Nanoscale characterisation and imaging of partially amorphous materials using local thermomechanical analysis and heated tip AFM.

PURPOSE: The purpose is to investigate the use of thermal nanoprobes in thermomechanical and heated tip pulsed force modes as novel means of discriminating between amorphous and crystalline material on a sub-micron scale.
MATERIALS AND METHODS: Indometacin powder was compressed and partially converted into amorphous material. Thermal nanoprobes were used to perform localised thermomechanical analysis (L-TMA) and heated tip pulsed force mode imaging as a function of temperature.
RESULTS: L-TMA with submicron lateral spatial resolution and sub-100 nm depth penetration was achieved, allowing us to thermomechanically discriminate between amorphous and crystalline material at a nanoscale for the first time. The amorphous and crystalline regions were imaged as a function of temperature using heated tip pulsed force AFM and a resolution of circa 50 nm was achieved. We are also able to observe tip-induced recrystallisation of the amorphous material. DISCUSSION: The study demonstrates that we are able to discriminate and characterise amorphous and crystalline regions at a submicron scale of scrutiny. We have demonstrated the utility of two methods, L-TMA and heated tip pulsed force mode AFM, that allow us to respectively characterise and image adjacent amorphous and crystalline regions at a nanoscale.
CONCLUSIONS: The study has demonstrated that thermal nanoprobes represent a novel method of characterising and imaging partially amorphous materials.