Nanocalorimetry: Calorimetry of ultra-small materials

In chemistry and materials science, the thermodynamical properties of bulk materials, such as phase transition temperatures and enthalpies, are obtained by calorimetry, making it an indispensible metrology technique. However, conventional differential scanning calorimeters require large sample mass to acquire data with reasonable accuracy. It is also known that nano-scale particles and materials show distinctly different thermodynamical properties than their bulk counterparts due to surface and interfacial effects. These effects are negligible in the bulk material but they become dominant at small scales where the total fraction of atoms at the surface is significant. With the ever increasing nanotechnology research, it is therefore desirable to have a means of studying thermodynamical properties of small volume samples, ultimately a single nanoparticle.

We demonstrated an alternative approach for the measurement of changes in heat capacity, elastic modulus and viscosity of very small volumes (~ attoliters) of materials during their thermal transitions by micro- and nano- electromechanical systems (MEMS/ NEMS). The sample to be studied is placed on a mechanical platform and heated by a resistive heater with a time varying external voltage. When DC heating and small signal harmonic heating are applied simultaneously, it is observed that the platform vibrates near its resonant frequency by electrothermal excitations. It was also demonstrated that the measurement can be done simultaneously at multiple frequencies and mechanical resonant modes.

During heating the following parameters are monitored: DC deflection, amplitude and phase of the displacement of the platform due at the applied voltage frequency. The sample’s thermal behavior such as glass transition, melting and evaporation are observed and described in terms of the heat capacity, elastic modulus and thermal expansion coefficients. By using analytical and numerical techniques thermo- electro- mechanical response of the system is modeled. A first approach to obtain quantitative thermodynamical is carried out.

The thermodynamical properties of chalcogenide thin films, As2S3 and Ge-As-Se-Te (GAST) glasses are studied. Chalcogenide glasses, both in bulk and as thin films, are finding wide applications in numerous photonic devices.

O. Senlik, A. Dâna, M. Bayındır