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Previous issue date: 2016-08-08 === In this work, molecular dynamics simulations of thin organic films irradiated by fast heavy ions were implemented. In order to represent the ion energy deposition, it was used a Thermal Spike Model, in which the ion track is represented as a cylindrical region with high temperature. Two papers were submitted for publication based on this study. In the first paper, it was studied the impact of film thickness and the ion energy in the topological effects of radiation (such as crater diameter, crater depth and rim volume) and in the sputtering, comparing the results for a crystalline and amorphous solids modeled by the Lennard-Jones potential. In the second paper, the FENE potential was implemented to build samples with molecular chains. The ionic radiation effects were then compared between films with molecular chains (modeled by the FENE potential) and without molecular chains (using the Lennard-Jones potential). In both works, the effects of radiation were explained by analyzing the different mechanisms of energy dissipation: evaporation, melt flow and plastic deformation. Our results show that radiation effects are strongly determined by film thickness. The simulations with FENE potential show that the presence of molecular chains reduces significantly the effects of radiation. In solids thinner than the mean gyration radius of the sample, there was not any radiation effect, indicating that the effect reduction is related not only to the decreasing of mobility but also to molecular conformation and entanglement. === Nesse trabalho foram realizadas simula??es computacionais por din?mica molecular de filmes finos org?nicos irradiados por ?ons pesados e r?pidos. Para representar a deposi??o de energia pelo ?on foi utilizado o Modelo de Thermal Spike, atrav?s do qual a trilha i?nica ? representada como uma regi?o cil?ndrica de alta temperatura ao longo do material. Dois artigos foram submetidos para publica??o a partir desse estudo. No primeiro artigo, o impacto da espessura do filme e da energia do ?on incidente nos efeitos topol?gicos da radia??o (como di?metro da cratera, profundidade da cratera e volume da protuber?ncia) e do sputtering foram investigados, comparando-se os resultados de s?lidos cristalinos e amorfos modelados pelo potencial de Lennard-Jones. No segundo artigo, o potencial FENE foi implementado para construir amostras com cadeias moleculares. Os efeitos da radia??o i?nica foram ent?o comparados entre os filmes com cadeias moleculares (modelados pelo potencial FENE) e filmes sem cadeias moleculares (modelados com o potencial de Lennard-Jones). Em ambos os trabalhos, os efeitos da radia??o foram explicados verificando-se os diferentes mecanismos de dissipa??o de energia: evapora??o, melt flow e deforma??o pl?stica. Nossos resultados mostram que os efeitos da radia??o s?o fortemente impactados pela espessura do filme. As simula??es com o potencial FENE mostram que a presen?a de cadeias moleculares reduz significativamente todos os efeitos da radia??o. Para s?lidos mais finos que o raio de gira??o m?dio das mol?culas, nenhum efeito da radia??o foi observado, indicando que a redu??o dos efeitos est? relacionada n?o s? ? diminui??o de mobilidade, mas tamb?m ? conforma??o e emaranhamento molecular.
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