Hammiche, A.; Price, D. M.; Dupas, E., Mills, G.; Kulik, A; Reading, M.; Weaver, J. M. R.; Pollock, H. M.; Two new microscopic applications of thermomechanical modulation: scanning thermal expansion microscopy and dynamic localised thermomechanical analysis. Journal of Microscopy 199(3) (2000) 180-190
We describe two ways in which thermomechanical modulation may be used in conjunction with scanning thermal microscopy, in order to distinguish between different components of an inhomogeneous sample. The sample is subjected to a modulated mechanical stress, and the heating is supplied locally by the probe itself.
Scanning thermal expansion microscopy is an imaging mode, in which an imposed localised temperature modulation is used to generate thermal expansion, which in turn produces mechanical strain and gives thermal expansion contrast images. We present results using two types of active thermal probe. For polymer / resin samples, the depth of material contributing to the measured thermal expansion is typically a few microns. Under certain conditions we observe a reversal in contrast as the frequency is increased.
In dynamic localised thermomechanical analysis, the modulated stress is applied directly, and accompanied by a localised temperature ramp as used in other forms of localised thermal analysis. The resulting modulated lateral force signals are obtained. The glass transition is polystyrene is detected, and shows a significant variation with frequency. The amplitude or phase signal may be used to obtain image contrast.