BL02B01 Near-Ambient Pressure Photoelectron Spectroscopy End-station:
The experimental pressure at the near-ambient pressure photoelectron spectroscopy end-station can range from ultra-high vacuum to 20 mbar, with sample temperatures between 69-2000 K and spatial resolution better than 2.8 μm. The end-station enables in situ sample processing, including argon ion etching and vacuum (atmosphere) annealing, with low-energy electron diffraction characterization. Besides measuring photoelectron spectra under electrical gas atmosphere conditions, the station also supports testing of resonant Auger absorption spectroscopy (mRAS) and total electron yield absorption spectroscopy (TEY).
Photoelectron spectroscopy is an experimental technique for detecting material surface chemical compositions and electronic structures. It uses X-rays to excite electrons in materials and analyzes the kinetic energy and momentum of the emitted photoelectrons to obtain information on the surface chemical compositions and electronic structures of materials. When the kinetic energy of photoelectrons ranges from a few electron volts to several thousand electron volts, the inelastic mean free path (IMFP) of photoelectrons is only a few to several tens of angstroms, equivalent to the thickness of a few to several tens of atomic layers. This makes photoelectron spectroscopy a surface-sensitive detection technique, widely applied in surface science, catalysis mechanisms, and environmental science. Electrons have a high cross-section of interaction with matter, leading to very short travel distances in the atmosphere. Thus, photoelectron spectroscopy experiments need to be conducted in an ultra-high vacuum environment, limiting its application in actual atmospheric conditions.
In many research fields, materials or devices operate or work in actual atmospheres. Whether the surface chemical composition and electronic state information obtained through photoelectron spectroscopy in an ultra-high vacuum environment can reflect the conditions in the atmosphere remains uncertain, often leading to misinformation and misguiding researchers. This is referred to as the "pressure gap" in surface science. To overcome this gap, new experimental techniques and methods have been proposed, including near-ambient pressure photoelectron spectroscopy, allowing samples to be tested in millibar (mbar) atmospheric pressure. This advanced experimental technique offers researchers the opportunity to study the surface state of materials or devices in real reaction atmospheres.
Based on the project plan for "A Comprehensive Study Platform for In Situ Electronic Structure of New Energy and Environmental Materials at Shanghai Synchrotron Radiation Facility (SiP·ME2)", a new near-ambient pressure photoelectron spectroscopy station was constructed at the Shanghai Light Source 02B beamline. The 02B beamline, a bending magnet line, has a photon energy range of 40 - 2000 eV. The station is equipped with a Scienta Omicron-produced HiPP-3 electron energy analyzer, capable of spatial resolution. The photoelectron spectroscopy experiments at the entire station can be conducted from ultra-high vacuum to near-ambient pressure conditions while maintaining high energy resolution. Tests have shown that the station's maximum working pressure can reach 20 mbar. Compared to similar near-ambient pressure photoelectron spectroscopy equipment internationally, this system's spatial resolution is 7.5 μm, the highest for synchrotron radiation-based near-ambient pressure photoelectron spectrometers.
BL02B02 Photon In/Photon Out End-station:
The Photon In/Photon Out end-station can perform tests on samples using Total Electron Yield Absorption Spectroscopy (TEY) and Partial Fluorescence Yield Absorption Spectroscopy (PFY), testing elements include the K-edge of C, N, O, Na, Mg, Al, and the L-edge of transition metals. Sample temperatures range from room temperature to 800℃, allowing for in situ electrochemical condition characterizations and characterizations of gas/solid, liquid/solid surfaces through reaction devices.
Soft X-ray Absorption Spectroscopy (sXAS) is a spectroscopic technique based on the principle of X-ray absorption, primarily used to study the electronic structure and chemical state of materials. sXAS focuses on the absorption phenomena within the soft X-ray energy range (typically 100-2000 eV), which is particularly sensitive to the inner shell electron transitions of many elements. Depending on the method of testing, soft X-ray absorption spectroscopy is mainly divided into TEY mode, TFY mode, and PFY mode, which differ mainly in their detection depths: TEY mode has a detection depth of about 10nm, whereas TFY and PFY modes are about 100nm.
The basic principles of sXAS involve the following key steps:
1. X-ray Excitation: When a beam of soft X-rays hits the sample, X-rays of specific energy can be absorbed by the sample's inner shell electrons (such as 1s electrons), causing these electrons to transition from the inner shell to an outer vacancy or to be ionized from the atom.
2. Absorption Edge: At the energy where the X-ray reaches the binding energy of the inner shell electrons, an absorption edge occurs, indicating a sudden change in the X-ray absorption coefficient. The energy position of this edge is directly related to the binding energy of the atom's inner shell electrons, allowing for the identification of different elements and chemical states. Soft X-ray absorption spectroscopy often observes changes in elemental spectral shapes.
3. Extended Edge: Beyond the absorption edge, within a certain energy range, the absorption coefficient of X-rays gradually decreases, defining the extended edge region. The shape and structure of the extended edge contain information about the atomic coordination environment and electronic state. Soft X-rays can test the extended edge of Na, Mg, and Al.
4. Fine Structure: Within the extended edge, finer absorption changes, known as X-ray Absorption Fine Structure (EXAFS), can be observed. EXAFS can provide information on interatomic distances, coordination numbers, and coordination symmetry.
5. Data Analysis: Mathematical processing of the absorption spectra, such as Fourier transformation, allows for the extraction of quantitative information on interatomic distances and coordination environments from EXAFS. By comparing with standard samples, the valence state of elements can be clearly determined.
sXAS is an extremely surface sensitive technique that can be used to study thin films, nanostructures, and local chemical environments in complex settings. In the fields of battery materials, catalysts, and biomolecules, sXAS offers a powerful tool for exploring the microstructure and function of materials.
