Photon Factory Activity Report 2019 #37 (2020)

BL-11D/2018G640

Development of Soft X-ray Spectro-Microscope with Wolter mirror
Norio WATANABE1, * and Sadao AOKI2,1
Faculty of Pure and Applied Sciences, University of Tsukuba,Tsukuba, Ibaraki, 305-8573, Japan
2CROSS, 1601 Kamitakatsu, Tsuchiura, Ibaraki, 300-0811, Japan
11 Introduction
A Wolter mirror is an optical element that uses total
external reflection and has no chromatic aberration. In aWolter mirror imaging system, the magnification does notchange even if the soft X-ray energy is changed, so it ispossible to easily compare changes in the image when theenergy is changed. Therefore, it is an optimum opticalelement for a full-field spectroscopic microscope. Since aWolter mirror has a ring aperture, it is necessary to adjust
the NA so that the illumination light enters the mirror ring.
In this study, a plane mirror was used to illuminate asample at the angle of the average NA. The imaging
performance was evaluated in a wide energy range from100 eV to 900 eV.
2 Experiment
Figure 1 shows the optical system. The Wolter mirror
has a magnification ratio of 32, an average grazingincidence angle of about 40 mrad, and the surface materialof Pyrex glass [1]. A sample was illuminated with a quartz
plane mirror. As a test sample, diamond powder (size: 4-8m, Nilaco) placed on a carbon foil (Quantifoil R1.2/1.3,1.2 m diameter holes spaced at 2.5 m intervals, ElsevierScience) was used. The optical system was mounted on thesample stage of the reflectometer system[2] installed on
the beam line. The observation was performed at amagnification of 19, which was two-third of thespecification, due to the restriction of the beam line length.
Therefore, the image was slightly distorted. The soft x-ray
images were recorded with a cooled CCD camera(Hamamatsu Photonics, C4742, pixel size: 13 m).
3 Results and Discussion
Figure 2 shows the observed soft X-ray images. Figure2(a) is the image at 280 eV and Fig. 2(b) is the image at290 eV. Figure 2(b) has good contrast since 290 eV is thehigher energy side of the absorption edge of carbon. Figure2(c) is the image at 800 eV. At 800 eV, the exposure time
was doubled due to the decrease in the mirror reflectance,
but it did not affect the image contrast. Figure 2(d) is a partof Fig 2(c). The holes of 1.2 m in the carbon film could
be observed.
Since these images do not change the observation
location, it is possible to easily analyze the change inabsorption with respect to the change in energy of soft Xrays. Therefore, it is considered to be very useful for XAFS
measurement of microscopic area.

Sample~170 mrad

Wolter mirror

CCD

Plane mirror

Fig. 1: Optical system of microscope with a Wolter
mirror objective.

(a)

(b)

20 m

20 m

(c)
(d)

5 m
20 m
Fig. 2: Soft x-ray images of diamond powder (4 – 8m) at (a) 280 eV, (b) 290 eV, and (c) 800 eV. (d) isthe area of white dash line in (b) with enhanced
contrast. The holes of 1.2m diameter and 2.5 m pitchof the carbon foil can be observed. The exposure timeof (a) and (b) was 5 s ×10 accumulation. That of (c)was 10 s×10 accumulation.
References[1] M. Hoshino and S. Aoki, Jpn. J. Appl. Phys. 45, 989(2006).
[2] Tadashi Hatano and Shogaku Aihara, J. Phys.: Conf.
Ser. 425 152018 (2013).
* watanabe@bk.tsukuba.ac.jp