The soft branch of the Energy materials research beamline (E-line) (BL20U2) is one of the beamlines given birth by Shanghai Synchrotron Radiation Facility (SSRF) Beamlines Project (SSRF - Phase II). It has passed CAS- process testing in October 2022 and is currently open to users. This branch beamline belongs to the E-line complex. It can operate completely independently as a soft X-ray beamline. It adopts an elliptical polarization oscillator (EPU60) as the light source and relies on a grating monochromator to deliver photons in the energy range of 130-1500eV to the experimental station called Soft X-ray Scattering station (Soft X-ray RXES/REXS station), featured with soft X-ray scattering methods. These includes both inelastic methods such as Soft X-ray Resonance emission (RXES) or Soft X-ray Resonance Inelastic Scattering (RIXS), and elastic methods such as Soft X-ray Resonance Elastic Scattering (REXS) .

 

Soft X-ray resonance emission spectroscopy (RXES) is applicable in the research field of energy materials, which includes: (a) the electronic structure and chemical state characterization of power batteries, photovoltaic devices, solar cells, and fuel cell electrode materials that play an important role in clean energy technology; (b) the electronic structure characterization of new generation catalysts (e.g those for carbon dioxide reduction and conversion to renewable energy, high-efficiency and energy-saving synthetic ammonia catalysts) providing a key basis for establishing reliable structure-activity relationships and catalytic mechanisms, furthermore guidance for the rational design of advanced catalysts and purposeful regulation of catalytic processes in the future; (c) the true bulk properties of nano-structured materials, and those even under oxide passivation. Soft X-ray elastic scattering (REXS) can be applied not only to single crystal/superlattice inorganic materials, but also to the study of semi-crystalline and even polycrystalline organic materials. In studies for inorganic materials mainly long-range information such as charge ordering, orbital ordering, and spin ordering in quantum and magnetic materials are explored. This method, combined with synchrotron radiation light sources, endows it with superior characteristics: (a) element specific - sensitivity to chemical elements comes from element specific absorption edges; (b) orbital specific - selecting the absorption edge energy of an element to excite electrons, and identifying different final orbitals through multipole transitions; (c) multipole moment analysis - REXS is sensitive to multipole moments. The study of symmetry parameters can distinguish between magnetic and non-magnetic effects, etc. In studies for organic materials mainly phase separation and the size distribution of phase domains in soft condensed structures are investigated, which can help optimizing e.g. the charge transfer characteristics of organic solar cell films and fabricating high-performance devices; This method can also be used as a highly promising non-destructive testing method to characterize the edge roughness of critical dimensions (CD) in photoresist films, one of the key materials for micro pattern processing in microelectronics technology, to meet the needs of the development of ultra large scale integrated circuits.

 

Figure 2. BL20U2 experimental station layout

(1) Collection and processing of emission spectra:

The emission spectrum is collected by a vacuum internal CCD. The basic parameters of CCD are set by the beamline staff before the experiment, and the CCD detector should always be cooled under the low temperature (about -65 ° C) during the experiment. The parameters that users need to modify currently only include exposure time and the file name for data storage.

 

User data collection instructions:

Step 1: Tune the beamline photon energy to the appropriate value;

Step 2: Set the CCD exposure time and start the exposure;

Step 3: Wait for the exposure to end, and the data collection software will refresh;

Step 4: Save the data in TIF format, number and record relevant parameter information;

Repeat the above steps

 

Data saving format:

Number_ Sample abbreviation_ Incident energy in (eV)_ slit opening in μm2_ Spectrometer parameters _ Exposure time in seconds.tif

 

The setting of emission spectrograph parameters, CCD exposure time, and selection of incident energy in the RXES experiment need to be explored and tested by the beamline staff, and determined through interaction with users based on actual emission spectra data.

 

The correction and preprocessing of CCD image data are achieved through a homemade software independently developed by the beamline staff, and the specific operation steps are to follow the guidance of the beamline staff.

Spectral information acquisition and data copying

a)The 2D imaging data collected by CCD will be processed by the software and output as spectral data, saved in Excel spreadsheet and image format. There is currently no reference tutorial available, and users will be instructed on site. 

b)All CCD data and processed spectral data are stored in the data folder established on the same day. Users need to copy and backup them in a safe and reliable USB flash drive brought by themselves in a timely manner, and may not delete raw data.

 

(2) Collection and processing of elastic scattering data:

(to be launched)