Abstract
X-ray photoelectron spectroscopy (XPS) normally requires ultra-high vacuum to suppress scattering of photoelectrons. Such a requirement creates a gap between the XPS experimental condition and the realistic working environments of functional materials such as catalysts. To meet the demand of studying functional materials at work, the technique of ambient pressure X-ray photoelectron spectroscopy (APXPS) has been developed. At SPring-8 BL07LSU, which was operated as a University of Tokyo soft X-ray outstation beamline[1] until August 2022, an APXPS system was constructed and enabled measurements under 100 mbar of gas pressure[2-4]. To further enhance the capability of this APXPS system and realize XPS measurement at 1 bar, we are modifying the design and developing a new APXPS system at the new synchrotron facility NanoTerasu, currently under construction in Tohoku university. The greatly enhanced brilliance in the soft X-ray region makes NanoTerasu an ideal place to set up a soft X-ray APXPS system.
In APXPS systems, ultra-high vacuum must be maintained inside electron analyzer and the beamline, while the sample is placed under near ambient pressure. To realize this, a SiN window and aperture nozzle are placed at the sample-beamline and sample-analyzer interfaces. To secure enough photoelectron signals at 1 bar, the key point is to suppress attenuation of incident X-rays as well as scattering of outgoing photoelectrons by gas molecules. Therefore, we modified the sample environment in which the SiN window and nozzle can be brought as close as 10 mm and 15 um, respectively, to the sample while they were 23 mm and 50 um at SPring-8 BL07LSU. To irradiate the sample in front of the nozzle with X-rays, we adopted extremely grazing incidence (< 5 degrees) condition while the grazing angle of incident X-rays was set at 22 degrees at SPring-8 BL07LSU. With these modifications and high brilliance of NanoTerasu, we expect realistic possibilities of APXPS measurements at 1 bar. In addition, we are modifying the system from the cell type, where only a small cell around the sample in the analysis chamber is filled with gases, to the back-filling type, where the whole analysis chamber is filled with gases. The modification not only simplifies the system and makes operation easier, but also increases the space around the sample. This will enhance the flexibility of measurement conditions, which for example enable electronic field application or the study of liquid-solid interfaces.
[1] S.Yamamoto et al. J.Synchrotron Radiat. 21, 352 (2014)
[2] T. Koitaya, S. Yamamoto et al., Top. Catal. 59, 526-531 (2016).
[3] S. Yamamoto et al., Phys. Chem. Chem. Phys. 20, 19532-19538 (2018).
[4] Y. Ishihara et al., Adv. Mater. Interfaces 10, 2300258 (2023).
