H.G. Jones

Metrological challenges for reconstruction of 3-D microstructures by focused ion beam tomography methods.

The development of combined focused ion beam and scanning electron microscopes has enabled significant advances in the characterization of the 3‐D structure of materials. The repeated removal of thin layers or slices with an ion beam and imaging or mapping the chemical or crystallographic structure of each slice enables a 3‐D reconstruction from the images or maps. The accuracy of the reconstruction thus depends on the accuracy with which the slice thickness is measured and maintained throughout the process, and the alignment accuracy of the slices achieved during acquisition or by postacquisition corrections. A survey of papers published in this field suggests that the reconstruction accuracy is not often considered or reported. Using examples from examination of the 3‐D structure of hardmetals, issues affecting the accuracy of slice thicknesses and image realignments are examined and illustrated and potential errors quantified by the use of fiducial markers and the expected isotropy of the hardmetal structure itself.

FIB / SEM Determination of Sub-Surface Damage Caused by Micro-Tribology Scratching of WC/Co Hardmetal Samples

WC/Co hardmetals are composite materials that are used in many wear resistant applications. Micro-tribology experiments were carried out on polished samples of WC/Co as model single point abrasion tests to determine the microstructural mechanisms of wear. The mechanisms of wear included plastic deformation and micro-fracture of the WC grains leading to fragmentation of the grains with re-embedment in the binder phase to form layers covering and protecting further damage to the surface.

Metrology of Three-Dimensional Techniques in Focused Ion Beam Microscopy

The use of focused ion beam (FIB) microscopes to characterise the microstructure of materials in three dimensions, by reconstruction of serial sections, has rapidly grown during the last decade. This is due to improved capabilities in material characterisation and more effective control of the ion beam to cut cross sections in a wide range of materials. It is easy to assume that a visual reconstruction of a stack of images produced by FIB is a fairly accurate representation of the true 3D structure and subsequently carry out measurements based on these data. However, it will be shown that this is not straightforward and in practice, errors or uncertainties in the sectioning, imaging or mapping, and reconstruction can combine to produce misleading results. This paper discusses the metrological challenges faced, but often disregarded, in measurement of the errors and uncertainties that occur throughout FIB 3D characterisation of materials. This was done by studying image stacks and 3D reconstructions from purpose-made structures of known geometries and composition.