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This is the biggest congress in science field in Thailand. It will be held annually around October.

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This is the physics congress in Thailand. It will be held annually around March.

International conference in Thailand

Photoemission technique

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Check list before the application to the PES beamtime

(1) The most important thing is to submit the beamtime proposal before the deadline!
    - The safety and PI information are quite important to implement user's projects.
    - Note that all of proposals are reviewed and scored by external reviewers.
    - No proposal, no chance (except the industrial service, collaboration projects).
    - Clear description on why SR-XPS, and why not XAS, XRF, EPMA, mass spectrometry (SIMS, FABMS etc.) or XPS using AlKa?
    - The standalone XPS system is available in SUT-NANOTEC-SLRI BL5.1 XPS.

(2) Sample size must be large enough compared to the detection area.
    - XPS samples should be more than 5x5mm^2 at least. (See pictures)

    - XAS samples should be more than at least 5x5mm^2 larger than the beam size at XPS position.
    - Powders had better be attached as a pellet on carbon tape.

(3) Surface ex-situ impurities such as carbon and oxygen are negligible sometimes.
    - Handle with care on surface as clean as possible until loading sample into vacuum.
    - In-situ ion sputtering is available at XPS and PES, and PES has an sample heater.

(4) The sample surface needs to be conductive.
    - Surface must be conductive by doping or coating.
    - Charging effect might be reduced at lower photon flux, but more poor S/N.

(5) The probing target is whether surface or bulk.
    - Depth profile is required to get into bulk elements by ion sputtering method.
    - To do with ion sputtering, it is necesary to get more beamtime.

(6) The concentration of target elements in surface or bulk.
    - 1at% on surface is a detection limit in the low photon energy (BE < 100 eV).
    - To analyze the chemical states, 10% of element concentration is at least required.

(7) The binding energy of core levels and kinetic energy of Auger peaks.
    - Non overlapped spectral profile within the photon energy range (PE < 1000 eV) without sample charging condition.
    - The binding energy calibration is always required on the standard peaks or samples due to the instability of instruments.
    - The literature survey reported previously on samples by XPS may give us a great help to proceed the experiment.

(8) The chemical analysis by XPS or XAS in the total electron yield mode.
    - The standard samples are required to get information on chemical shifts.
    - XAS might be time-consuming experiment due to a slow undulator-gap changing speed.
 

Check list for the beamtime

(1) You need to have the ID card and radiation detector to get into our facility.
    - We are prepared for ID cards and radiation detectors for participants you described in your proposal.
    - Get ID cards and radiation detectors from the SLRI security guard in front of SLRI building (Contact the safety office if any problems).

(2) Sample must be prepared for UHV.
    - Loading samples into UHV takes at least an hour.
    - Visit the web on sample requirement.

(3) Local contacts assist your measurements.
    - Data can be served as ascii text or excel files.
    - The PES and PEEM annual workshop will be held for experts' help to data analysis.

Techniques using SR: Soft x-ray angle-resolved photoemission spectroscopy (ARPES)

                                    Soft x-ray angle-integral photoemission spectroscopy (SXPS)

                                    Soft x-ray absorption spectroscopy in the total electron yield mode (SXAS)

Applications:                Electronic structural investigation of materials

Radiation source:        A planar Halbach-type undulator (Danfysik)

Magnetic field: 0.5467 T@26.5 mm of gap
Period length: 60 mm
Number of periods: 41
Total length: 2.460 m

Photon flux at sample:    1.0 x 10¹⁰ photons/s/100 mA @E/DE ~ 10,000 (designed)

Photon energy ranges:    40 – 160, 220 – 1040 eV

G#1 (600 lines/mm) 40-160 eV
G#2 (1200 lines/mm) 220-520 eV
G#3 (2400 lines/mm) 440-1040 eV

5 keV for AES electron energy

Beam sizes in simulations:                  

Two pre-focusing mirrors are available for two point focusing.
0.2 mm (H) x 0.2 mm(V) at SXPS
0.3 mm (H) x 0.1 mm(V) at ARPES

100 micron for AES electron beam spot size

Monochromator type:      Grazing incidence varied line spacing plane grating monochromator (TOYAMA)

Sample types:                  < 8 mm x 8 mm x t1 mm @ARPES for in-situ thermal treatments

                                        < 20 mm x 20 mm x t3 mm @SXPS and SXAS

Sample environment:      In the ultra high vacuum (< 2x10^-10 mbar)

Beamline status:             General user service since Mar. 2011

Facilities in the ARPES end-station

The ARPES end-station consists of the photoelectron analysis, sample preparation, rotary sample-transfer, MBE, and SMOKE chambers. Angle-resolved (VG Scienta, R4000) electron energy analyzer is installed in the photoelectron analysis chamber with the electron gun for AES (5 keV; 100 micron spot size) and LEED optics (1 keV). The sample preparation can be carried out in the sample preparation chamber, located above the photoelectron analysis chamber, with the Ar ion sputtering gun (3 keV@ion energy), electron-bombardment heater (1400K@max.), and gas-inlet variable leak valves connected with the roughing pump. A sample could be handled on the temperature-controlled manipulator down to 40 K in near future. Rotary sample transfer system (R2P2) transfers samples between the vacuum chambers without breaking UHV. The MBE chamber consists of the effusion cell, e-beam evaporator, temperature-controlled sample manipulator (1400K@max.), and RHEED optics (15 keV@electron energy). The residual gas analyzers (100 atomic mass@max) are installed in the ARPES and MBE.

Facilities in the SXPS end-station

The SXPS station consists of the angle-integral (Thermo VG Scientific, CLAM2) electron energy analyzer and Ar ion sputtering gun (3 keV@ion energy). Samples are loaded into the UHV chamber using the magnetic linear transfer rod from the first-entry air-lock system, pumped by the turbo-molecular pump, to the XPS analysis chamber, pumped by the 500 l/s ion and titanium sublimation pumps. The residual gas analyzer (100 atomic mass@max) is also available.

Note: XAS is a complementary technique with XPS to study a chemical state of elements in materials. XPS probes occupied-state electron densities excited to unoccupied states, while XAS probes unoccupied-state electron densities excited from occupied states. Both techniques are based on the free-electron-like unoccupied states to probe the occupied state electron densities. However, XPS directly probes electron energies at a fixed photon energy, so the charging and surface effects cannot be avoidable. XAS has an advantage to measure the insulating samples if the unoccupied states are almost equivalent in materials to be compared. Soft x-rays do not penetrate the beryllium window for a hard x-ray beamline, so UHV conditions at the analysis system are nessesary to measure absorption spectra involving core levels in the soft x-ray energy range such as C, N, and O K edges. Soft x-ray absorption in materials is mainly governed by Auger electron emissions resulting from a small probability on fluorescence process to release the absorbed photon energy. Therefore, the workfunction difference formed at surfaces in materials are negligible. In the "soft" XAS measurement in BL3.2a, the photon flux, energy resolving power, and polarization and surface sensitivities are much higher than those obtained in BL8. However, the soft XAS measurement is performed only in the electron yield mode, because the transmission of samples and its holder materials are quite low.

Some results on the commissioning of the undulator beamline 3.2 by gas-phase photoionization spectroscopy are shown.