BL3U Varied-Line-Spacing Plane Grating Monochromator for Molecular Soft X-Ray Spectroscopy

Description

  The beamline BL3U is equipped with an in-vacuum undulator composed of 50 periods of 3.8 cm period length. The emitted photons are monochromatized by the varied-line-spacing plane grating monochromator (VLS-PGM) designed for various spectroscopic investigations in the soft X-ray range. Three holographically ruled laminar profile plane gratings are designed to cover the photon energy range from 40 to 800 eV. The beamline has liquid cells for soft X-ray absorption spectroscopy (XAS) in transmission mode as shown in Fig. 1. The liquid cell is in the atmospheric helium condition, which is separated by a 100 nm thick Si₃N₄ membrane with the window size of 0.2 × 0.2 mm² from the beamline in an ultrahigh vacuum condition. The thin liquid layer is assembled by using two 100 nm thick Si₃N₄ membranes. The thickness of the liquid layer is controllable from 20 to 2000 nm by adjusting the helium pressures around the liquid cell in order to transmit soft X-rays. Liquid samples are exchangeable in situ by using a tubing pump. The liquid cell has two types of windows: one is the liquid part to obtain the soft X-ray transmission of liquid (I), and the other is the blank part to obtain the transmission without liquid (I₀). We can obtain the reliable XAS spectra based on the Lambert-Beer law ln(I₀/I). Since the liquid cell is in the atmospheric condition, we can measure XAS of liquid samples in the real environment. Operando XAS observation of several chemical reactions such as catalytic, electrochemical reactions are also possible by using our liquid cells developed for these purposes.

　　　　　
  Fig. 1. (a) Schematics of a liquid cell for XAS in transmission mode settled in BL3U. The blowup shows a
thin liquid layer assembled by two Si₃N₄ membranes with the thickness of 100 nm. (b) Flux at the sample
position with the resolving power of λ/Δλ=10⁴.

Technical Data

BL3U in Activity Report 2024