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

Subgrain structure and dislocations in WC-Co hard metals revealed by electron channelling contrast imaging
Jablon BM, Mingard K, Winkelmann A, Naresh-Kumar G, Hourahine B, Trager-Cowan C
International Journal of Refractory Metals and Hard Materials (2019)
https://doi.org/10.1016/j.ijrmhm.2019.105159
AlN overgrowth of nano-pillar-patterned sapphire with different offcut angle by metalorganic vapor phase epitaxy
Walde S, Hagedorn S, Coulon P-M, Mogilatenko A, Netzel C, Weinrich J, Susilo N, Ziffer E, Matiwe L, Hartmann C, Kusch G, Alasmari A, Naresh-Kumar G, Trager-Cowan C, Wernicke T, Straubinger T, Bickermann M, Martin R W, Shields P A, Kneissl M, Weyers M
Journal of Crystal Growth (2019)
https://doi.org/10.1016/j.jcrysgro.2019.125343
Scanning electron microscopy as a flexible tool for investigating the properties of UV-emitting nitride semiconductor thin films
Trager-Cowan C, Alasmari A, Avis W, Bruckbauer J, Edwards P R, Hourahine B, Kraeusel S, Kusch G, Johnston R, Naresh-Kumar G, Martin R W, Nouf-Allehiani M, Pascal E, Spasevski L, Thomson D, Vespucci S, Parbrook P J, Smith M D, Enslin J, Mehnke F, Kneissl M, Kuhn C, Wernicke T, Hagedorn S, Knauer A, Kueller V, Walde S, Weyers M, Coulon P-M, Shields P A, Zhang Y, Jiu L, Gong Yipin, Smith R M, Wang T, Winkelmann A
Photonics Research Vol 7, pp. B73-B82 (2019)
https://doi.org/10.1364/PRJ.7.000B73
Determining GaN nanowire polarity and its influence on light emission in the scanning electron microscope
Naresh-Kumar G, Bruckbauer J, Winkelmann A, Yu X, Hourahine B, Edwards P R, Wang T, Trager-Cowan C, Martin R W
Nano Letters Vol 19, pp. 3863-3870 (2019)
https://doi.org/10.1021/acs.nanolett.9b01054
Imaging basal plane stacking faults and dislocations in (11-22) GaN using electron channelling contrast imaging
Naresh-Kumar G, Thomson David, Zhang Y, Bai J, Jiu L, Yu X, Gong Y P, Martin Richard Smith, Wang Tao, Trager-Cowan Carol
Journal of Applied Physics Vol 124 (2018)
https://doi.org/10.1063/1.5042515
You do what in your microprobe?! The EPMA as a multimode platform for nitride semiconductor characterization
Edwards Paul R, Naresh-Kumar G, Kusch Gunnar, Bruckbauer Jochen, Spasevski Lucia, Brasser Catherine G, Wallace Michael J, Trager-Cowan Carol, Martin Robert W
Microscopy & Microanalysis 2018, pp. 2026-2027 (2018)
https://doi.org/10.1017/S1431927618010619

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

STEMFest 2019
Contributor
14/11/2019
Invited talk: International Workshop on Nitride Semiconductor, Japan, November 2018 Title: Visualization and investigation of defects using electron channeling (electron diffraction) in the scanning electron microscope
Speaker
14/11/2018
Invited talk: State-of-the-art trends of scientific research of artificial and natural nanoobjects (STRANN), Russia, October 2018 Title: Investigating the Structural and Luminescence Properties of Semiconductors in the Scanning Electron Microscope
Speaker
17/10/2018
Invited talk: Gordon Research Conference on Defects in Semiconductors, New London, US, August 2018 Title: Investigating the Structural and Luminescence Properties of Semiconductors in the Scanning Electron Microscope
Speaker
22/8/2018
Invited Talk: International Workshop on UV Materials and Devices 2017, Fukuoka, Japan, November 2017 Title: Nanocharacterisation of the structural and luminescence properties of UV light-emitting materials in the scanning electron microscope
Speaker
11/2017
Plenary Lecture: International Workshop on Advance Materials and Device Technology, Chennai, India, November 2017 Title: Characterisation of the structural and luminescence properties of nitride materials in the scanning electron microscope
Speaker
11/2017

more professional activities

Projects

Doctoral Training Partnership 2018-19 University of Strathclyde | Waters, Dale
Trager-Cowan, Carol (Principal Investigator) Martin, Robert (Co-investigator) Waters, Dale (Research Co-investigator)
01-Jan-2019 - 01-Jan-2023
Doctoral Training Partnership (DTP 2016-2017 University of Strathclyde) | McDermott, Ryan
Trager-Cowan, Carol (Principal Investigator) Martin, Robert (Co-investigator) McDermott, Ryan (Research Co-investigator)
01-Jan-2017 - 01-Jan-2021
Quantitative non-destructive nanoscale characterisation of advanced materials
Hourahine, Ben (Principal Investigator) Edwards, Paul (Co-investigator) Roper, Marc (Co-investigator) Trager-Cowan, Carol (Co-investigator) Gunasekar, Naresh (Research Co-investigator)
"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."
01-Jan-2017 - 30-Jan-2020
Novel applications of direct electron imaging in the scanning electron microscope
Trager-Cowan, Carol (Principal Investigator)
01-Jan-2016 - 31-Jan-2016
Nanoanalysis for Advanced Materials and Healthcare - EPSRC strategic equipment
Martin, Robert (Principal Investigator) Edwards, Paul (Co-investigator) Faulds, Karen (Co-investigator) Florence, Alastair (Co-investigator) Graham, Duncan (Co-investigator) Sefcik, Jan (Co-investigator) Ter Horst, Joop (Co-investigator) Trager-Cowan, Carol (Co-investigator) Uttamchandani, Deepak (Co-investigator) Wark, Alastair (Co-investigator)
This proposal seeks funding to deliver enhanced capability for characterising and assessing advanced nanomaterials using three complementary, leading edge techniques: Field-emission microprobe (EPMA), combined Raman/multiphoton confocal microscope (Raman/MP) and small angle X-ray scattering (SAXS). This suite of equipment will be used to generate a step-change in nanoanalysis capability for a multi-disciplinary team of researchers who together form a key part of Strathclyde's new Technology and Innovation Centre (TIC). The equipment will support an extensive research portfolio with an emphasis on functional materials and healthcare applications. The requested equipment suite will enable Strathclyde and other UK academics to partner with other world-leading groups having complementary analytical facilities, thereby creating an international collaborative network of non-duplicated facilities for trans-national access. Moreover the equipment will generate new research opportunities in advanced materials science in partnership with the National Physical Laboratory, UK industry and academia.
08-Jan-2015 - 07-Jan-2019
Doctoral Training Partnership (DTP - University of Strathclyde) | Brasser, Catherine Geraldine
Martin, Robert (Principal Investigator) Trager-Cowan, Carol (Co-investigator) Brasser, Catherine Geraldine (Research Co-investigator)
01-Jan-2015 - 01-Jan-2019

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