Imperial College London - Equipment Account

For over 50 years, x-ray photoelectron spectroscopy (XPS) has demonstrated itself as an invaluable technique in the study of filled electronic states of solids, as well helping to determine the nature of interactions between solid surfaces and molecular species. Unfortunately there is one main drawback in the technique, that being that typical XPS measurements are performed in ultra high vacuum (UHV) conditions (10-10 mbar), due to the need of minimising the chances of unfavourable collisions occurring before the excited photoelectrons reach the energy analyser. Due to this restraint, studying the surfaces of technologically important materials occurs at a pressure many orders of magnitude lower than the operational conditions of the systems themselves (1-50 bar). Bridging this so-called "Pressure Gap" has remained a significant technological challenge. Very recent developments in electron energy analyser and sample holder design have for the first time allowed photoelectron spectroscopic measurements to be performed in ambient pressures of up to 25 mbar. The opportunity to study "real" surfaces in-situ and in-operando is a step change in the field of photoelectron spectroscopy, and opens a new and vital chapter in the area of surface science. The ambient pressure photoelectron spectroscopy (APPES) system is a state-of-the-art laboratory-based instrument with capabilities of performing high-energy resolution, low signal-to-noise photoemission measurements in up to 25 mbar ambient pressure with a number of different gases (O2, N2, H2, ethylene, acetylene). The instrument is equipped with a monochromated x-ray source and a high transmission, differentially pumped electron energy analyser. The system is fitted with an in-situ sample cell, which can provide a temperature range of 80 - 1100 K in the ambient atmospheres, permitting in-operando measurements. This specially designed modular in-situ cell, which is fully retractable from the analysis chamber, also allows standard UHV XPS comparative measurements to be performed with ease. The APPES instrument based at the Department of Materials, Imperial College London will be highly multidisciplinary, covering five broad research themes (i) Energy; (ii) Catalysis; (iii) Electronic Materials; (iv) Biomaterials; (v) Environmental and Heritage Science. The instrument, while hosted at Imperial is engaged in highly collaborative research at a regional, national (including the Diamond Light Source) and international level, with access arrangements also provided through coordination the National XPS Facility (NEXUS) at the University of Newcastle. This new approach to providing wide-reaching access will allow the APPES technique to be fully exploited and generate world-leading cutting edge scientific output.