Figure 2. BL20U2 experimental station layout
The overall layout of the experimental stations is shown in Figure 2. After soft X-ray beam exits the optical hutch, it passes first through the REXS (polymer) station (dedicated for organic materials, such as polymers or photo resists etc) or the REXS (quantum) station (dedicated for quantum materials, such as high Tc super-conductors, or topological insulators etc) and finally reaches RXES station (dedicated for battery materials or catalysis ). When the post-focusing mirror SM4 cuts into the optical path, the light is focused on the sample position of the REXS (quantum) station. The REXS (polymer) station adopts a guide rail sliding in/out method, which can switch over in operation in defocus mode upstream of the REXS (quantum) station. When the post-focusing mirror SM4 is moved out of the optical path, the light passes through and is focused to the emission RXES station by the two post-focusing KB mirrors SM5/SM6.
Experimental methods and principles:
(1) Soft X-ray resonance emission spectrum (RXES): When a photon with energy in the soft X-ray range (Ω) is irradiated on an object, the electrons at its core level will be excited into the conduction band, and the system will emit a certain energy (ω) of X-ray photons and de-excite to a low energy state (ω<Ω). If the core electrons are resonant excited near a certain absorption edge (similar to X-ray absorption), the subsequent X-ray emission spectrum strongly depends on the energy of the incident photon, so it is called resonant X-ray emission spectrum (RXES).
(2) Soft X-ray resonance elastic scattering (REXS): When a photon with energy in the soft X-ray range (Ω) is irradiated on an object, the electrons on the core level will be excited into the conduction band, in an intermediate state, and then still be de-excited with the same energy (Ω) of X-ray photons. Due to the absence of energy loss in this process, it is equivalent to complete an elastic scattering. If the core electrons are resonant excited near a certain absorption edge (similar to X-ray absorption), the subsequent X-ray elastic scattering cross-section strongly depends on the energy of the incident photon, so it is called resonant elastic X-ray scattering (REXS).
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