Structures of a Long-Chain n-Alkane, n-C44H90, on a Au(111) Surface: An Infrared Reflection Absorption Spectroscopic Study

Abstract

Vacuum-deposited films of a long-chain n-alkane, n-C44H90, tetratetracontane (TTC), on a Au(111) surface were investigated by infrared reflection absorption spectroscopy. We found four different structures for TTC on the Au surface. One is a “flat-on” structure formed by molecules in an all-trans conformation with the molecular plane composed of carbon atoms parallel to the surface. This structure was found in the first monolayer physisorbed on the surface. The second structure includes the gauche conformation, which shows a change in the orientation of the methylene groups with an increase in the thickness of TTC. The third structure is the crystalline state formed by all-trans molecules, which was found in the third and thicker layers with the molecular long axis parallel to the surface. These three structures were found for films deposited and measured at room temperature. With an increase in temperature after deposition at room temperature, the first and second structures were easily converted to anot...