Jerzy Bodzenta

Thin palladium film as a sensor of hydrogen gas dissolved in transformer oil

A sensor for the detection of hydrogen gas dissolved in the transformer oil is proposed. The absorption of hydrogen in thin palladium film causes changes in the electrical and optical properties of the film. The proposed structure can be simultaneously used as a resistance and optical sensor. The sensor has been tested for different hydrogen concentration and in different temperatures. The hydrogen concentration was varied from 200 to 1500 ppm (in the transformer oil) and the oil temperature was changed from 20 to 120 °C. The sensor exhibits good sensitivity for low hydrogen concentration and the long-term stability of parameters in the transformer oil up to 90 °C. The sensitivity and the reaction time of the sensor strongly depend on the operation temperature. It should be possible to use such a sensor structure for the continuous monitoring of electric power systems.

The complex ray theory of photodeflection signal formation: Comparison with the ray theory and the experimental results

A theoretical study of Gaussian probe beam interaction with thermal waves on the basis of the complex geometrical optics equations is presented. This method of describing probe beam propagation in a nonhomogeneous medium, called the complex ray theory, takes into account the influence of the thermal wave on both amplitude and phase of electric field in the probe Gaussian beam. A comparison between the complex ray theory and previously proposed theories is made. Adequate experimental data confirming the correctness of the presented theory are also given. The least-squares procedure was used in multiparameter fitting the theoretical results to the experimental data and some parameters of the experimental setup were determined. It is proven that the complex ray theory allows correct quantitative interpretation of the data obtained in photodeflection experiments.

Influence of Order–Disorder Transition on Thermal Conductivity of Solids

Abstract The relation between the crystalline structure and thermal properties of solids is analyzed. The brief description of the theories of heat conduction in polycrystalline solids (Callaway model) and amorphous solids (Cahill–Pohl) model is carried out. It is shown that transition from the heat transport by phonons in polycrystals to the random energy transfer between localized oscillators in glasses leads to the meaningful reduction of the thermal conductivity. This conclusion is illustrated by experimental data. The limitations of obtaining thin films with good thermal properties are underlined.

A new FTIR-ATR cell for drug diffusion studies

The drug diffusion of most compounds, particularly hydrophilic molecules through the skin is limited by the permeation of the outermost cell layers of the epidermis, the stratum corneum(SC). For this reason it is of interest to characterize drug diffusion processes through this skin layer. A new FTIR-ATR cell was developed for non-invasive real time measurements of drug diffusion. The diffusion of water through an artificial polyethyleneglycol-polydimethylsiloxane membrane was studied. Additionally the diffusion of urea in human SC was analyzed. Based on a mathematical model the diffusion coefficients were derived. We could reveal that this cell associates the advantages of the Franz diffusion cell and the FTIR-ATR spectroscopy as a new powerful method for determining drug diffusion through biological membranes.

Quantitative scanning thermal microscopy based on determination of thermal probe dynamic resistance

Resistive thermal probes used in scanning thermal microscopy provide high spatial resolution of measurement accompanied with high sensitivity to temperature changes. At the same time their sensitivity to variations of thermal conductivity of a sample is relatively low. In typical dc operation mode the static resistance of the thermal probe is measured. It is shown both analytically and experimentally that the sensitivity of measurement can be improved by a factor of three by measuring the dynamic resistance of a dc biased probe superimposed with small ac current. The dynamic resistance can be treated as a complex value. Its amplitude represents the slope of the static voltage-current U-I characteristic for a given I while its phase describes the delay between the measured ac voltage and applied ac current component in the probe. The phase signal also reveals dependence on the sample thermal conductivity. Signal changes are relatively small but very repeatable. In contrast, the difference between dynamic and static resistance has higher sensitivity (the same maximum value as that of the 2nd and 3rd harmonics), and also much higher amplitude than higher harmonics. The proposed dc + ac excitation scheme combines the benefits of dc excitation (mechanical stability of probe-sample contact, average temperature control) with those of ac excitation (base-line stability, rejection of ambient temperature influence, high sensitivity, lock-in signal processing), when the experimental conditions prohibit large ac excitation.

Photodeflection signal formation in photothermal measurements: comparison of the complex ray theory, the ray theory, the wave theory, and experimental results

A comparison is made of three methods for modeling the interaction of a laser probe beam with the temperature field of a thermal wave. The three methods include: (1) a new method based on complex ray theory, which allows us to take into account the disturbance of the amplitude and phase of the electric field of the probe beam, (2) the ray deflection averaging theory of Aamodt and Murphy, and (3) the wave theory (WT) of Glazov and Muratikov. To carry out this comparison, it is necessary to reformulate the description of the photodeflection signal in either the WT or the ray deflection averaging theory. It is shown that the differences between calculated signals using the different theories are most pronounced when the radius of the probe beam is comparable with the length of the thermal wave in the region of their interaction. Predictions of the theories are compared with experimental results. A few parameters of the experimental setup are determined through multiparameter fitting of the theoretical curves to the experimental data. A least-squares procedure was chosen as a fitting method. The conclusion is that the calculation of the photodeflection signal in the framework of the complex ray theory is a more accurate approach than the ray deflection averaging theory or the wave one.

Correlation between morphology and local thermal properties of iron (II) phthalocyanine thin layers

The effect of substrate temperature and post-deposition annealing temperature on the surface morphology, topography and local thermal properties of iron(II) phthalocyanine (FePc) 500 nm thick films was investigated. The investigations were conducted by a combination of scanning probe microscopies (atomic force microscopy, scanning thermal microscopy) and scanning electron microscopy with structural (x-ray diffraction) and chemical (energy-dispersive x-ray spectroscopy) analysis. FePc is always obtained in its α-form. While for heated substrates, FePc crystallites lie flat on the surface, so post-deposition annealing leads to vertically oriented crystallites. The total surface area obtained does not depend significantly on the substrate temperature, while it is strongly dependent on the annealing temperature. For both groups of samples, the increase of roughness was accompanied by a decrease of the samples thermal resistivity, which is in agreement with the picture of a decreased number of grain boundaries resulting in higher heat transport. The results obtained here show that the exposed surface area of an organic film strongly depends on the thermal treatments; hence surface morphology can be tailored to particular needs.

Reduced thermal quadrupole heat transport modeling in harmonic and transient regime scanning thermal microscopy using nanofabricated thermal probes

The thermal model of a nanofabricated thermal probe (NTP) used in scanning thermal microscopy is proposed. It is based on consideration of the heat exchange channels between electrically heated probe, a sample, and their surroundings, in transient and harmonic regimes. Three zones in the probe-sample system were distinguished and modeled by using electrical analogies of heat flow through a chain of quadrupoles built from thermal resistances and thermal capacitances. The analytical transfer functions for two- and three-cell quadrupoles are derived. A reduced thermal quadrupole with merged RC elements allows for thermo-electrical modeling of the complex architecture of a NTP, with a minimum of independent parameters (two resistance ratios and two time constants). The validity of the model is examined by comparing computed values of discrete RC elements with results of finite element simulations and with experimental data. It is proved that the model consisting of two or three-cell quadrupole is sufficient f...

Photoacoustic detection of drug diffusion into a membrane: theory and numerical analysis

Abstract Possibility of the analysis of drug penetration through membranes using photoacoustic effect is considered. Based on Ficks second law the problem of the spatial and time dependent distribution of drugs in membranes is solved. The solution allows to derive the distribution of heat sources arising in the membrane from intensity modulated light illumination. Subsequently the temperature of the illuminated membrane surface is analysed numerically. This temperature is directly correlated to the signal registered in photoacoustic measurements. The influence of different parameters of the theoretical model on the ac component of the temperature of illuminated membrane surface has been analysed. Conclusions about possibilities and limitations of the considered method are discussed.

Photothermal methods for determination of thermal properties of bulk materials and thin films

Information on the thermal properties of materials is very important both in fundamental physical research and in engineering applications. The development of materials with desirable heat transport properties requires methods for their experimental determination. In this paper basic concepts of the measurement of parameters describing the heat transport in solids are discussed. Attention is paid to methods utilizing nonstationary temperature fields, especially to photothermal methods in which the temperature disturbance in the investigated sample is generated through light absorption. Exemplary photothermal measuring techniques, which can be realized using common experimental equipment, are described in detail. It is shown that using these techniques it is possible to determine the thermal diffusivity of bulk transparent samples, opaque and semi-transparent plate-form samples, and the thermal conductivity of thin films deposited on thick substrates. Results of the investigation of thermal diffusivity of the ground in the polar region, which is based on the analysis of the propagation of the thermal wave generated by sun-light, are also presented. Based on chosen examples one can state that photothermal techniques can be used for determination of the thermal properties of very different materials.