Investigations Of The Low And High Frequency Response Of 3ω-Sensors Used In Dynamic Heat Capacity Measurements

• The 3ω-method is used to study time dependent processes through measurements of dynamic heat capacity. The 3ω-sensor is a thin (∼ 0.1 μm) metal strip which is evaporated onto a substrate. The sample is probed by periodic diffusive thermal waves of frequency 2ω emitted from the strip. The heater temperature T0 measured at frequency 3ω yields the dynamic heat capacity. The validity of a one-dimensional heat flow model, assuming an infinitely thin heater, is here studied using a finite element modelling (FEM) technique as well as experiments. To obtain results within 1% of the theory, FEM shows that the ratio between the heater width and the heat wave penetration depth (=√D/ω, where D is the thermal diffusivity) must be greater than 30, which sets a low-frequency limit for the model. At high frequencies, the finite thickness of the heater causes a deviation from the model. For a thickness of 0.1 μm, the deviation is <1% at 200 Hz, reaching 5% at 5 kHz. A small 3ω-component intrinsic to the electronics together with a thermal resistance between heater and sample can explain deviations from T0 ∝ ω-υ, at high frequencies, where υ = 0.5 is predicted by the model but experiments generally show smaller values.

Ämnesord

NATURVETENSKAP  -- Fysik -- Den kondenserade materiens fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Condensed Matter Physics (hsv//eng)

Nyckelord

dynamic heat capacity

modulated calorimetry

3-omega method

hot strip

glass transition

Condensed matter physics

Kondenserade materiens fysik

fasta tillståndets fysik

Solid State Physics

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