Yoshiaki Horikawa

Design and fabrication of the Schwarzschild objective for soft x-ray microscopes

The design of the Schwarzschild objective considering an alignment error is discussed and its fabrication for a soft x-ray microscope is described. It is shown that performance degradation of a Schwarzschild objective by an alignment error can be reduced in a heterocentric system, in which the center of a curvature of a concave mirror is not coincident with that of a convex mirror. Objectives with a magnification of 100 and 224 have been fabricated. To complete an indispensable and difficult alignment within the objective itself, the two mirrors are mounted together in the same frame. The alignment errors of the mirrors are detected and their positions are corrected in a newly developed alignment system, which allows the alignment to achieve the tolerance of 0.3 micrometers . The fabrication of Mo/Si multilayers used for the mirrors are also described briefly. A reflectometer using a laser produced plasma source has been developed to measure reflectances of multilayers. The Mo/Si multilayer deposited by magnetron sputtering shows a reflectance over 40% at a wavelength of roughly 135 angstroms.

Soft x-ray reflectometry with a laser-produced plasma source

A compact soft x-ray reflectometer usable in a small laboratory is developed for measurement of the soft x-ray reflectance of a multilayer mirror in a wide wavelength range, i.e. , including the water window (23 to 44A). In this reflectometer, the reflectance can be measured as a function of wavelength or incidence angle. A laser-produced plasma soft x-ray source, which is small but has high brightness, makes it possible to construct the compact soft x-ray reflectometer. The soft x rays generated by the source are monochromatized with a grazing incidence reflection grating. Incidence angle dependency of the reflectance can be measured from 2 deg (almost normal incidence) to 85 deg. Reflectances of a Ni/Ti multilayer and a Mo/Si multilayer are measured, and 10.9% at a wavelength of 40.8A and an angle of 75.1 deg and 38% at a wavelength of 135.5A and an angle of 25.7 deg from normal incidence are obtained, respectively.

Measurement of Knife-Edge Responses of a Schwarzschild X-Ray Objective

The spatial resolution of a Schwarzschild objective was evaluated at the wavelength of 135 A by means of an apparatus constructed using the knife-edge method which is suitable to the measurement of higher resolution. The knife-edge response of the objective was measured with the apparatus. Then the results were compared with the theoretical responses calculated using ray tracing. It is found that the measured responses of the objective are almost the same as the theoretical ones. We conclude that the objective has the spatial resolution of 0.2 µm.

Formation of an X-ray microbeam using a Schwarzschild X-ray objective

A soft X-ray microbeam was formed using a Schwarzschild X-ray objective designed to have transmittance at a wavelength of 14 nm. The widths of the X-ray beam on and off the focal plane were measured using a knife-edge method, and it was found that the size of the X-ray microbeam was 70 nm on the focal plane. We obtained X-ray transmission images of a silicon etching pattern and demonstrated that an image at a spatial resolution of better than 100 nm was obtained using the microbeam. We also discuss practical applicability of the microbeam.

Submicrometre-area high-energy-resolution photoelectron spectroscopy system

A submicrometre-area photoelectron spectroscopy system that uses a multi-layer-coated Schwarzschild objective as the soft X-ray microbeam optics has been developed. The system is located at an undulator beamline (BL-16U) at the Photon Factory in the High Energy Accelerator Research Organization. By knife-edge measurement, the microbeam size was estimated to be 160 nm at the sample position using a 25-75% criterion. Photoelectron spectral measurements revealed that the Fermi edge width was 0.12 eV, which means that the instrumental resolution was 0.05 eV, after removing the natural broadening of the Fermi edge at room temperature. This system offers both high energy resolution and high spatial resolution.

Study of the X-ray microbeam for scanning microscopes

Abstract We fabricated a Schwarzschild X-ray objective which has the maximum X-ray transmittance of 9% at the wavelength of 14.1nm and evaluated an X-ray microbeam formed by the objective. We measured the knife-edge response of the microbeam and performed a fitting calculation of the response, using the point-spread function for the objective. It was found that the beam diameter of the microbeam was 45nm. In this paper, details of these experiments and the application of the microbeam will be discussed.

Soft X-ray microscope with zone plate at UVSOR

Abstract A soft X-ray microscope with zone plates was set up at UVSOR [synchrotron radiation facility (750MeV, 200mA) at Institute for Molecular Science, Okazaki, Japan]. A 50nm line & space pattern could be resolved at λ=3.2nm. With an environmental chamber (wet cell) using SiN windows, wet biological specimens, such as letus protoplasts, rabbit myofibrils, tubulin of COS cell and Deinococcus radiodurans strains, could be observed at λ=2.5nm. In the present microscope, the numerical aperture of the condenser was much smaller than that of the objective. To adjust both the numerical apertures, an ellipsoidal condenser mirror system was tested, and preliminary result (an image of Cu mesh, 12.7μm pitch) was obtained.

Photoelectron microspectroscopy observations of a cleaved surface of semiconductor double heterostructure

We have developed a submicron-area high energy resolution photoelectron spectroscopy system equipped with a multilayer-coated Schwarzschild objective for forming a soft x-ray microbeam. We show the photoelectron microspectroscopy results of the cross section of a semiconductor double heterostructure sample, namely an epitaxial film [InP (50 nm thick)/ In0.53Ga0.47As (2.3 μm thick)/InP (100) substrate] grown by metalorganic chemical vapor deposition. The core-level photoelectron spectra were obtained from the cross section of the cleaved sample. The As 3d, Ga 3d, and In 4d peaks were observed in the In0.53Ga0.47As region. In the InP region, the As 3d and Ga 3d peaks were not observed, and only the In 4d peak was. This result corresponds to the structure observed by cross-sectional scanning electron microscopy. Moreover, we observed an irradiation effect that was caused by the microbeam. These results suggest that this photoelectron microspectroscopy system is a powerful tool for studying chemical and elect...