| |
I am interested in the application of x-ray spectroscopic techniques to the investigation of the electronic structure of materials. Materials studied range from organic semiconductors, wide bandgap nitride semiconductors, wide band gap oxide semiconductors, doped magnetic semiconductors, transition metal oxides and highly correlated electron systems exhibiting metal-insulator transitions and superconductivity as well as capped magnetic atomic nanowires.
More specifically my current research has a number of distinct strands. The first and second strands of research are the measuring of site-specific, symmetry-, state- and polarisation-dependent electronic structure of transition metal oxides, specifically the study of chemical bonding in rutile type transition metal oxides.
and secondly the investigation of electronic structure in organic molecular semiconductors such as the phthalocyanine family of compounds.
For both of these strands I am also interested in the simulation of the electronic structure of these materials and the RXES and XAS via density-functional theory (DFT) methods employing Wien2K and StoBe codes; as well as atomic-multiplet methods for resonant inelastic x-ray scattering (RIXS);
The third strand of my research concerns the magnetic behaviour of low-dimensional atomic nanowires; the growth of low-dimensional several-atom-width nanowires on stepped vivinal single crystal metal surfaces and their characterisation by x-ray magnetic circular dichroism (XMCD), element-specific hysteresis loops and magneto-optic spectroscopies.
An earlier strand was the investigation of electronic structure of doped magnetic semiconductor materials.
These investigations all use high-brightness synchrotron x-ray sources such as MAX-lab (Swedish National Synchrotron facility), the NSLS (National Synchrotron Light Source, New York), the ALS (Advanced Light Source, California) and the SLS (Swiss Light Source) and ELettra (Italy). The techniques used are soft x-ray absorption spectroscopy (XAS), soft x-ray emission spectroscopy (XES), soft x-ray photoemission spectroscopy (XPS) and x-ray magnetic circular dichroism (XMCD). These techniques reveal detailed information about the conduction band structure, the valence band structure and the core-level structure of the material respectively. Further, through the use of resonant soft x-ray emission (RXES) the low-energy electronic excitations in a material can be directly probed leading to a resonant inelastic x-ray scattering (RIXS) spectrum, or chemical site dependent XES spectra can be obtained, particularly in the case of organic compounds. |
| Project title |
Novel element-selective symmetry, polarisation and state resolved investigations of chemical bonding |
| Summary |
No topic is more fundamental to Chemistry than the nature of the chemical bond. In crystalline solids, the chemical bond gives rise to the electronic bandstructure of the material, this then determines whether the material is a metal, semiconductor, semi-metal, etc.; it determines the optical characteristics, the transport properties and the usefulness of any given crystalline solid. Novel x-ray spectroscopic techniques are now available to probe the electronic structure of crystalline solids, element-by-element and even state-by-state. These synchrotron radiation based methods will be applied to a particular class of crystalline solids to study more fully their basic electronic structure.
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. This project is in collaboration with Prof. Graeme Watson of the School of Chemistry and Prof. Russell Egdell, of the Chemistry Department, University of Oxford. |
| Funding Agency |
Science Foundation Ireland |
| Programme |
Research Frontiers Programme 2007 |
| Type of Project |
Research Project |
| Date from |
September 2007 |
| Date to |
August 2010 |
| Person Months |
60 |
|
|
| Project title |
X-ray magnetic dichroism of nanoscale magnetism in atomic wires protected by capping layers |
| Summary |
Progress in ICT is driven by making electronic and magnetic devices with ever smaller active regions producing faster, more efficient devices. Single atomic wires of cobalt, possessing unusual magnetic properties, have been successfully grown on single crystal platinum surfaces. To be useful, these nanowires must be capped by ultra-thin films protecting them from contamination. The interfacial region formed by capping these nanoscale magnetic structures can enhance their magnetic properties, as measured by optical laser-interface interactions. These enhanced magnetic properties will be studied by x-ray based magnetic-spectroscopic imaging techniques and will allow for magnetic tuning of devices based on these wires.
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.
This project is in collaboration with John McGilp of the School of Physics |
| Funding Agency |
Science Foundation Ireland |
| Programme |
Research Frontiers Programme 2007 |
| Type of Project |
Research Project |
| Date from |
September 2007 |
| Date to |
August 2010 |
| Person Months |
60 |
|
|
| Project title |
Synchrotron X-ray Spectroscopic Investigations of Electronic Structure in Organic Semiconductors |
| Summary |
Organic molecular semiconductor materials are of increasing technological importance. Ultrathin pure films of organic molecular semiconductors can be created by organic molecular beam deposition. The electronic structure of organic molecular semiconductors is generally studied by photoemission spectroscopy, especially using synchrotron radiation. Additionally, synchrotron based soft x-ray emission spectroscopy and its resonant counterpart provides another powerful investigative tool. It is proposed to combine these two regimes in a multi-technique, multi-theme investigation of the metal-phthalocyanine family of organic semiconductors. The themes include, energetics, beam damage, growth modes and interfacial reaction/interaction. Specific attention is paid to a comparison of electron-emission and photon-absorption/emission methods.
This project is in collaborations with Prof. I. T. McGovern of the School of Physics. |
| Funding Agency |
Science Foundation Ireland |
| Programme |
Basic Research Grants 2004 |
| Type of Project |
Research project |
| Date from |
October 2004 |
| Date to |
October 2007 |
| Person Months |
80 |
|
|
| Project title |
Soft x-ray spectroscopic investigations of dilute magnetic semiconductors |
| Summary |
Dilute magnetic semiconductor (DMS) materials for use in functional room temperature magnetic semiconductor devices are being actively developed. Detailed knowledge of their electronic and magnetic structure is urgently needed. This can be obtained through the use of soft x-ray synchrotron radiation based spectroscopic techniques which are especially useful due to their elemental selectivity. The proposal seeks to apply these techniques to a number of DMS materials, specifically transition metal doped semiconductor oxides and nitrides such as Co–doped ZnO, Co-doped SnO2 and Mn-doped GaN and AlN.
Thin films of these DMS materials are being grown by pulsed laser deposition. The quality and observed ferromagnetic moments of these films are critically sensitive to growth conditions during deposition, as is the observed electronic structure. In Co-doped ZnO these phenomena, including magnetism, are directly linked to oxygen vacancies. This can be verified by studying their electronic structure by element-specific soft x-ray spectroscopy. Correlation between observed electronic structure, measured magnetic moment & growth conditions will give insight into producing better thin film ferromagnetic semiconductors. Further, the application of these techniques may help address the question of the detailed physical origin of magnetism in these dilute magnetic semiconductors, a matter of some controversy. |
| Funding Agency |
Enterprise Ireland |
| Programme |
International Collaboration Travel Programme |
| Type of Project |
Research Project |
| Date from |
01-05-2006 |
| Date to |
30-04-2007 |
| Person Months |
2 |
|
|
| Project title |
Soft x-ray spectroscopic investigations of transition metal oxide and nitride magnetic semiconductors |
| Summary |
Candidate materials for functional room temperature magnetic semiconductor devices are currently being actively developed and detailed knowledge of the electronic and magnetic structure of these candidate materials is needed. This information can be obtained through the use of spectroscopic techniques where synchrotron radiation based techniques are especially useful due to their elemental selectivity. This proposed collaboration seeks to apply these synchrotron radiation based techniques to a number of these materials, specifically transition metal doped semiconductor oxides such as Co–doped ZnO and Co-doped SnO2. Two other materials, HfO2 and CaB6, will also be targeted as thin films of these materials unexpectedly exhibit magnetic behaviour even though nominally they are d0 materials.
The techniques applied to investigate these materials will be soft x-ray emission spectroscopy, x-ray absorption spectroscopy and x-ray photoemission spectroscopy and their resonant counterparts to elucidate the electronic structure. It is anticipated that x-ray magnetic circular dichroism will also be applied to measure the spin and orbital moments of the constituent elements within the materials. Information obtained from such measurements will help confirm theoretical models and also elucidate current questions regarding the roles of dopants and non-magnetic elements in their magnetic behaviour.
This project is a collaborative investigation with Prof. K. E. Smith of Boston University. |
| Funding Agency |
Enterprise Ireland |
| Programme |
International Collaboration Travel Award |
| Type of Project |
Research Collaboration |
| Date from |
June 2005 |
| Date to |
April 2006 |
| Person Months |
2 |
|
|
| More Research Projects>>> |
S. Krishnamurthy, C. McGuinness, L. S. Dorneles, M. Venkatesan, J. M. D. Coey, J. G. Lunney, C. H. Patterson, K. E. Smith, T. Learmonth, P.A. Glans, T. Schmitt, J.-H. Guo, Soft x-ray spectroscopic investigation of ferromagnetic Co-doped ZnO, Journal of Applied Physics, 99, (08M111), 2006, p1 - 3 TARA - Full Text
DOI |
Cormac McGuinness, James E. Downes, Paul Sheridan, P.-A. Glans, Kevin E. Smith, W. Si, Peter D. Johnson, X-ray spectroscopic study of the electronic structure of the high-dielectric-constant material CaCu3Ti4O12, Physical Review B, 71, (19), 2005, p195111 - 195111-9
Url |
Downes, J. E., McGuinness, C., Glans, P.-A., Learmonth, T., Fu, D., Sheridan, P. and Smith, K. E., Electronic structure near the Fermi level of the organic semiconductor copper phthalocyanine, Chemical Physics Letters, 390, 2004, p203 - 207
Url
DOI |
McGuinness, C., Stagarescu, C.B., Ryan, P.J., Downes, J.E., Fu, D., Smith, K. E. and Egdell, R.G., Influence of shallow core-level hybridization on the electronic structure of post-transition-metal oxides studied using soft x-ray emission and absorption, Physical Review B: Condensed Matter and Materials Physics, 68, (16), 2003, p165104 - 1:165104-9
Url
DOI |
McGuinness, C., Fu, D., Downes, J. E., Smith, K. E., Hughes, G. and Roche J., Electronic structure of thin film silicon oxynitrides measured using soft x-ray emission and absorption, Journal of Applied Physics, 94, (6), 2003, p3919 - 3922
Url
DOI |
| More Publications>>> |
Contact:helpdesk@tcd.ie
Last Updated:16-MAY-2012 |