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We investigated the growth conditions and electrical properties of MgO epitaxial thin films, which have potential applications as insulating layers for spin-dependent tunneling devices where Fe 3 O 4 serves as one of the magnetic electrodes. Our investigation showed that epitaxial MgO films with high crystalline quality can be successfully grown at temperatures as low as 473 K in oxygen pressures less than 1ϫ10 Ϫ5 Torr. This is a very important result because it indicates that the oxidation of the underlying Fe 3 O 4 electrode is not a factor in fabrication of spin-dependent tunneling devices. We also examined the electron tunneling properties of Au/MgO/Fe 3 O 4 junction with an ultrathin MgO layer prepared under the conditions described above and found excellent electron tunneling properties, as will be discussed. Barrier height and thickness estimated by curve fitting current density-voltage curves using the Simmons equation yielded barrier height and thicknesses of 0.9 eV and 2.5 nm, respectively. These values were consistent with those estimated by taking into account the reduction of the barrier height due to image forces. These results indicate that the MgO insulating layers grown under the restricted conditions have satisfactory electrical qualities required for spin tunneling devices.

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Monitoring the gases released during breathing or via the skin has gained significance towards diagnosing diseases. In this study, a sensor chip capable of detecting nonanal gas, which is known to be a marker of lung cancer, was developed. The gas detection agent used was vanillin, which underwent aldol condensation with nonanal in the presence of a basic catalyst, resulting in the formation of an unsaturated aldehyde. Porous glass was used as the reaction field to carry the detection agent. Alkali-resistant porous glass was chosen because conventional porous glasses show low durabilities under basic conditions, as they primarily consist of SiO 2 . Nonanal can be detected through changes in the absorption spectrum of the sensor. An accumulatetype sensor was used in this study, which exhibited a linear relationship between the degree of absorption changes at 470 nm and nonanal concentration in the 60 ppb-1.3 ppm range. Therefore, this biological marker gas sensor is effective for the early diagnosis of diseases. The alkali-resistant porous glass sensor chip exhibited a higher degree of absorption change than the conventional porous glass sensor chip.

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