Research Interests

Structure and properties of surfaces, especially studies with synchrotron radiation.

Further details

Introduction

Phil Woodruff could be described as a founder member of the Physics Department at Warwick, although he arrived in 1965 as a fresh young PhD student. Quite a few years later he finds himself an established Professor in the Department, strictly having been a member of the Department for all the intervening period.

However, with several periods of sabbatical leave in the USA and Germany, together with a lot of international collaborations, many based on the use of synchrotron radiation facilities in Wisconsin, New York, California, Paris, Berlin and Grenoble (as well as Cheshire!), there are those who have sometimes questioned whether he was ever in the Department.

In some ways this became more true than ever in October 1998 when he took up a five-year EPSRC Senior Research Fellowship concurrent with his Professorship, allowing  him to concentrate almost 100% of his time on research. The award of the Fellowship coincided with a need to take over primary responsibility for a long-standing collaboration with the Fritz Haber Institute of the Max Planck Society in Berlin, and since that time he has spent roughly one week each month in this institute, with some of his PhD students and post-docs being based there.

His research interests all fall within the general area of surface science - trying to understanding the structural, electronic and chemical properties of well-characterised solid surfaces (mainly, but not exclusively, of metals) at the atomistic level. This is achieved through a mixture of Warwick-based (and Berlin-based) experiments and the use of large-scale facilities, especially synchrotron radiation but also including the medium energy ion scattering facility at Daresbury Laboratory in Cheshire.

Research

Phil Woodruff's research programme covers a wide range of techniques and includes work on geometrical structure, electronic structure, and reactivity of predominantly metal surfaces. A particularly strong theme, however, is the development and application of quantitative structural methods to studies of adsorbate structures, especially of molecular species (including reaction intermediates) on transition and noble metal surfaces.

Much of the important technique development has been (and is) in synchrotron radiation methods. The two main techniques used in this part of the programme are (backscattering) photoelectron diffraction (PhD) and normal incidence X-ray standing wavefield absorption ( NIXSW). The photoelectron diffraction technique has been developed in collaboration with Prof. Alex Bradshaw at the Fritz Haber Institute (FHI) in Berlin and uses the BESSY storage ring in Berlin. As a result of Alex Bradshaw's transfer to Scientific Director of the Institute for Plasma Physics in Munich in 1999, Phil now spends about one week each month in Berlin at the FHI managing this project and its associated collaborations within a 'Sonderforschungsbereich' funded by the German research council (Deutsche Forschungsgemeinschaft); he therefore supervises PhD students in both Warwick and Berlin.

The photoelectron diffraction programme has been particularly fruitful in the study of molecular species containing C, N and O atoms and has led to quantitative structural analyses of intermediates such as the methoxy, formate and acetate species and to increasing understanding of the structural aspects of simple hydrocarbon species and even more complex molecules such as glycine (the simplest amino acid) and methyl pyridine with Ni and Cu surfaces. The availability of new third-generation soft X-ray synchrotron radiation sources offers important new opportunities for a 'chemical-shift' variant of this technique (the figure shows the structure determined from such an experiment on coadsorbed PF₃, PF₂ and PF), and this work is now proceeding on the BESSY II source in Berlin. Recently we have devoted increasing attention to the generally ill-understood problem of oxide surface structure.

NIXSW is a modification of the more general XSW method developed by the Warwick group which is particularly applicable to metal surfaces, and has been used to study atomic (e.g. Cl, S, O, Na, Rb) and molecular (e.g. methyl thiolate and longer-chain alkyl thiolates) on Cu, Ni and Al surfaces. All the early development was conducted at the Daresbury SRS facility in Cheshire, but subsequently some of this work transferred to the third-generation ESRF X-ray source in Grenoble in France where it has proved possible to exploit chemical state sensitivity and extend studies even to light atoms like C, N and O..

One further structural probe now being integrated into the programme is MEIS - medium energy ion scattering - an experimental technique to probe both surface structure and the structure of near-surface buried interfaces. This project uses the UK national MEIS facility also based at Daresbury Laboratory near Warrington, a facility originally constructed through a Daresbury-Warwick-Salford collaboration. This project is proving especially effective in the study of surface alloys, alloy surfaces and interface reconstruction.

At Warwick scanning tunnelling microscopy (STM) is also being used to study structural aspects of adsorption and reactions at surfaces with a particular emphasis on the role of adsorbate-induced restructuring of surfaces. Laboratory-based structural methods supporting this programme include X-ray photoelectron diffraction (XPD) and low energy electron diffraction (LEED).

A quite separate activity has been the study of the surface electronic structure of metals and metal films, especially those of interest as magnetic materials, using angle-resolved ultraviolet photoemission and momentum(k)-resolved inverse photoemission (ARUPS & KRIPES). Early work focussed on the KRIPES studies at Warwick and included investigations of Mn and Rh layers on Cu(100). Subsequently the emphasis of this work shifted to angle-resolved photoemission studies of the occupied states, and especially of quantum well states in the metallic overlayers, making use of synchrotron radiation in the vacuum ultra-violet at the SRS and at the NSLS in Brookhaven, New York. This has involved a very fruitful collaboration with the group of Petar Pervan and Milorad Milun in the Institute of Physics in Zagreb.

A further important strand to the research in the last few years has been a collaboration within the Surface Science group with Dr. Jim Robinson on the application of Density Functional Theory calculations to gain further insight into some of the adsorbate structures we have been solving experimentally. The Surface Science group homepage also lists opportunities for PhD research studentships and postdoctoral assistantships.

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Surface Science Group