Profile

Career

MPhys (Leeds), PhD (Leeds)

Summary of expertise

• Electron and ion dynamics in polycrystalline materials
• Nanoparticles at finite temperature and pressure
• Electronic transport in spintronic devices
  

Research

Overview

My research is unified under the general theme "modelling the properties of surfaces and interfaces". In recent work I have focussed on nanometre sized and nano-structured systems, such as nanoparticles, nanopowders and thin film heterostructures, which posses unique properties (e.g. electronic, magnetic, optical and chemical) and have wide-ranging applications in fields such as electronics, catalysis, energy and medicine. There is constant demand for improved functionality of these systems and theoretical modelling plays a vital role. I address these problems, in close collaboration with experiment, by developing and employing a range of multi-scale theoretical and computational techniques to model the relevant conditions (i.e. temperature and pressure) and characteristic scales (e.g. time and length) relevant to real applications. Below, I summarise some of the main areas of my recent research

Electron and ion dynamics in polycrystalline materials

The dynamics of electrons and ions near grain boundaries in semiconducting and insulating materials is important for a wide range of physical problems, for example, relating to: electroceramic materials with applications as sensors, varistors and fuel cells, reliability issues for solar cell and semiconductor technologies, superconductors, tribocharging and electromagnetic seismic phenomena in the Earth's crust. In recent work I have addressed some of these issues using a combination of semi-empirical, first principles and embedded cluster techniques. For example, I demonstrated that holes can be trapped at interfaces in MgO nanopowders and I have discussed the various dynamical processes that can occur on UV illumination (JACS). Calculations on silicon grain boundaries, in collaboration with experiment, have also helped to explain the origin of asymmetry in the statistical variability of n- and p- channel poly-Si gate MOSFETs (Electron Device Letters). I am now developing approaches to model the electronic properties of grain boundaries, including associated defects, such as vacancies, in the oxide materials MgO and HfO₂ (e.g. see Nature Materials, Microelectronics Engineering and PRB).

Nanoparticles at finite temperature and pressure

When modelling the properties of nanoparticles it important to recognise that their structure is strongly influenced by their environment, which in many cases consists of an ambient atmosphere or solution at a finite temperature. Dynamical interactions between NPs and surrounding molecules can induce both overall morphology transformations and atomic scale fluctuations in their structure. As a consequence NP properties (optical, electronic and chemical, for example) can be significantly different from those predicted by simple models. This is important for numerous technological applications, e.g. heterogeneous catalysis, gas sensing, drug delivery (nanotoxicology), biological labelling technologies and also for the interpretation of fundamental studies in nanotechnology. In situ experimental studies on these systems are at present less well developed, however, dramatic morphological transformations have been observed recently. To model these systems I have developed new statistical methodologies, linked to first principles calculations. For example, in recent papers I demonstrated how dynamical interactions between nanoparticles and surrounding molecules can induce both overall morphology transformations and atomic scale fluctuations in their structure (J. Phys. Chem. C and PCCP ).

Publications

Selected publications

Silica and High-k Dielectric Thin Films in Microelectronics
G. Bersuker, K. McKenna and A. Shluger
Book chapter in "Oxide Ultrathin Films: Science and Technology (1st Edition)
Eds. Gianfranco Pacchioni and Sergio Valeri, Wiley (2012)
http://dx.doi.org/10.1002/9783527640171.ch5

Atom-Resolved Imaging of Ordered Defect Superstructures at Individual Grain Boundaries
Z. Wang, M. Saito, K. McKenna, L. Gu, S. Tsukimoto, A. Shluger and Y. Ikuhara
Nature 479, 380-383 (2011)
http://dx.doi.org/10.1038/nature10593

Optical Properties of Nanocrystal Interfaces in Compressed MgO Nanopowders
K. P. McKenna, D. Koller, A. Sternig, N. Siedl, N. Govind, P. Sushko and O. Diwald
ACS Nano, 5, 3003-3009 (2011)
http://dx.doi.org/10.1021/nn200062d

The interaction of oxygen vacancies with grain boundaries in monoclinic HfO2
K. P. McKenna and A. L. Shluger
Applied Physics Letters, 95, 222111 (2009)
h ttp://link.aip.org/link/?APL/95/222111

Gold Nanoparticles Under Gas Pressure
K. P. McKenna
Phys. Chem. Chem. Phys., 11, 4145-4151 (2009)
http://dx.doi.org/10.1039/B821408P

Electron Trapping Polycrystalline Materials with Negative Electron Affinity
K. P. McKenna and A. L. Shluger
Nature Materials, 7, 859-862 (2008)
http://dx.doi.org/10. 1038/nmat2289