(a) Calorimetric sensor XI274 on ceramic housing XEN-40014. (b) Enlarged view of the chip with the free standing SiNx membrane (green square) and the bond pads (small white squares). (c) The working area with the heater and the thermocouple hot junction.
(a) Measured amplitude of thermocouple voltage for the empty sensor at second (red squares) and first (black open squares) harmonic of the heater voltage as a function of frequency. The resistive heater is used to generate a mean oscillating power of 41 μW. (b) Transfer function (thermocouple voltage amplitude times frequency) for the signal at the second harmonic. The green triangles show the thermocouple signal and the transfer function for the laser heated device at the first harmonic of the power oscillation.
Voltage across the heater (black) and thermocouple voltage (red) at different frequencies. At 20 Hz the thermocouple voltage at the second harmonic is clearly seen. At 7.5 kHz the thermocouple signal at the second harmonic (maxima indicated by arrows) is already superimposed by a voltage at the first harmonic. At 100 kHz and above a signal at the first harmonic dominates the thermocouple signal.
Schematics of the working area of the calorimeter chip XI274 (the SiNx membrane is omitted). The heater and its electronic connections are in blue. The thermocouple junction and its connections are in red. The distance between the heater and thermocouple in the lateral direction is ∼500 nm and ∼100 nm in the vertical direction.
Modulated laser beam shining on a sample and on only the hot junction of the thermocouple. The two heaters and the aluminum electric connections are shown in blue. The doped poly-Si stripes of the thermocouple are in red and the hot junction, made by an aluminum connection, in gray.
Measuring cell for holding, positioning, and heating the calorimetric sensor. (a) The two axis stage (1, blue) is stationed on the microscope for positioning the sensor relative to the objective (not shown) underneath the white hole. (b) The thermostat is made from aluminum (2, magenta) with the heated part (3, cyan). The thermal isolation between the thermostat and the stage is made through MACOR™ (4, green). The calorimetric sensor (5, grey) is held tight to the bottom of the heated part of the thermostat (3, cyan). (c) The optical fiber (6, red) shines from the top. (d) The optical fiber is positioned by a 3 axis mechanical stage (7, black), and the optical fiber position is observed with the microscope from the bottom (8). (e) Complete view of the system.
(a) Electronic scheme for the sensor used as conventional AC calorimeter when the oscillating power is provided by the resistive heater and the mean temperature is controlled by the thermostat. (b) Laser heated AC calorimeter: Here the oscillating power is provided by the laser and the membrane heater is used for controlling the mean temperature, while the thermostat is kept at constant temperature.
(a)–(d) Inverse thermographs at modulation frequency 1 kHz for different distances between the optical fiber and sensor (∼±10%), for details see text. The color code is normalized to the maximum value (red). The scanned surface of the empty sensor (100 × 100 μm2) is shown in (e). Graph (f) shows the as measured intensity profiles across the diagonal (0,0 to 100,100) for the different distances.
(a)–(d) Inverse thermographs of an empty sensor at different frequencies. The fiber is at (20 ± 5) μm from the membrane. The color code is normalized to the maximum value (red). The surface scan area (40 × 40 μm2) is shown in (e).
Part of the sensor membrane (a) covered with a thin film made of soot and a small PMMA sample on top of the working area and (b) uncoated sensor membrane for comparison.
Frequency dependent inverse thermographs from the sensor coated with less than 1 μm graphite and a less than 1 μm thick PMMA sample. The fiber distance is (10 ± 5) μm from the membrane.
Laser heated AC calorimetric measurement in the temperature range of the glass transition of PMMA at frequency 5 kHz. (a) Thermocouple voltage amplitude as measured. The red lines indicate the tangent construction for the determination of T g . (b) Phase angle between oscillator voltage and thermocouple voltage as measured. (c) Corrected phase angle.
As measured reciprocal product of thermocouple voltage amplitude times frequency as function of temperature for PMMA at different frequencies.
Normalized heat capacity (reciprocal product of thermocouple voltage amplitude times frequency) at the dynamic glass transition for frequencies ranging from 3 Hz to 900 kHz.
Relaxation map showing data from different calorimetric devices and from dielectric spectroscopy.
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