Nanoscale Characterisation and Imaging of Partially Amorphous Materials using Local Thermomechanical Analysis and Heated Tip AFM
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- Harding, L., King, W.P., Dai, X. et al. Pharm Res (2007) 24: 2048. doi:10.1007/s11095-007-9339-8
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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.
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.
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.
The study has demonstrated that thermal nanoprobes represent a novel method of characterising and imaging partially amorphous materials.
Key wordsamorphous atomic force microscopy glass transition indometacin microthermal analysis
atomic force microscopy
localised thermomechanical analysis
pulsed force mode