Kenji Tamasaku

High resolution-high energy x-ray photoelectron spectroscopy using third-generation synchrotron radiation source, and its application to Si-high k insulator systems

High-resolution x-ray photoelectron spectroscopy (XPS) at 6 keV photon energy has been realized utilizing high-flux-density x rays from the third generation high-energy synchrotron radiation facility, SPring-8. The method has been applied to analysis of high-k HfO2/interlayer/Si complementary metal–oxide–semiconductor gate-dielectric structures. With the high energy resolution and high throughput of our system, chemical-state differences were observed in the Si 1s, Hf 3d, and O 1s peaks for as-deposited and annealed samples. The results revealed that a SiOxNy interlayer is more effective in controlling the interface structure than SiO2. Our results show the wide applicability of high resolution XPS with hard x rays from a synchrotron source.

Efficient focusing of hard x rays to 25nm by a total reflection mirror

Nanofocused x rays are indispensable because they can provide high spatial resolution and high sensitivity for x-ray nanoscopy/spectroscopy. A focusing system using total reflection mirrors is one of the most promising methods for producing nanofocused x rays due to its high efficiency and energy-tunable focusing. The authors have developed a fabrication system for hard x-ray mirrors by developing elastic emission machining, microstitching interferometry, and relative angle determinable stitching interferometry. By using an ultraprecisely figured mirror, they realized hard x-ray line focusing with a beam width of 25nm at 15keV. The focusing test was performed at the 1-km-long beamline of SPring-8.

Microstitching interferometry for x-ray reflective optics

A new stitching interferometry based on a microscopic interferometer having peak-to-valley height accuracy of subnanometer order and lateral resolution higher than 20 μm was developed to measure surface figures of large-size x-ray mirror optics. Cumulative errors of the stitching angle in a long spatial wavelength range were effectively reduced to be 1×10−7 rad levels using another interferometer having a large cross section in the optical cavity. Some optical performances of ultraprecise x-ray mirrors, such as submicrofocused beam profile, were wave optically calculated from the measured surface figure profiles and observed at the 1 km long beamline (BL29XUL) of SPring-8. Observed and wave optically calculated results were in good agreement with a high degree of accuracy.

Relative angle determinable stitching interferometry for hard x-ray reflective optics

Metrology plays an important role in surface figuring with subnanometer accuracy. We have developed relative angle determinable stitching interferometry for the surface figuring of elliptical mirrors, in order to realize hard x-ray nanofocusing. In a stitching system, stitching angles are determined not by the general method using a common area between neighboring shots, but by the new method using the mirror’s tilt angles measured at times when profile data are acquired. The high measurement accuracy of approximately 4nm (peak-to-valley) was achieved in the measurement of a cylindrical surface having the same curvature as the elliptically designed shape to enable hard x-ray nanofocusing.Metrology plays an important role in surface figuring with subnanometer accuracy. We have developed relative angle determinable stitching interferometry for the surface figuring of elliptical mirrors, in order to realize hard x-ray nanofocusing. In a stitching system, stitching angles are determined not by the general method using a common area between neighboring shots, but by the new method using the mirror’s tilt angles measured at times when profile data are acquired. The high measurement accuracy of approximately 4nm (peak-to-valley) was achieved in the measurement of a cylindrical surface having the same curvature as the elliptically designed shape to enable hard x-ray nanofocusing.

Single-nanometer focusing of hard x-rays by Kirkpatrick-Baez mirrors.

We have constructed an extremely precise optical system for hard-x-ray nanofocusing in a synchrotron radiation beamline. Precision multilayer mirrors were fabricated, tested, and employed as Kirkpatrick-Baez mirrors with a novel phase error compensator. In the phase compensator, an at-wavelength wavefront error sensing method based on x-ray interferometry and an in situ phase compensator mirror, which adaptively deforms with nanometer precision, were developed to satisfy the Rayleigh criterion to achieve diffraction-limited focusing in a single-nanometer range. The performance of the optics was tested at BL29XUL of SPring-8 and was confirmed to realize a spot size of approximately 7 nm.

A probe of intrinsic valence band electronic structure: Hard x-ray photoemission

Hard x-ray valence band photoemission spectroscopy (PES) is realized using high-energy and high-brilliance synchrotron radiation. High-energy (∼6 keV) excitation results in larger probing depths of photoelectrons compared to conventional PES, and enables a study of intrinsic electronic property of materials in actual device structures much less influenced by surface condition. With this technique, requirements for surface preparation are greatly reduced, if not eliminated. It is a nondestructive tool to determine electronic structure from surface to genuine bulk as shown by a study on SiO2/Si(100). Electronic structure modification related to the ferromagnetism in the diluted magnetic semiconductor Ga0.96Mn0.04N is also observed.

Doping dependent density of states and pseudogap behavior in La2-xSrxCuO4

We have made a high-resolution photoemission study of

Extreme ultraviolet free electron laser seeded with high-order harmonic of Ti:sapphire laser

{\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Cu}{\mathrm{O}}_{4}

Hard X-ray Diffraction-Limited Nanofocusing with Kirkpatrick-Baez Mirrors

in a wide hole concentration (

Nature of the well screened state in hard X-ray mn 2p core-level photoemission measurements of La1-xSrxMnO3 films

x