Dr Naresh Gunasekar

Research Associate

Physics

Publications

Metrology of crystal defects through intensity variations in secondary electrons from the diffraction of primary electrons in a scanning electron microscope
Naresh-Kumar G, Alasamari A, Kusch G, Edwards P R, Martin R W, Mingard K P, Trager-Cowan C
Ultramicroscopy Vol 213 (2020)
https://doi.org/10.1016/j.ultramic.2020.112977
Structural and luminescence imaging and characterisation of semiconductors in the scanning electron microscope
Trager-Cowan Carol, Alasmari Aeshah, Avis William, Bruckbauer Jochen, Edwards Paul R, Ferenczi Gergely, Hourahine Benjamin, Kotzai Almpes, Kraeusel Simon, Kusch Gunnar, Martin Robert W, McDermott Ryan, Gunasekar Naresh, Nouf-Allehiani M, Pascal Elena, Thomson David, Vespucci Stefano, Smith Matthew David, Parbrook Peter J, Enslin Johannes, Mehnke Frank, Kuhn Christian, Wernicke Tim, Kneissl Michael, Hagedorn Sylvia, Knauer Arne, Walde Sebastian, Weyers Markus, Coulon Pierre-Marie, Shields Philip, Bai J, Gong Y, Jiu Ling, Zhang Y, Smith Richard, Wang Tao, Winkelmann Aimo
Semiconductor Science and Technology Vol 35 (2020)
https://doi.org/10.1088/1361-6641/ab75a5
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 Vol 87 (2020)
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 Vol 531 (2020)
https://doi.org/10.1016/j.jcrysgro.2019.125343
Luminescence behavior of semipolar (10 11) InGaN/GaN "bow-tie" structures on patterned Si substrates
Bruckbauer Jochen, Trager-Cowan Carol, Hourahine Ben, Winkelmann Aimo, Vennéguès Philippe, Ipsen Anja, Yu Xiang, Zhao Xunming, Wallace Michael J, Edwards Paul R, Naresh-Kumar G, Hocker Matthias, Bauer Sebastian, Müller Raphael, Bai Jie, Thonke Klaus, Wang Tao, Martin Robert W
Journal of Applied Physics Vol 127 (2020)
https://doi.org/10.1063/1.5129049
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

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Projects

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 - 31-Jan-2021

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