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.

Since the first development of x-ray photoelectron spectroscopy (XPS) over 50 years ago, the technique has formed the basis of numerous scientific breakthroughs providing vast economic and societal benefits. The proposed APPES technique, has the potential to have an even greater impact, due to the fact that the surface electronic structure of a wide array of different materials, each with their own technological applications will be be studied under conditions close to which they operate.

The obvious beneficiary of APPES measurements is in the commercial private sector, with emphasis on businesses operating in all the identified research themes. For example, Johnson-Matthey who work within the area of catalysis, could utilise the technique for understanding how catalysts behave in near-operational conditions. This could lead to significant improvements in reactor design and lowering catalyst cost, thereby the technique will have a direct economic impact.

The impact to the planned VERSOX beamline at the Diamond Light Source is important to stress. This proposal seeks to help to coordinate and develop the national capability, and strategy, in the APPES technique at a personnel, instrumentation and scientific output level.

There are a number of government agencies who would benefit from this research including the Health Protection Agency (HPA - Biosafety Unit, Decontamination Studies and Molecular Identification Services), the Environment Agency (National Laboratory Service). We would also seek to liaise and seek collaborative research efforts with the National Physical Laboratory (NPL). Understanding how pathogens behave in contact with surgical instruments, without exposing the samples to extreme UHV environments would have great national and international health benefits. One experiment could look at the growth of pathogens under aerobic and anaerobic conditions within a specially designed in-situ high pressure cell.

The APPES technique would also have a great impact on the area of conservation and heritage science, where we have already sought interest in the study of paint pigments from a colleague at Tate Britain. As the instrument is hosted geographically close to many museums (Natural History, Science Museum, V&A) we would seek to establish collaborative research with those institutions. We would also use the Institute of Conservation as a point of contact for planned heritage science research.

At a more specific project level, the Lead Co-I will develop a range of skills including public communication (training by the Royal Society), a well as opportunities to interact with government and policy makers at a national level (again through the Royal Society MP-Scientist pairing scheme).