Opportunities and pitfalls in characterisation of nanoscale features

Abstract

Thermally assisted field emission gun TEM (FEGTEM), with associated electron energy loss spectroscopy (EELS) and electron spectroscopic imaging (ESI) is used to characterise nanoscale features in technologically important materials. The exceptionally high spatial and temporal coherence of the FEG source allows high resolution image information down to 0.1 nm to be routinely imaged, but the complexity of the atomic contrast makes interpretation of interface structure more difficult than with LaB₆ sources. A spatial resolution of 0.9 nm for through thickness features and 2 nm for embedded particles is demonstrated for ESI, illustrating the remarkable sensitivity of this technique. The energy resolution of the FEG source (0.65 eV) is sufficient to resolve the fine near edge structure in EELS spectra to allow bonding information to be obtained with a spatial resolution of 1 nm or possibly better. X-ray energy dispersive spectroscopy can be performed on a similar scale, sufficiently small to identify submonolayer segregates at interfaces. The limitations of each technique are discussed in relation to the critical microstructural information required for each material investigated.