RESUMEN
Aberration-corrected transmission electron microscopy allows us to image the structure of matter at genuine atomic resolution. A prominent role for the imaging of crystalline samples is played by the negative spherical aberration imaging (NCSI) technique. The physical background of this technique is reviewed. The especially high contrast observed under these conditions owes its origin to an enhancing combination of amplitude contrast due to electron diffraction channelling and phase contrast. A number of examples of the application of NCSI are reviewed in order to illustrate the applicability and the state-of-the-art of this technique.
RESUMEN
The structural properties of beta-phase tantalum nanocrystallites prepared by room temperature magnetron sputter deposition on amorphous carbon substrates are investigated at atomic resolution. For these purposes spherical aberration-corrected high-resolution transmission electron microscopy is applied in tandem with the numerical retrieval of the exit-plane wavefunction as obtained from a through-focus series of experimental micrographs. We demonstrate that recent improvements in the resolving power of electron microscopes enable the imaging of the atomic structure of beta-tantalum with column spacings of solely 0.127 nm with directly interpretable contrast features. For the first time ever, we substantiate the existence of grain boundaries of 30 degrees tilt type in beta-Ta whose formation may be well explained by atomic agglomeration processes taking place during sputter deposition.
