Si boride-coated Si nanoparticles with improved thermal oxidation resistance

Abstract

A new fabrication technique is devised to synthesize conformal Si core-shell nanoparticles (NPs) with Si boride nanoshell by reacting the surface atoms of Si NPs (50-200nm diameter) with a molten salt of sodium borohydride. The shell layer, about 10-20nm thick, consists of a mixture of crystalline phase (SiBx) and other amorphous phases as identified by TEM and EELS analysis. New absorbance peaks for Si-Si boride core-shell NPs appear at the wavenumber of 940 and 777-677cm-1 in FT-IR analysis. TGA analysis reveals that the core-shell structured Si-Si boride NPs exhibit a remarkably improved resistance to thermal oxidation by a factor of 4.6 at 750°C and at by a factor of 3.5 at 850°C compared to bare Si. Optical measurements show that spectrally selective coating (SSC) layers made of Si-Si boride NPs have a superior optical stability to that of the bare Si NPs after annealing at high temperature, and desirably exhibit a lower reflectance in the visible spectrum range than the bare Si NPs. These surface-protected, oxidation-resistant semiconductor materials and their novel fabrication methods exhibit further broad applicability of boride nanolayers which can be used for high temperature applications such as solar thermal power generation. © 2014 Elsevier Ltd.