Amorphous silicon (a-Si) is an important industrial material. It is used widely in electronic devices such as thin-film transistors (TFTs). Solar energy generation also relies heavily on a-Si for mass produced photovoltaic cells. Amorphous silicon is prepared via chemical vapour deposition (CVD) from silanes (e.g. SiH4), in which small, unsaturated silicon clusters are short-lived gas-phase intermediates. Significantly, such clusters are incorporated into the bulk a-Si and are critical in determining fundamental properties of the material, such as optical and electronic band-gaps. Crucial details of structure and bonding in these clusters are elusive.We propose to build on the emerging chemistry of isolable, stable unsaturated silicon clusters. Using a novel systematic synthetic approach, we will prepare stable unsaturated silicon cluster compounds as models for the unsaturated clusters present in CVD processes. We will exploit the reactivity of these compounds to use them as solution-phase nucleation sites for cluster expansion. The electronic and photo-physical characteristics of these compounds will be investigated, shedding light on the analytically elusive clusters present in a-Si.We will use unsaturated silicon clusters as gas-phase nucleation sites for the CVD of a-Si (Cluster Assisted Silicon CVD - CASi-CVD). By depositing a-Si from gas phase mixtures of silanes and our novel clusters we will be able to control the concentration and properties of the residual unsaturated clusters in the a-Si produced. Improved control over these parameters is directly relevant to industry: it would allow improved materials for semi-conducting electronics and solar-energy generation. Such advances would increase the global competitiveness of the EU.The fellow will gain high quality training in main group chemistry and materials chemistry (deposition of a-Si) as well as complementary skills training that will equip the fellow for a top level independent research career.