Simulating the formation of Pt nanostructures utilizing molecular dynamic calculations
Wessels, Leon Adolf Leopold
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Platinum (Pt) is an important catalyst for applications such as catalytic converters. In this thesis the formation of platinum nanoparticles was investigated by means of simulations. For the first part of the thesis a molecular dynamics simulation using the Sutton-Chen potential was implemented. This program was used for the simulations. Low energy structures were found. It was found that the number of nearest neighbours are maximised in the low energy structures. The energy barriers that have to be overcome as atoms move around the structures were also calculated. A model is proposed for the prediction of energy barriers. The model is useful for understanding the factors that influence the energy barriers and thus the mobility of atoms. The model will also be useful for Monte Carlo simulations. Simulations were done modelling physical vapour deposition onto the Pt(111) surface and a graphite surface represented by the Steele potential. It was found that higher temperatures and lower evaporation rates lead to lower energy structures. The smaller interaction between the graphite surface and the Pt leads to structures that have more layers. The parameters of the Steele potential that determine nearest neighbour distance and interaction strength between Pt and the substrate were adjusted to simulate other materials. It was found that a mismatch between the nearest neighbour distance of the substrate and Pt causes an increase in the mobility of the Pt atoms on the surface. The results of the simulations will enable the choice of suitable substrate and experimental parameters for the growth of Pt nanoparticles of desired shapes.