Construction of semiconductor nanoparticle layers on gold by self-assembly technique

Cadmium sulfide (CdS) nanoparticles were prepared using the Aerosol-OT (AOT)/heptane inverse-micelle method. The particle size was controlled by changing the [H2O]/[AOT] ratio in the preparation process to be ca. 3 nm, which was estimated from their absorption maximum (ca. 385 nm) and absorption edge (ca. 450 nm) in heptane solutions. Self-assembled monolayers (SAMs) of alpha,omega-dithiols were prepared on (Ill)-oriented gold substrates. They were highly stable in aqueous solutions and showed a blocking effect toward electron exchange between the gold substrate and the electroactive species in the solution. Mono-and multi-layers of CdS nanoparticles were prepared by immersing the SAM-covered gold substrates in a heptane solution containing CdS particles. Infrared reflection-absorption spectra revealed that CdS particles on SAMs were surrounded by AOT and that a sequential immersion procedure led to the alternately layered structure of CdS particles and dithiol molecules.