A full‐field energy dispersive X‐ray fluorescence (FF‐EDXRF) imaging spectrometer that utilizes single‐photon counting analysis with a charge‐coupled device was developed in our laboratory. We evaluated the developed spectrometer with respect to its energy resolution, spatial resolution, quantitative performance, and elemental imaging and compared it with the corresponding characteristics of scanning‐type EDXRF spectrometers. In addition, we demonstrate that the limit of detection and sensitivity deteriorate as the analytical area decreases. Finally, compressed sensing, which is a widely used information‐processing technique, was applied for clearing XRF images.

We have found that current-voltage characteristics of resonant tunneling diodes ͑RTDs͒ with a structure of Al/upper-SiO 2 /p Ϫ -Si-well/lower-SiO 2 /n ϩ -Si substrate are distinctly categorized by the kinetic energy of electrons in the Si well injected from the n ϩ -Si substrate. For RTDs with a lower-SiO 2 -layer thickness below 4 nm, negative differential conductance is observed in accordance with our previous work ͓Y. Ishikawa, T. Ishihara, M. Iwasaki, and M. Tabe, Electron. Lett. 37, 1200 ͑2001͔͒, where electrons have relatively low kinetic energies below 2.7 eV in the Si well. On the other hand, RTDs with a lower-SiO 2 layer thicker than 5 nm have specific characteristics of a large current peak and a large hysteresis at higher kinetic energies above 2.9 eV, indicating that hot electrons are readily stored in the Si well, probably due to enhanced impact ionization scattering.

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