BL09U

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Scientific Scope
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The scientific objective of "Dreamline" is to achieve ultra-wide energy coverage (20-2000eV) and ultra-high energy resolution (25meV@867eV), while organically integrating three experimental stations - Angle-Resolved Photoemission Spectroscopy (ARPES), Photoemission Electron Microscopy (PEEM), and Resonance Inelastic X-ray Scattering (RIXS) - with the beamline to create an excellent soft X-ray experimental environment. ARPES is the only experimental technique that can directly obtain information on the direction, velocity, and scattering process of the valence band electrons near the Fermi level in reciprocal space. It is suitable for studying strongly correlated electron systems (such as superconductivity and graphene), spintronics (topological insulators, anomalous quantum Hall effect, and magnetic materials), nanostructures, and nanomaterials. PEEM dynamically analyzes the structures of these materials in real space with high spatial resolution. Meanwhile, RIXS can be used to measure the electronic structure information of materials' conduction bands, valence bands, and low-energy excited states, such as dd (or ff) electron transitions, charge transfer, and magnetic excitations, thereby studying phenomena like charge transport, magnetism, superconductivity, and electron-phonon interactions.
Beamline Layout
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Specifications
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Endstations
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Experiment endstation 1 - ARPES
The Angular Resolved Photoemission Spectroscopy (ARPES) Experimental Station 
The ARPES experimental station is equipped with a Scienta DA30L electron energy analyzer and an integrated VLEED spin detector. It achieves efficient Fermi surface mapping through the Deflection spectrum acquisition mode, particularly suitable for small-sized or uneven-surfaced samples. The sample attitude adjustment is facilitated by a 6-axis open-loop cryogenic sample holder, incorporating 3 translational degrees of freedom and 3 rotational degrees of freedom, providing high-precision sample attitude manipulation for convenient measurements of large-scale electronic structures in momentum space. The lowest temperature near the sample can reach 4K, offering opportunities for research on low-temperature phase transitions in materials.
In terms of the vacuum system, the ARPES is equipped with a sample loading chamber, a transfer chamber, an annealing chamber, a sample preparation chamber, and a measurement chamber. The sample loading chamber reserves six sample parking positions. The annealing chamber allows for argon etching and annealing treatments of the sample surface. The sample preparation chamber is equipped with Low-Energy Electron Diffraction (LEED) and K-cell for probing the surface structure and modulating electron doping of the sample.
The primary methods employed include UVU/Soft X-ray/Resonant ARPES.
Experiment endstation 2 - PEEM
PEEM, based on the photoelectric effect, provides a multi-mode experimental platform with high spatial resolution and chemical composition discrimination for studying the surface properties of solid materials. The core of the PEEM experimental station is the Elmitec PEEM system, which has been integrated with a high-performance energy analyzer. In addition to X-ray synchrotron radiation, the light sources used include mercury lamps and femtosecond lasers to meet various experimental requirements. Leveraging the temporal resolution capability of femtosecond lasers, the experimental station has realized ultrafast PEEM methods, satisfying the research demands for dynamic processes at surfaces and interfaces.
The primary methods: LEEM (Low-Energy Electron Microscopy), MEM (Microscopy and Microanalysis), LEED (Low-Energy Electron Diffraction), UV/X-ray/Laser-PEEM (Photoemission Electron Microscopy using Ultraviolet, X-ray, or Laser light), Spectroscopy.
Experiment endstation 3 - RIXS
RIXS is used for study the collective mode in solid materials, such as phonons, spin excitations, d-d transfer, charge transfer, ect.
RIXS endstation consist of the experimental sample chanmber system, the spectrometer. The main components includes the UHV sample chamber, crygenic sample manipulator, monochromator, X-ray CCD detector. 
The primary methods : RIXS (Resonant Inelastic X-ray Scattering，RXES (Resonant X-ray Emission Spectroscopy，XAS (X-ray Absorption Spectroscopy)
Data Acquisition and Processing
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Experimental Process
After the sample holder reaches the measurement position, the beamline shutter can be opened to start the experiment. The steps are as follows:
1. Open the manual valve between the beamline pipe and the main chamber (usually already open).
2. Open the light shutter by pressing and holding the buttons in the sequence. The red light will illuminate, indicating that the light shutter is open. (To close the light shutter, press and hold the green buttons in sequence.)
• Temperature Control: The temperature range of the sample holder is 6K-340K. The cooling capacity is controlled by turning the needle valve of the liquid helium Dewar. Looking from the top down, turning clockwise opens the valve wider, while turning counterclockwise closes it. Approximately 180° of rotation achieves maximum cooling capacity. The sample holder is equipped with a built-in heating function, which can be controlled by a temperature controller or control software. For large temperature increases, staged heating (with intervals of 20K) is required. During this process, gases are released, requiring the main chamber vacuum to be no worse than 2.0 × 10-10 Torr. If the heating function is insufficient to reach the desired temperature, the needle valve should be opened slightly to reduce the cooling capacity.
• Switching Polarization: The Dreamline can achieve three different polarization states: horizontal, vertical, and circular polarization. These can be switched by adjusting the polar mode in the DEPU.
• Switching EPU: The EPU148 is used in the low-energy region, while the EPU58 is used in the high-energy region. The EPU should be selected based on the Photon Energy vs. EPU Gap relationship table. Before switching the EPU, first switch the polarization to LH, then adjust the Gap value of the current EPU to its maximum (EPU148 max is 118, EPU58 max is 160), close the light shutter, and call the central control room for remote switching.
• Switching Gratings: Use grating1 for photon energies below 250eV and grating2 for energies above 250eV. Switching can be done in the Mono, but the light shutter should be closed before switching.
• Switching Photon Energy: The photon energy of BL09U can be varied from 22eV to 2000eV. To switch the energy, adjust the Gap value of the EPU according to the Photon Energy vs. EPU Gap relationship table and change the photon energy in the Mono. Note that when crossing the 250eV threshold, the grating should be switched at a higher energy level before and after the switch to avoid open-loop conditions caused by the monochromator grating and plane mirror hitting the limit. For example, when switching from 100eV to 300eV, switch the grating at 300eV, and vice versa. Additionally, when performing ARPES experiments, the selected photon energy must not exceed the energy range specified by the ARPES analyzer lens table to prevent damage to the MCP detector of the analyzer.
• Adjusting Monochromatic Exit Slit: Users can adjust the light intensity by adjusting the opening size of exit slit. The maximum adjustment range is Y: size motion = 100-400 microns, with 200 microns recommended.