Surface plasmon resonance method for probing interactions in nanostructures: CdS nanoparticles linked to Au and Ag substrates by self-assembled hexanedithiol and aminoethanethiol monolayers

Self-assembled hexanedithiol (HDT) and aminoethanethiol (AET) monolayers (S AMs), similar to0.4-0.8 nm in thickness, are used to link similar to5 nm di am CdS nanoparticles covalently and electrostatically onto Au and Ag substr ates. The resulting nanostructures are probed with scanning electron micros copy (SEM) and surface plasmon resonance (SPR) measurements. The CdS nanopa rticle-SAM-substrate interactions manifesting themselves in the dielectric functions of the multilayered systems, are detected in the SPR data, and ar e discussed in terms of a phenomenological six-layer model. The SPR respons e of the Ag substrate is more sensitive to neighboring interactions than th e Au substrate. The SEM images show that the CdS, connected either by HDT o r AET onto Ag substrates, forms crystalline structures. The interactions re sponsible for this crystallization are absent in samples employing Au subst rates, in which case only similar to5 nm diam CdS nanoparticles are detecte d by SEM. The experimental results of the present article, analyzed in deta il using Fresnel and Maxwell equations, demonstrate how the SPR technique c an be used to characterize layered nanostructured materials. (C) 2001 Ameri can Institute of Physics.