Electron backscattered diffraction analyses combined with environmental scanning electron microscopy: Potential applications for non-conducting,uncoated mineralogical samples

Abstract

Operational techniques have been developed which combine electron backscattered diffraction (EBSD) analysis with orientation contrast and secondary electron imaging in environmental scanning electron microscopy (ESEM). This is specifically directed towards the analysis of uncoated, non-conducting materials such as ceramics and mineral surfaces, where surface charge effects have a severe detrimental effect on EBSD microstructural analysis. Initial experimentation to establish optimum chamber conditions was based on single Ge crystals, using both H₂O vapour and N₂ imaging gases. Reliable EBSPs with correct crystallographic solutions were collected up to pressures of ∼4 torr (1 torr ≈1.33 mbar) under H₂O vapour conditions and ∼2 torr in N₂, well above the minimal values for gaseous secondary electron detector imaging and surface charge neutralisation. Using these initial pressure and gas type guidelines, polycrystalline structures (with grain mosaics of 50–100 µm) in etched steel were analysed by automated, long duration crystal orientation mapping (COM). Optimum chamber conditions were established at ∼1 torr pressure in H₂O vapour environments. At higher gas pressures, increased electron scattering generated more unsolved EBSPs, requiring advanced filtering to reduce map noise. For tests with non-conductors, a suite of single crystal and polycrystalline minerals (garnet, calcite, and olivine) were analysed. Optimum EBSPs were obtained under H₂O vapour conditions at pressures of 0.6–1.8 torr, and beam conditions were sufficiently stable for the collection of manual COMs. This new method of combining EBSD and ESEM will greatly improve the potential for microstructural analysis of sensitive, non-conducting ceramic surfaces.