Binary mixtures of self-assembled monolayers of 1,8-octanedithiol and 1-octanethiol for a controlled growth of gold nanoparticles

The physical response of gold nanoparticles, e.g. electronic, magnetic, and photonic behaviours due to quantum confinement effects, does not only depend on their size, but also on the shape and the density of the nanoparticles and therefore on the probability for the formation of clusters of nanoparticles. Nanocluster-based devices are envisioned as the next generation in electronics miniaturization. Organometallic chemical vapor deposition (OMCVD) is a straight forward method to grow these kinds of Au nanoparticles and clusters covatently attached on self-assembled monolayers (SAMs) carrying nucleation sites for particle growth. The control of density and location of these nucleation sites is a crucial point for the development of new nanoparticle based devices. The OMCVD particles grown here are nucleated by -SH groups at the head group of a SAM. Therefore, it is important to control and understand structure, order, composition, and lateral distribution of the SH-terminated molecules in a templating SAM for OMCVD grown gold nanoparticles. This paper presents a characterization of self-assembled monolayers of 1-octanethiol (C8-T) and 1,8-octanedithiol (C8-DT) and their binary mixtures immobilized on gold substrates using contact angle investigations, spontaneous desorption time-of-flight mass spectrometry (SD-ToF-MS) and X-ray photoelectron spectroscopy (XPS). We examined the relationship between the molar ratio of C8-T and C8-DT molecules in solution versus their corresponding molar ratio in the binary mixed SAMs and the ratio between standing up and lying down species of C8-DT. The growth of gold nanoparticles was investigated with respect to the dilution of the nucleation sites in the templating SAM. Influences on the growth velocities were found depending on the amount of available nucleation sites. (C) 2006 Elsevier B.V. All rights reserved.