Seminars Archive

Laboratory-based High Pressure XPS: Past, Present and Future

Abstract
Photoelectron spectroscopy (PES) is perhaps the most direct probe of electronic structure available to the physical scientist, as well as an invaluable tool for elucidating bulk and surface chemical composition. It is commonplace to use PES for the characterization of samples held in high or ultra-high vacuum (HV, UHV), yet what is gained in understanding the fundamental surface physics of a material, is lost when this knowledge needs to be transferred to the material operating in real-world conditions. This so-called “pressure-gap” has been the focus of intense technological development over the last 40 years, culminating in the latest generation of high-pressure X-ray photoelectron spectroscopy (HPXPS) instruments [1]. Recently a state-of-the-art laboratory-based HPXPS system housed in the Department of Materials, Imperial College London has been developed and commissioned. The system allows key in-situ and in-operando XPS analysis of the surfaces of materials in a wide range of technologically relevant areas including energy, catalysis, electronic materials and biomaterials.
The system is equipped with state of the art monochromatic X-ray and ultraviolet light sources and a differenyially pumped hemispherical electron analyser. This dual capability instrument can operate at pressures from UHV (10^-10 mbar) up to 30 mbar using a variety (and controllable mixtures) of gases (air, N₂, O₂, H₂, H₂O, CO₂, CO etc) and over a wide temperature range (room temperature to over 800°C). This is achieved using a two-piece titanium reaction-cell in-built with the cone and aperture necessary for HPXPS measurements. The high-pressure retractable reaction-cell is designed to provide flexibility between near-ambient pressure and UHV conditions. A specially designed “BioCell” has been developed for the study of biomaterial surfaces, and enables the transfer and measurement of vacuum sensitive materials without ever exposing the surfaces to vacuum conditions.
This talk will place into context the history of high-pressure photoemission, the current capability and the future opportunities. I will discuss recent results on the instrument development and improved capabilities,[1-4] as well as demonstrations of the application of the HPXPS technique to catalysis.[5]

References
[1] S.K. Eriksson, M. Hahlin, J.M. Kahk, I.J. Villar-Garcia, M.J. Webb, H. Grennberg, R.Yakimova, H. Rensmo, K. Edstrom, A. Hagfeldt, H. Siegbahn, M.O.M. Edwards, P.G. Karlsson, K. Backlund, J. Ahlund, D.J. Payne, Rev. Sci. Instrum. 85 075119 (2014)
[2] M. O. M. Edwards, P. G. Karlsson, S. K. Eriksson, M. Hahlin, H. Siegbahn, H. Rensmo, M. Kahk, I. J. Villar-Garcia, D. J. Payne, J. Åhlund, Nuclear Instruments and Methods in Physics Research Section A 785 191 (2015)
[3] J.M. Kahk, I.J. Villar-Garcia, L. Grechy, P.J.K. Bruce, P.E. Vincent, S.K. Eriksson, H. Rensmo, M. Hahlin, J. Åhlund, M.O.M. Edwards, D.J. Payne, Journal of Electron Spectroscopy and Related Phenomena 205, 57 (2015).
[4] G. Kerherve, A. Regoutz, D. Bentley, C. Hood, K. Feeley, S. Knight, A. Robson, C. Turner, N. Singh, J. Pontefract, J. Ahlund, J.M. Kahk, I.J. Villar-Garcia, D.J. Payne (submitted to Rev. Sci. Instrum.) 2016.
[5] A. Regoutz, G. Kerherve, I. Villar-Garcia, C.K. Williams, D.J. Payne (under review) 2016.