Licentiate Thesis: Development and characterization of a membranebased nanocalorimeter for low temperatures
by
Stella Tagliati(Stockholm University, Department of Physics)
→
Europe/Stockholm
A2:1041
A2:1041
Description
A differential, membrane-based nanocalorimeter has been constructed for thermal
studies of mesoscopic samples at low temperatures. The calorimeter is designed for
sample masses from milligram to sub-microgram and a temperature range from room
temperature to the sub-Kelvin region. In particular, it finds applications in the study of
phase transitions and phase diagrams of superconductors and magnetic systems.
Effort was spent to achieve high resolution and good absolute accuracy to be able to
investigate the electronic contribution of the heat capacity of superconductors. The
device is based on two free-standing silicon nitride membranes that, combined with
thin film heaters and temperature sensors, give a background heat capacity < 200 nJ/K
at 300 K, decreasing to sub-nJ/K at 10 K. The device has several unique features. i) In
differential mode, used for small samples, the background at room temperature is
reduced to » 2 nJ/K. ii) The resistive thermometer, made of GeAu alloy, has a high
dlnR/dlnT » -1 over the entire temperature range. iii) The sample is placed in direct
contact with the thermometer which is allowed to self-heat. The thermometer can thus
be operated at high DC current to increase the resolution. iv) Data are acquired with a
set of eight synchronized lock-in amplifiers measuring DC, 1st and 2nd harmonic
signals of heater powers and temperature oscillations with combined good absolute
accuracy and high resolution. The design allows concurrent use of AC state steady
and relaxation methods for general studies of specific heat, latent heat and dynamic
heat capacity. The properties of the nanocalorimeter were studied both analytically
and numerically with excellent agreement with experimental results. The operation of
the experimental setup was tested with successful calibration and characterization
measurements which suggest promising results.
