Temperature-Dependent Thickness Variation of Ultrathin Trimethyl β-Cyclodextrin Film Supported by a Si Substrate

Abstract

X-ray reflectivity analysis is an effective method to investigate the unusual behavior of ultrathin sugar films, in particular, the temperature dependence of their physical parameters. In this study, the change in thickness of ultrathin trimethyl β-cyclodextrin (TMβCD) films due to variation in temperature was verified under anhydrous condition for films with thickness less than 25 nm. As a result, the irreversible change in film-thickness during cooling and heating was confirmed by measurements. The irreversible change appeared above the glass transition temperature (Tg). Above this temperature, in addition to thickness change in the perpendicular direction, an irreversible linear expansion of the film occurred in the parallel direction. It is assumed that this behavior is due to the lack of strong interactions between the TMβCD molecules in ultrathin films and/or between the TMβCD molecule and Si substrate.