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Nanocrystalline silicon (nc-Si) particles have been extremely expected for the photo-electronics and biology applications because they are harmless, low environmental impact and visible luminescent materials. We have been prepared the solution dispersible nc-Si particles in order to apply them to various kinds of application fields. The luminescent intensity from the nc-Si particles was drastically degraded by aging after several hours under the dispersion of particles into pure water. This was caused by the termination of unstable chemical element on the surface of nc-Si particles. In this study, the surface of nc-Si particles was passivated with a hydrogen, carbon or oxygen atoms to improve the stability of luminescence in pure water. The correlation between the surface composition and luminescent property of each surface-passivated nc-Si particles will be discussed.
The nc-Si particles with an average size of 2.5 nm were formed in an oxidized layer by sputtering of target material and post-annealing at high temperature. The target materials of the hydrogen or oxygen-passivated samples used 36 pieces of Si chips placed on silica glass, while that of the carbon-passivated one utilized 36 pieces of Si chips and 4 pieces of graphite chips placed on silica glass. The sample, which was prepared by cosputtering of Si chips/silica glass targets, then, was treated in a hydrofluoric (HF) acid steam to effectively passivate the surface of nc-Si particles with the hydrogen atoms. The oxygen-passivation onto the surface of nc-Si particles was carried out by exposing the hydrogen-passivated sample to air for 2 days. Each sample was immersed in pure water for several days.
The hydrogen- or carbon-passivated samples resulted in the degradation of intensity of red luminescence with the progress of day, because of the formation of non-radiative related defects due to desorption of hydrogen or carbon atoms from the particle surface. On the other hand, the oxygen-passivated sample showed stable red luminescence in pure water for several days. This was attributed to the formation of Si-O bonds with high chemical resistance onto the particle surface.
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