BL practice

BL17SU : Site-selective Observations of the Electronic States for Solid and Liquid Phase
Molecules by Means of Soft X-ray Emission Spectroscopy
Takashi Tokushima, Yuka Horikawa and Masaki Oura (RIKEN/SPring-8)
1. Introduction
Knowledge of an electronic structure is very important for understanding the properties ofmaterials. Occupied states in valence band of the materials have been commonly investigated bymeans of x-ray or soft x-ray photoemission spectroscopy (PES). An ordinary PES is, however,unsuited for studying the electronic structure of materials in liquid phase. As an alternative method tostudy the electronic structure of valence band of liquid sample, the x-ray emission (XE) spectroscopy
in soft x-ray region has been developed in this decade in order to promote the spectroscopic study for
liquids [1-3].
In the course, the participants will learn a principle of the XE spectrometer as well as the liquidflow-cell, and gain experience in soft x-ray absorption and emission spectroscopies for the typicalsamples, such as acetate in aqueous solution and in solid salt.
2. Outline of the soft x-ray undulator beamline BL17SU and the experimental apparatus
Soft x-ray beamline BL17SU [4] is constructed to advance the spectroscopic studies for mainly
solid state physics and materials science using high brilliant soft x-ray undulator radiation.
Photoabsorption, photoemission and XE spectroscopies in soft x-ray region are adopted toinvestigate the electronic structure of various kinds of materials. A novel insertion device ID17,
called a multi- polarization-mode undulator, has been developed for BL17SU [5], and ID17 can be
operated as a helical, elliptical, pseudo-linear or pseudo-vertical undulator. The intense soft x-ray
beam of circularly / linearly polarized light or the mixed polarization state of the beam can thus beobtained by changing the operational mode of ID17. The BL has branched beamlines (branch-a and-b) which can be switched by the pre-focusing mirrors and used alternatively. Each branch has
high-resolution and highly stabilized monochromator [4,6] and several end-stations. The available
energy is ranged between 300 and 1800 eV. The resolving power E/∆E of the monochromator isachievable to be higher than 10,000 and the photon flux is of the order of 1011 photons/s.
At A3 station of the branch-a, High Efficiency Photon “energy” Analyzer (HEPA) [7], which is
aimed at advancing site-selective observations of the electronic states for liquid phase molecules bymeans of the XE spectroscopy in soft x-ray region [3,8-12], is installed and we will mainly utilize
this instruments for the XE spectroscopy in this course. The apparatus consists of the XE
spectrometer and the main chamber equipped with the compact flange-mount liquid flow-cell.
3. Experimental procedure
3.1 Preparation of the powdered sample

In the beginning of the course, the participants will be asked to prepare the powdered sample ofacetate in solid salt. The sample will be supported by the carbon tape sticked on the sample
holder.
3.2 Explanation of the beamline and the SXE spectroscopy
During the evacuation of the chamber, the whole of the beamline as well as the principles of theXE spectrometer will be explained to the participants.
3.3 Calibration of the beamline monochromator
After explanation, calibration of the beamline monochromator will be performed by using ahemispherical electron energy analyzer (SES-2002, VG-SCIENTA) installed at the different
station. The kinetic energy spectrum of Au 4f electrons will be measured as a function of theexciting photon energy in order to establish the relationship between the wavelength of theexciting photons and the setup of the beamline monochromator.
3.4 X-ray absorption (XA) and XE measurements for the powdered sample
An XA spectrum of the powdered sample in near O 1s-edge region will be measured by meansof the total photon yield (TPY) method. After the XA spectrum measurement, calibration of thespectrometer will be carried out by measuring the elastically scattered photons from the sample.
Resonant photon-in－photon-out measurements will be performed at some energy points where
the XA spectrum shows characteristic features.
3.5 Change the setup of sample chamber for the measurement of liquid sample
When the XE measurements for the powdered sample is finished, the participants will be asked
to change the setup of sample chamber for the liquid sample measurement. During theevacuation of the chamber, a preparation of the liquid sample will be carried out.
3.6 XA and XE measurements for the liquid sample
The spectrometer will be adjusted for the measurements of the liquid sample prior to the sample
measurement. When the spectrometer is ready for the measurement, an XA spectrum of theliquid sample in near O 1s-edge region will be performed by means of the TPY method.
Resonant photon-in－photon-out measurements will be performed at some energy points as in
the case of the powdered sample.
3.7 Data analysis and discussions
When all the measurements are finished, the spectrum for each sample will be analyzed andcompared. The participants will be able to compare the results of the XE measurements for solidand liquid samples.
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