Luminescent Silicon Nanoparticles: An improved inverse micelle synthesis and oxide-dependent photoluminescence studies

The luminescence of silicon nanoparticles has been an active area of study for a number of years. These nanoparticles luminesce when excited by ultraviolet (UV) light in the ~340 nm region, displaying either a blueish or a reddish colour. The control and origin of these colours has been debated, with researchers such as Veinot, Kauzlarich and Tilley claiming that the luminescence can be controlled with the use of nitrogen. In this thesis, a new synthetic procedure is presented that improves upon the established inversemicelle technique by replacing the methanol or ethanol quenching agent with copper chloride. It is found that this new technique lowers the level of surface oxide present in the form of alcohols on the surface of the nanoparticles, giving blue luminescent particles with improved surfaces for further chemistry. Photoluminescence studies are also performed on samples of silicon nanoparticles synthesised by electrochemical etching, using a variety of oxygen-containing compounds to probe the behaviour of the photoluminescence spectrum. It is found that there are typically five Gaussian peaks present in a typical spectrum; occurring at 405 nm, 430 nm, 460 nm 485-90 nm, 500 nm, and 640 nm, subsequently labelled a, b, g, e, and z . It is also found that molecular oxygen increases the b peak and suppresses the z peak, and that water has the opposite effect on these two peaks. It is shown that the peaks a, b, and z are all due to a single site on the surface of the silicon nanoparticle, corresponding to the cases when the site is oxide-free, occupied by molecular oxygen, and water, respectively. It is also hypothesised that the luminescence can be controlled via the use of compounds of different sizes and polarities, with electron-withdrawing molecules increasing the blue luminescence, and electron-donating molecules increasing the red. g and e are used as normalising peaks to compare between samples, and are not affected by oxygen