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.

Dependence of surface facet period on the diameter of nanowires.

Axial heterostructured silicon nanowires with varying n- and p-doping were synthesized using a vapor-liquid-solid approach. The nanowire sidewalls exhibit periodic nanofaceting in the silicon deposited directly on the sidewalls when diborane dopant gas is introduced during growth. For such nanofaceting, a model predicting the distance between facets (the facet period) is developed. For a nanowire structure, an extra energy cost term arising from the formation of apexes between facets is considered, and the facet size is predicted to decrease as the wire diameter increases. It is found that the model fits the experimental data well, and the fitted parameters in the model lie within the ranges of their expected values.

Direct imaging and chemical identification of the encapsulated metal atoms in bimetallic endofullerene peapods.

In this paper, a chemically sensitive local characterization technique is used to characterize fullerene peapods containing two metal atoms within each fullerene. By combining bright-field imaging, high-angle annular dark-field imaging, and electron energy loss spectroscopy in a scanning transmission electron microscope, unambiguous identification of the metal atoms present is possible. Key to making this possible is aberration correction, which allows atomic resolution at lower beam energies. The peapods can be imaged for several consecutive scans at 80 keV beam energy, and the combination of techniques allows the position as well as the species of the encapsulated atoms to be identified. Movements of the encapsulated atoms are monitored.

Rapid fabrication of nanoneedle arrays by ion sputtering.

We report a novel method for rapidly fabricating ordered nanoneedles using an ion beam that cuts through the Fe/GaAs single thin layer or the Fe/MgO/Fe/GaAs multilayer producing a pillar pattern followed by raster-scanning normal to the patterned area. However, such ordered nanoneedles were not formed on the pure GaAs substrate surface without the thin Fe film coating, nor were nanoneedles formed on the GaAs substrate coated with a thin Cr epitaxial film, when this method was used. It has advantages over other methods, being simple, fast and well controlled for fabricating one-dimensional nanostructure arrays, leading to a range of applications such as high aspect ratio sharp tips for atomic force microscope/atom probes and consequent possible quantum confinement effects or arrays of nanostructures for field-optical/photoluminescence emission and data recording.

The preferred CSL misorientation distribution in polycrystalline SrTiO3.

Electron backscattered diffraction is used to investigate the preferred CSL (coincidence site lattice) distribution of polycrystalline SrTiO(3) as a function of annealing times (1 h and 16 h). Comparison of the CSL misorientations suggests that the CSL boundary energy plays a role in the preferred grain growth.

The interpretation of indexing of high Sigma CSL grain boundaries from ceramics.

Electron backscatter diffraction (EBSD) is a useful technique for measuring the orientation of individual grains and for determining grain boundary misorientations in polycrystals. However, its application to ceramics is more difficult than to metals, because the surface quality that can be achieved often makes the Kikuchi patterns blurred. As a consequence, it can be difficult, even for automated systems, to differentiate between different grain orientations, which have similar patterns. In this paper, we carry out EBSD analyses of SrTiO(3) polycrystalline material prepared with different polishing methods, and we consider the effect of different criteria in interpreting the EBSD patterns from them. In particular, we investigate the CSL statistics using both the Palumbo and Aust and the Brandon criteria in this situation.

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.