Three-dimensional photothermal radiometry for the determination of the thermal diffusivity of solids

Abstract

A radiometric method for measuring the thermal diffusivity of solids is presented. This method is based on the dynamic detection of an ac-temperature three-dimensional-distribution induced by the application of a localized and periodic optical excitation. Specifically the signal phase profile of the ac-temperature was detected along the sample surface. This procedure gives direct information on the material thermal diffusion length and, therefore, on its thermal diffusivity. Measurements on different bulk materials (i.e., Poco Graphite AXM-5Q, Armco Iron, Al2O3, and ZrO2) were performed and compared to the data obtained by the laser-flash method on the same set of samples. A further investigation on a very thin Si specimen (292 μm) showed the effect of thermal wave reflections at the sample backsurface on the measured thermal diffusivity. All the data obtained with this technique agreed to within 5% with those obtained using the laser-flash method and with the values taken from the literature for similar materials. Values in the range (8×10−7–0.9×10−4 m2/s) were obtained.

Interlayer thermal conductivity of rubrene measured by ac-calorimetry

“…A number of frequency dependent techniques, in which oscillating power is applied to the sample and resulting temperature oscillations measured, have been developed to measure thermal conductivity of small samples. [7][8][9][10][11][12][13][14][15] For these, the power transported out of the sample by leads and radiation determines the "external" thermal time constant,  1 , but measurements are typically made at frequencies  >>1/ 1 , 8 so that heat loss and radiation corrections are negligible.…”

“…One disadvantage of the 3 technique is that for a layered, anisotropic crystal the heater's oscillating temperature will be a function of the geometric mean of the "in-plane" and transverse thermal conductivities, 15 so the two components are not separately determined; in addition, it may be difficult to apply a low-noise Joule heater to some organic materials without damaging the material. Alternatively, other investigators have used chopped light to apply oscillating power to one surface of the sample and measured the oscillating temperature at different positions and/or frequencies; [6][7][8][9][10][12][13][14] the frequency dependent response is a function of the thermal diffusivity, D  /c, where c is the specific heat,  the mass density, and  the thermal conductivity. Most commonly, the oscillating temperature is measured on the opposite surface as a function of the lateral distance from the light, either by screening the light from part of the sample [8][9][10]14 or by using a laser to illuminate a small spot.…”

Simple Thermal Wave Method for the Determination of Longitudinal Thermal Diffusivity of SiC-Based Fiber

“…(1) (2) where r is the distance from the heating, a the thermal diffusivity, f.l the thermal diffusion length and (0 the angular frequency of the excitation. The measurement principle is shown in Fig.…”

“…In this paper a photothermal method, three dimensional photothermal radiometry (3D-PTR), [2] is proposed for the direct measurement of longitudinal thermal diffusivity of thin, fibre-type samples. This method belongs to the thermal-wave techniques that have been successfully used for determining thermal diffusivity even in complex geometry and materials [3,4,5].…”

Phase lock-in thermography for thermal diffusivity measurement and layer surface characterization

“…The phase shift has several advantages over the temperature amplitude such as it is independent of the sample's reflectivity and the light power 2,3 . Nowadays, there are several methods to measure these parameters but each one has its disadvantages: can only be applied to bulk materials 4,5,6 , requires use of a small focused beam 7 and requires the variation of the sample surface temperature which can be influenced by the heat loss effect 8 .…”