| AVS 54th International Symposium | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS1+NS-WeM |
| Session: | Plasmas in Nanotechnology |
| Presenter: | N.A. Brunelli, California Institute of Technology |
| Authors: | N.A. Brunelli, California Institute of Technology K.P. Giapis, California Institute of Technology |
| Correspondent: | Click to Email |
Size manipulation and control of nanoparticles produced from atmospheric-pressure microplasmas Atmospheric-pressure microdischarges have been shown to produce silicon nanoparticles between 1-2 nm in diameter, which exhibit intense photoluminescence emission at 420 nm with quantum efficiency of 30%.1 For imaging applications, it is desirable to have an emission at longer wavelengths which requires larger diameter nanoparticles. However, it has been exceedingly difficult to manipulate the nanoparticle size in a single microdischarge, where perturbations to the growth conditions seem to only influence the number of particles produced while the size remains invariant. We demonstrate here that the combination of a microdischarge with a CVD reactor can overcome this problem by achieving overgrowth of the seed particles produced in the microdischarge. For example, silicon nanoparticles can be enlarged from 2.5 nm to 3.5, 4.5 and 5 nm by mixing an additional 150, 300 and 600 ppm of sila4ne in argon, respectively. In fact, the CVD overgrowth allows not only tuning of the particle size but also permits selection of an alternate overgrowth layer, creating core-shell structures. Examples of Ge and Fe cores overgrown with Si will be shown. We quantify this claim by using a new ultrafine radial differential mobility analyzer immediately after the furnace to monitor in real-time the particle size. We characterize the nanoparticles by AFM, photoluminescence (PL) spectroscopy and transmission electron microscopy. As oxidation has been shown to affect the PL emission,2 we have encapsulated the particles in thin films to ensure observed light emission is from radiative recombination. Beyond enlarging the seed particle diameter, we demonstrate the synthesis of core-shell structures consisting of an inexpensive metallic core and a thin overlayer of catalytically active material as the shell. Electrochemical measurements demonstrate the catalytic activity and performance of Fe-Pt and Co-Pt core-shell nanoparticles for fuel cell type applications.
1 Sankaran, R. M., D. Holunga, et al. (2005). "Synthesis of blue luminescent Si nanoparticles using atmospheric-pressure microdischarges." Nano Letters 5(3): 537-541.
2 Biteen, J. S., N. S. Lewis, et al. (2004). "Size-dependent oxygen-related electronic states in silicon nanocrystals." Applied Physics Letters 84(26): 5389-5391.