Geoelectric voltages have been continuously observed at Kakioka, Kanoya, and Memambetsu for more than 50 years. The geoelectric fields obtained at the three sites for a recent 11-year period (2000 to 2011) were examined. The fields are mainly induced by variations in the geomagnetic field at periods of less than 10 5 s. The instability of the observation system causes a long-term trend in the longer period band. This long-term trend can be estimated and removed using the robust Kalman filter procedure which we modified to accommodate data containing outliers. The magnetotelluric (MT) impedance at the three sites was estimated using the original geoelectric field and the geomagnetic field at periods of 6 to 10 4 s, and the period was extended to 10 7 s at Kakioka and Memambetsu. Although the geomagnetically induced currents (GIC) at these sites may potentially be estimated using the MT impedance and geomagnetic data (if technological network information is available), the distortion effect should be corrected in order to obtain the correct regional geoelectric field. The eastward component of the geoelectric field at Kakioka shows a severe distortion effect, and the amplification factor was estimated to be approximately 10 from comparison with the C response at Kakioka. Conversely, the distortion effect on the eastward component of the geoelectric field at Memambetsu is almost none. The amplification factor for the northward component of the geoelectric field has not been estimated because of the lack of an independent response for comparison, although the MT response indicates a potentially large distortion at Memambetsu. Numerical modeling would be a useful tool to enable an improved estimation of this distortion.
Fluorescence-yield X-ray absorption fine structure (FY-XAFS) is extensively used for investigating atomic-scale local structures around specific elements in functional materials. However, conventional FY-XAFS instruments frequently cannot cover trace light elements, for example dopants in wide gap semiconductors, because of insufficient energy resolution of semiconductor X-ray detectors. Here we introduce a superconducting XAFS (SC-XAFS) apparatus to measure X-ray absorption near-edge structure (XANES) of n-type dopant N atoms (4 ×1019 cm−3) implanted at 500°C into 4H-SiC substrates annealed subsequently. The XANES spectra and ab initio multiple scattering calculations indicate that the N atoms almost completely substitute for the C sites, associated with a possible existence of local CN regions, in the as-implanted state. This is a reason why hot implantation is necessary for dopant activation in ion implantation. The SC-XAFS apparatus may play an important role in improving doping processes for energy-saving wide-gap semiconductors and other functional materials.
Focused ion beam direct deposition has been developed as a new technique for making patterned metal film directly on substrates. The 20 keV Au+ ion beam is focused, deflected, and finally decelerated to 30–200 eV between the objective lens and substrate. The decelerated beam is deposited on the substrate at room temperature. The beam diameter can be tuned between 0.5 and 8 μm and the beam current varies from 40 pA to 10 nA, corresponding to the beam diameter. Current density was about 20 mA/cm2, so that the deposition rate in the beam spot was estimated about 0.02 μm/s. The purity of gold film was measured with Auger electron spectroscopy and contents of carbon and oxygen, undesirable impurities, were below detection limits. The resistivity was constant at 3.7±0.1 μΩ cm for deposition over the ion energy range of 34–194 eV.
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