Au@MO2 (M = Ti, Zr, Si) Films by Ex Situ Incorporation Approach

Au NPs (average diameter similar to 20 nm) incorporated MO2 (M = Ti, Zr and Si) films on glass substrate were synthesized using an ex situ approach. Au NPs were first synthesized and then incorporated into the respective alkoxide derived sols with control of pH. The Au plasmon band was red-shifted in cases of Au@TiO2 and Au@ZrO2 films after annealing at 300 and 500 degrees C mainly due to the increase of refractive index (RI) with matrix crystallizations. Au@SiO2 film showed decrease in RI after annealing, and consequently the Au plasmon was blue-shifted. All heat-treated films appeared spot-free, optically homogeneous and colorful. The surface hardness of heat-treated Au@TiO2 and Au@ZrO2 films were >2H and 4H, respectively. The heat-treated Au@TiO2 and Au@ZrO2 films showed strong anatase TiO2 and cubic ZrO2 crystalline phases, respectively whereas in case of Au@SiO2, silica remained amorphous and porous.