The silicon nanocrystals (SiNCs) were prepared using a plasma synthesis technique. Untreated SiNCs, which have hydrogen on the surface, oxidize when exposed to air. These NCs have a poor photoluminescent quantum yield (PLQY). They degrade further upon environmental exposure. Previously, the group has demonstrated SiNCs passivated with 1-dodecene that exhibit PLQY exceeding 60%. However, these materials degrade sharply on exposure to air and UV.

The scientists added a second stage to the plasma system, which allowed the surface of the SiNC to be treated in situ in a low-power SF6 plasma. These F-terminated SiNCs oxidize quickly in air. In a surprising development, the team found that SiNCs covered with a fluorinated silicon oxide shell have remarkable environmental stability with respect to exposure to air, UV irradiation and heat, while retaining PL quantum yields of up to ~50%.

These NCs also have much lower trap densities, as measured by electron spin resonance, compared with hydrogen-terminated NCs, both as-produced and after native oxide growth. The results suggest that the inclusion of fluorine into the silicon-oxide shell produces a more relaxed silicon-oxide network, which plays a critical role in improving the photostability.

Additional information can be found in journal Nanotechnology.