Mühendislik Fakültesi

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Citation - WoS: 107
Citation - Scopus: 111
Determination of Complete Melting and Surface Premelting Points of Silver Nanoparticles by Molecular Dynamics Simulation
(Amer Chemical Soc, 2013) Yavuz, M.; Zhou, Y.; Alarifi, H. A.; Atis, M.; Ozdogan, C.; Hu, A.
A molecular dynamics simulation based on the embedded-atom method was conducted at different sizes of single-crystal Ag nanoparticles (NPs) with diameters of 4 to 20 nm to find complete melting and surface premelting points. Unlike the previous theoretical models, our model can predict both complete melting and surface premelting points for a wider size range of NPs. Programmed heating at an equal rate was applied to all sizes of NPs. Melting kinetics showed three different trends that are, respectively, associated with NPs in the size ranges of 4 to 7 rim, 8 to 10 nm, and 12 to 20 nm. NPs in the first range melted at a single temperature without passing through a surface premelting stage. Melting of the second range started by forming a quasi-liquid layer that expanded to the core, followed by the formation of a liquid layer of 1.8 nm thickness that also subsequently expanded to the core with increasing temperature and completed the melting process. For particles in the third range, the 1.8 nm liquid layer was formed once the thickness of the quasi-liquid layer reached S rim. The liquid layer expanded to the core and formed thicker stable liquid layers as the temperature increased toward the complete melting point. The ratio of the quasi-liquid layer thickness to the NP radius showed a linear relationship with temperature.
Citation - WoS: 27
Citation - Scopus: 31
The Effects of Lattice Motion on Eley-Rideal and Hot Atom Reactions: Quasiclassical Studies of Hydrogen Recombination on Ni(100)
(Amer Chemical Soc, 2002) Guvenc, ZB; Sha, XW; Jackson, B
Quasiclassical methods are used to simulate the interactions of H or D atom beams with D- or H-covered Ni(100) surfaces. The Ni substrate is treated as a multilayer slab, and the Ni atoms are allowed to move. The model potential energy surface is fit to the results of detailed total-energy calculations based on density functional theory. Most of the incident atoms trap to form hot atoms, which can eventually react with an adsorbate, or dissipate their energy and stick. The incident atom is found to lose several tenths of an eV of energy into the metal, upon initially colliding with the surface. This limits reflection to a few percent, at all coverages, and secondary reactions between adsorbates are significantly lowered. Long time hot atom reactions are also found to be damped out by the inclusion of lattice motion, leading to increased sticking, even at high coverages where dissipation into the adsorbates should be the primary energy loss mechanism. Overall, the inclusion of lattice motion is found to improve agreement with experiment.
Citation - WoS: 158
The Unusually Stable B100 Fullerene, Structural Transitions in Boron Nanostructures, and a Comparative Study of Α- and Γ-Boron and Sheets
(Amer Chemical Soc, 2010) Mukhopadhyay, S.; Hayami, W.; Guvenc, Z. B.; Pandey, R.; Boustani, I.; Ozdogan, C.
Solid alpha-B-12 rhombohedral and gamma-B-28 orthorhombic boron as well as boron nanostructures in the form of spheres, sheets, and multirings beside a ring consisting of icosahedral B-12 units were investigated using ab initio quantum chemical and density functional methods. The structure of the 131(x) fullerene exhibits unusual stability among all noninteracting free-standing Clusters, and is more stable than the 13120 cluster fragment of the gamma-B-28 solid, recently predicted and observed by Oganov et al. (Nature 2009, 457, 863). In addition, we compared the stability of the multirings and reported the structural transition from double-ring to triple-ring systems. This structural transition Occurs between B-52 and B-54 Clusters. We confirm that the noninteracting free-standing triangular buckled-sheet is more stable than the gamma-sheet, assembled in this work, and than the a-sheet, proposed by Tang and Ismail-Beigi (Phys. Rev. Lett. 2007, 99, 115501). In contrast, however, when these sheets are considered as infinite periodic systems, then the a-sheet remains the most stable one.

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