Preparation of large scale monolayers of gold nanoparticles on modified silicon substrates using a controlled pulling method

The preparation of large scale monolayers of gold nanoparticles on modified silicon substrates for use in storage media is reported. Gold nanoparticles were synthesized in reverse microemulsions using the surfactant cetyltrimethylammonium bromide (CTAB). Dodecanethiol was then attached to the surface of the particles, which were subsequently purified by liquid phase extraction. The formation of nanoparticle monolayers was accomplished by vertically pulling various modified silicon substrates at controlled speeds from nanoparticle solutions. The silicon substrates used were 1 cm(2) in size, had silanol and hydrogen terminated surfaces, had surfaces chemically modified by (CH3)(3)SiNHSi(CH3)(3) and (CH3O)(3)Si(CH2)(2)-(CF2)(7)CF3, and one was coated with amorphous carbon. All of these substrates have different surface polarities. The effects of the substrate pulling speed and solvent were also investigated. The results assessed using atomic force microscopy (AFM) indicated that the surface modification was the most significant factor. Silanol terminated silicon substrates were found to have very low coverage, and the carbon fluoride modified substrates, very high monolayer coverage. It was also found that lowering the substrate pulling speed and using higher boiling point solvents favored monolayer formation, and by optimizing these factors, a 95% monolayer coverage on the carbon fluoride modified substrate has been achieved. Conclusions from the results about the mechanism of the monolayer formation are also discussed.