On the thermal characterization of two-layer systems by means of the photoacoustic effect

Abstract

In this work, the problem of the thermal characterization of two-layer systems by means of the photoacoustic technique is discussed. For a two-layer system under rear-side illumination conditions, we have applied the Rosencwaig and Gersho model for calculating the pressure fluctuation in the photoacoustic gas chamber. The limiting cases in which both layers are thermally thin, thermally thick and one layer is thermally thin and the other is thermally thick are discussed. When both layers are thermally thin, a consistent equation for the heat capacity is obtained and an effective thermal diffusivity equation is derived when both layers are thermally thick. In order to test our theoretical results, we apply them to two-layer systems consisting of AlGaAs layers of different Al concentrations, grown by liquid phase epitaxy on GaAs substrates. The results of our measurements are in good agreement with the theoretical predictions. Our results show the general character of the expression for the effective thermal diffusivity of two-layer systems reported by Mansanares et al (1990 Phys. Rev. B 42 4477).

Photothermal Characterization of Electrochemical Etching Processed n-Type Porous Silicon

“…Of the several techniques [15] used for measuring the thermal diffusivity, we resorted to the so-called "open cell" technique described in Refs. [16] and [17]. It consists of mounting the sample directly onto a cylindrical electret microphone and using the front air chamber of the microphone itself as the usual gas chamber of conventional photoacoustics, as indicated in Fig.…”

“…The thermal diffusivity is obtained from the modulation frequency dependence of the detected PA signal, as discussed in detail in Refs. [16] and [17]. That is, using the thermal diffusion model for the PA effect, the measurement signal S in the modulation frequency range, where the sample is thermally thick, may be written as [16] S ͑A͞f͒ exp͑2a p f͒ ,…”

Thermal properties of composite two-layer systems with a fractal inclusion structure

“…Layers with thicknesses larger than 400 µm are already thermally thick for the modulation frequencies used. Measuring the thermal diffusivity of bilayers consisting in layers with different thermal thicknesses requires a special care, as it is known that their thermal properties tend to the values of the thermally thick layer [22]. In this way, the PA spectrum of RCBs with layers of different thermal thicknesses were measured with their thermally thin layer facing the modulated light beam.…”

“…About the first, there has been an ongoing effort to extend the photoacoustic technique for the characterization of multilayered systems, with the purpose to determine their effective thermal diffusivity from the knowledge of the thermal properties of the layers themselves [16,17,18,19,20]. In particular, for two-layer systems, there are some aspects to be taken into account such as the thermal thickness of the layers and their effusivity, that becomes important at the interface in relation to its thermal resistance [21,22,23]. On the other hand, the TRM has been complimentarily used for the measurement of the heat capacity of small samples [24,25,26].…”

Thermal characterisation of dye-intercalated K-10 montmorillonite ceramics using photoacoustic technique

“…This non-radiative relaxation produces temperature fluctuations in the sample. These temperature fluctuations facilitate an indirect measurement of the thermal and optical properties of the sample [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. In photoacoustics (PA), the pressure variations produced within the cell are detected using a sensitive microphone.…”