Dresden 2017 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 58: Nanomaterials I

MM 58.4: Vortrag

Donnerstag, 23. März 2017, 11:00–11:15, IFW D

Quantitative heat capacity measurements of Au nanoparticles using a nanocalorimeter — •Emanuel Franke¹, David A. LaVan², and Cynthia A. Volkert¹ — ¹Inst. für Materialphysik, Uni Göttingen, 37077 — ²MML, NIST, Gaithersburg, USA 20899

As sample length scales reach down to nanometers, and the surface influence becomes large, thermal properties such as the heat capacity change. The involved heat in such samples is very small and can only be measured via convent. calorimetry by pressing milligrams of sample material together, whereby the surface influence of the sample is reduced. However, nanoscale samples can be directly measured by MEMS-based differential nanocalorimeters which have sufficient res. to measure with nJ sensitivity. Nonetheless, it is well known that heat losses of the MEMS sensors may change in the presence of a sample, leading to large changes in the nanocalorimetric signal and quantitative determination of heat capacity. In this study, FEA is used to investigate the interplay of heat losses (rad. and cond.), sample properties (therm. emissivity and conductivity), and temp. distr. on the sensor. On the basis of this analysis, the influence of exp. issues (misaligned sample, amb. temp.) can be evaluated. Furthermore, the sample geometry could be adapted to minimize the influence of the sample prop. on the measurement. With this knowledge, the heat capacity of Au nanoparticles (1 nm to 20 nm) was measured from 30 K to 300 K with a heating rate of 18,000 K/s with a resolution of better than 1 nJ/K. Together with TEM investigations, this reveals an enhancement in the heat capacity at low temp. that decr. with incr. particle size.