No abstract

Ligand-stabilized colloidal metallic nanoparticles are prized in science and technology for their electronic properties and tunable surface chemistry. However, little is known about the interplay between these two aspects of the particles. A particularly glaring absence concerns the density of electronic states, which is fundamental in explaining the electronic properties of solid-state materials. In part, this absence owes to the difficulty in the experimental determination of the parameter for colloidal systems. Herein, we demonstrate the density of electronic states for metallic colloidal particles can be determined from their magnetic susceptibility, measured using nuclear magnetic resonance spectroscopy. For this study, we use small alkanethiolate protected gold nanoparticles and demonstrate that changes in the surface chemistry, as subtle as changes in alkane chain length, can result inasmuch as a 3-fold change in the density of states at the Fermi level for these particles. This suggests that surface chemistry can be a powerful tool for controlling the electronic behavior of the materials to which they are attached, and suggests a paradigm that could be applied to other metallic systems, such as other metal nanoparticles, doped semiconductor systems, and even 2D metals. For all of these metallic systems, the Evans method can serve as a simple means to probe the density of states near the Fermi level.

We report on the reaction between methyltriethoxysilane (MTES) and micrometer-sized aluminum particles, facilitated by HCl. This reaction ultimately produces silane-coated aluminum particles. Using 27Al magic-angle spinning solid-state nuclear magnetic resonance, we find that aluminum powder starts with a mixture of tetrahedrally, pentahedrally, and octahedrally coordinated aluminum, with the pentahedral species dominating. In the presence of HCl, however, the aluminum undergoes a restructuring, so that octahedrally coordinated aluminum is the dominant species. Using diffuse reflectance infrared spectroscopy to confirm the deposition of silane, we find that this restructuring of the aluminum in the presence of HCl is both a sufficient and necessary condition for the deposition of the silane.