Solution-Deposited Gold Nanoparticles on a Sulfur-Terminated Self-Assembled Monolayer

Abstract

Methods to deposit nanoparticles on surfaces are needed for future manufacturing of electronic devices and coatings with applications in aerospace, biosensors, and solar cells. In this study, gold nanoparticles were deposited from solution on a silica substrate that was coated with an organosilane self-assembled monolayer. Gold nanoparticles with nominal diameters of 13 nm were synthesized in water as seed particles to grow into 50 nm diameter particles through citrate reduction. The silica substrate was hydroxylated and a layer of 3-mercatoptopropyltrimethoxysilane (MPTMS) was deposited providing a sulfur terminal group to adhere the nanoparticles to the surface. The substrate was dip coated in the aqueous gold nanoparticle solution. This study investigated a mixture of sulfuric acid and hydrogen peroxide and dilute nitric acid to hydroxylate the surface, an anneal prior to depositing the silane, and the time in the MPTMS deposition bath to form an adhesion layer on the surface. The layers and surface were characterized with ellipsometry, goniometry, UV-Vis, AFM, SEM, XPS, and EDS. A UV-vis peak at 527 nm confirmed that gold nanoparticles were present in the deposition solution. Ellipsometry and goniometry showed that the average MPTMS thickness was 6.9 ± 1.8 Å and the contact angle was 23°. Gold nanoparticles were visible on the surface in the AFM and SEM images and were about 40-50 nm in diameter. XPS and EDS did not detect gold nanoparticles on the surface due to contamination and low resolution. However, the XPS spectra survey did identify strong sulfur peaks at 226.4 eV and 162.0 eV and a carbon peak at 284.0 eV. These strong sulfur and carbon states reveal a multitude of ligands on the surface for bonding with gold nanoparticles. The results demonstrate that gold nanoparticles can be deposited on an insulating surface and has applications in selective deposition of thin conductive layers to form wires or electrodes for devices.