Critical analysis of micro-thermogravimetry of CuSO_4·5H₂O crystals using heatable microcantilevers

Micro/nano thermogravimetry (TG) employing MEMS has significant potential to improve the minimum sample mass and mass resolution as compared to commercial TG instruments. Although there have been a few previous reports on MEMS TG, none of them have critically analysed the obtained TG curve in detail. In this work, we have designed and fabricated a microelectromechanical thermogravimetric device (MMTG) with integrated microheaters and temperature sensors. The mass sensitivity of the device was estimated to be 0.89 pg Hz⁻¹ which outperforms the standard TG approaches. We tested the MMTG performance with CuSO₄·5H₂O crystals. The final mass loss ratio corresponds to the theoretically expected value, although the obtained TG curve deviated from the standard TG curve of CuSO₄·5H₂O obtained from commercial TG instruments. We attributed the deviation to the inherent temperature non-uniformity, non-isothermal conditions and temperature gradients of metallic-wire based microheaters. Finite element (FE) simulations were carried out in order to confirm and gain insights into the non-uniform heating phenomena of microheater and sample. Based on the simulation results, we propose designs that can be realized to make MEMS TG a successful enterprise. (paper)