The effective thermal conductivity and thermal diffusivity of a two‐layer system are investigated from the theoretical point of view for application to photoacoustic experiments. The effective thermal parameters are obtained by comparing the temperature distribution on the left or right surface of the layered structure and some effective one‐layer material. These effective thermal parameters are calculated for some special cases as for example, low and high chopper frequency. The influence of the interface thermal contact between the layers plays an important role on the effective thermal parameters. It is shown that the effective thermal conductivity and thermal diffusivity depend strongly upon the used photothermal technique.

Undoped ZnO thin films were prepared using the ultrasonic spray pyrolysis deposition technique with zinc acetylacetonate dissolved in N,N‐dimethylformamide as the source materials solution. The addition of water mist in a parallel flux to the spray solution stream was also used during deposition of the films. The addition of water mist improved the electrical characteristics of the ZnO films. Fresh ZnO samples were then thermally annealed in a H2 reducing atmosphere. X‐ray diffraction patterns show mainly the wurzite crystalline ZnO phase in the films. An electrical resistivity (ρ ) of around 2.7 × 10−2 Ω cm was measured at room temperature for the best undoped ZnO film. ρ is approximately one order of magnitude lower than the resistivities found in undoped ZnO films obtained by means of similar non‐vacuum deposition techniques. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

It is well known that the development and determination of optical properties of ultrathin films is an important issue in many technological areas. In this work organic polyethylene (PE) and cobalt phthalocyanines (CoPc) ultrathin films were deposited over metal films using the r.f. sputtering and thermal evaporation techniques, respectively. Attenuated total reflection (ATR) measurements for the system organic film/metal at the surface plasmon resonance (SPR) were used for determining the thicknesses and optical properties of the PE and CoPc thin films. Thicknesses of the order of some nanometers were found, fitting the theoretical multilayer ATR model, for p polarization monochromatic light, to the experimental reflection data. The dielectric function of CoPc ultrathin films was determined at a wavelength of 632.8 nm. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Using a high density polyethylene thin film over gold layer, a Surface Plasmon Resonance sensor for detecting n-dodecane vapor is developed. Preliminary results will be presented, showing that samples in the range of a few hundred ppm(V) of n-dodecane vapor in butane gas can be sensed. Also, studying the response as a function of time, it is demonstrated that the sensing process is quickly reversible.

Aluminum doped ZnO thin films were synthesized by the water-mist assisted spray pyrolysis technique. The structural characterization by means of X-Ray diffraction measurements is reported. By means of Atomic Force Microscopy, the superficial electrical characteristics of the thin films are studied. Specifically, contact current images are shown and discussed. It is important to emphasize that in spite of no voltage is applied to the Atomic Force Microscopy contact conductive tip, current images are getting.

The dependence on chopper frequency of the effective thermal diffusivity and effective thermal conductivity in photoacoustic experiments is discussed. The theoretical model of a two-layer structure at rear-surface illumination in the high frequency limit is considered. It is shown that the effective thermal diffusivity presents "resonance" while the effective thermal conductivity sharply changes its magnitude and sign. Such "resonant" behavior strongly depends on the surface thermal conductivities associated with the interface thermal contacts.

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From the theoretical point of view, the influence of the solid–gas interface on the effective thermal parameters in a two-layer structure of the photoacoustic technique is discussed. It is shown that the effective thermal parameters depend strongly upon the thermal resistance value associated with the solid–gas interface. New expressions for the effective thermal conductivity and thermal diffusivity in the low frequency limit are obtained. In the high frequency limit, the ‘resonant’ behaviour of the effective thermal diffusivity is maintained and a new complex dependence on frequency of the effective thermal conductivity is shown.