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Dr Carol Trager-Cowan

Reader

Physics

Personal statement

I use electron beams to interrogate the structure, defects and light emission from solids. Together with students and colleagues here at Strathclyde and from across the world, I work on new developments and novel applications of the scanning electron microscopy techniques of electron backscatter diffraction, electron channelling contrast imaging and cathodoluminescence imaging. In particular we have developed novel techniques to rapidly and non-destructively analyse defects in nitride semiconductors used for production of UV and visible LEDs and transistor structures.

I currently lecture on solid state physics, electron and scanning probe microscopy and public engagement of research and supervise student projects.

I am also committed to public engagement giving lectures, writing articles, running workshops, quizzes, street busking, leading science street tours and providing kits to schools and am an enthusiastic contributor to the Royal Philosophical Society of Glasgow, the Glasgow Science Festival and to Explorathon (European Researchers Night Scotland). I was elected as a Fellow of the Royal Society of Edinburgh in 2014.

Publications

Practical application of direct electron detectors to EBSD mapping in 2D and 3D
Mingard K.P., Stewart M., Gee M.G., Vespucci S., Trager-Cowan C.
Ultramicroscopy Vol 184, pp. 242-251, (2018)
http://dx.doi.org/10.1016/j.ultramic.2017.09.008
Quantitative imaging of anti-phase domains by polarity sensitive orientation mapping using electron backscatter diffraction
Naresh-Kumar G., Vilalta-Clemente A., Jussila H., Winkelmann A., Nolze G., Vespucci S., Nagarajan S., Wilkinson A.J., Trager-Cowan C.
Scientific Reports Vol 7, (2017)
http://dx.doi.org/10.1038/s41598-017-11187-z
Spatially-resolved optical and structural properties of semi-polar (11-22) AlxGa1-xN with x up to 0.56
Bruckbauer Jochen, Li Zhi, Naresh-Kumar G., Warzecha Monika, Edwards Paul R., Jiu Ling, Gong Yipin, Bai Jie, Wang Tao, Trager-Cowan Carol, Martin Robert W.
Scientific Reports Vol 7, (2017)
http://dx.doi.org/10.1038/s41598-017-10923-9
Design and fabrication of enhanced lateral growth for dislocation reduction in GaN using nanodashes
Le Boulbar E. D., Priesol J. , Nouf-Allehiani M., Naresh-Kumar G., Fox S., Trager-Cowan C., Šatka A., Allsopp D. W. E., Shields P. A.
Journal of Crystal Growth, pp. 30-38, (2017)
http://dx.doi.org/10.1016/j.jcrysgro.2017.02.047
Diffraction effects and inelastic electron transport in angle-resolved microscopic imaging applications
Winkelmann A., Nolze G., Vespucci S., Gunasekar N., Trager-Cowan C., Vilalta-Clemente A., Wilkinson A. J., Vos M.
Journal of Microscopy, (2017)
http://dx.doi.org/10.1111/jmi.12571
Diffractive triangulation of radiative point sources
Vespucci S., Naresh-Kumar G., Trager-Cowan C., Mingard K. P., Maneuski D., O'Shea V., Winkelmann A.
Applied Physics Letters Vol 110, (2017)
http://dx.doi.org/10.1063/1.4978858

more publications

Research interests

Our research is driven by the need for rapid, non-destructive techniques to reveal and analyse defects in crystalline materials, in particular in nitride semiconductor thin films. III-nitride materials are presently the basis of a fast-growing, multi-billion dollar solid-state lighting industry and commercial AlGaN/GaN electronic devices are now in use in cell phone base stations, satellite communication systems and cable television networks. However, the ultimate performance of these nitride semiconductor based light emitters and electronic devices is limited by extended defects such as threading dislocations (TDs), partial dislocations (PDs), stacking faults (SFs) and grain boundaries (GBs). If we want to develop LEDs to be an effective replacement for the light bulb, or have sufficient power to purify water or develop efficient power electronics for electric vehicles, we need to eliminate these defects as they act as scattering centres for light and charge carriers and give rise to nonradiative recombination and to leakage currents, severely limiting device performance. The first step to this goal is the detection of these defects – we exploit electron channeling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) in a field emission scanning electron microscope to rapidly and non-destructively detect and analyze TDs, PDs, SFs, GBs and map crystal structure, texture, and strain with a lateral and depth resolution on the order of tens of nanometers.

We are involved in both the development and exploitation of the ECCI and EBSD techniques. For example, in collaboration with the Universities of Glasgow and Oxford and the National Physical Laboratory, we are developing new direct electron imaging detectors for electron backscatter diffraction. We are exploiting the digital complementary metal-oxide-semiconductor hybrid pixel detector, Timepix. Timepix is one of the outcomes of an international collaboration (Medipix) hosted at CERN, established to provide a solution for a range of problems in X-ray and gamma-ray imaging in hostile conditions. Using the Timepix allows digital direct electron detection and energy filtering; it enables electron backscatter diffraction patterns to be acquired with reduced noise and increased contrast, and an unprecedented increase in detail is observed in the patterns. This is allowing us to interrogate the fundamental physics of pattern formation and will enable, in the longer term, the application of the EBSD technique to be expanded to materials for which conventional EBSD analysis is not presently practicable. For more information see: Scanning electron microscopy of nitrides: Nanoscale characterisation of nitride semiconductor thin films using EBSD, ECCI, CL and EBIC.

Collaborators

We collaborate with researchers from around the globe including the Universities of Sheffield; Nottingham; Cambridge; Oxford; Bristol; Bath; Tyndall Institute/University College Cork; Aalto University;Technischen Universität Berlin; The National Physical Laboratory and Bruker Nano, Berlin.

Professional activities

UVLED Technology and Application Requirements Workshop
Organiser
22/3/2017
German Physical Society Spring Meeting, Regensburg, Germany. March 2016. Title: Nanocharacterisation of the structural and luminescence properties of materials in the scanning electron microscope
Invited speaker
8/3/2016
Lecture at the Birla Industrial and Technological Museum (BITM), Kolkata, India, January 2015 "Nitrides - The Rainbow Material"
Speaker
18/1/2016
Lecture Series in India as part of "Science and Beyond" organised by the British Council, January 2016. Gave talks on - "Studying structure and light emission in the scanning electron microscope" and "Engaging the Public with Science and Technology – from statues to rainbows"
Invited speaker
10/1/2016
Scientific Organiser of Royal Microscopical Society Electron Backscatter Diffraction Conference, Glasgow, March 2015
Organiser
29/3/2015
Maxwell Lecture at King's College London, March 2015 "Nitrides – The Rainbow Material"
Speaker
2/3/2015

more professional activities

Projects

Impact Acceleration Account - University Of Strathclyde 2012 / R120526-239
Trager-Cowan, Carol (Principal Investigator)
Period 01-Oct-2012 - 31-Mar-2017
Enhanced Electron Backscatter Diffraction by Energy Filtered Direct Electron Detection
Trager-Cowan, Carol (Principal Investigator)
Period 01-Oct-2014 - 31-Mar-2018
An EPSRC Life Sciences Interface Doctoral Training Centre for Medical Devices | Dowd, Peter Dylan
Trager-Cowan, Carol (Principal Investigator) Dowd, Peter Dylan (Research Co-investigator)
Period 01-Oct-2006 - 15-Nov-2014
Quantitative non-destructive nanoscale characterisation of advanced materials
Hourahine, Benjamin (Principal Investigator) Edwards, Paul (Co-investigator) Roper, Richard (Co-investigator) Trager-Cowan, Carol (Co-investigator) Gunasekar, Naresh (Researcher)
"To satisfy the performance requirements for near term developments in electronic and optoelectronic devices will require pioneering materials growth, device fabrication and advances in characterisation techniques. The imminent arrival of devices a few atoms thick that are based on lighter materials such as graphene or boron nitride and also advanced silicon and diamond nano-structures. These devices pose new challenges to the currently available techniques for producing and understanding the resulting devices and how they fail. Optimising the performance of such devices will require a detailed understanding of extended structural defects and their influence on the properties of technologically relevant materials. These defects include threading dislocations and grain boundaries, and are often electrically active and so are strongly detrimental to the efficiency and lifetimes of nano-scale devices (a single badly-behaved defect can cause catastrophic device failure). These defects are especially problematic for devices such as silicon solar cells, advanced ultraviolet light emitting diodes, and advanced silicon carbide and gallium nitride based high power devices (used for efficient switching of large electrical currents or for high power microwave telecoms). For graphene and similar modern 2D materials, grain boundaries have significant impact on their properties as they easily span the whole size of devices. Resolving all of these problems requires new characterisation techniques for imaging of extended defects which are simultaneously rapid to use, are non-destructive and are structurally definitive on the nanoscale. Electron channelling contrast imaging (ECCI) is an effective structural characterisation tool which allows rapid non-destructive visualisation of extended crystal defects in the scanning electron microscope. However ECCI is usually applied as a qualitative method of investigating nano-scale materials, has limitations on the smallest size features that it can resolve, and suffers from difficulties in interpreting the resulting images. This limits this technique's ability to work out the nature of defects in these advanced materials. We will make use of new developments in energy resolving electron detectors, new advances in the modelling of electron beams with solids and the knowledge and experience of our research team and partners, to obtain a 6 fold improvement in the spatial resolution of the ECCI technique. This new energy-filtered way of making ECCI measurements will radically improve the quality of the information that can be obtained with this technique. We will couple our new capabilities to accurately measure and interpret images of defects to other advanced characterisation techniques. This will enable ECCI to be adopted as the technique of choice for non-destructive quantitative structural characterisation of defects in a wide range of important materials and provide a new technique to analyse the role of extended defects in electronic device failure."
Period 01-Jun-2017 - 30-Nov-2020
Novel applications of direct electron imaging in the scanning electron microscope
Trager-Cowan, Carol (Principal Investigator)
Period 01-Sep-2016 - 31-Oct-2016
EBSD Research project with NPL
Trager-Cowan, Carol (Principal Investigator)
Period 01-Oct-2015 - 31-Dec-2015

more projects