Adsorption of heptanethiol on Cu(110)

The adsorption kinetics of heptanethiol [CH3(CH2)(6)SH] on Cu(110) and the ordering of monolayer films prepared by ultrahigh vacuum vapor deposition have been studied by means of thermal-desorption spectroscopy, X-ray photoelectron spectroscopy, low-energy electron diffraction, and scanning tunneling microscopy. Below 200 K, heptanethiol is found to grow in multilayers for which a molecular binding energy of 63 kJ/mol was determined. The formation of the chemisorbed monolayer takes place via a physisorbed precursor. Heating the chemisorbed layer leads to a dissociative desorption of the alkyl chain with an enthalpy of 117 kJ/mol. In contrast to the rather disordered physisorbed overlayer, several superstructures for the various coverages have been observed for the chemisorbed phase. Heating the saturated monolayer to 350 K results in a well-ordered ((4)(-1)(0)(2)) structure.