Heat capacity measurements of two-dimensional self-assembled hexadecanethiol monolayers on polycrystalline gold

Abstract

The melting characteristics of hexadecanethiol two-dimensional self-assembled monolayers (SAMs) grown on polycrystalline Au surfaces are obtained via heat capacity measurements using nanocalorimetry at scanning rates of ∼30 000°C∕s. The analyzed amount of alkanethiol in the form of SAMs is typically in the 10−11 mol range. Melting occurs over a broad (full width on the half height ∼100°C) temperature range with a melting temperature of about 70°C, if the alkanethiol is partially desorbed from the Au surface during thermal treatment. SAMs in their as-deposited state without desorption have melting temperatures above 100°C. The heat of fusion is about 20kJ∕mol. Partial desorption of the alkanethiol is directly observed. The melting characteristics of three-dimensional SAMs on Au nanoparticles are comparable to earlier studies using conventional calorimetry.