(46d) Aberration Corrected Stem Analysis of Nanowires [Invited]

Analysis of nanomaterials such as nanowires is a task that is ideally suited to electron microscopy because of the ability to perform high-resolution analysis of individual nanostructures. However, the resolution of all transmission electron microscopes was conventionally limited by the aberrations of the objective lens. Thus the recent success in aberration correction is probably one of the most exciting developments to have occurred in the field of electron microscopy for the last few decades. Scanning transmission electron microscopy (STEM) has particularly benefited from this achievement because of the availability of the Z-contrast imaging mode. Z-contrast imaging is so called because the intensity in the image is approximately proportional to the thickness and the square of the atomic number, allowing the identification and characterization of unexpected or even unknown structures. This allows a variety of new materials to be examined with unprecedented resolution and single atom sensitivity.

Nanowires have a variety of exciting applications in nanoscale electronics and photonics. Furthermore, embedding quantum structures in a nanowire is likely to enable exciting new properties to be exploited [1]. However, a detailed understanding of the macroscopic physical properties of such systems relies on their analysis at the atomic scale. One of the benefits of using a STEM to analyze nanomaterials is the variety of signals that are available. Z-contrast, bright-field imaging and convergent beam electron diffraction can be used to analyze the structure at atomic resolution. Simultaneous electron energy loss spectroscopy provides a convenient way to probe the electronic and chemical compositions with atomic resolution. Cathodoluminescence combined with Z-contrast imaging allows the light emitting properties to be correlated with individual nano-objects. In this talk several examples of the application of STEM and EELS to nanowires and other novel materials will be presented.

[1] W.I. Park, G-C Yi, M. Kim and S.J. Pennycook, 2003, Advanced Materials 15(6) 526-529