Surface chemistry of aerosolized silicon nanoparticles: evolution and desorption of hydrogen from 6-nm diameter particles.

The surface chemistry of pristine, 6-nm silicon nanoparticles has been investigated. The particles were produced in an RF plasma and studied using a tandem differential mobility analysis apparatus, Fourier transform infrared spectroscopy (FTIR), time-of-flight secondary ion mass spectrometry (ToF-SIMS), and transmission electron microscopy. Particles were extracted from the plasma, which operates at approximately 20 Torr, into an atmospheric pressure aerosol flow tube, and then through a variable-temperature furnace that could be adjusted between room temperature and 1200 degrees C. DMA measurements show that freshly generated silicon particles shrink with heating, with particle diameters decreasing by approximately 0.25 nm between 350 and 400 degrees C. FTIR results indicate that freshly generated particles are primarily covered with SiH2 groups and smaller amounts of SiH and SiH3. Spectra recorded as a function of heating temperature indicate that the amount of surface hydrogen, as measured by the intensity of modes associated with SiH, SiH2, and SiH3, decreases with heating. ToF-SIMS measurements also suggest that hydrogen desorbs from the particles surfaces over the same temperature range that the particles shrink.