Advanced transmission electron microscopy for nano-optics

Abstract

In order to understand and control the fabrication of nanomaterials, it is essential that they be characterized at close to the atomic scale. The atomic structure of interfaces, defects and nanostructures can be investigated by atomic resolution transmission electron microscopy (TEM), using either high resolution TEM accompanied by simulation or high angle annular dark-field scanning TEM (HAADF-STEM), usually referred to as Z-contrast imaging. Just as atomic force microscopy, scanning tunneling microscopy and the atom probe have become the primary tool for studying surfaces, so TEM has become the method of choice for studying defects and nanostructures within materials. Many analytical signals are available on modern small-probe-forming TEMs. These techniques include convergent beam electron diffraction (CBED), electron energy loss spectroscopy (EELS) and energy dispersive X-ray (EDX) microanalysis. Atomic scale information can be obtained about defects, strain, chemical content, site occupancy, crystallographic and electronic structure. The combination of reciprocal, real space and analytical information with atomic resolution Z-contrast imaging and EELS spectroscopy offers great potential for unraveling structure-property relationships in nanostructures. Examples of two types of nanostructures: quantum well and quantum dot structures in SiC are given as well as of optical multiplayer structures for the deep UV. The strain state in SiC-quantum well structures will be determined and atomic-resolution and EELS spectroscopy illustrations are given for the chemically dissimilar cases of nanocrystals formed after erbium and germanium implantation in silicon carbide. The crystallographic and electronic structure of single nanocrystals will be determined and finally the longstanding question of whether the cluster nucleation is defect-mediated or spontaneous will be addressed.