Influence of HSiO1.5 Sol-Gel Polymer Structure and Composition on the Size and Luminescent Properties of Silicon Nanocrystals

We report the preparation of SiO2-embedded silicon nanocrystals (Si-NCs) from the thermal processing of sol-gel polymers derived from trichlorosilane (HSiCl3). Straightforward addition of water to HSiCl3 generates a cross-linked (HSiO1.5)(n) sol-gel polymer suitable for the generation of bulk quantities of SiO2-embedded Si-NCs. It is shown that structural differences between the present (HSiO1.5)(n) polymer and hydrogen silsesquioxane (HSQ) result in controllable differences in the resulting oxide-embedded Si-NCs produced from these precursors. A polymer structure/NC size relationship is further delineated through the preparation and evaluation of methyl-modified (HSiO1.5)(n)(CH3SiO1.5)(m) (m << n, m + n = 1) sol-gel copolymers, in which a low concentration of methyl groups acts as a polymer network modifier and influences the formation of Si-NCs during thermal processing. Si-NC size is readily tailored by controlled variations to peak processing temperature for (HSiO1.5)(n) and composition (n and m) for (HSiO1.5)(n)(CH3SiO1.5)(m). Furthermore, the present Si-NCs exhibit size-dependent photoluminescence (PL) in accordance with the principles of quantum confinement. Freestanding Si-NCs are obtained through chemical etching of the oxide matrix and exhibit tunable PL throughout the visible spectrum.