@Article{strathprints70604,
author = {B. M. Jablon and K. Mingard and A. Winkelmann and G. Naresh-Kumar and B. Hourahine and C. Trager-Cowan},
journal = {International Journal of Refractory Metals and Hard Materials},
title = {Subgrain structure and dislocations in {WC-Co} hard metals revealed by electron channelling contrast imaging},
year = {2020},
month = {November},
pages = {105159},
volume = {87},
abstract = {In this study, electron channelling contrast imaging (ECCI) and electron backscatter diffraction (EBSD) have been used to examine the substructure and dislocations in tungsten carbide (WC) grains in tungsten carbide-cobalt (WC-Co) hardmetals. These complimentary scanning electron microscopy (SEM) diffraction techniques provide quantifiable information of the substructure without the difficulty of transmission electron microscopy (TEM) sample preparation and examination. Subgrain structures in WC grains have rarely been reported previously because of the sample preparation difficulty, but this study has found they can occur frequently and may provide information on grain growth during sintering. ECCI has also shown for the first time complex dislocation networks across large grains, indicating accumulation of stress in as-sintered materials. To identify the defects revealed by ECCI more precisely, WC grains with surface normals [0001], [1-100] and [11-20], were identified using inverse pole figure orientation maps generated from EBSD data. ECC images from these grains reveal defects intersecting the surface and subgrains bound by dislocations. The combination of ECCI and EBSD allows for new insights into dislocation networks in a WC-Co hardmetal sample over a large, in this case 75 µm × 75 µm, field of view.},
keywords = {hardmetal, subgrain, dislocations, ECCI, EBSD, WC, Physics, Physics and Astronomy(all)},
url = {https://strathprints.strath.ac.uk/70604/},
}

@Article{strathprints73784,
author = {F. De Luca and H. Zhang and K. Mingard and M. Stewart and B. M. Jablon and C. Trager-Cowan and M. G. Gee},
journal = {Materialia},
title = {Nanomechanical behaviour of individual phases in {WC-Co} cemented carbides, from ambient to high temperature},
year = {2020},
month = {August},
volume = {12},
abstract = {The dependence of the mechanical behaviour of individual phases in WC-Co on microstructural parameters such as grain size and orientation were investigated by means of nanoindentation and electron microscopy. A broad range of WC grain dimensions, from about 1 to 1000 µm², were selected and subsequently indented to investigate any size effect. A decrease in hardness as a function of grain dimensions was observed, due to an increase in dislocation mobility in larger grains. Whilst the binder phase only exhibits a hardness of about 11 GPa, the hardness of WC grains was measured about 29 and 53 GPa for the prismatic and basal orientations, respectively, in ambient conditions. All WC orientations exhibited a similar decrease in hardness with temperature, up to 700 °C. Damage mechanisms occurring in WC-Co during nanoindentation were investigated for the different grain orientations at various temperatures. The damage was visualised using electron microscopy near the residual indent coupled with Focused Ion Beam (FIB) sectioning across the indent. The three-dimensional distribution of plastic deformation across multiple grains in the vicinity of an indent was examined using Electron Channelling Contrast Imaging (ECCI). ECCI micrographs enabled the observation of crystal defects, especially dislocations, and slip lines as well as the entire plastic zone. The defect density and spatial distribution in the deformed WC grains were compared to that of an untested WC grain to identify the type of deformation originating from spherical indentation. The work provides important information on the relationship between WC-Co microstructure and performance at operating temperatures.},
keywords = {electron microscopy, high temperature deformation, mechanical properties, microstructure, nanoindentation, WC-Co, Physics, Materials Science(all)},
url = {https://strathprints.strath.ac.uk/73784/},
}

@article{strathprints74728,
volume = {891},
number = {1},
month = {August},
title = {Advances in electron channelling contrast imaging and electron backscatter diffraction for imaging and analysis of structural defects in the scanning electron microscope},
year = {2020},
doi = {10.1088/1757-899X/891/1/012023},
journal = {IOP Conference Series: Materials Science and Engineering},
keywords = {scanning electron microscopy, contrast imaging, imaging techniques, Physics, Materials Science(all), Engineering(all), Physics and Astronomy(all)},
url = {https://doi.org/10.1088/1757-899X/891/1/012023},
issn = {1757-899X},
abstract = {In this article we describe the scanning electron microscopy (SEM) techniques of electron channelling contrast imaging and electron backscatter diffraction. These techniques provide information on crystal structure, crystal misorientation, grain boundaries, strain and structural defects on length scales from tens of nanometres to tens of micrometres. Here we report on the imaging and analysis of dislocations and sub-grains in nitride semiconductor thin films (GaN and AlN) and tungsten carbide-cobalt (WC-Co) hard metals. Our aim is to illustrate the capability of these techniques for investigating structural defects in the SEM and the benefits of combining these diffraction-based imaging techniques.},
author = {Trager-Cowan, C. and Alasmari, A. and Avis, W. and Bruckbauer, J. and Edwards, P. R. and Hourahine, B. and Kraeusel, S. and Kusch, G. and Jablon, B. M. and Johnston, R. and Martin, R. W. and McDermott, R. and Naresh-Kumar, G. and Nouf-Allehiani, M. and Pascal, E. and Thomson, D. and Vespucci, S. and Mingard, K. and Parbrook, P. J. and Smith, M. D. and Enslin, J. and Mehnke, F. and Kneissl, M. and Kuhn, C. and Wernicke, T. and Knauer, A. and Hagedorn, S. and Walde, S. and Weyers, M. and Coulon, P-M and Shields, P. A. and Zhang, Y. and Jiu, L. and Gong, Y. and Smith, R. M. and Wang, T. and Winkelmann, A.}
}

@Article{strathprints72016,
author = {G. Naresh-Kumar and A. Alasamari and G. Kusch and P. R. Edwards and R. W. Martin and K. P. Mingard and C. Trager-Cowan},
journal = {Ultramicroscopy},
title = {Metrology of crystal defects through intensity variations in secondary electrons from the diffraction of primary electrons in a scanning electron microscope},
year = {2020},
month = {March},
pages = {112977},
volume = {213},
abstract = {Understanding defects and their roles in plastic deformation and device reliability is important for the development of a wide range of novel materials for the next generation of electronic and optoelectronic devices. We introduce the use of gaseous secondary electron detectors in a variable pressure scanning electron microscope for non-destructive imaging of extended defects using electron channelling contrast imaging. We demonstrate that all scattered electrons, including the secondary electrons, can provide diffraction contrast as long as the sample is positioned appropriately with respect to the incident electron beam. Extracting diffraction information through monitoring the modulation of the intensity of secondary electrons as a result of diffraction of the incident electron beam, opens up the possibility of performing low energy electron channelling contrast imaging to characterise low atomic weight and ultra-thin film materials. Our methodology can be adopted for large area, nanoscale structural characterisation of a wide range of crystalline materials including metals and semiconductors, and we illustrate this using the examples of aluminium nitride and gallium nitride. The capability of performing electron channelling contrast imaging, using the variable pressure mode, extends the application of this technique to insulators, which usually require conducting coatings on the sample surface for traditional scanning electron microscope based microstructural characterisation.},
keywords = {electron channelling, secondary electrons, semiconductors, extended defects, SEM, Physics, Atomic and Molecular Physics, and Optics},
url = {https://strathprints.strath.ac.uk/72016/},
}

@Article{strathprints71326,
author = {Aimo Winkelmann and B. Matat Jablon and Vivian Tong and Carol Trager-Cowan and Ken Mingard},
journal = {Journal of Microscopy},
title = {Improving {EBSD} precision by orientation refinement with full pattern matching},
year = {2020},
month = {January},
number = {2},
pages = {79--92},
volume = {277},
abstract = {We present a comparison of the precision of different approaches for orientation imaging using electron backscatter diffraction (EBSD) in the scanning electron microscope. We have used EBSD to image the internal structure of WC grains, which contain features due to dislocations and subgrains. We compare the conventional, Hough-transform based orientation results from the EBSD system software with results of a high-precision orientation refinement using simulated pattern matching at the full available detector resolution of 640 × 480 pixels. Electron channeling contrast imaging (ECCI) is used to verify the correspondence of qualitative ECCI features with the quantitative orientation data from pattern matching. For the investigated sample, this leads to an estimated pattern matching sensitivity of about 0.5mrad (0.03°) and a spatial feature resolution of about 100nm. In order to investigate the alternative approach of post-processing noisy orientation data, we analyse the effects of two different types of orientation filters. Using reference features in the high-precision pattern matching results for comparison, we find that denoising of orientation data can reduce the spatial resolution, and can lead to the creation of orientation artefacts for crystallographic features near the spatial and orientational resolution limits of EBSD.},
doi = {10.1111/jmi.12870},
keywords = {EBSD analysis, orientation imaging, pattern matching, Physics, Physics and Astronomy(all)},
url = {https://strathprints.strath.ac.uk/71326/},
}

@article{strathprints62078,
volume = {184},
number = {Part A},
month = {January},
author = {K.P. Mingard and M. Stewart and M.G. Gee and S. Vespucci and C. Trager-Cowan},
title = {Practical application of direct electron detectors to EBSD mapping in 2D and 3D},
journal = {Ultramicroscopy},
pages = {242--251},
year = {2018},
keywords = {EBSD, direct electron detector, medipix, 3D EBSD, SEM image drift, focused ion beam, Optics. Light, Instrumentation, Atomic and Molecular Physics, and Optics, Electronic, Optical and Magnetic Materials},
url = {https://strathprints.strath.ac.uk/62078/},
abstract = {The use of a direct electron detector for the simple acquisition of 2D electron backscatter diffraction (EBSD) maps and 3D EBSD datasets with a static sample geometry has been demonstrated in a focused ion beam scanning electron microscope. The small size and flexible connection of the Medipix direct electron detector enabled the mounting of sample and detector on the same stage at the short working distance required for the FIB. Comparison of 3D EBSD datasets acquired by this means and with conventional phosphor based EBSD detectors requiring sample movement showed that the former method with a static sample gave improved slice registration. However, for this sample detector configuration, significant heating by the detector caused sample drift. This drift and ion beam reheating both necessitated the use of fiducial marks to maintain stability during data acquisition.}
}

@Article{strathprints63048,
author = {E. Pascal and B. Hourahine and G. Naresh-Kumar and K. Mingard and C. Trager-Cowan},
title = {Dislocation contrast in electron channelling contrast images as projections of strain-like components},
journal = {Materials Today: Proceedings},
year = {2017},
volume = {5},
number = {6},
pages = {14652-14661},
month = {July},
abstract = {The forward scattering geometry in the scanning electron microscope enables the acquisition of electron channelling contrast imaging (ECCI) micrographs. These images contain diffraction information from the beam of electrons ``channelling in'' into the sample. Since small, localised strains strongly affect the electron diffraction, defects which introduce lattice displacement in the region of the surface the electron beam is interacting with will be revealed as district variation in backscattered electron intensity. By acquiring multiple images from the same area in different diffraction conditions and comparing them against modelled predictions of defect strain sampled by diffraction, it is possible to characterise these defects. Here we discuss the relation between the elastic strain introduced by a threading dislocation intersecting the surface and the contrast features observed in the electron channelling contrast image of that region. Preliminary simulated channelling contrast images are shown for dislocations with known line direction and Burgers vectors using a two-beam dynamical diffraction model. These are demonstrated to be in qualitative agreement with measured images of dislocated polar wurtzite GaN acquired with two different diffraction condition.},
keywords = {electron channelling contrast imaging (ECCI), dislocations, scanning electron microscope (SEM), image simulation, defect imaging, Physics, Physics and Astronomy(all)},
url = {https://strathprints.strath.ac.uk/63048/}
}

@Article{strathprints60196,
author = {S. Vespucci and G. Naresh-Kumar and C. Trager-Cowan and K. P. Mingard and D. Maneuski and V. O'Shea and A. Winkelmann},
title = {Diffractive triangulation of radiative point sources},
journal = {Applied Physics Letters},
year = {2017},
volume = {110},
number = {12},
pages = {124103},
month = {March},
abstract = {We describe a general method to determine the location of a point source of waves relative to a two-dimensional single-crystalline active pixel detector. Based on the inherent structural sensitivity of crystalline sensor materials, characteristic detector diffraction patterns can be used to triangulate the location of a wave emitter. The principle described here can be applied to various types of waves provided that the detector elements are suitably structured. As a prototypical practical application of the general detection principle, a digital hybrid pixel detector is used to localize a source of electrons for Kikuchi diffraction pattern measurements in the scanning electron microscope. This approach provides a promising alternative method to calibrate Kikuchi patterns for accurate measurements of microstructural crystal orientations, strains, and phase distributions.},
keywords = {instrumentation, pixel detector, crystalline sensor materials, Physics, Physics and Astronomy (miscellaneous), Radiation},
url = {http://strathprints.strath.ac.uk/60196/}
}

@Article{strathprints59555,
author = {S. Vespucci and A. Winkelmann and K. Mingard and D. Maneuski and V. O'Shea and C. Trager-Cowan},
title = {Exploring transmission {K}ikuchi diffraction using a {T}imepix detector},
journal = {Journal of Instrumentation},
year = {2017},
volume = {12},
number = {2},
pages = {C02075},
month = {February},
abstract = {Electron backscatter diffraction (EBSD) is a well-established scanning electron microscope (SEM)-based technique [1]. It allows the non-destructive mapping of the crystal structure, texture, crystal phase and strain with a spatial resolution of tens of nanometers. Conventionally this is performed by placing an electron sensitive screen, typically consisting of a phosphor screen combined with a charge coupled device (CCD) camera, in front of a specimen, usually tilted 70? to the normal of the exciting electron beam. Recently, a number of authors have shown that a significant increase in spatial resolution is achievable when Kikuchi diffraction patterns are acquired in transmission geometry; that is when diffraction patterns are generated by electrons transmitted through an electron-transparent, usually thinned, specimen. The resolution of this technique, called transmission Kikuchi diffraction (TKD), has been demonstrated to be better than 10 nm [2, 3]. We have recently demonstrated the advantages of a direct electron detector, Timepix [4, 5], for the acquisition of standard EBSD patterns [5]. In this article we will discuss the advantages of Timepix to perform TKD and for acquiring spot diffraction patterns and more generally for acquiring scanning transmission electron microscopy micrographs in the SEM. Particularly relevant for TKD, is its very compact size, which allows much more flexibility in the positioning of the detector in the SEM chamber. We will furthermore show recent results using Timepix as a virtual forward scatter detector, and will illustrate the information derivable on producing images through processing of data acquired from different areas of the detector. We will show results from samples ranging from gold nanoparticles to nitride semiconductor nanorods.},
keywords = {radiation, imaging detectors, electron backscatter diffraction, Kikuchi diffraction patterns, transmission Kikuchi diffraction, direct electron detector, Timepix, scanning transmission electron microscopy micrographs, Physics, Instrumentation, Mathematical Physics},
url = {http://strathprints.strath.ac.uk/59555/}
}

@Article{strathprints54220,
author = {S. Vespucci and A. Winkelmann and G. Naresh-Kumar and K. P. Mingard and D. Maneuski and P. R. Edwards and A. P. Day and V. O'Shea and C. Trager-Cowan},
title = {Digital direct electron imaging of energy-filtered electron backscatter diffraction patterns},
journal = {Physical Review B (Condensed Matter)},
year = {2015},
volume = {92},
number = {20},
pages = {205301},
month = {November},
abstract = {Electron backscatter diffraction is a scanning electron microscopy technique used to obtain crystallographic information on materials. It allows the nondestructive mapping of crystal structure, texture, and strain with a lateral and depth resolution on the order of tens of nanometers. Electron backscatter diffraction patterns (EBSPs) are presently acquired using a detector comprising a scintillator coupled to a digital camera, and the crystallographic information obtainable is limited by the conversion of electrons to photons and then back to electrons again. In this article we will report the direct acquisition of energy-filtered EBSPs using a digital complementary metal-oxide-semiconductor hybrid pixel detector, Timepix. We show results from a range of samples with different mass and density, namely diamond, silicon, and GaN. Direct electron detection allows the acquisition of EBSPs at lower ({$\leq$}5 keV) electron beam energies. This results in a reduction in the depth and lateral extension of the volume of the specimen contributing to the pattern and will lead to a significant improvement in lateral and depth resolution. Direct electron detection together with energy filtering (electrons having energy below a specific value are excluded) also leads to an improvement in spatial resolution but in addition provides an unprecedented increase in the detail in the acquired EBSPs. An increase in contrast and higher-order diffraction features are observed. In addition, excess-deficiency effects appear to be suppressed on energy filtering. This allows the fundamental physics of pattern formation to be interrogated and will enable a change in the use of electron backscatter diffraction (EBSD) for crystal phase identification and the mapping of strain. The enhancement in the contrast in high-pass energy-filtered EBSD patterns is found to be stronger for lighter, less dense materials. The improved contrast for such materials will enable the application of the EBSD technique to be expanded to materials for which conventional EBSD analysis is not presently practicable.},
keywords = {electron backscatter diffraction patterns, EBSPs, electron detection, energy filtering, Physics, Condensed Matter Physics},
url = {http://strathprints.strath.ac.uk/54220/}
}

@Article{strathprints49409,
author = {C. Trager-Cowan and G. Naresh-Kumar and N. Allehiani and S. Kraeusel and B. Hourahine and S. Vespucci and D. Thomson and J. Bruckbauer and G. Kusch and P. R. Edwards and R. W. Martin and C. Mauder and A. P. Day and A. Winkelmann and A. Vilalta-Clemente and A. J. Wilkinson and P. J. Parbrook and M. J. Kappers and M. A. Moram and R. A. Oliver and C. J. Humphreys and P. Shields and E. D. Le Boulbar and D. Maneuski and V. O'Shea and K. P. Mingard},
title = {Electron channeling contrast imaging of defects in {III}-nitride semiconductors},
journal = {Microscopy and Microanalysis},
year = {2014},
volume = {20},
number = {S3},
pages = {1024--1025},
month = {August},
keywords = {Physics, Instrumentation},
url = {http://strathprints.strath.ac.uk/49409/}
}