Evaporation and decomposition of acrylic acid grafted luminescent silicon quantum dots in ultrahigh vacuum

A thin film of silicon quantum dots (Si-QDs) is a potential thermoelectric material with a high figure of merit. Evaporation and deposition in ultrahigh vacuum is a novel method to produce such a thin film of high quality. Acrylic acid grafted luminescent Si-QDs have been synthesized by a simplified method. Their surface electronic core levels were investigated by X-ray photoelectron spectroscopy (XPS) at various temperatures. At room temperature, three components at 100.4, 102, and 104.4 eV were identified, corresponding to Si core, Si-C, and silicon oxide on surface, respectively. The appearance of Si-C component showed that acrylic acid has been successfully grafted onto Si-QDs surface. At 200° C, intact evaporation took place and the ratios of silicon to carbon in core levels remained constant as the annealing time increased. Decomposition occured at 340°C, where the ratios of Si2p to C1s began to change. The XPS results are in agreement with thermogravimetric analysis (TGA) measurements which showed a sharp weight loss of 80% at 200° C, which is the intact evaporation temperature. Another slow weight loss of 14% took place between 300°C and 500°C, which is a footprint of surface Si-C decomposition.