Functional nanostructures and nanocomposites - numerical modeling approach and experiment

Abstract

This chapter reports numerical models devoted to predict the optical and vibrational properties of nanoparticles treated as isolated objects or confined in host matrixes. The theoretical data obtained by the numerical simulations were confronted with the experimental investigations carried out by several spectroscopic methods such as Raman, IR, and UV-Vis absorption as well as photoluminescence. As model cluster systems, the physical properties of nanosized silicon carbide (SiC) particles in vacuum were numerically modeled. The computer simulations were also performed for SiC confined in polymeric matrix, namely, poly(methyl methacrylate), poly-N-vinylcarbazole, and polycarbonate. The obtained host- guest nanocomposites exhibit original optical and electro-optical features. The considered systems were built using molecular dynamic simulations method and the full atomistic modeling of the composite materials was performed using CVFF method. The equilibrated geometries of nanocomposites were used to evaluate their key physical features. Particularly, the electronic and vibrational properties of SiC were calculated in the cluster approach model. The suitable cluster size and the nature of terminating bonds used to saturate the outermost nanograin surface were judiciously evaluated with the criterion to achieve consistent agreementwith experimental results such as IR absorption, Raman, vibrational density of states and photoluminescence responses. The role of SiC clusters and its interaction with the surrounding polymer were investigated for the hybrid host-guest nanocomposites and their electro-optical functionalitieswere evaluated.The polarizability and first-order hyperpolarizabilities responsible for second harmonic generation and Pockels effect were calculated using DFT method.Then, taking into account the environmental interaction between host and guest molecules the optical susceptibilities were predicted.The effect of the local electric fields involved at the organic-inorganic interfaces on the NLO parameters was taken into account for each system.Additionally it was found that polymer environment reconstructs the surface of the SiC nanograin, which contributes critically to the NLO properties of hybrid materials. Finally, the chapter shows in exhaustive way that the developed methodologies associating key experimental works and relevant numerical methods allows to tailor the suitable nanostructured materials with the optimal physical responses.