Photon Factory Activity Report 2014 #32 (2015) B	

BL-11D/2011G661, 2013G702

Software for operating varied deviation-angle monochromator at BL-11D
Tadashi Hatano*
IMRAM, Tohoku University 980-8577, Japan
1 Introduction
The beamline BL-11D was used for photoemission
measurements during 1996 – 2009 [1]. The
monochromator was designed to cover 20 – 1300 eV
energy range with a target resolving power of 5,000. It is
composed of a cylindrical mirror Mf, a plane mirror Mp
and a spherical grating G as shown in Fig. 1. G rotatesaround the center of its surface and Mp around the point
C behind G. Monochromatization is achieved by suitableselection of Mp and G angles. It should be noticed thatthe footprint moves on Mp surface because of the offcenter rotation of Mp. Gratings G1 and G3 are mounted
for soft X-ray and VUV regions, respectively.

Fig. 1: Side view of monochromator optics of BL-11D.
In the previous operating software was based on theexperimental data of photoelectron spectroscopy. Several
Mp-G angle pairs that made spectral shape sharpest, werechosen to be fitted by fourth polynomial functions ofphoton energy. Consequently the monochromator did notwork beyond the energy range where photoelectron
experiments were performed. The operable range were300 – 700 eV and 60 – 200 eV with G1 and G3,
respectively [2].
Recently BL-11D was redesigned as a reflectometry
beamline for VUV and soft X-ray curved mirrors.
Spectral measurements are usually carried out with angleof incidence fixed. A new software was programmed forthe purpose of extending the operable energy range
including the dead zone of 200 – 300 eV. Transmission ofthin films and absorption of gasses have been measured toconfirm focus condition and energy calibration.
2 Theory
Above Mf, Mp and G geometry makes a negative
incidence-length varied deviation-angle monochromator.
It is similar to the Padmore type except for employing Mf

which makes a convergent incidence to G. Without Mp,
Mf makes an image of the entrance slit S1 at a fixed
position S1’. The grazing angle of Mf is 2°, that is ∠S1Mf-S1’ = 176°. Mp makes an image of S1’ at S1” whichmoves depending on the Mp angle θMp. The origin of θMpis taken to be the angle when the surface of Mp is parallelto the optical axis of Mf-S1’. The grazing angle of Mp
agrees with θMp.
The geometry of S1”, G and the exit slit S2 determines
the defocus and the wavelength. The optical axis from G
to S2 is parallel to Mf-S1’. ∠S1”-G-S2, which agrees
with the difference between 180° and the deviation angle
α – β, is a function of Mp and approximately equals 2θMp
though the reflected optical axis does not exactly passthrough the center of G. The negative incidence length r =–(G-S1”) is also a function of θMp. The distance r’ = G-S2
is constant, and the diffraction angle β equals θG – 90°,
where θG is the angle of G with the origin the angle when
the surface of G parallel to G-S2. Quite simply, a 1°
increase of θMp makes a 2° decrease of α, and a 1°
increase of θG makes 1° increases of both α and β. θMpand θG changes the wavelength λ similarly but in theopposite direction.
Now the focus equationand the grating equation

can be written by parameters θMp, θG. and λ, where R andσ are the radius of curvature and the groove constant ofG, respectively. R is 55.21 m for G1 or 22.945 m for G3.
The groove density σ−1 is 2400 lines/mm for both G1 andG3.
Although solutions for θMp and θG should be obtained
from a given λ in the practical monochromator use, itrequires too complicated calculation. On the other hand,
numerical solutions for θG and λ from a given θMp is notdifficult to obtain. Therefore a numerical list of θG and λas a function of θMp was prepared and an algorithm forselection of suitable θMp and θG from a given λ by

Photon Factory Activity Report 2014 #32 (2015) B	interpolation procedure was included in themonochromator operating software. Obtained θMp and θGare plotted in Fig. 2 as functions of photon energy. The
difference θG – θMp, which approximately equals α + β isalmost constant. It means that the blaze angle of G works
over the whole energy range.

transition metals were measured in 280 – 950 eV region.
N-K absorption was measured at 401 eV. Spectralreflectometry experiments up to 1200 eV was carried out[2, 4]. As a result, it has been confirmed that themonochromator works in 230 – 1200 eV with G1.

0.435G32520θG1510θMp

0.3

height (mm)angle (deg)30

G1 1200 eV
G1 1000 eV
G1 800 eV

0.2
0.1
0G1

G1 600 eV
G1 400 eV
G1 200 eV
G3 300 eV
G3 200 eV
G3 100 eV

-0.1

50

θG

200

00.2 0.4 0.6 0.8

11.2 1.4 1.6 1.8600

800position (mm)θMp

0400Fig. 3: Result of surface deformation analysis of Mp.

photon energy (keV)

3 Experiments
With a new monochromator operating software,
spectral transmittances of Al, Si, Zr, Ti and C thin films
were measured in 50 – 290 eV region using G3. Al-L2,3,Si-L2,3, Zr-M4,5 and C-K absorptions were observed.
Because of second order diffraction constituent of thegrating monochromator, Si-L2,3 and Ti-L2,3 absorptions
were also observed around 50 eV and 230 eV,respectively. Energy difference between spectra throughw > 0 and through w < 0 gives defocus, where w means
the position on the grating surface. Therefore grating area
resolved spectra were measured using the angle selection
slit after the post focusing mirror.
Unexpected behavior was found on the focus, that is
the focal point moves toward outside S2 as photon energy
increases. It can not be interpreted as an error in radius ofcurvature of Mf or G. It seemed as if R had changed
depending on energy. This problem was fixed when asurface deformation in a third polynomial function asshown in Fig. 3 was assumed with Mp. The reflection
point which moves depending on the photon energy isshown by arrows. The minimum radius of curvature is
200 m. Possible other causes such as unsmooth rotationof Mp were also converted into the deformation
parameters.
Kr-M4,5 absorption was measured using an ion detector[3] mounted between the post-focusing mirror and thereflectometer. Results are shown in Fig. 4. The line
structure was clearly observed.
Using G1, C-K, Zr-M2,3 and L2,3 absorptions of 3d

6photoion yield (104 cps)

Fig. 2: Mp and G angles satisfying focus and grating
equations.

Kr3d5/2-5p

43d3/2-5p
3d5/2-6p
3d3/2-6p

209092949698

photon energy (eV)Fig. 4: Measured absorption spectrum of Kr.
4 Conclusions
The monochromator operation software at BL-11D has
been renewed on the basis of no defocus condition tocover 60 – 1200 eV energy range.
Acknowledgement
The author is grateful to Mr. K. Watanabe for his
LabVIEW programming. He is also grateful to Prof. K.
Mase for his help in gas measurements.
References[1] PF	 Act. Rep. 1997 A, #15, 101 (1998).
[2] T.	 Hatano et al., J. Phys.: Conf. Ser. 425, 152018(2013).
[3]	

N. Fujita et al., J. Vac. Soc. Jpn., 50, 583 (2007).
[4] T.	 Hatano et al., J. Electron Spectrosc. Relat. Phenom.
196, 156 (2014).
* hatano@tagen.tohoku.ac.jp