We present a gas-phase, non-thermal plasma approach for the synthesis of silicon quantum dots. Silicon is non-toxic to the human body, cheap, abundant, and compatible with the current micro-electronic technology, and thus presents many advantages with respect to other quantum dot materials, such as CdSe. The research in the field of silicon quantum dots has suffered from the lack of a synthesis technique capable of producing high-quality nanocrystals. Liquid-phase synthetic routes produce samples with a broad size distribution and with poor crystalline fraction. Gas-phase synthesis techniques are affected by fast particle agglomeration rates, which make it difficult to produce very small silicon crystals. Silane-containing non-thermal plasmas are well known to be prone to gas-phase nucleation of particles. Dust nucleated in non-thermal plasmas is well-known to acquire a negative charge, and the resulting Coulomb interaction between the particles greatly reduces the agglomeration rate. Moreover, the particle temperature can largely exceed the background gas temperature because of the recombination of ions and electrons at the particle surface and because of reactions with gas-phase radicals. This allows obtaining high-quality single-crystal particles. The reactor that we have developed consist of a 3/8” OD, 1/4” ID quartz tube with two ring electrodes mounted outside of the tube. An argon-silane-hydrogen mixture is fed into the system and a radiofrequency (RF) signal is applied to the electrodes, resulting in gas-breakdown and formation of a plasma. The system is a continuous flow-through reactor; particles are extracted from the plasma by aerodynamic drag and deposited on a filter downstream of the discharge. The mass yield of the system has been determined by measuring the mass of the reactor quartz tube and the mass of the filter before and after collection. From mass spectroscopy measurements we know that the reactor consumes completely the silane that is fed into the system. Half of the silicon mass introduced in the reactor as silane is converted into a film deposited onto the reactor wall and half is converted into particles. The measured mass yield can be as high as 50 mg/hour of material that has visible photoluminescence after oxidation in air. Extensive TEM analysis suggests that the process is capable of producing very small (<5 nm) crystallites, and it confirms that quantum confinement effects should be observed from the plasma-produced silicon nanocrystals. The quantum yield of the fluorescent particles, defined as the ratio of the number of photons emitted in the visible over the number of UV photons absorbed by the sample, has been measured using an integrating sphere and a USB spectrometer (Ocean Optics USB2000). A UV-LED emitting at 390 nm is used to excite the particle fluorescence. The hydrogen-termination of the plasma produced silicon nanocrystals does not prevent surface oxidation, and the quantum yield of the surface-oxidized silicon nanoparticles rarely exceeds 10%. It is in fact well known that the growth of a native oxide is associated with the formation of defects at the Si/SiOx interface. An alternative surface passivation technique is the grafting of organic molecules onto the hydrogen-terminated surface of the as-produced nanocrystals. Two different approaches have been explored 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 we report quantum yield values 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. Our approach to the problem is to use a second non-thermal plasma to provide the necessary reaction activation energy. The same molecule used for the liquid-phase passivation, 1-dodecene, is fed into a second-stage plasma reactor using a bubbler system. Particles produced in the first stage are dragged by the flow into the second stage where the in-flight hydrosilylation takes place. The in-flight grafted material is soluble in non-polar solvents without any further processing. When the particles are collected on the stainless steel filter they are heavily agglomerated, but the agglomerates dissolve into the solvent and freestanding particles are present in solution. FTIR data will be presented confirming that for gas-phase treated particles 1-dodecene has reacted with the particle surface, since the IR absorption spectrum from the in-flight hydrosilylated material practically overlaps with the IR absorption spectrum from the liquid-phase treated material. Unfortunately the quantum yield of the in-flight hydrosilylated material is typically <10%, and further annealing is necessary to improve the optical properties. The gas-phase reactor is undergoing further development to obtain silicon nanoparticles that are readily soluble after gas-phase production and that have optical properties as good as those of the liquid-phase reacted particles.