We performed capacitance–voltage analysis of 5-nm-thick LaAlO3/SrTiO3 heterostructure containing two-dimensional-electron-gas (2DEG) at the interface. The complex impedance of the heterostructure was measured as a function of frequency for a wide range of gate biases. The impedance spectra showed a different behavior above and below an applied voltage of −1.8 V. The capacitance determined from the impedance was approximately 1.2 nF above −1.8 V and was drastically reduced to ∼0.01 nF below this voltage, owing to depletion of 2DEG and the insulating SrTiO3 underneath it. This suggests that devices utilizing LaAlO3/SrTiO3 can facilitate switching operations in a very small voltage range.
Carbon-based materials allows for their derivatives such as fullerenes, carbon nano-tubes (CNTs), and graphenes in addition to the conventional bulk carbon materials. The high conductive feature of carbon-based derivatives can be exploited as the conduction path of the carbon/inorganic mixture. In this work, carbon-based materials are combined with cement-based materials in order to being fabricated as the pressure-sensors under the high-impact condition. In particular, the CNTs are combined with cement-based materials. The corresponding hydration is monitored as a function of time using impedance spectroscopy. The addition of CNTs into the cement matrix system modifies the conventional conduction path, forming a conductive one, leading to the significant change in impedance spectra. The frequency-dependent impedance information allows for an equivalent circuit model which reflects the microstructure composed of CNTs and cement-based products. Based on the microstructural/electrical understanding, a possibility of being a piezoresistive sensor is discussed as a novel application involving the peculiar features of 1-dimensional CNT materials.
We reports on a unique characterization method for the electrode reactions of SOFCs via impedance spectroscopy combined with a spatially-constricted contact based on a robust electrolyte which is expected to give more reliable measurement set-up. Various electrode materials were chosen to validate our method and the corresponding impedance phenomena were analyzed to give an insight for optimization of the SOFC electrode. The ramifications of "limited-contact" impedance spectroscopy are discussed for an exhaustive understanding of electrode-related polarizations in SOFCs
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