Micro and nanostructured devices for thermal analysis

Abstract

The recent advent of micro and nano devices increased the interest in small scale material properties, such as elasticity, conductivity or heat capacity, which are considerably different from their bulk counterparts due to, primarily, increasing surface to volume ratios. These novel properties must be analyzed by using ultra-sensitive devices since characterization of these properties is not possible with conventional probing instrumentation due to their large mass or volume which decreases signal to noise ratio. Microelectromechanical systems (MEMS) with short response time and high sensitivity are suitable for such measurements, such as very small mass detection (zeptograms) and calorimetry of small volume materials (yoctocalories). In this thesis a MEMS cantilever was used for thermomechanical characterization of thin film amorphous semiconductors. 100 nm thick As2S3 and Ge-As-Se-Te glasses were thermally evaporated onto a bilayer microcantilever. The microcantilever was deflected and vibrated by electrothermal actuation. By monitoring deflection, amplitude and phase of the cantilever oscillation, multiple glass transition and melting points were identified; the effects of the variation of thermal expansion coefficients (CTE), reversible and irreversible heat capacities and Young’s modulus of the thin film samples were observed simultaneously. Hence the possibility of the integration of calorimetry, thermomechanical analysis (TMA) and dynamical mechanical thermal analysis (DMTA) in a single MEMS device was demonstrate