Two new microscopical variants of thermomechanical modulation: scanning thermal expansion microscopy and dynamic localized thermomechanical analysis

We describe two ways in which thermomechanical modulation may be used in co njunction with scanning thermal microscopy, in order to distinguish between different components of an inhomogeneous sample. The sample is subjected t o 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 impos ed localized temperature modulation is used to generate thermal expansion, which in turn produces mechanical strain and gives thermal expansion contra st images. We present results using two types of active thermal probe. For polymer/resin samples, the depth of material contributing to the measured t hermal expansion is typically a few micrometres. Under certain conditions w e observe a reversal in contrast as the frequency of the temperature modula tion is increased. In dynamic localized thermomechanical analysis, the modulated stress is app lied directly, and accompanied by a localized temperature change, as used i n other forms of localized thermal analysis. The resulting modulated latera l force signals are obtained. The glass transition of polystyrene is detect ed, and shows a significant variation with frequency. The amplitude or phas e signal may be used to obtain image contrast for inhomogeneous samples.