My research focus is using computational and mathematical methods to model the properties of low dimensional nanostructures, particularly doped and/or strained graphene and carbon nanotubes. A hallmark of my work is endeavouring to achieve the maximum amount of mathematical transparency possible to these models, as this can provide a deeper understanding of the physics at play in these systems.
- 2012-2016 Ph.D. Computational & Mathematical Physics, Trinity College Dublin, Ireland.
- 2006-2010 MPhys. Theoretical Physics, Lancaster University, U.K.
Carbon-based nanostructures have been the focus of much scientific research over the past couple of decades, with a veritable smorgasbord of technological applications. Due to their unique properties and reduced dimensionality, a lot of this attention has been directed towards their use in novel electronic technologies. The electronics in these systems, for instance the existence and size of band gaps in the electronic structure, are determined by their atomic composition and underlying lattice symmetry - as a consequence they are highly sensitive to symmetry breaking operations such as doping. While this has advantages, particularly in the case of graphene which lacks a band gap in its native state, there are many unwanted consequences associated with doping such as increased carrier scattering which degrades the quality of electronic transport in the system. It follows that if the response of a system's properties to doping can be understood, this would present clearly defined paths to guide future research.
My research is focussed on the development and application of a mathematical framework, based on tight-binding Green functions, to characterise the physics of the doping of carbon-based nanostructures - in particular graphene and carbon nanotubes - and the various phenomena associated with doping. A central theme is the effect of symmetry breaking in the lattice, and endeavours are made to provide a maximum amount of mathematical transparency to all aspects of the work. This yields the advantage of providing a deeper understanding of the physics in these systems. Using a Green functions description of the low dimensional nanoscale systems many useful properties and phenomena can be investigated, such as: self-consistent impurity modelling procedures; impurity-induced Friedel oscillations in the spatially-resolved density of states and carrier density; the role of bonding symmetry on scattering and electronic transport properties; and even an explanation of the recent experimental observation of impurity segregation in nitrogen doped graphene.
- Impurity invisibility in graphene: Symmetry guidelines for the design of efficient sensors, J. Duffy, J. A. Lawlor, C. Lewenkopf and M. S. Ferreira, Submitted to PRB (2016)
- The influence of Gaussian strain on sublattice selectivity of impurities in graphene JA Lawlor, CG Rocha, V Torres, A Latgé, MS Ferreira Journal of Physics: Condensed Matter 28 (23), 235001 (2016) DOI: 10.1088/0953-8984/28/23/235001 View Paper
- Sublattice segregation of hydrogen adsorbates in carbon nanotubes J Lawlor, MS Ferreira Physical Review B 92 (11), 115405 (2015) DOI: 10.1103/physrevb.92.115405 View Paper
- Green functions of graphene: An analytic approach JA Lawlor, MS Ferreira Physica B: Condensed Matter 463, 48-53 (2015) DOI: 10.1016/j.physb.2015.01.032 View Paper
- Sublattice imbalance of substitutionally doped nitrogen in graphene JA Lawlor, PD Gorman, SR Power, CG Bezerra, MS Ferreira Carbon 77, 645-650 (2014) DOI: 10.1016/j.carbon.2014.05.069 View Paper
- Sublattice asymmetry of impurity doping in graphene: A review JA Lawlor, MS Ferreira Beilstein journal of nanotechnology 5 (1), 1210-1217 (2014) DOI: 10.3762/bjnano.5.133 View Paper
- Density of states of helically symmetric boron carbon nitride nanotubes ACM Carvalho, CG Bezerra, JA Lawlor, MS Ferreira Journal of Physics: Condensed Matter 26 (1), 015303 (2013) DOI: 10.1088/0953-8984/26/1/015303 View Paper
- Friedel oscillations in graphene: Sublattice asymmetry in doping JA Lawlor, SR Power, MS Ferreira Physical Review B 88 (20), 205416 (2013) DOI: 10.1103/physrevb.88.205416 View Paper