (N50, 100, 150, 200) Nano Atom Yığınlarının Yapısal Özellikleri(2017) Taran, Songül; Arslan, HaydarBu çalışmada, MgO(001) yüzeyi üzerinde desteklenen toplam atom sayısı N 50,100, 150 ve 200 olan Au ve Pd atom yığınlarıile atom sayısı bakımından 1:1 (%50-%50) oranına sahip AuPd ikili metal nanoalaşımların yapısal özellikleri incelenmiştir. Teklive ikili metal atom yığınlarının en kararlı yapılarını veren global minimumları Basin-Hopping optimizasyon yöntemi kullanılarakincelenmiştir. Basin-Hopping algoritmasında kararlı durumlar çalkalama hareketi (move shake) yötemi ile araştırılmıştır. Au, Pd atomyığınlarının ve Au-Pd nanoalaşımların global minimum yapıları incelenirken atomlar arası etkileşmelerde Gupta çok cisim potansiyelenerji fonksiyonu kullanılmıştır. Optimizasyonu yapılan nanoparçacıkların MgO(001) yüzeyi üzerindeki epitaksiyel yerleşimleri vekoordinasyon sayıları nano parçacık büyüklüğüne bağlı olarak incelenmiştir.Öğe A molecular dynamics study: structural and thermal evolution of 147 atom ComAun nanoalloys(Springer, 2019) Arslan, Haydar; Garip, Ali Kemal; Taran, SongülIn this study, the classical molecular dynamics simulations in canonical ensemble conditions (NVT) were used to investigate the dynamical properties of bimetallic Co-Au nanoalloy clusters with the interatomic interactions modeled by Gupta many-body potential. Global optimizations were performed using basin-hopping algorithm for all compositions of 147 atom Co-Au bimetallic clusters. A structure based on icosahedron was obtained for the majority of the compositions. Structural analysis results showed that lower surface and cohesive energy of Au atoms give rise to Au atoms on the surface sites preferably. The global minimum structures were taken as the initial configurations for MD simulations. We obtained caloric curves and also Lindemann parameters to investigate melting transitions. In general, the melting temperatures were fluctuated around 675K for Au-rich compositions and 750K for Co-rich compositions.Öğe Theoretical study of the structures and chemical ordering of CoPd nanoalloys supported on MgO(001)(World Scientific Publ Co Pte Ltd, 2016) Taran, Songül; Garip, Ali Kemal; Arslan, HaydarMetal nanoalloys on oxide surface are a widely studied topic in surface science and technology. In this study, the structures of CoPd nanoalloys adsorbed on MgO(001) have been searched by basin-hopping global optimization method within an atomistic model. Two different sizes (34 and 38 atom) have been considered for all compositions of CoPd/MgO(001) nanoalloys. Co and Pd atoms, for all the compositions, have cube-on-cube (001) epitaxy with substrate at interface. For both sizes, we have found that Pd rich composition nanoalloys have three layers, Co rich composition nanoalloys have four layers in morphology. Excess energy and second difference in energy analyzes have been performed to investigate the relative stability of nanoalloys with respect to their size and composition.
