| AVS 56th International Symposium & Exhibition | |
| Applied Surface Science | Wednesday Sessions |
| Session AS+NS-WeM |
| Session: | Nanoparticle and Nanoscale Surface Chemistry II |
| Presenter: | N. Salivati, University of Texas at Austin |
| Authors: | N. Salivati, University of Texas at Austin J.G. Ekerdt, University of Texas at Austin |
| Correspondent: | Click to Email |
Although silicon nanostructures exhibit size dependent light emission, which can be attributed to quantum confinement, the role of surface passivation has not yet been fully understood. Since the ratio of surface atoms to the total number of atoms is large in nanoscale systems, surface effects play an important role in determining the electronic properties. Uncompensated dangling bonds at the surface establish localized defect states within the forbidden gap of silicon nanocrystals, providing sites for non-radiative recombination of excitons. Defect states are also associated with surface reconstructions that minimize the number of dangling bonds but result in severe distortion of the surface bonds. An effective way of capping the remaining dangling bonds is by using atomic hydrogen or deuterium. Si nanocrystals less than 8 nm in diameter are grown on SiO2 surfaces in an ultra high vacuum chamber and the as grown surfaces are exposed to atomic deuterium. Desorption spectra are interpreted using analogies to Si (100). TPD spectra show that the nanocrystal surfaces are covered by a mix of monodeuteride, dideuteride and trideuteride species. The manner of filling of the deuteride states on nanocrystals differs from that for extended surfaces as the formation of the dideuteride and trideuteride species is facilitated by the curvature of the nanocrystal. Etching of the nanocrystal surface is observed during TPD, which is a confirmation of the presence of trideuteride species on the nanocrystal surface. No photoluminescence (PL) is observed from the as grown unpassivated nanocrystals. As the deuterium dose is increased, the PL intensity also begins to increase. Strong PL is observed only when the nanocrystals are covered with trideuteride species. The trideuteride species helps in reducing the surface stress and this is expected to enhance PL. When the deuterium dose is increased beyond a point the surface structure breaks down and amorphization of top layer of the nanocrystal takes place. Amorphization reduces the PL intensity. Finally, as the nanocrystal size is varied, the PL peak shifts, which is characteristic of quantum confinement.