Thermal-mechanical properties of a monomolecular film detected by a vibrating reed

Abstract

Thin films of organic materials are finding many applications in modern technology. The microelectronics industry, in particular, uses very thin organic films both as photoresists and as insulating layers. The ultimate in organic thin films is represented by molecular monolayers of the order of 2.0 nm thick as deposited by the Langmuir–Blodgett technique¹. By adapting a vibrating reed apparatus² we have investigated the thermal–mechanical properties of a supported 6-nm thick monolayer film.Although a monolayer melting transition could not be found in the resultant spectra, at least two other, low-temperature peaks (at −150 and −20 °C) were detected which seem to be due to relaxation processes both within the film as well as at interfaces of the monolayer structure. Our main aim was to determine whether the mechanical properties of ultrathin films could be measured by the vibrating reed technique, and to detect any thermal–mechanical relaxations which may occur in such films, inparticular whether or not a melting transition could be detected at elevated temperatures. Such thermal–mechanical measurements have long been used in theplastics industry to characterize the mechanical properties of resin materials in bulk. The vibrating reed technique may provide an analogous service for very thin organic coatings.