Application of microplasma to synthesis of silicon nanoparticles

We developed microplasma to synthesize nanocrystalline silicon particles (nc-Si). Gas residence time in micro plasma reactor is of the order of $\mu $s, while time required for particle nucleation by three-body collision? is about ms. Thus it is possible to separate crystal nucleation and growth in a single reactor. This process is very important for synthesis nc-Si. Microplasma was formed in a capillary tube of diameter 470 $\mu $m which is connected to the VHF power source. We used Ar/SiCl$_{4}$ mixtures for nc-Si source for safety. H$_{2}$ was added to convert exhausted Cl to HCl. Electron density of micro plasma (N$_{e})$ was estimated by Stark broadening of H$_{\beta }$, and found that N$_{e}$ is 1-3*10$^{15}$ cm$^{-3}$. Rotation temperature was measured to be approximately 1500 K. Intensity ratio of Si(288 nm)/Ar(750 nm) increased linearly with increasing initial concentration of SiCl$_{4}$. If the residence time was 30 $\mu $s, particle nucleation seemed to start in the discharge region, and particles keep growing involving impurity elements such as N or Cl. On the other hand, when residence time was set to shorter than 10 $\mu $s, the amount of impurities can be minimized. Under this condition, Raman spectra showed crystalline silicon peak around 520 cm$^{-1}$. TEM image also indicated the size of synthesized nc-Si to be in the range of 4-20 nm.