Yazar "Van Duin, Adri C. T." seçeneğine göre listele

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    Development of the reaxff reactive force field for inherent point defects in the si/silica system
    (Amer Chemical Soc, 2019) Nayir, Nadire; Van Duin, Adri C. T.; Erkoç, Şakir
    We redeveloped the ReaxFF force field parameters for Si/O/H interactions that enable molecular dynamics (MD) simulations of Si/SiO2 interfaces and O diffusion in bulk Si at high temperatures, in particular with respect to point defect stability and migration. Our calculations show that the new force field framework (ReaxFF(present)), which was guided by the extensive quantum mechanical-based training set, describes correctly the underlying mechanism of the O-migration in Si network, namely, the diffusion of O in bulk Si occurs by jumping between the neighboring bond-centered sites along a path in the (110) plane, and during the jumping, O goes through the asymmetric transition state at a saddle point. Additionally, the ReaxFF(present) predicts the diffusion barrier of O-interstitial in the bulk Si of 64.8 kcal/mol, showing a good agreement with the experimental and density functional theory values in the literature. The new force field description was further applied to MD simulations addressing O diffusion in bulk Si at different target temperatures ranging between 800 and 2400 K. According to our results, 0 diffusion initiates at the temperatures over 1400 K, and the atom diffuses only between the bond-centered sites even at high temperatures. In addition, the diffusion coefficient of O in Si matrix as a function of temperature is in overall good agreement with experimental results. As a further step of the force field validation, we also prepared amorphous SiO2 (a-SiO2) with a mass density of 2.21 gr/cm(3), which excellently agrees with the experimental value of 2.20 gr/cm(3), to model a-SiO2/Si system. After annealing the a-SiO2/Si system at high temperatures until below the computed melting point of bulk Si, the results show that ReaxFF(present) successfully reproduces the experimentally and theoretically defined diffusion mechanism in the system and succeeded in overcoming the diffusion problem observed with Reax(FFsiOH)(2010), which results in O diffusion in the Si substrate even at the low temperature such as 300 K.
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    Effect of Nitrogen Doping and Oxidation of Graphene on the Deposition of Platinum from Trimethyl(methylcyclopentadienyl)platinum(IV)
    (American Chemical Society, 2022) Campbell, Ian E.; Nayir, Nadire; Van Duin, Adri C. T.; Mohney, Suzanne E.
    Materials composed of nitrogen-doped carbon are useful as catalyst supports due to their low cost, low density, and enhanced metal-support interaction. One way to synthesize catalytic single atoms and nuclei on these supports is via vapor phase deposition processes. Here, density functional theory (DFT) was used to evaluate the effects of N doping and oxidation of graphene on the adsorption and dissociation of trimethyl(methylcyclopentadienyl) platinum (MeCpPtMe3), which is a commonly used precursor in vapor deposition of platinum. DFT calculations confirmed that oxygen incorporation into graphene via oxidation of vacancies is thermodynamically favorable with and without N dopants. N doping was found to elongate substrate-oxygen bonds, thereby enhancing the interaction between MeCpPtMe3 and oxidized defective graphene. According to nudged elastic band calculations, MeCpPtMe3 dissociation on all oxidized substrates, with or without N doping, displayed positive enthalpies of reaction and activation energies. However, N doping drives the reactions by lowering the enthalpy of reaction and activation energy for the dissociation of MeCpPtMe3 and the enthalpy of reaction for the subsequent chemisorption of MeCpPtMe2, which was exothermic in all cases. Finally, the entire reaction beginning with MeCpPtMe3 and two unreacted oxidized monovacancies and ending with MeCpPtMe2 and a methyl group each bound to an oxidized monovacancy is exothermic for substrates containing pyridinic-N dopants. © 2022 American Chemical Society.
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    Role of tilt grain boundaries on the structural integrity of WSe2 monolayers
    (Royal Soc Chemistry, 2022) Sakib, Nuruzzaman; Paul, Shiddartha; Nayir, Nadire; Van Duin, Adri C. T.; Neshani, Sara; Momeni, Kasra
    Transition metal dichalcogenides (TMDCs) are potential materials for future optoelectronic devices. Grain boundaries (GBs) can significantly influence the optoelectronic properties of TMDC materials. Here, we have investigated the mechanical characteristics of tungsten diselenide (WSe2) monolayers and failure process with symmetric tilt GBs using ReaxFF molecular dynamics simulations. In particular, the effects of topological defects, loading rates, and temperatures are investigated. We considered nine different grain boundary structures of monolayer WSe2, of which six are armchair (AC) tilt structures, and the remaining three are zigzag (ZZ) tilt structures. Our results indicate that both tensile strength and fracture strain of WSe2 with symmetric tilt GBs decrease as the temperature increases. We revealed an interfacial phase transition for high-angle GBs reduces the elastic strain energy within the interface at finite temperatures. Furthermore, brittle cracking is the dominant failure mode in the WSe2 monolayer with tilted GBs. WSe2 GB structures showed more strain rate sensitivity at high temperatures than at low temperatures.