Silicon nanocrystals (NCs) 8-10 nm in diameter are grown on SiO 2 surfaces in an ultrahigh-vacuum chamber using hot wire chemical vapor deposition. These NCs are subjected to varying exposures of deuterated ammonia (ND 3 ). The surface chemistry of Si NCs is studied using X-ray photoelectron (XP) spectroscopy and temperature-programmed desorption (TPD). The dissociative adsorption of ND 3 on Si NCs results in the formation of ND 2 species prior to TPD, and Si 3 N (nitride) formation is observed after TPD. D 2 desorption is observed only from the monodeuteride species at 780 K. In separate experiments, a hot tungsten filament is used to predissociate ND 3 before adsorption on the NC surface. XP spectra reveal that ND 2 species form initially, and as the dose is increased, ND species dominate. After TPD, a Si x N y species is observed. D 2 desorption is observed from the mono-, di-, and trideuteride species when ND 3 is predissociated. Irrespective of the technique used for dosing ammonia, TPD spectra do not contain any ND 3 fragments, indicating that the ND 2 species are not thermally stable on the NC surface. The photoluminescence (PL) emitted from Si NCs (diameter ∼ 4.1 nm) is reported for an excitation wavelength of 405 nm. PL is observed only when the hot filament is used to predissociate ND 3 , and this can be attributed to the presence of di-and trideuteride species on the nanocrystal surface, which results in better passivation.
Silicon (Si) nanocrystals (NCs) less than 5 nm in diameter are grown on SiO 2 surfaces using hot wire chemical vapor deposition, and the dangling bonds and the reconstructed bonds at the NC surface are passivated and transformed with D and ND x by using deuterated ammonia (ND 3 ), which is predissociated over a hot filament. At low hot wire ND 3 doses, photoluminescence (PL) emission is observed from a defect state at 1000 nm corresponding to reconstructed surface bonds capped by predominantly monodeuteride and Si-ND 2 species. As the hot wire ND 3 dose is increased, di-and trideuteride species form, and intense PL is observed around 800 nm, which does not shift with NC size and is associated with defect levels resulting from ND x insertion into the strained Si-Si bonds forming Si 2 dND. A clean bandgap can be realized with fully relaxed and fully terminated NC surfaces consisting of di-and trideuterides and SiND 2 .
SECTION Nanoparticles and Nanostructures
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