Facile and Efficient Gas-Phase Pressure-Controlled Thermal Functionalization of Nanocrystalline Porous Silicon with 1-Hexene

Abstract

Substitution of hydrogen at porous silicon (PSi) surface by organic groups can be done via thermally activated hydrosilylation reactions in which PSi is left for several hours into liquid alkenes at temperatures typically over 100°C. For alkenes whose boiling points are below 100°C (e.g. 1-heptene and shorter molecules), the process suffers from high reagent boiling and evaporation. Gas-phase hydrosilylation is an alternative when using short molecules. It has not been as extensively studied, and was mainly done in plasma reactors with silicon nanocrystals. Here we present a new method for facile gas-phase thermally-activated hydrosilylation in PSi, but using liquid solutions as reagent (1-hexene was used here). PSi and liquid alkene are loaded at room temperature into a chamber which is then closed and heated up to a temperature greater than the alkene boiling point. The effects of process temperature, time and pressure were investigated by means of Fourier transform infrared spectroscopy. The maximum theoretical derivatization efficiency was achieved with optimized parameters. The derivatization was uniform across the PSi layer depth. PSi luminescence was effectively stabilized by the process. The new gas-phase method presented here is facile, requires very small amount of liquid reagent, and is useful for attachment of short molecules to PSi or other materials surface.