Electrochemical detection of the thermal stability of n-alkanethiolate monolayers on Au(111)

Abstract

The thermal stability of alkanethiolate monolayers of different chain lengths was investigated on Au(1 1 1) by means of electrochemical reductive desorption and AC impedance measurements. The thermal desorption was performed by heating the freshly prepared monolayers between 298 and 573 K in a home-built device under a nitrogen atmosphere. The samples were then transferred to an electrochemical cell and were examined by means of AC impedance spectroscopy and reductive desorption experiments at 298 K. The electrochemical experiments allowed an accurate detection of the coverage of alkanethiolate molecules as a function of heating temperature. The electrochemical detection of the thermal stability allowed us to determine the desorption temperature and the activation energy barrier for the desorption process without the need for ultra-high vacuum (UHV) conditions. The energy barriers for the desorption process are nearly insensitive to the chain length. Density function theory calculations including van der Waals (vdW) interactions were performed to obtain some insights into the nature of the desorption process. We conclude that the monolayer is in a disordered liquid state prior to desorption with most vdW interactions broken.