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Thermoelectric generators (TEGs) make use of the Seebeck effect in semiconductors for the direct conversion of heat to electrical energy. The possible use of a device consisting of numerous TEG modules for waste heat recovery from an internal combustion (IC) engine could considerably help worldwide efforts towards energy saving. However, commercially available TEGs operate at temperatures much lower than the actual operating temperature range in the exhaust pipe of an automobile, which could cause structural failure of the thermoelectric elements. Furthermore, continuous thermal cycling could lead to reduced efficiency and lifetime of the TEG. In this work we investigate the long-term performance and stability of a commercially available TEG under temperature and power cycling. The module was subjected to sequential hotside heating (at 200°C) and cooling for long times (3000 h) in order to measure changes in the TEG's performance. A reduction in Seebeck coefficient and an increase in resistivity were observed. Alternating-current (AC) impedance measurements and scanning electron microscope (SEM) observations were performed on the module, and results are presented and discussed.

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Dependence of the leakage current on the film quality in polycrystalline silicon thin-film transistors Empirical relationship between low-frequency drain current noise and grain-boundary potential barrier height in high-temperature-processed polycrystalline silicon thin-film transistorsThe off-state current in n-and p-channel polycrystalline silicon thin-film transistors ͑polysilicon TFTs͒ is investigated systematically by conduction measurements at various temperatures and low-frequency noise measurements at room temperature. It is demonstrated that the leakage current is controlled by the reverse biased drain junction. The main conduction mechanisms are due to thermal generation at low electric fields and Poole-Frenkel accompanied by thermionic filed emission at high electric fields. The leakage current is correlated with the traps present in the polysilicon bulk and at the gate oxide/polysilicon interface which are estimated from the on-state current activation energy data. Analysis of the leakage current noise spectral density confirms that deep levels with uniform energy distribution in the silicon band gap are the main factors in determining the leakage current. The density of deep levels determined from noise analysis is in agreement with the value obtained from conductance activation energy analysis. The substantially lower leakage current observed in the n-channel polysilicon TFT is explained by the development of positive fixed charges at the interface near the drain junction which suppress the electric field.

We present the main properties of ferroelectricity, with emphasis given to a specific family of hydrated ferroelectric crystals, which can serve as model systems for corresponding configurations in biology like the microtubules. An experimental method is described, which allows to establish the ferroelectric property of microtubules in suspension.

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