Investigating silicon precursors
An interesting alternative to crystalline silicon is amorphous silicon that is widely used in electronic devices and in the mass photovoltaic cell production. It is grown by silane chemical vapour deposition (CVD), in which small, unsaturated silicon clusters are short-lived gas-phase intermediates. Scientists in the EU-funded project 'Stable unsaturated silicon clusters as nucleation sites in solution and the gas phase' (CASI-CVD) worked to prepare stable derivatives of unsaturated silicon clusters. Their aim was to further explore their chemistry and demonstrate their use as CVD precursors for amorphous silicon deposition. These clusters are critical in determining fundamental silicon properties, such as optical and electronic band-gaps. By using novel synthetic approaches, model stable unsaturated silicon cluster compounds were prepared. Project members exploited the compound reactivity to use them as solution-phase nucleation sites for cluster expansion, thus generating novel precursors for larger unsaturated cluster compounds. A remarkable solution-phase model for growing silicon clusters through unsaturated intermediates was discovered and studied in depth. Furthermore, significant results concerning the reaction chemistry of the smallest unsaturated silicon clusters — cyclotrisilenes — were obtained. CASI-CVD achieved the plurality of its planned objectives. To date, five high-profile publications have been produced.
