BL PracticeBL27SU : Soft X-ray Photoemission and Photoabsorption Spectroscopy
1.

Introduction
In this course, the participants will practice experimental methods of soft x-ray

photoemission and photoabsorption spectroscopy.
Photoemission spectroscopy (PES) is a technique to study electronic states of solids.
One of the advantages of using soft x-rays with photon energies ∼ 1keV for theexcitation light is to increase bulk sensitivity compared to the use of low energy light (≤100 eV). Furthermore, highly energy-resolved soft x-rays obtained by combining thehigh-brilliance synchrotron light source and high-resolution monochromator of SPring-8
make it possible to observe detailed electronic structures.
Soft x-ray absorption spectroscopy is also useful to study electronic states of various
materials, because the energy range of soft x-rays includes many absorption edges oflight elements as well as transition and rare-earth metals. For metallic materials, thetotal electron yield method is conventionally used, where the drain current of samples ismeasured. This method is, however, not applicable to insulators. In this course, we willtry to obtain some photoabsorption spectra by means of the fluorescence yield method
which can be applied to insulators.
2.

Experiments
2.1. Photoemission spectroscopy
The participants will mount a sample on a sample carrier. Silicon single crystal will

be used for the sample. The sample carrier will be installed into the airlock of theultrahigh vacuum system. After pumping the airlock, the sample carrier will betransferred to the measurement chamber and set on the sample manipulator. For PES
measurements, clean surfaces of samples are required. In this course, a clean surface
will be obtained by cleaving the sample in the vacuum. A hemispherical-type
photoelectron analyzer is used for the PES measurements. Before the measurements,
we have to set the parameters of the beamline such as the gap of the undulator, photon
energy, and resolving power of the monochromator. This can easily be done with acontrol software. After setting the beamline parameters, the sample position will beadjusted by the motor-driven sample manipulator to the best position where we can get
the maximum photoemission intensity. Then we will observe some valence band andcore level photoemission spectra.

2.2. Photoabsorption spectroscopy
A fluorescence yield detector is mounted on the chamber for the PES measurements.
The detector is mainly composed of a couple of microchannel plates (MCPs) and a gridplaced in front of the MCPs. The grid is used to prevent ions from coming into the MCPs.
A negative high voltage is applied on the entrance of the MCPs to repel electrons. Then,the fluorescence can exclusively be detected by the MCPs. This detector is used formeasurements by means of the total fluorescence yield. There is also another type ofdetector called silicon drift detector (SDD) mounted on another chamber of the beamline.
By using the SDD, we can measure the partial fluorescence yield, which is effective
particularly for elements with low densities in solids like dopants. The partial
fluorescence yield method will also be tried in this course. Absorption spectra aremeasured by scanning the undulator gap as well as the monochromator to keep themaximum intensity of the incident soft x-rays. The drain current of a post-focusingmirror is used to normalize the photon flux.

Photoelectron analyzer
SPECS: PHOIBOS 150

Transferrod

Preparationchamber

AirlockSRThe fluorescence yielddetector is mounted here.

Vacuumpumps

Slit-lesssoft x-ray emission
spectrometer