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Trinity College Dublin

Cormac McGuinness, School of Physics

X-ray Spectroscopy Group

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C McGuinness
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The X-ray Spectroscopy group - September 2012

Pictured are Martin Duignan, Cormac McGuinness, Stephen Callaghan, Declan Cockburn and Brian Kennedy (Maxlab)

X-ray Photoemission Spectroscopy (XPS) instrument in CRANN

A monochromated Al-Kalpha Omicron XPS instrument with surface science preparation chamber is a vital part of the TCD equipment base within the group.

Travel to synchrotrons is a necessity for x-ray spectroscopy

There are more than 40 synchrotron or x-ray facilities worlwide of which the TCD group regularly uses five. These are Maxlab in Sweden, the ALS in California, the NSLS in New York, the Swiss Light Source and Elettra in Trieste.

Martin Duignan at beamline 6.3.2 in the ALS

Martin Duignan observes hysteresis from single atom wide capped cobalt nanowires at beamline 6.3.2 in the Advanced Light Source, Lawrence Berkeley Laboratory, CA, USA.

Beamline I1011, Maxlab, Sweden

Shown is the octupole vector magnet and scattering chamber at Beamline I1011 in Maxlab, Sweden, where much of our magnetic research takes place using the techniques of X-ray Magnetic Circular Dichroism (XMCD).

Group at I1011, Maxlab, Sweden

Pictured are Daniel McNally (TCD), John Cunniffe (TCD) and Iwona Kowalik (Maxlab) in the I1011 beamline hutch at Maxlab. Collaboration with beamline scientists at synchrotrons is essential

Beamline 4.0.2, Advanced Light Source (ALS), Lawrence Berkeley Lab., CA, USA

X-ray Magnetic Circular Dichroism (XMCD) measurements are made at beamline 4.0.2 in collaboration with Elke Arenholz of the ALS, where we have been a frequent visitor.

Beamline I511-3, Maxlab, Sweden

Fine adjustments needed for X-ray Emission Spectroscopy (XES) at the I511-3 XES and RIXS endstation at Maxlab. Pictured are Brendan Arnold (left) and Brian Kennedy (right)

Beamline 7.0.1 at the ALS, Lawrence Berkeley Lab., CA, USA

In front of the rack are Per Anders Glans, Timothy Learmonth and Brian Kennedy. Behind the equipment rack is the XES spectrometer and chamber at beamline 7.0.1 at the Advanced Light Source (ALS). Fortune cookies from past chinese meals decorate the rack!

National Synchrotron Light Source (NSLS), Brookhaven Lab., New York

Our group has been a frequent user of beamline X1B at the NSLS in Brookhaven National Laboratory, New York, in collaboration with the Boston University group of Kevin Smith. The geese pictured are an even more regular visitor to the NSLS.

At beamline X1B, NSLS, Brookhaven Lab., New York

The Boston University X1B endstation with organic molecular beam deposition chamber and x-ray emission spectrometer is pictured with Nikos Peltekis, Halvar Trodahl, James Downes and Satheesh Krishnamurthy (left to right)

Scientific discussion at beamline X1B, NSLS, NY, USA

James Downes (Macquarie University) and Nikos Peltekis discuss XES and RIXS from organic molecular semiconductors while at beamline X1B of the NSLS.

Organic molecular beam deposition chamber at X1B beamline

The filament in the manipulator is being degassed in preparation for an organic thin film deposition for in-situ measurements of the x-ray emission spectra (XES) of organic molecular semiconductor materials at the X1B beamline at the NSLS in New York.

ADRESS beamline at the Swiss Light Source, Paul Scherrer Institut

The world leading beamline for RIXS measurements at the Swiss Light Source.

The TCD group at the ADRESS beamline in the Swiss Light Source

From the left is Brian Kennedy, Declan Cockburn and Thorsten Schmitt (PSI), the beamline manager

X-ray Spectroscopy Group photo from 2008.

Back: Daniel McNally, Nikos Peltekis. Front: Brian Kennedy, Patrick Grace, Cormac McGuinness, Iggy McGovern, Brendan Arnold.



Research: (See group photos if within TCD)

  • My research interests all involve the application of x-ray spectroscopic techniques to the investigation of the electronic structure and magnetic behaviour of materials. These investigations use high-brightness synchrotron x-ray sources such as 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. 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 behaviou 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. More complete details of my research interests will appear here when I have time to do so - I regret this page gets updated about once every two years. You can also find a complete listing of the scientific publications that I have helped to contribute to the literature.

    There is also a TCD maintained research profile.

Proposed new PhD projects to begin in autumn 2013

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 (G. Duesberg), Dublin City University (A. Cafolla), Aberystwyth, Wales (A. Evans) and Boston U. (K. Smith) with measurements at synchrotron radiation facilities such as MAXLAB in Sweden or National Synchroton 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.
  • Click on image of project to download complete description.


Ongoing research themes:

  1. 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.
  2. 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.
  3. 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

  4. 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)

Please contact me by e-mail, phone or knock on my door if you are interested in learning more about any of these projects.

Current Funding:

  • Postgraduate funding:

    Postgraduate funding is available through The Irish Research Council (formerly IRCSET) Postgraduate Research Scholarship Scheme. Such postgraduate funding is at a rate of €16,000 per annum.
    (The next round of applications have opened and are closing in mid February.)

    Visit the Irish Research Council website for details on post graduate funding, this is open to all EU citizens.

    TCD Scholarships are also available as partial fellowships.

    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:

X-ray emission group

There are currently 2 students studying under my direction. They are:
  • Stephen Callaghan
  • Martin Duignan
I have graduated five students from my research group
  • Declan Cockburn, Ph.D. - now working for ASML, Eindhoven, Holland
  • Brian Kennedy, Ph.D. - now working at MAX-lab, Lund, Sweden.
  • Nikolaos Peltekis, Ph.D. - now working in Intel, Leixlip and Arizona.
  • Brendan Arnold, M.Sc. - now studying for Ph.D. at Bristol University
  • Daniel McNally, M.Sc. - now studying for Ph.D. at State University of New York, Stonybrook
I have closely worked with two other students in their Ph.D. projects under other supervisors within Trinity College Dublin as well as one external to Trinity.
  • Brendan Holland, Ph.D. - supervised by Prof. McGovern, TCD.
  • John Cunniffe, Ph.D. - supervised by Prof. McGilp, TCD.
  • Timothy Learmonth, Ph.D. - supervised by Prof. Smith, Boston University.

Collaborators

These projects will be carried out in collaboration with the following groups within Trinity:
And other collaborators within Ireland:
I also collaborate with the following international groups:

Facilities

The synchrotron radiation facilities and beamlines at which I have been working are:

Soft x-ray spectroscopy on the web:



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