Journal of the Korean Physical Society, Vol. 75, No. 7, October 2019, pp. 541∼546 Performance Test of a Laboratory-Based Ambient Pressure X-ray Photoelectron Spectroscopy System at the Gwangju Institute of Science and Technology Hojoon Lim, Youngseok Yu, Dongwoo Kim, Yoobin Esther Koh and Bongjin Simon Mun ∗ Department of Physics and Photon Science, Gwangju Institute of Science and Technology, Gwangju 61005, Korea Vincent Lehane Scienta Omicron AB, P.O. Box 15120 SE-750 15 Uppsala, Sweden (Received 19 April 2019; accepted 29 April 2019) The performance test of a laboratory based ambient pressure X-ray photoelectron spectroscopy (AP-XPS) system at the Gwangju Institute of Science and Technology (GIST) was carried out. The system, consisted of a Scienta R4000 HiPP-3 electron analyzer and a monochromatized Al Kα X-ray source, is designed to operate a gas pressure of up to 25 Torr. An Al polyimide X-ray window is used to isolate the X-ray source from the back-filled-type ambient pressure measurement chamber. Two modes of XPS operations were tested, a one-dimensional chemical imaging mode and a transmission mode. In the transmission mode, the lens voltage of analyzer was optimized for maximum detection of photo-excited electrons under elevated pressure condition, i.e., a typical standard lens operation mode. On the other hand, in the imaging mode, spatial information on the outgoing electrons is conserved to generate a one-dimensional chemical image of surface being measured. The test of the imaging mode on a Au/Si reference sample showed a spatial resolution of ∼10 μm under an Ar gas pressure of 500 mTorr. With the superb design of the differential pump and the electron transfer optics, a good signal-to-noise ratio was obtained for the XPS core-level spectra at Ar gas pressure up to 1 Torr. PACS numbers: 82.80.Pv, 82.80.-d Keywords: Ambient Pressure XPS (AP-XPS), Transmission mode, 1D chemical imaging mode DOI: 10.3938/jkps.75.541 I. INTRODUCTION Over the years, the community in the field of sur- face science has developed various in situ characteri- zation surface-sensitive techniques that detect photons, electrons, and ions generated or scattered at a surface. The development of these diverse in situ tools was out of the need to monitor the surface chemical reactions under the reaction conditions so that reaction mecha- nisms that are more relevant to real life can be identified. Clearly, the applications of in situ operando tools have generated significant progress in the fields of environmen- tal science, heterogeneous catalysis, and energy-related nanomaterials [1, 2]. Among numerous surface analysis techniques, X-ray photoelectron spectroscopy (XPS) has been widely accepted as a powerful technique for prob- ing the chemical states and the electronic properties of surfaces by detecting photoelectrons emitted from the surface [3]. Since Sighbahn first developed XPS based * E-mail: bsmun@gist.ac.kr on the Einstein’s photoelectric effect in 1969, physicists and chemists in the surface science community have fur- ther developed XPS and applied it to fundamental basic science and practical applications in industry [4–9]. In general, an ultra-high vacuum (UHV) condition is always required for normal XPS system in order to avoid any inelastic scattering of photoemitted electrons from gas molecules. Under gaseous environment, the ki- netic energy of photo-emitted electrons decreases rapidly due to inelastic scatterings from gas molecules, which causes the intensity of detected electrons drop signifi- cantly. Also, due to the characteristics of an electron detection scheme, e.g., high-voltage electron multiplier unit in an electron detector, an electron analyzer always requires an UHV environment for its operation [3,10]. While the UHV requirement in XPS is an ideal condi- tion for the study of model systems and clean surface analysis, surface studies at elevated pressures are not possible with the application of XPS. Considering that chemical reactions take place at atmospheric pressure and high temperature, a conventional XPS has many critical limitations. On the other hand, from a ther- pISSN:0374-4884/eISSN:1976-8524 -541- c 2019 The Korean Physical Society