Multilayers of 4-methylbenzenethiol functionalized gold nanoparticles fabricated by Langmuir–Blodgett and Langmuir–Schaefer deposition

Langmuir films of gold nanoparticles functionalized by 4-methylbenzenethiol on a water subphase were studied. Multilayers on Si and glass substrates were successfully fabricated by both the Langmuir–Blodgett (LB) and Langmuir–Schaefer (LS) deposition techniques. The multilayers were characterized by UV–vis spectroscopy, X-ray photoelectron spectra (XPS), spectroscopic ellipsometry and tapping mode AFM. Thickness measurements by XPS and ellipsometry showed that the multilayers formed from both techniques displayed a linear increase of film thickness with the number of layers, indicating a reproducible deposition process. However, it is found that the average thickness increase after each LS stroke is about double of that in the LB transfer, indicating two monolayers were deposited in one LS stroke. AFM data revealed that the films deposited at different surface pressures exhibit different morphology. The films generally showed less defects and larger domain size at higher surface pressure. It is also found that films prepared using LS technique are more uniform and smoother than the LB films prepared under similar conditions. The possible nanoparticle deposition mechanisms of LB and LS techniques have been discussed.