On the aggregation phenomena of Au nanoparticles: Effect of substrate roughness on the particle size

A monolayer of chemically prepared gold nanoparticles (AuNPs, with an initial average particle size of 2.3 nm) was immobilized on three Au substrates with different roughness. 1,4-Benzenedimethanethiol (BDMT) was used as the immobilizing binder to connect the AuNPs to the underlying Au substrates. Surprisingly, the AuNPs were found to aggregate during their immobilization to different extents depending on the substrate roughness. Transmission electron microscopy (TEM), atomic force microscopy (AFM), and UV–vis spectrophotometry were used to probe the aggregation phenomena of AuNPs in the solution phase (i.e., before immobilization) and after being anchored on the different Au substrates. The extent of AuNPs’ aggregation is inversely proportional to the Au substrate roughness (which is directly related to the surface coverage of the self-assembled monolayer (SAM) of the BDMT binder). AuNPs with average particle size of 4.0, 5.5 and 8.0 nm were obtained upon the immobilization onto Au substrates with roughness factor of 3.07, 2.49 and 1.1, respectively.