Numerical modelling is used to interpret experimental observations and predict new materials properties.  Understanding physical phenomena requires analysis at the atomic scale, where both system size and the geometric arrangement of atoms plays a crucial role.  Our aim is always to attempt to model systems as close as possible to those produced in reality in the laboratory.

The complexity, both in terms of geometry and chemical composition, of nanomaterial systems requires the use of a range of different approaches, from semi-empirical calculations to handle very complex systems through to “ab-initio” approaches for more precise results on easier to handle systems.

The computer modelling work in our group is based around electronic structure calculations within the framework of density functional theory (DFT).  Such codes are commonly developed for specific materials, and a calculation framework optimised for studying metallic systems may not give sufficient precision when applied to semi-conducting or polymer systems for example.  For this reason, when studying hybrid materials such as the interface between metal/semiconductors, or organic-inorganic hybrids, one must be very careful in applying these techniques.

Study of surface interaction between metal nanoparticles and carbon nanotube surfaces, as part of a European STREP project, “nano2hybrids” (www.nano2hybrids.net).  Using density functional and density functional tight binding calculations to simulate the tube and metal nanoparticles to understand the nature of the chemical bonding, charge transfer and change in properties of these hybrid metal-carbon systems, in particular for gas absorption in order to develop ultra-sensitive, ultra-rapid gas sensors.    Gas plasma pre-treatment of the nanotube surfaces can optionally introduce defects in the carbon walls, and the second aspect of the modelling is to better understand the nature of defect formation in carbon nanotube walls, and defect interaction with gas plasma, and later with absorption of different gas types such as benzene and ammonia.

Science Research Partners:

• Facultés Universitaires Notre-Dame de la Paix FUNDP (project coordinator)
• Université Libre de Bruxelles
• Centre de Recherche Public Gabriel Lippmann
• Université Catholique de Louvain (PCPM)
• Institut des Matériaux de Nantes
• University Rovira I Virgili
• Sensotran, s.l.

Science Communication Partners:

• The Vega Science Trust
• Ed Goldwyn Productions

(C₅₉N)₂

Collaborative partners include :

Nanotubes:

• Dr Marianne Glerup, University of Oslo, Norway
• Dr Odile Stephan, Prof. Christian Colliex, Laboratoire de Physique des Solides, Universite Paris Sud
• Dr Brigette Bouchet-Fabre, CEA Saclay
• Dr Tiberiu Minea, Universite Paris Sud
• Dr Vojislav Krstic, National Pulsed Magnetic Field Laboratory (LNCMP), Toulouse
• A. Gohier, M.A. Djouadi, A. Granier, IMN-PCM

Fullerenes:

• Prof Denis Arcon, Institute Jozef Stefan, Ljubljana, Slovenia
• Nikos Tagmatarchis, Theoretical and Physical Chemistry Institute, National Hellenic Research Foundation, Athens

Recent Publications:

• 'Nitrogen Violation of the Isolated Pentagon Rule' (C.P. Ewels)
• 'Review of Nitrogen doping in carbon nanotubes' ( C. P. Ewels, M. Glerup)

We study fluorine binding and migration on carbon nanotube surfaces.  We have recently shown that fluorine forms varying surface superlattices at increasing temperatures.  The ordering transition is controlled by the surface migration barrier for fluorine atoms to pass through next neighbor sites on the nanotube, explaining the transition from semi-ionic low coverage to covalent high coverage fluorination observed experimentally for gas phase fluorination between 200 and 250°C.    Fluorine addition along the nanotube axis direction is favored by a mechanism of carbon framework distortion. The experimentally observed formation of fluorine bands may be thus explained in terms of multiple axial C₂F rows expanding by contiguous axial addition.

Collaborative partners include :

• Dr Gregory van Lier, Professor P. Geerlings (VUB, Brussels)
• Prof. Jean-Christophe Charlier, UCL, Louvain-la-Neuve

Recent Publications

• 'Pattern formation on carbon nanotubes'
  C. P. Ewels, G. Van Lier, J. -C. Charlier, M. I. Heggie, P. R. Briddon,
  Physical Review Letters, 96 216103 (2006).
• 'Theoretical Analysis of Fluorine addition to Carbon Nanotubes: Functionalisation Routes and Addition Patterns.'
  G. Van Lier, C. P. Ewels, F. Zuliani, A. De Vita, J. -C. Charlier,
  J. Phys. Chem. B, 109(13), 6153-6158 (2005).
• 'Theoretical Study of the Addition Patterns of C60 Fluorination: C60Fn (n = 1-60)'
  G. Van Lier, M. Cases, C. P. EWELS, R. Taylor, P. Geerlings,
  J. Org. Chem. 70, 1565-1579 (2005).

Collaborative partners include :

• Prof. D. Arcon, Dr. P. Umek, Institut Josef Stefan, Ljubjana, Slovenia.
• Dr. A. Gloter, CNRS UMR8502, LPS, Universite Paris Sud

Recent Publications

• 'Impact of Structure and Morphology on Gas Adsorption of Titanate-Based Nanotubes and Nanoribbons'
  P. Umek, P. Cevc, A. Jesih, A. Gloter, C. P. Ewels, D. Arcon
  Chem. Mater. 17 (24), 5945-5950 (2005).

Intimate interstitial-vacancy metastable pair in graphite

Intrinsic defects such as vacancies and interstitials can play a crucial role in the mechnical, chemical and electronic behaviour of nanoscale materials.  Recent advances in electron microscopy mean that for the first time it is possible to image individual point defects, and this enables a new range of theoretical and experimental collaborations into the precise structure of point and line defects.  In particular we are interested in metastable defect configurations, defect diffusion and aggregation, and the effect of irradiation on nanoscale materials in creating and modifying localised damage sites.

Collaborative partners include :

• A. Zobelli, Dr. A. Gloter, Prof. C. Colliex, LPS, Universite Paris Sud
• Prof. M. I. Heggie, Dr. G. Savini, G. Haffenden,  Chemistry, University of Sussex
• Prof. K. Suenaga, AIST, Tsukuba, Japan
• Prof. P. Briddon, Dr. J. Goss, Newcastle University, UK
• Dr. A. El Barbary, Cairo, Egypt.

Recent Publications

• 'Vacancy migration in hexagonal boron nitride'
  A. Zobelli, C. P. Ewels, A. Gloter, G. Seifert, C. Colliex,
  Physical Review B, Accepted (2007).

• 'Defective Structure of BN Nanotubes: From Single Vacancies to Dislocation Lines'
  A. Zobelli, C. P. Ewels, A. Gloter, G. Seifert, O. Stephan, S. Csillag, C. Colliex,
  Nano Letters 6 (9), 1955-1960 (2006).

Semi-conducting materials displaying ferromagnetic behavioru at room temperature are currently the subject of many theoretical and experimental studies. One way to obtain such materials is to use hybrid structures consisting of a ferromagnetic metal and a semi-conductor, either in a bulk form, a super-structure, or in the form of a heterostructure.  The lattice parameter compatibility of germanium and iron allow construction of FeGe alloys in which the atomic poliarisation of iron can create magnetic ordering. 

Collaborations

• C. Demangeat, Institut de Physique et Chimie des Matériaux de Strasbourg.
• A. Vega, Universite Valladolid, Espagne.
• A. Siad Université Oran, Algérie