Our research interests all involve the application of x-ray spectroscopic techniques to the investigation of the electronic structure, chemical interactions and magnetic behaviour of materials. These investigations use high-brightness synchrotron x-ray sources such as the MAX IV laboratory, HZB Bessy-II, Diamond Light Source, MAX-lab, the NSLS and the ALS. The techniques used are soft x-ray absorption spectroscopy (XAS), soft x-ray emission spectroscopy (XES) and soft x-ray photoemission spectroscopy (XPS) and x-ray magnetic circular dichroism (XMCD).

Polarisation dependent soft x-ray absorption spectroscopies can measure either x-ray natural linear dichroism (XNLD) for alternately linearly polarised light, or x-ray magnetic circular dichroism (XMCD) for alternately circularly polarised light.

The application of x-ray magnetic circular dichroism (XMCD), and the associated XMCD sum rules, to materials can probe on an element specific basis the orbital and spin components of the magnetic moment within a material.

The anisotropic electronic structure or anisotropic chemical bonding revealed via XNLD can give further insight into electronic structure, and not just act as a probe of molecular orientation on surfaces, though this is its most common usage and is properly termed NEXAFS.

Our most recent studies have been in the field of on-surface synthesis whereby one- and two-dimensional nanostructures derived from component organic precursor molecules are formed through temperature-activated coupling mechanisms on noble metal growth surfaces. 

These x-ray spectroscopic techniques reveal detailed information about the conduction band structure, the valence band structure, the core-level structure of the material and its magnetic behaviour respectively. Further, through the use of resonant soft x-ray emission spectroscopy (RXES) either the low-energy electronic excitations can be directly probed where this is known as resonant inelastic x-ray scattering (RIXS), or site-selective probes of the valence band via XES from differing chemical species can be exploited, e.g. in organic molecules; or lastly bandstructure effects are prominent. The latter two are more adequately described as RXES rather than RIXS though the quantum mechanics make no distinction. Polarisation dependent RXES of both pure and doped transition metal oxides and fluorides, as well as from organic molecular semiconductors, are one of my principal research interests. My other principal research interest is in the magnetic behaviour of atomic width nanowires arrays capped with noble metals.

You can also find a complete listing of the scientific publications that I have helped to contribute to the literature.

Templating of organic thin film growth: organic molecular semiconductors, nanomeshes and graphene nanoribbons

Controlled structured growth of organic materials, organic molecular semiconductor thin films as well as graphene in particular, is of importance for future devices where either interfaces or local intermolecular forces dominate in determining the structure and, as it turns out, the most useful device characteristics. This project will seek to perform measurements of the adsorption, chemical bonding and electronic structure of organic molecular semiconductor materials forming either heteroepitaxial organic thin films on inorganic semiconductor or metal surfaces, or in the formation of covalently bonded organic nanostructured networks on inorganic semiconductor or metal surfaces. Where possible real-time in-situ measurements will be made to probe intermolecular forces in thin films. Of particular interest is growth templating on stepped or terraced vicinal single crystal metal surfaces which may allow for useful regular nanoribbons of graphene to be formed by MOCVD. Associated density functional theory calculations of adsorption, electronic structure, and x-ray spectroscopy on these surfaces may play a significant part of this project.

Measuring adsorption, chemical bonding and electronic structure of organic molecular semiconductors or thin films requires ultra high vacuum chambers organic molecular beam deposition or MOCVD growth and XPS or UPS photoemission, all available in TCD. Other x-ray spectroscopic techniques are available at international synchrotron radiation facilities, while real- time in-situ measurements, as well as scanning probe measurements of these interfaces, surfaces and films to occur in collaborators laboratories. Research will be in collaboration with groups in Chemistry (M. O. Senge), Dublin City University (K. Fleischer and A. Cafolla), and MAX IV Labroatory, Sweden (A. Preobrajenski). This has emcompassed experimental measurements at synchrotron radiation facilities such as MAX-IV in Sweden, HZB BESSY-II in Germany and the Diamond Light Source in the UK. Earlier work occurred in this theme at the MaxLab facility in Sweden and at the National Synchrotron Light Source, NY USA.

Resonant inelastic x-ray scattering - Probing local electronic structure and chemical bonding in transition metal compounds

To measure the symmetry dependent resonant x-ray emission spectroscopy or resonant inelastic x-ray scattering for a variety of structurally similar transition metal oxides and fluorides of formula unit MA2, where excitations at the anion K-edge exciting the anion A 1s electron allows us to probe the anion A 2p densities of states.

Defects can be created in transition metal oxide (TMO) thin films or bulk samples, e.g by high temperature annealing, or by oxidation or reduction of the surfaces in ultra high vacuum. The distribution of these defects can then be controlled by applying electric fields, where the migration of these defects is called electromigration. With defect density gradients established the resultant optical properties are also changed (electrocoloration). The conductivity of defect rich TMOs is significantly changed, and the local physical and local electronic structure surrounding these defects will be probed. Local physical structure can be probed in TCD using electron microscopies. Local electronic structure will be probed by synchrotron radiation based x-ray emission and x-ray absorption and resonant inelastic x-ray scattering (RIXS) spectroscopies at the Advanced Light Source, Lawrence Berkeley Laboratory, California or MAXLAB in Sweden, among others.

Research themes

  1. The electronic structure and chemical formation via on-surface synthesis of novel nanostructures and their applications
    • The study of on-surface synthesis in-situ by advanced x-ray spectroscopies such as core level XPS and NEXAFS during the tempterature dependent coupling and cyclodehydrogenation of a a variety of novel nanostructures on gold and silver growth surfaces has been our highest priority activity. The extension of this to the measurement and simulation of electronic structure and of the chemical interactions between these novel nanostructures is our continuing theme of research.
  2. Novel element-selective symmetry, polarisation and state resolved investigations of chemical bonding in rutile metal oxide and fluoride systems

    • The electronic structure of a class of crystalline solids will be investigated through a novel application of polarisation dependent synchrotron radiation based resonant soft x-ray emission spectroscopy and x-ray absorption spectroscopies to obtain element specific, symmetry and state selective measurements of the occupied partial density of states or occupied molecular orbitals of these solids. Systematic investigations of the chemical bonding in these rutile systems can thus be carried out and compared to electronic bandstructure calculations. Opportunities then exist to examine the bonding within these systems to alternative transition metals substitutionally doped onto the cation sites in these rutile systems.
  3. X-ray magnetic dichroism of nanoscale magnetism in atomic wires protected by capping layers

    • Atomic wires of cobalt, possessing unusual magnetic properties, have been successfully grown on platinum single crystal surfaces but, to be useful, such nanowires must be capped by ultra-thin films to protect them from contamination. The interfacial region formed by capping will affect the properties of these nanoscale magnetic structures; for certain capping layers and thicknesses enhanced Curie temperatures are expected. X-ray magnetic circular dichroism spectromicroscopy will be used to probe the magnetisation of these atomic wires on an element and electronic orbital specific basis, to complement and extend new non-linear magneto-optic studies of the same advanced materials.
      In collaboration with Prof. John McGilp of the Surface Physics Group.
  4. Electronic structure of magnetic semiconductor materials: element-specific soft x-ray spectroscopies

    The project on electronic structure of magnetic semiconductors as measured by x-ray absorption and emission spectroscopy is already underway, but interested students are still invited to apply.
    • Ferromagnetic semiconductor devices are the future basis of magnetic semiconductor devices are the future basis of "spintronics". Some of the most promising candidate materials for room temperature ferromagnetic semiconductor are magnetically doped wide band gap transition metal oxides and nitrides. Specific examples are Co-doped ZnO or SnO2 or Mn-doped GaN. The electronic structure of these materials will be studied by resonant soft x-ray emission at the transition metal 2p edge and oxygen (or nitrogen) 1s edges. The resulting resonant inelastic x-ray scattering spectrum and its energy dependence will be studied to obtain information about the local electronic structure of the dopant transition metal cations within these oxide (or nitride) systems. These absorption and emission spectra will be modelled through use of atomic multiplet structure packages. The element specific spin and orbital moments will also be studied through x-ray magnetic circular dichroism measurements. All these measurements take place at synchrotron radiation facilities.
      The ultimate goal of the project is to correlate the spectral information with both the electronic structure and with the magnetic properties of these materials.

      Download this paper on Co-doped ZnO

  5. Synchrotron X-ray Spectroscopic Investigations of Electronic Structure in Organic Semiconductors

    The project on organic molecular semiconductors has started some time ago but interested students are still invited to apply.
    • Organic molecular semiconductors are of increasing technological importance. Ultrathin pure films of organic molecular semiconductors can be created by organic molecular beam deposition in ultrahigh vacuum environments. The electronic structure of selected organic molecular semiconductors will be studied using synchrotron based soft x-ray emission spectroscopy. This probes the valence band or highest occupied molecular orbitals of the material and combined with excitation on resonance can provide information which is unavailable through the standard tools of x-ray photoemission spectroscopy. This project focuses on combining this information obtained from x-ray emission spectroscopy with that obtained from photo-emission spectroscopy in a multi-technique multi-theme investigation of the metal-phthalocyanine family of organic semiconductors. The experiments will take place at synchrotron radiation facilities throughout Europe and in the USA. Much of this investigation will be coordinated with that of  Prof. McGovern of the Surface Physics Group.

      (Download this paper on copper phthalocyanine)

Current Funding

  • Postgraduate funding:

    Postgraduate funding is currently available available for one open position at a rate of €19,000 per annum.

    Further details on funding and on postgraduate fees may be found on the School of Physics website.

  • Beamtime funding:
    Funding for experimental beamtime at the synchrotron facilities is often obtained separately through the facilities themselves and is currently funded under the CALIPSO FP7 Integrating Activity.

Previous Funding

  • Project funding:
    The first and second projects have just been approved for funding (March 2007) through the 2007 Research Frontiers Programme of Science Foundation Ireland.
    The third and fourth projects have previously received funding through the Basic Research Award scheme of Science Foundation Ireland, and also through the Nanomaterials and Nanoscience, PRTLI initiative in the Sami Nasr Institute for Advanced Materials.
  • Funding has also been received from IRCSET with Intel as an industrial co-sponsor as well as the School of Physics.


These projects will be carried out in collaboration with the following groups

As well as earlier collaborations with the groups of

  • Surface Physics Group of Prof. I. T. McGovern.
  • Surface Physics Group of Prof. J. McGilp.
  • Laser and Plasma Applications Group of Prof. J. G. Lunney.
  • Magnetism and Spin Electronics Group of Prof. J. M. D. Coey.
  • Electronic Structure Theory Group of Dr. Charles Patterson.
  • The Novel Materials Group, Boston University, MA, USA, of Prof. Kevin Smith.
  • Oxford University, UK and the group of Prof. Russell Egdell.
  • Uppsala University, Sweden, and Dr. Laurent Duda in the group of Molecular and Condensed Matter Physics.
  • Macquarie University, Sydney, Australia and the group of Dr. James Downes.