Fabrication and characterization of CdS-nanoparticle mono- and multilayers on a self-assembled monolayer of alkanedithiols on gold

Mono- and multilayers of cadmium sulfide (CdS) nanoparticles were fabricated on a gold substrate covered with alkanedithiol self-assembled monolayers (SAMs) by an alternate immersion of the substrate into ethanolic solutions of dithiol, i.e., 1,6-hexanedithiol or 1,10-decanedithiol, and dispersion of CdS nanoparticles (ca. 3 nm in diameter), the latter of which was prepared in sodium bis(2-ethylhexyl)sulfosuccinate (Aerosol OT, AOT)/H₂O/heptane reversed micelles. A layer-by-layer structure of dithiol SAM and CdS monolayer was confirmed with Fourier transform infrared reflection - absorption spectroscopy (FT-IRRAS) and X-ray photoelectron spectroscopy (XPS) at each step of composite-film preparation. It was revealed that CdS nanoparticles on SAMs were surrounded by AOT, which was then substituted by dithiols when the film was treated with the dithiol solution. The amount of CdS nanoparticles on the sample was measured by inductively coupled plasma mass spectrometry (ICP-MS) to be consistent with the above-mentioned monolayer structure. The photoinduced anodic current was observed when the composite film was immersed in an electrolyte solution containing triethanolamine as an electron donor. An action spectrum, which was quite similar to the absorption spectrum of CdS dispersion, indicates that the CdS nanoparticle keeps its size without mutual aggregation, and semiconducting properties even after being immobilized on the substrate.