Roadmap for Photoelectron Spectroscopy

Home , Electron spectroscopy, Wendy Flavell

Prepared on behalf of EPSRC by

Preface

This roadmap has been prepared in consultation with the community over the last few years, during which time there have been a number of significant developments that have either directly or indirectly affected the PES community. These include the recently announced EPSRC Mid-Range Facility for XPS at the Research Complex at Harwell (HarwellXPS), as well new equipment being acquired as part of the Sir Henry Royce Institute. Whilst the conclusions from this exercise, and the recommendations remain unchanged, an exercise is now underway to capture some of the impacts of these changes. It is planned for an updated roadmap to become available in the next 6 months.

2 Contents

page

1. Executive Summary...... 3

2. Key Findings and Recommendations...... 4

3. Introduction...... 6

4. Context...... 7

5. Current UK Capability...... 10

6. International Competitiveness...... 13

7. User Landscape...... 14

8. Future Needs...... 16

9. Town Hall Meeting...... 18

10. Summary and Outlook...... 21

11. Working Group...... 22

12. Further Acknowledgements...... 22

3 1. Executive Summary

The aim of this exercise is to produce a picture of the current photoelectron spectroscopy (PES) landscape within the UK research sector, and to map out the potential future direction of PES in the UK for the next 5 years. This has been achieved through a series of national surveys as well as a Town Hall meeting held in Birmingham in 2016, as well as numerous discussions with key stakeholders in the community. The results of these consultation exercises were collated and analysed by a working group (see end of document for membership). The results have been presented to EPSRC and reviewed by the EPSRC Capital Infrastructure Strategic Advisory Team for dissemination to the UK research base. Overall we have had evidence and support from 150 users of PES in the UK. A “Current Capability” survey captured information on 42 current photoelectron spectroscopy instruments in the UK. The “Future Developments” survey captured information from 79 people, with another 30 people attending the Town Hall meeting. Overall, the information provided has allowed this roadmap to develop, with a series of recommendations made on the basis of this evidence. It is important to stress, that whilst this roadmap was completed for the EPSRC’s capital equipment road-mapping exercise, its contents are owned by the PES community, and for the entire PES community. We invite anyone who missed the opportunity to engage in the preparation of this document, to email the Chair of the roadmap working group.

4 2. Key Findings and Recommendations

2.1 Key Findings

• The field of PES research in the UK is strong, and can be considered second only to the USA (when comparing the field-weighted citation index).

• To maintain this international lead, it is critical to upgrade or replace a number of out-of- date instruments, and invest in the latest technologies for future characterisation and research.

• The community recognises the need maintain a strong base of XPS instruments for traditional measurements, as well as to ensure ready availability to more specialist instruments for state-of-the-art advanced photoemission spectroscopy experiments.

5 2.2 Recommendations As this is a capital infrastructure roadmap it is important to stress that these recommendations should not stray beyond the remit of the exercise,1 but it has become apparent from the evidence collected from the PES community, that apart from refreshing and upgrading the infrastructure, the requirements of increased networking opportunities, coupled to dedicated training in PES is crucial in underpinning the core of the discipline. It is therefore on the evidence collected through the surveys, at the Town Hall meeting, as well as consultations with others in the UK PES community that this series of recommendations are based. They focus on three aspects. Networking, Infrastructure and Training. We believe that by investing, as a community, in these three areas, we will not only maintain the UK’s international standing in PES, but strengthen its competitiveness considerably.

Strengthening the PES community. A new UK network should be created and be fully inclusive of all researchers who utilise the technique. We would seek to create a national network (based similarly on the recently funded network grants in terahertz science2 and infrared and Raman spectroscopy).3 We would estimate the cost of this to be ~£0.5m. In addition, there was wide-spread acknowledgement from community members that the diverse research activities being performed utilising photoelectron- based spectroscopies would benefit from more cohesion and interaction across the community.

Investment in the core discipline. It is clear that photoelectron spectroscopy in the UK is a very strong, internationally competitive research area, which needs to be maintained and strengthened by significant capital investment. It is the recommendation that funding be sought to support the replacement of old spectrometers, and enable new spectrometers to be acquired by institutions that currently lack the equipment, but have the expertise to be able to successfully operate and maintain spectrometers. We recommend ~£10m for the acquisition of new, modern XPS instruments to replace older equipment. This would expect to deliver 15-20 new spectrometers. We also recommend ~£20m for the acquisition of instruments to perform cutting-edge PES experiments. This latter investment will ensure that the UK (at a minimum) maintains its position close to the USA, but would also provide the opportunity for the UK to become the world-leader in photoelectron spectroscopy over the next 5-10 years.

Creating the PES leaders of the future. The long-term future of the technique is critically dependent on the pipeline of researchers. We recommend that the community addresses the need for PhD training in the area “Photoelectron Spectroscopy”, and proposes mechanisms to promote this. We would like to add that highly creative suggestions to PhD training whether through funders or via inter- university cooperation should be explored. In addition we suggest that funders promote PES either through specific EPSRC fellowship schemes (preferentially post-doctoral and early career stage), or through supported applications to the Royal Society, or Royal Academy of Engineering.

1 https://www.epsrc.ac.uk/research/ourportfolio/themes/researchinfrastructure/strategy/equipmentroadmaps/ 2 TERANET: An EPSRC Network for UK researchers in terahertz science and technology. http://gow.epsrc.ac.uk/NGBOViewGrant.aspx?GrantRef=EP/M00306X/1 3 Clinical Infrared and Raman Spectroscopy Network (CLIRSPEC) http://gow.epsrc.ac.uk/NGBOViewGrant.aspx?GrantRef=EP/L012952/1

6 3. Introduction

The ability to build and maintain a world-class research base in the 21st century is directly linked to the capital infrastructure which underpins it. Photoelectron spectroscopy (PES) is an extremely widely-applied technique and research area in its own right. It underpins research activities within a broad range of fields, including numerous priority areas such as Advanced Materials, Catalysis, and Energy. Due to the complexity and cost of the instrumentation which it requires, however, particularly given the necessity of ultra-high vacuum conditions (10-10 mbar or lower), PES-based techniques are exposed to the challenges of a difficult capital funding environment to a greater degree than other capital-intensive research areas. The situation with regards instrumentation for photoelectron spectroscopy has evolved considerably over the last 10-20 years. A general trend is that instrumentation has become more automated in recent years, particularly in the area of basic X-ray Photoelectron Spectroscopy (XPS), which has become, in many instances, a critical routine analytical technique, used by researchers in a similar way to X-ray Diffraction (XRD) and Nuclear Magnetic Resonance (NMR). Whether this change has resulted in a change to the UK landscape for traditional surface science will be explored in this roadmap.

The UK has played a central role in the development of photoelectron spectroscopy over the last century. One of the very first pioneers was Henry Robinson in the 1920’s in the University of Cambridge who first started to explore the nature of photo-emitted electrons from metals,2 through to the development of ultra violet photoelectron spectroscopy (UPS) by David Turner3 at Imperial College/University of Oxford in the 1960’s and Wyn Roberts designing instruments in the 1970’s that led to the first commercial spectrometers being delivered to research groups around the world. The UK is also home to some of the world-leading instrument manufacturers including Kratos Analytical Ltd (Manchester) and Thermo Fisher Scientific (East Grinstead), with UK manufacturers currently supplying roughly two-thirds of the XPS instruments sold worldwide.4 As a result of this strong heritage the UK is one of the leading centres for photoelectron spectroscopy research, but finds itself in very strong competition with a number of countries around the world, detailed later in this document.

The roadmap is based upon three major consultation exercises. These include two surveys, the first was on “Current Capability”, in an effort to determine the current level of XPS provision in the UK. This survey elicited 30 institutional responses, of which 6 of them indicated that they currently had no PES capability. The second was a “Future developments” survey, which was to capture the current usage of photoelectron spectroscopy by UK-based researchers at all stages of their careers, to future technique developments that they would like to see realised. This survey elicited 80 responses. A Town Hall meeting was held in Birmingham on the 5th April 2016, with 40 attendees present. The attendee’s responses to a series of questions were captured and incorporated into the current roadmap. The working group would like to express their deep gratitude to the people who gave up their valuable time to respond to the surveys and/or attended the meeting.

The result of these consultations will be analysed in the following sections, and conclusions and recommendations will be drawn from the evidence provided. It has been a considerable

2 H. Robinson, The Secondary Corpuscular Rays Produced by Homogeneous X-Rays, Proc. Royal Soc. A, 104, 455 (1923). 3 D.W. Turner, M.I. Al Jobory, Determination of Ionization Potentials by Photoelectron Energy Measurement. J. Chem. Phys. 37, 3007 (1962) 4 Mid-range Facility Statement of Need for X-Ray Photoelectron Spectroscopy Services (2015). 7 exercise, broad in scope and depth, that will hopefully highlight opportunities and provide strategic direction to the PES field for the coming, challenging, years ahead.

This roadmap is a living document, owned by the UK PES community and as such, a copy of it will be hosted on an independent website, where the community will have an opportunity to suggest updates and changes.

4. Context

The general field of PES encompasses a broad range of experimental configurations, but they all share a common basis, that being the photoelectric effect which is the emission of electrons from a solid/liquid/gas when irradiated with photons of sufficient energy and measurement of the kinetic energies of the emitted photoelectrons using an electrostatic deflection analyser, which transmits electrons entering via a lens system. This roadmap is concerned with a specific number of techniques that exploit this phenomenon, which are listed below. It is very important to note early that there are of course more PES techniques than listed below, but to ensure that this roadmap to be an effective exercise, there needs to be a limit to the techniques that could be captured. In order to define the areas clearly, brief outlines of the techniques are given below. It should be noted that this list may feature nearly all of the main PES techniques currently employed in the UK, and in the interest of brevity we have chosen the following below.

4.1 X-ray, Ultra-Violet and Combinatorial Photoelectron Spectroscopy X-ray photoelectron spectroscopy (XPS) is a crucial technique applied in an unusually wide range of applied areas involving surfaces and interfaces, since electron path lengths are typically of the order of 1-3 nm. Different elements are characterised by different core level binding energies and at the simplest level core XPS provides a means of chemical analysis, hence the alternative acronym ESCA (Electron Spectroscopy for Chemical Analysis). Chemical state information is also provided by small shifts in core level binding energies. The shape of the core-level line is also influenced by the response of the electrons within the system to the generation of a core hole meaning that XPS provides a means of probing electron dynamics and electron correlation. Valence level XPS is one of the most direct probes of electronic structure that is available and for non-correlated systems the technique basically measures the electronic density of states weighted by the cross sections of the different orbitals which contribute to the valence levels. In addition, ultraviolet photoelectron spectroscopy (UPS) measures molecular orbital energies for comparison with theoretical values from quantum chemistry. Also, the high resolution allowed the observation of fine structure due to vibrational levels of the molecular ion, which facilitates the assignment of peaks to bonding, nonbonding or antibonding molecular orbitals. Combinatorial Photoelectron Spectroscopy is simply a description where XPS or UPS (and occasionally ARPES), are used in addition to other (normally thin film deposition-based) techniques.

UK Universities that have activity in XPS/UPS and Combinatorial Spectroscopy are shown in Figure 1. Please note that this figure also shows other instruments in addition to the above.

4.2 Angle Resolved Photoelectron Spectroscopy Angle-resolved photoelectron spectroscopy (ARPES) enables the observation of the distribution of electrons in the reciprocal space of solids, and is one of the most direct methods

8 of probing the electronic structure of solids and their surfaces. ARPES provides information on the direction, speed and scattering process of valence electrons in the sample being studied (usually a solid). As a direct probe of the occupied part of the momentum-resolved single- particle spectral function, it thus allows mapping the detailed momentum-resolved band dispersions and Fermi surfaces as well as probing the influence and effect of many-body interactions in the solid. It can be performed with extremely high energy and momentum- resolutions using laser-based technique. As such, it has become a premier probe of quantum materials such as high-temperature superconductors, and is arguably the leading technique underpinning the recent discovery of three-dimensional topological insulators. Extensions to incorporate spin-selective detection (spin-ARPES) enables probing all the quantum numbers of such materials, while pump-probe variants further extend this to the study of ultrafast carrier dynamics.

UK Universities that have a significant activity in this area include: University of St Andrews, University of Oxford, University of Warwick, Bath University. The UK hosts one of the world’s leading synchrotron beamlines for ARPES at Diamond Light Source (Beamline I05).

4.3 Photoemission Electron Microscopy Photoemission electron microscopy (PEEM) is a widely used type of emission microscopy. PEEM utilizes local variations in electron emission to generate image contrast. The excitation is usually produced by UV light, synchrotron radiation or X-ray sources. PEEM measures the coefficient indirectly by collecting the emitted secondary electrons generated in the electron cascade that follows the creation of the primary core hole in the absorption process. PEEM is a surface sensitive technique because the emitted electrons originate from a very shallow layer. In physics, this technique is referred to as PEEM, which goes together naturally with low-energy electron diffraction (LEED), and low-energy electron microscopy (LEEM). In biology, it is called photoelectron microscopy (PEM), which fits with photoelectron spectroscopy (PES), transmission electron microscopy (TEM), and scanning electron microscopy (SEM).

UK Universities and facilities that have activity in PEEM: University of Bristol, University College London, Natural History Museum, University of Reading, University of Aberystwyth, Diamond Light Source (Beamline I06).

4.4 High- or ambient-pressure, Gas- and Liquid-phase Photoelectron Spectroscopy A major recent development has been in laboratory-based “non-UHV” X-ray photoelectron spectroscopy. High- or Ambient- pressure X-ray photoelectron spectroscopy (HPXPS/APXPS) is the study of solid surfaces under a high-pressure gas atmosphere (0.1-10 mbar), and incorporate a small-volume cell or a back-filled analysis chamber. The crucial development has been of hemispherical analysers which incorporate electrostatic lensing within the different pumping stages to maximize photoelectron transmission. Until recently the technique has been primarily developed at synchrotron radiation sources utilizing a high photon flux. While the use of synchrotron light sources has obvious advantages, it severely restricts the widespread use of the technique due to the limited number of synchrotron end stations with HPXPS capabilities. Increasing availability is one of the key challenges if HPXPS is to be utilized to its full potential in a wide variety of subject areas, and indeed in the recent years there has been renewed interest in the development of laboratory-based HPXPS instruments utilizing differentially pumped analysers and focused X-ray sources. H/APXPS is a fast-growing addition to the suite of advanced PES techniques available to the scientific community. 9

UK Universities and facilities that have activity in HPXPS: University of Cambridge, University of Leeds, University of Manchester, University of Nottingham, Imperial College London, Cardiff University, Diamond Light Source (VERSOX beamline).

4.5 Hard X-ray Photoelectron Spectroscopy PES is generally a surface sensitive technique, meaning it is challenging to probe bulk chemical and physical properties. The most direct way to increasing the probing depth in PES experiments is to increase the excitation energy, and correspondingly increase the kinetic energy of the outgoing photoelectrons. This can result in Hard X-ray photoelectron spectroscopy (HAXPES) measurements providing information from a depth of up to 15–20 nm for electron kinetic energies > 5 keV. Although relatively straightforward to achieve at synchrotrons, the technique has some crucial drawbacks, such as decreased photoionization cross-sections at high photon energies, as well as lower photon flux when using laboratory- based hard X-ray photon sources.

UK Universities and facilities that have activity in HAXPES: Imperial College London, University of Liverpool, University of Warwick, University of Manchester, University of Oxford, Diamond Light Source (Beamline I09).

4.6 Time-Resolved Photoelectron Spectroscopy Time-resolved photoelectron spectroscopy and two-photon photoelectron spectroscopy (2PPE) are important extensions to the core PES discipline. These methods employ a pump-probe setup, where the pump and probe are generated from the same ultrafast laser system, generally operating in the near IR. Frequency conversion is often employed, converting NIR into visible or UV through optical parametric amplification or into XUV through high harmonic generation. The pump excites the atom or molecule of interest, and the probe ionizes it, with the electrons or positive ions then detected, carrying information related to the excited state. As the time delay between the pump and the probe are changed, a change in the energy (and sometimes emission direction) of the photo-products is observed. Simultaneous absorption of multiple photons of a lower energy can also be used as the pump or probe, taking advantage from the high peak intensities available in ultrafast laser pulses, thereby inducing nonlinear or exotic transient states. Recording the two or three dimensional distribution of electron or ion momenta is advantageous when studying molecular or solid systems, realized in velocity map imaging (VMI) and cold target ion recoil ion momentum spectroscopy (COLTRIMS).

UK Universities and facilities that have activity in gas-phase VMI and TR-ARPES: Heriot-Watt University, University of Warwick, University of Bristol, University of Swansea, University of Manchester, University of Oxford, University of Edinburgh, University of Leeds, University of St Andrews, Diamond Light Source. The UK also has the ARTEMIS beamline at the Central Laser Facility, Harwell.

10 5. Current UK capability

The survey captured a considerable number of operational photoelectron spectrometers, with 42 instruments reported in total, based at 25 institutions. The map below shows the location of the all these spectrometers in the UK. It also includes known locations of spectrometers (red solid circle), but of which there was no response to the survey (blue empty circle). It is hoped that further information regarding these systems will be offered in the near future. It is clear that there is a reasonable geographic spread of XPS provision throughout the UK, except for noticeable absences in the the West of Scotland, South West of England and Northern Ireland (although lack of XPS provision in the latter has only occurred recently).

It was found that 43% of respondents were doing so on behalf of their research group, with the remaining 57% responding on behalf of department/faculty/institution. Some of the following responses were not used in the subsequent analysis, due to incomplete information provided.

Figure 1. The map of the UK showing the locations of XPS systems. The locations in red are from institutions that reported their system(s) on the Capability survey. The locations in blue are systems that are known to exist.

11 Age of Instruments We have analysed the age of instruments and found a reasonable spread of ages. There are 24 % of instruments which could be described as new, purchased within the last 2 years, with another 24 % are within the last 3-5 years and the remaining 52 % of instruments being 6-21+ years old. An analysis of the types of instruments purchased in the last 5 years (20 in total) shows that 50 % are for (relatively) routine XPS analysis, and the remaining 50 % are more focused on specialised areas of research, such as high-pressure, angle resolved, small-spot imaging, combinatorial (e.g. incorporating with scanning tunnelling microscopy). Whilst it is encouraging that the survey captured that “new” i.e. instruments that are up to 5 years old, it is still very concerning that the majority of spectrometers are older than this, even more so that 10 % of the reported spectrometers are 21+ years old. The recent rapid improvements in XPS instrumentation, particularly sample manipulation/automation, charge neutralisation, small X-ray spot size and analyser design with greater collection (over wider angles) and transmission of photoelectrons means that capability has dramatically improved. It should also be noted that a balance should be struck between high-throughput, modern XPS systems, and instruments capable of a much wider range of surface science measurements, and sample handling/preparation capability. As the latter are considerably more expensive (on average twice as much), any proposed funding ratio should be 1:2 in favour of the latter. Therefore, there are a significant number of instruments that in an ideal world would be replaced, which is a significant capital liability.

Figure 2. Word cloud responses to the question “Which research areas does the instrument support?”

Number of users We found that the reported total number of users is roughly estimated to be 400 - 450. This means that there are on average 10 users per instrument, although this number doesn’t perhaps fully reflect the true usage landscape of the instruments surveyed, nor does it reflect the

12 different timescales for measurements on the different types of systems. Some responses indicated that there are 50+ users for a spectrometer, where they are clearly providing a departmental or institutional XPS service. Others reported 2-5 users, which are typically on dedicated scientific instruments focussed on one (or more) focused research areas, and led by a single principal investigator.

Types of use One question in the survey was “Which research areas does the instrument support?”, and with the responses we then generated a word cloud from (Figure 2), where the higher the number of entries, the larger the font size of the text. The broad and varied responses evidence the widespread underpinning nature of PES research across a wide portfolio of research streams. The most numerous answer to this question was “surface science” followed closely by “catalysis”. “Energy” and “Energy Materials” were also well represented, along with the broader response of “Materials”, “Materials Science” and “Chemistry”. Interestingly, there wasn’t a significant response for physics, although this is likely due to finer grading of the response (e.g. “condensed matter physics”, “spintronics”, “graphene”, “electronic structure”). The broad and varied responses thus evidence the widespread use of PES, and in particular the underpinning nature of Surface Science and related activities to a wide portfolio of research streams.

Sustainability of instruments In the survey we asked whether the instrument has a service contract. Out of 35 responses, 8 indicated that they have a service contract, whereas for the remaining 27, it was stated that they did not, a figure of just over 20 %. This very low number can be explained in part by some instruments being old, and companies being unable/unwilling to offer continued servicing, along with different methods of funding equipment maintenance in UK universities. The number, (1 in 5), also reflects the precarious financial status of many of these instruments with many users finding it challenging to fund the repair and maintenance of ageing spectrometers. It is our view that new instruments, where possible, could be negotiated to include extended service cover (warranty), and suggest that ongoing service costs beyond this are discussed with instrument manufacturers early on in the process. This is difficult though if a user’s institution does not have sound methodology for sustaining long-term significant capital equipment.

The day-to-day management of instruments was also captured. We found that 40 % of the instruments are managed by a research/experimental facility manager/officer, with 63 % of such research officers dedicated to looking after the PES instruments alone. We also found that 55 % of instruments are managed by PhD and PDRA students. We believe that this reflects the varied nature of the service being provided and the science being performed, although there is some evidence of students and PDRAs providing experimental expertise and access in a service capacity, which is not an ideal use of their skills. It is clear that staffing should be appropriate for the type of science being performed, which, on the whole, seems to be adequate in the UK.

Sources of funding It is clear from the survey that the vast majority of spectrometers have been funded either by research councils (46 %), or by government organisations (HEFCE, Welsh Assembly, Regional Development Agencies) (25 %). There is also a significant contribution from universities themselves (17 %), with some instruments bought outright, but mostly the institution has part- funded the acquisition. There is some support from industry/charity sector, accounting for around 10 % of funding for systems.

13 6. International Competitiveness

The performance of the United Kingdom in the area of photoelectron spectroscopy has been bench-marked against the main global scientific competitors. The total number of publications published (by the top 10 countries globally) was 35,538 over the time period 2011-2016. The UK in this time published 1116 (3 %), placing it 9th in this list. Whilst the share of the total publications is relatively small, the field-weighted citation index5 of those publications is 1.62, placing the UK 2nd in ranking, only just behind the United States. This shows, for example, that the XPS and photoelectron spectroscopy publications from the UK are 62% more likely to be cited than the average paper in the same research area. It must be acknowledged, citation/quality data must be treated carefully, but this does clearly show that even though the UK produces a relatively small amount of research publications in the area, the publications that are produced are of significantly greater average impact than many international competitors, including China and Japan. This success could be attributed to the rich heritage that the UK has in the area of photoelectron spectroscopy, both academically and commercially.

5 Field-Weighted Citation Impact takes into account the differences in research behaviour across disciplines. Sourced from SciVal, this metric indicates how the number of citations received by a researcher’s publications compares with the average number of citations received by all other similar publications indexed in the Scopus database. 14 7. User landscape A survey entitled “Future Developments in Photoelectron Spectroscopy” received 80 responses. This questionnaire was for current users or planned future users of photoemission-based techniques, and asked them to highlight the future developments they envision in the field within the next 5-10 years with respect to the equipment requirements.

Of the 79 respondents XPS for chemical analysis to Question 1 Ultra-violet PES (“Photoelectron High (gas) pressure XPS Spectroscopy is...”), 30

Hard X-ray photoelectron spectroscopy (HAXPES) % said “the main focus of my research”, 48 % Angle-resolved photoelectron spectroscopy (ARPES) said “Regular Laser ARPES characterization tool” Soft X-ray ARPES and 19% said Spin-resolved PES/ARPES “occasional user”, with

Photoemission-based microscopy the remainder (3 %) saying that “Have not Time-resolved PES/ARPES used yet, but plan to”. Other The graph (left) displays 0 10 20 30 40 50 60 70 the total responses to Number of responses the question, before Table 1, breaks it down into sub-categories of usage. It is clear from the table that the most utilised technique by the respondents is for XPS, followed by ARPES and then UPS. What is clear though is the broad range of PES techniques that the respondents to the survey utilise. Table 1 below, breaks the responses down further. The coloured highlights indicate the level of response in that category (blue – above 40%, yellow – 25-40 % and red – 10-25 %). To note, the total number of responses per technique can be greater than the number of responses to the survey (80) if more than one option was chosen.

15 Table 1. Table showing distribution of different experimental activity in the UK and abroad.

Mid- Own Own Other UK UK EU Worldwide Worldwid Total range universit regiona universitie synchrotro synchrotro synchrotro e Response facilit y l group s n n n university s y

XPS 54.9% 3.9% 11.8% 2.9% 7.8% 10.8% 4.9% 2.9% 102

UPS 48.0% 2.0% 2.0% 4.0% 10.0% 22.0% 4.0% 8.0% 50

HPXPS 28.6% 0.0% 0.0% 0.0% 14.3% 23.8% 23.8% 9.5% 21

HAXPE 15 6.7% 0.0% 0.0% 0.0% 60.0% 20.0% 6.7% 6.7% S

ARPES 24.2% 3.2% 3.2% 3.2% 22.6% 27.4% 9.7% 6.5% 62

Laser- 15 33.3% 6.7% 0.0% 33.3% 0.0% 6.7% 0.0% 20.0% ARPES

Soft X- 29 ray 6.9% 0.0% 0.0% 3.4% 27.6% 55.2% 3.4% 3.4% ARPES

SR-PES 10.0% 10.0% 0.0% 20.0% 20.0% 30.0% 0.0% 10.0% 10

PEEM 13.0% 0.0% 0.0% 0.0% 21.7% 47.8% 13.0% 4.3% 23

TR-PES 30.4% 4.3% 0.0% 26.1% 0.0% 26.1% 4.3% 8.7% 23

Other* 37.5% 0.0% 0.0% 25.0% 0.0% 12.5% 0.0% 25.0% 8

10- Range 40%+ 25-40% 25%

It is clear that the majority of XPS users have access to the technique in their own university (54.9 %), although a significant amount (11.8 %) use other university facilities. Unusually, 10.8 % stated that XPS is performed at a European synchrotron (although this is most likely more advanced experiments, with variable photon energy). What is interesting is that 3 % of respondents perform XPS worldwide. This may be due to long standing collaborations, rather than lack of access to UK-based facilities. UPS follows a very similar trend to XPS, with a strong usage in the university of the respondent. UK and European synchrotron’s are also well utilised by people wanting to access this technique, and interestingly there is a larger proportion of respondents who perform UPS worldwide than XPS (but these total numbers are still small). HPXPS is dominated by research activity outside of the UK (47.6 %). It is puzzling how any research is being conducted at the Diamond Light Source, as the VERSOX beamline is still being commissioned, although this may be also capturing future/planned near-term usage. HAXPES on the other hand seems to be dominated (60 %) by UK synchrotron usage (beamline I09), as well as some European synchrotron work (20 %). There is some availability for laboratory based HAXPES, typically using a silver source (hn = 3000 eV). ARPES and laser ARPES are utilised in the laboratory with (24.2 % and 33.3 % respectively), but soft X-ray ARPES is understandably dominated by synchrotron use (27.6 % UK and 55.2 % European). It can also be noted that laser ARPES is the most utilised single technique worldwide (20 %). It should be noted as well that the mid-range facility in this table does not refer to the EPSRC XPS national facility, particularly when laser, spin and time-resolved ARPES are mentioned. These are more likely to be use of facilities

16 such as ARTEMIS at Harwell, UK. That is not to say though that some of the 2.9 % XPS usage in that column does not refer to national facility.

What this highlights is the relatively good provision for performing XPS and UPS in the home- laboratory of many UK universities, although it is clear from the current capability survey that many users are still reliant on access to synchrotron radiation. Whilst the need for synchrotron light is necessary for many different experiments, and almost exclusively so for techniques such as soft X-ray ARPES, the other techniques such as HPXPS, HAXPES, ARPES, SR-PES, TR-PES and PEEM, can (and are) performed in the laboratory. Therefore, there is clearly a need to increase and improve capacity in these areas. Another interesting finding is the lack of sharing/collaboration between universities on nearly all the techniques, although there is some regional activity going on. It seems that the community is more likely to collaborate internationally, than with UK users, which could be a sign of a relatively small yet competitive research field. The international competitiveness certainly fits this narrative – that of a significant number of internationally recognised PES research groups. We do not believe that we have just resurveyed the respondents to the “current capability” survey, as this has a significantly larger number of responses. Many of the respondents (it can be assumed) do not have access to their own spectrometer.

8. Future needs Question 4 of the survey stated: “Which of these techniques do you currently need but cannot access?”. The responses are plotted below. It is clear that provision in XPS/UPS is satisfied, and it is the state-of-the-art experiments and equipment that the respondents requested most – in particular the need for PEEM and time-resolved PES is clear. The “other” techniques include free electron laser (FEL) measurements, femtosecond electron microscopy, time-resolved PEEM, multiphoton PES and photoelectron photo-ion coincident measurements.

It is clear from the additional comments Question 5: What - in terms of PES - would be transformational to you research? The community responded in a number of areas highlighted below. Firstly, many researchers would like to see greater access to time-resolved PES, highlighted in the following comments: “New generation of laser sources with high repetition rate and high average power would revolutionise the information accessible by time resolved spectroscopy.” and “Being able to do time-resolved photoemission/ARPES/PES with high harmonics at high repetition rates (~100 kHz), and at higher photon energies (~100-300 eV) would be transformational.” as well as “time-resolved PES on free cluster beams and liquid jets containing solutes (this is already done outside the UK).” The need for greater access to high pressure HPXPS, where the need to work closely with industry, but also to attempt to achieve true ambient pressure was also stressed: “Working in catalysis (mainly surfaces) the PES is essential and in particular if we can use the HP-XPS to tackle phenomena of industrial relevant catalysts.” and “True ambient pressure capabilities (1 bar, not 1 mbar)”.

The desire for greater instrumentation to perform ARPES experiments (standard, laser, spin- resolved etc) was also evident: “Variable energy, high brightness photon sources for lab ARPES” as well as “High efficiency spin-resolved ARPES”, “New generation of laser sources with high repetition rate and high average power would revolutionise the information accessible by time resolved spectroscopy.”, “I think there is an opportunity for nanoARPES to bring electronic structure to a whole new community” and “It would be amazing to see the ARPES and spin- ARPES community in the UK grow in the coming years and this requires more facilities” and generally “More access to SR-ARPES for UK users”. There was also the comment that a “centralised index such as a website showing which facilities are available at which institutions and who is providing open or subsidised access (e.g. LENNF at Leeds Uni)” would be welcome. There is of course, www.equipment.data, but that seems to have only a very small number of PES instruments. Encouragement should be given to all owners of PES instruments to register them on this website. On the back of this, it is the view of the working group, that more work chould be done in building a network including a website for the PES community to share information and accessibility to spectrometers.

Finally, we asked the respondents in Question 5b: Is there anything else relevant to this exercise not covered in the questions, that you would like to tell us? This provided a number of thoughtful and strong responses. There was a clear frustration with the lack of coordination nationally, with respect to PES facilities: “National capabilities for PES are disorganised, uncoordinated and insufficient to meet current routine R&D needs for UK academia, let alone cutting-edge science.” and a concern that the XPS National Facility ) has not met the needs of the broadest possible PES community in the UK. An interesting point was raised that the EPSRC national facility, free at the point of use, has the potential to undercut service provision for photoemission at other facilities around the UK, where different methods of recovering the costs are met (e.g. charge out etc). It should be noted that EPSRC are moving away from this free access model of service provision. There was also a comment that the survey questions missed out some important, developing areas of PES that UK researchers are actively involved in. This 18 includes free electron laser (FEL) based experiments, and PES imaging techniques (often linked). The Central Laser Facility, including ARTEMIS and COLTRIMS were mentioned numerous times, and it is certainly a research area that the working group feels should be supported, and integrated into the wider UK PES community.

9. Town Hall Meeting

A Town Hall meeting, supported by EPSRC, was held in Birmingham on the 5th April 2016. The meeting was attended by around 40 researchers (an attendance list is at the end of this document). The day was spent discussing various aspects of the UK PES provision and community. A SWOT analysis was performed in small groups, and a summary of the results are discussed below.

Strengths: It was felt that the UK has a good spread of high performance instruments, and a wide range of university facilities with a large number of standard laboratory-based XPS kit. The internationalisation of the community was highlighted, as well as in the context of UK researchers being very successful at securing international beamtime, with Diamond users being well recognised. Another strength was that instrument production in the UK is excellent, with a number of world leading XPS instrument manufactures. Historically the UK has made pioneering contributions to the development of PES. Overall these comments, we feel closely mirror the general feedback received from the surveys.

Weaknesses: There were a number of weaknesses highlighted, a significant one being that the UK does not have enough instruments to satisfy demand, in particular from growth areas (not enough HPXPS or PEEM provision, no spin-resolved ARPES availability). There was a feeling that there has been weak investment, with the risk that we will become followers, instead of setting the research agenda. This has certainly been the case in HPXPS, although recent investments are starting to reverse this. There is also a concern that much of the standard XPS kit is old, and out of date. Again, this matches what we found in the surveys. The UK community has had to “make do and mend” over the last 10 years, which has had a detrimental impact on the ability to perform state-of-the-art experiments. A significant concern was in the training students (general users), where poor training can easily lead to incorrect interpretation of data. The rise of automated and high throughput XPS systems, over the last few years has been welcomed, but a problem exists, that with a significantly increased volume of data being produced, the issue of poor analysis, despite a number of training workshops offered, is of concern to the PES community. There is also a feeling that funding opportunities have, for PES, fallen short of what the community have been able to respond to ensure that the infrastructure is kept at the state- of-the-art. Finally, there is a feeling an arbitrary division has arisen in the PES community between “surface science” and “surface analysis”. There is a strong desire to overcome this division and build a strong and inclusive PES community, which enables community-driven and community-cohesive bids to be successfully considered for funding by EPSRC/BEIS. It was recognised by the working group for the need for the whole community and stakeholders (for example UKSAF) to help build a stronger PES community over the coming years.

Opportunities: The highlighted opportunities focused on three areas (1) community building; (2) investment in cutting-edge techniques; (3) stronger engagement with industry. Following on from the perceived weakness of a fragmented PES community, the is significant enthusiasm to

19 build a broad user community including chemistry, engineering, physics, biology, materials science, bioengineering, pharmacy, environmental sciences and life sciences to name but a few. Also the need to learn from other international centres of excellence in PES (such as synchrotrons) as well as UK research communities e.g. microscopy was highlighted. There was also the opportunity to build stronger relationships with the Diamond Light Source and collaborate with FEL groups. Many people felt that the chance for a wide range of the PES community to come together, for example, in this Town Hall meeting, was hugely beneficial, and that further meetings of this type should be organised. Training of the next generation of PES experts and leaders in the field was stated a number of times, including via a proposal for the development of a innovative doctoral training methods in PES. This would also provide an opportunity to tackle a weakness identified – by supporting the use of correct methodology in analysis and calibration during measurement. Also, targeted Fellowships in appropriate priority areas (in the case of EPSRC), actively supporting applications for Royal Society Fellowships, and Royal Academiy of Engineering Fellowships, as well as strengthening international links (e.g. Newton Fellowships etc) was discussed. The opportunity to build the UK capability in cutting- edge PES measurements is crucial, and a plethora of techniques were highlighted, including HPXPS, HAXPES, spin-resolved PES, time-resolved PES, PEEM, laser-PES as well as combinatorial (e.g. NEXAFS/XPS and microscopy/XPS). The town hall participants again closely mirrored the survey responses, demonstrating a consensus in thinking of a wide range of the PES community. The importance of engaging with industry, particularly around the funding of fundamental scientific studies was highlighted, and it is hoped that this roadmap will help make the UK capabilities in PES better known to potential industrial collaborators.

Threats: The main threats identified were (1) a loss of expertise and (2) the cost of replacing/upgrading/maintaining equipment. Both are of critical concern to the community. The budgetary constraints that the UK is facing, particularly around capital equipment, has had, and will continue to have a detrimental and serious long term implications to the PES community in the UK. Whilst there have been some investments in the technique over the last 5 years, it is not enough to keep the UK standing still, let alone be internationally leading in the PES field. The issue has been compounded by the EPSRC Surface Science theme being “reduce” for the last few years – with a result that many PES researchers have shifted their research focus to catalysis, materials science and energy materials. This has now been changed to a “maintain”, but if we are to continue to sustain our international excellence (as noted by the field weighted citation index), we need to make significant number of capital investments across a wide range of PES sub-disciplines over the next 5 years (2017-2022). A related threat is the loss of expertise in the community, where it has been noted, that there is a relative lack of early career academics in the field (compared to mid- to late-career). This continuity gap, will lead to expertise and knowledge loss. This threat, would be alleviated if some of the proposed activities in “opportunities” were delivered. Overall, there was a strong feeling, that we are currently managing to (just about) keep ahead of some areas of PES internationally, but other areas we are significantly lacking (time-resolved, ARPES, PEEM).

Future Investments There were a number of interesting suggestions for future investments for PES in the UK. They focussed again on three areas (1) investment in the latest PES innovations (2) investment in centres of excellence (either real or virtual) and (3) building a new UK network and annual conference.

20 There was an overwhelming consensus to invest in cutting-edge, world-leading PES instrumentation. In particular, there is a demand for the development of the next generation of photon sources (from bench-top lasers to FELs, and high-intensity laboratory-based hard X-ray generators). This activity will support the development of new instruments, such as k-space microscopes, and imaging, time-resolved and spin-resolved systems. This will also allow the further development of high-pressure (or near/ambient pressure) spectroscopies to develop – perhaps in combination with time-resolving capabilities to capture surface chemical dynamics.

The consensus was that PES investments should be done using a distributed model e.g. regional centres of excellence, and avoid the pursuit of a single co-location of many varieties of PES instrumentation. There is clearly a need to continue to focus on the locations in Figure 1, but there may be opportunities to explore networked centres (comprising of single institutions, or clusters of institutions), that specialise in different areas of PES. This could be supported by a distributed CDT model. A number of centres were suggested, and this can be taken forward by the community in the near future.

Finally, the momentum gained from engaging the community in this road-mapping exercise should be utilised to propose a new UK-based PES conference, which is science focussed, and ensuring that all areas (and more) that were highlighted in Section 4 were included. The added benefits of this, is to enable the community to be able to identify and capitalise on recent and emerging developments in the field, and to learn across disciplines, as well as sharing analysis advice and protocols/procedures. This is especially important, as it has been raised a number of times, concerns about the quality of spectra and analysis appearing in the scientific literature. The need to engage the community with theoreticians was also highlighted.

21 10. Summary and Outlook

The PES roadmap has provided an opportunity for the community to begin to build, in partnership with EPSRC, a strategic view for PES provision in the UK. Through a number of different mechanisms, surveys, town hall meeting and further visits to laboratories, meetings and discussions a clear picture of the UK PES landscape has emerged.

There are a number of crucial points that can be taken from this exercise.

• The field of PES research in the UK is strong, and can be considered second only to the USA. This is a very important finding, and strengthens considerably the need for stronger investment in our discipline.

• The UK is internationally competitive in PES. This builds on the UK having a strong historical legacy in the field. For this to be maintained over the next 5-10 years requires investment in capital equipment and in personnel.A number of instruments are out-of- date and need to be upgraded or replaced. There is clearly too much out-of-date equipment, that needs a significant, and increasing amount of resource to keep operational. This is unsustainable in the near term.

• The community recognises the need for a strong base of XPS instruments for traditional measurements, as well as a sufficient number of spectrometers for allowing us to excel also in advanced PES experiments.

• There is a pressing need for dedicated, high-quality training of students, from undergraduate to postgraduate level, and a need for increased support for postdoctoral researchers and early career academics to develop into the PES leaders of the future.

• The community wants an opportunity to network, and build stronger links between different sub-disciplines of the technique, which could be achieved through a new, national network and conference being created.

There are numerous additional points to be taken from this exercise, which are delivered in greater detail in the proceeding pages. The three main recommendations are to build up the UK networking, infrastructure and training capability. To achieve this requires significant capital investment, coupled to leadership and cooperation in the community. It is clear that should this be achieved, it would lead to the UK becoming the world-leading centre for photoelectron spectroscopy in the years ahead.

22 11. Working Group

Professor Philip Davies, Department of Chemistry, Cardiff University Professor Wendy Flavell, Photon Science Insitute, University of Manchester Dr Philip King, Department of Physics, University of St Andrews Professor Peter License, Department of Chemistry, University of Nottingham Dr Robert Lindsay, School of Materials, University of Manchester Dr David Payne (Chair), Department of Materials, Imperial College London Dr Robert Palgrave, Department of Chemistry, University College London Professor Sven Schroeder, School of Chemical and Process Engineering, University of Leeds Dr Lidija Siller, School of Chemical Engineering and Advanced Materials, University of Newcastle

12. Further Acknowledgments

David Payne would like to thanks the EPSRC staff who have supported the development of this roadmap over the last few years. They include Susan Peacock, Iain Larmour, Lucy Martin and Susan Morrell.

The working group would also like to thank the following people for either attending the Town Hall meeting in Birmingham for their general input into the creation of this roadmap.

Andrew Evans (Aberystwyth University), Nigel John Mason (The Open University), Graham Leggett (University of Sheffield), Mark Baker (University of Surrey), Scott Doak (Loughborough University), David Morgan (Cardiff University), Russell Egdell, Tom Penfold (Newcastle University), Filippo Mangolini (University of Leeds), Jörg Zegenhagen (Diamond Light Source Ltd.), Chris McConville (University of Warwick), Adam Lee (Aston University), Alice Harling (National Physical Laboratory), Kellye Curtis (University of Leeds), Emma Springate (STFC Central Laser Facility), Geoff Thornton (University College London), Will Bryan (University of Swansea), Neil Fox (University of Bristol), Marc Walker (University of Warwick), Giovanni Costantini (University of Warwick), Cephise Cacho (STFC-CLF Artemis), Elaine Seddon (University of Manchester) Alison Crossley (University of Oxford), Karen Wilson (Aston University), Robert Jacobs (University of Oxford), James McGettrick (University of Swansea), Tugce Eralp Erden (Johnson Matthey), Richard Thomson (RTA Instruments Ltd.), Emily Smith (University of Nottingham), Simon Hutton (Kratos Analytical Ltd.), James O'Shea (University of Nottingham), Richard Smith (Johnson Matthey).