To shorten the duration of x-ray pulses, we present a nonlinear optical technique using atoms with core-hole vacancies (core-hole atoms) generated by inner-shell photoionization. The weak Coulomb screening in the core-hole atoms results in decreased absorption at photon energies immediately above the absorption edge. By employing this phenomenon, referred to as saturable absorption, we successfully reduce the duration of x-ray free-electron laser pulses (photon energy: 9.000 keV, duration: 6–7 fs, fluence: $2.0–3.5\times {10}^5\mathrm{J}/{\mathrm{cm}}^2$) by $\sim 35\%$. This finding that core-hole atoms are applicable to nonlinear x-ray optics is an essential stepping stone for extending nonlinear technologies commonplace at optical wavelengths to the hard x-ray region.

SiOxNy films with a low nitrogen concentration (< 4%) have been prepared on Si substrates at 400°C by atmospheric-pressure plasma oxidation-nitridation process using O2 and N2 as gaseous precursors diluted in He. Interface properties of SiOxNy films have been investigated by analyzing high-frequency and quasistatic capacitance-voltage characteristics of metal-oxide-semiconductor capacitors. It is found that addition of N into the oxide increases both interface state density (D it) and positive fixed charge density (Q f). After forming gas anneal, D it decreases largely with decreasing N2/O2 flow ratio from 1 to 0.01 while the change of Q f is insignificant. These results suggest that low N2/O2 flow ratio is a key parameter to achieve a low D it and relatively high Q f, which is effective for field effect passivation of n-type Si surfaces.

X-ray full-field microscopy is a promising method for nondestructive observation of opaque materials because it can attain a high resolution and wide field of view without sample scanning. We recently developed hard x-ray objective optics, which are key devices for full-field microscopy, based on total-reflection mirrors with high throughput and achromatic properties. The objective optics consist of two types of advanced Kirkpatrick–Baez mirrors configured as crossed one-dimensional Wolter type I and type III optics. The designed optics possessed magnification factors of 42–45 with a compact camera length of approximately 2 m. The hard x-ray full-field microscope based on this system was tested at the BL29XU beamline at SPring-8. We were able to resolve 100-nm periods (50-nm line widths) of a resolution test chart at a photon energy of 15 keV over 30 h, which demonstrated the remarkable stability of this system. The image quality was preserved over a wide photon energy range from 9 to 15 keV. A periodic dot pattern with dot diameters of 300 nm, formed on a 775-µm-thick Si substrate, was three-dimensionally visualized by computed tomography.

X-ray single-grating interferometry was applied to conduct accurate wavefront corrections for hard X-ray nanofocusing mirrors. Systematic errors in the interferometer, originating from a grating, a detector, and alignment errors of the components, were carefully examined. Based on the measured wavefront errors, the mirror shapes were directly corrected using a differential deposition technique. The corrected X-ray focusing mirrors with a numerical aperture of 0.01 attained two-dimensionally diffraction-limited performance. The results of the correction indicate that the uncertainty of the wavefront measurement was less than λ/72 in root-mean-square value.