Surface control of optical properties in silicon nanocrystals produced by laser pyrolysis

Macroscopic quantities (g/h) of Si nanoparticles were prepared by laser pyrolysis of silane and showed photoluminescence (PL) emission in the range 700-1050 nm after oxidation in air at a temperature T ≥ 700 °C. Two different strategies were followed to reduce as-produced particle agglomeration which hinders most of the applications, namely etching with either acid or alkaline solutions. Well isolated single particles were detected after acid etching in HF. Disaggregation was also achieved by the combined effect of the high power sonication and alkaline etching by tetra-methyl ammonium hydroxide (TMAH), which leaves OH terminated surfaces. However, in both cases re-aggregation was observed within a few hours after oxide removal. Stable dispersions of Si nanoparticles in different solvents were obtained by treatments of H-terminated surfaces with the surfactant TOPO (C24H51PO, trioctylphospine oxide) and by treatment of OH-terminated surfaces with Na3PO4.