Heat Capacity Measurements for Nano-gram Sample Application
Chien-Hung Lin1*, Ping-Chung Lee1, Yi-Cheng Huang1, Yang-Yuan Chen1
1Institute of Physics, Academia Sinica, Nankang, Taiwan
* presenting author:林建宏, email:r02222013@ntu.edu.tw
A membrane-based nanocalorimeter is designed for wide-temperature heat capacity measurement. The dimension of sample is in micrometer range, and the mass of sample can be down to sub-nano gram scale. The sensor pad is suspended by six leading wires located in a 7000 µm x 70 µm open window. The 3500 µm-long free-standing Au-Cu alloy leading wires are designed for reasonable low thermal conductance in small sample measurements. The sensor pad is a 70 x 70 µm2 silicon nitride square membrane with deposited heater and thermometer. The nanocalorimeter is fabricated by photolithography processes. A silicon substrate with 7000 µm x 70 µm silicon nitride membrane in the center is prepared by KOH wet etching. The Au-Cu electrodes, Ni-Cr heater, and RuO2-Al2O3 thermometer are deposited by e-beam evaporator and RF sputtering, respectively. Followed by RIE dry etching, the suspended nanocalorimeter is thus fabricated with a nearly constant resistance Ni-Cr heater (~19k Ω)(TCR < 0.001 1/K), and a high dimensionless sensitivity of RuO2-Al2O3 thermometer |dlnR/dlnT|≧2.5 for T=10~300k. Thermal relaxation method and ac steady-state method were used both to achieve accurate measurements.

Keywords: heat capacity, nanocalorimeter, thermal relaxation, ac steady-state