Decorating thin film solar cells with plasmonic nanoparticles is being pursued, in order to improve device efficiency through increased scattering and local field enhancement. Gold nanoparticles are in particular interesting, due to their chemical inertness and plasmon resonance in the visible range of the spectrum. In this work, gold nanoparticles fabricated by a gas aggregation nanoparticle source and embedded in a-Si (a commercial solar cell material) are studied using x-ray photo-electron spectroscopy, transmission electron microscopy, electron energy-loss spectroscopy and energy dispersive X-ray spectroscopy. The formation of gold silicide around the nanoparticles is investigated, as it has important consequences for the optical and electronic properties of the structures. Differently from previous studies, in which the silicide formation is observed for gold nanoparticles and thin films grown on top of crystalline silicon or silica, it is found that silicide formation is largely enhanced around the nanoparticles, owing to their increased surface/volume ratio. A detailed gold silicide formation mechanism is presented based on the results, and strategies for optimizing the design of plasmonically enhanced solar cells with gold nanoparticles encapsulated in a-Si are discussed.