Can the Sublimation Enthalpy Be Obtained Using Atomic Force Microscopy with Heating? A PETN Nanofilm Case

Vaporization is an important aspect of the performance and detection of energetic materials. While the traditional techniques concentrate on bulk property changes during sublimation, atomic force microscopy (AFM) offers the possibility to track particle volume changes under heating. Ideally, this will enable the investigation of chemicals that are challenging to study using conventional vaporization analysis methods, i.e., those having low thermal stability and/or low volatility. However, prior studies have demonstrated that novel structural effects at the nanoscale may interfere with sublimation mass loss. The present work aims to provide a comprehensive investigation of the sublimation of pentaerythritol tetranitrate (PETN) thin films with respect to the measurement parameters, the heating technique, the sample composition, and the type of the substrate. We observed the low-temperature recrystallization of thin-film islands during heating together with the sublimation process; this was demonstrated by the unexpected local increase in volume with temperature. Overall, AFM allows us to set up a precise nanoscale vaporization experiment and, in some instances, to obtain a reliable estimate of the sublimation enthalpy. However, it is crucial to consider the sample's morphology as well as any concurrent structural transformations in order to ensure the validity of the results.