UV Photoelectron Spectroscopy (UVPES) at Near Ambient Pressure : A Necessary Tool to Explore Materials and Catalysis under in-situ/operando conditions
Conventional photoelectron spectrometer (PES) works at ultra-high vacuum (10 -9 Torr or lower) to minimize the inelastic scattering. Recent advances in electronics and mechanical design allowed PES to operate at 1 mbar and significantly high pressures. Near-ambient pressure photoelectron spectroscopy (NAPPES) is becoming increasingly popular to explore the materials and catalysis aspects at near ambient pressure (around 1 mbar) and high temperature conditions. NAPPES works fine with x-ray photons, or rather high kinetic energy (KE) electrons, mainly due to relatively lower inelastic scattering and hence good S/N is maintained. However, when the KE of photoelectrons are <100 eV, there are serious problems in observing the spectra with decent S/N ratio under NAPPES conditions. In the recently installed laboratory-based NAPPES system at NCL, Pune, 1 we are able to observe the ultraviolet PES (UVPES) with He-I and He-II excitation sources under near ambient conditions. As a test case we explored the oxidation of copper surfaces (Cu to CuO through Cu 2 O) under molecular O 2 at different partial pressures and temperatures to explore the change in
electronic structure. 2,3 Surface modification of Pd-metal surfaces, by oxygen diffusion into the subsurfaces, and its influence in heterogeneous catalysis was explored through CO oxidation. The most important point is the observation of UVPES under high pressure conditions, which demonstrate the direct evolution of electronic structure. Reasons for the observation of UVPES at NAPPES conditions will be presented along with important features of APPES unit in detail
1. K. Roy, C. P. Vinod, C. S. Gopinath, J. Phys. Chem. C 117, 4717 (2013).
2. K. Roy C. S. Gopinath, Anal. Chem. 86, 3683 (2014).
3. K. Roy, R. Jain, C. S. Gopinath, ACS Catal. 4, 1801 (2014); K. Roy and C. S. Gopinath, ChemCatChem 6, 531 (2014).
4. C. S. Gopinath, K. Roy and S. Nagarajan, ChemCatChem 7, 588 (2015).