Synthesis and functionalization of silicon nanocrystals by means of non-thermal plasmas

A gas-phase, non-thermal plasma approach for the synthesis of silicon quantum dots is presented. An alternative surface passivation technique is the grafting of organic molecules onto the hydrogen-terminated surface of the as-produced nanocrystals. Two different approaches were studied for this purpose. The first approach is a liquid-phase thermal reaction. The silicon particles have been collected on the usual stainless steel filter, then sonicated into a 5:1 mixture of mesitylene and 1-dodecene. The transfer from the system to the solution is done under air-exclusion by using a nitrogen purged glove bag mounted onto the system exhaust line. The liquid-phase reaction proceeds at the solvent boiling temperature and a clear colloidal solution of silicon nanoparticles is obtained in a few minutes. After hydrosilylation the particles can be dried and redispersed into non-polar solvents. The improved liquid-phase processibility of the material makes it very interesting for printed electronics applications. For liquid-phase hydrosilylated material, quantum yield values are presented exceeding 60% for samples with a peak emission wavelength around 800 nm. The second approach for the passivation of the silicon nanoparticle surface is a gas-phase approach. Gas-phase treatment avoids the use of solvents from the production scheme and allows a significant reduction in production time. The use of a second non-thermal plasma to provide the necessary reaction activation energy is presented. The same molecule used for the liquid-phase passivation, 1-dodecene, is fed into a second-stage plasma reactor using a bubbler system. This is an abstract of a paper presented at the AIChE Annual Meeting (Salt Lake City, UT 11/4-9/2007).