A versatile double aberration-corrected, energy filtered HREM/STEM for materials science.

A HREM/STEM incorporating aberration correctors in both the probe-forming and imaging lenses has been installed at Oxford University. This unique instrument is also equipped with an in-column energy-loss (Omega-type) filter, HAADF detectors above and beneath the filter, and an EDX system. Initial tests have shown it to be capable of approximately 0.1 nm resolution in both TEM and HAADF STEM imaging modes. Some examples of applications are finally presented.

Spectroscopic electron tomography.

The elemental mapping techniques in analytical transmission electron microscopy (TEM), energy filtered imaging (EFTEM) and EDX-mapping, are shown to provide new routes for tomographic reconstructions of 3D chemical maps on the nanoscale. The inelastic scattering does not only provide chemical sensitivity but also improves the linear projection relationship between mass density and image intensity, which often fails in bright field TEM of crystalline materials due to diffraction contrast. Instrumental requirements and artefact sources within the contrast formation mechanisms and within the numerical reconstruction are assessed.

Experimental evaluation of a spherical aberration-corrected TEM and STEM.

We have successfully developed a spherical aberration (Cs)-corrected electron microscope for probe- and image-forming systems using hexapole correctors. The performance of the microscope has been evaluated experimentally. The point resolution attained using the image-forming Cs-corrector is better than 0.12 nm. For scanning transmission electron microscopy, the Ronchigram flat area was >40 mrad in half-angle using the probe-forming Cs-corrector.

Characterization of magnetic nanoparticles using energy-selected transmission electron microscopy.

Fe, Co, and Ni magnetic nanoparticles have been characterized using energy-selected imaging in a high-resolution transmission electron microscope. The samples comprised Fe/FeO x and Co/CoO x nanoparticles synthesized by inert gas evaporation and a Ni/C nano-composite prepared by a sonochemical method. All of the particles examined were found to be between 5 and 30 nm in size, with the Fe and Co crystals coated in 5-10 nm of metal oxide layer and the Ni metallic crystallites embedded in an amorphous carbon spherical matrix.