Karl Franzens University Graz
Graz University of Technology
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Karl Franzens University Graz | Graz University of Technology | |
Prospects and Results of Aberration-Corrected Low-Voltage Electron Microscopy – the SALVE Project The ultimate goal of high-resolution analytical electron microscopy is the acquisition of detailed information about the structure, the chemical composition, and the local electronic states of the object on an atomic scale. Radiation damage resulting from atom displacement and from breaking of bonds by ionization is the fundamental limitation for the attainable specimen resolution. The tolerable electron dose D depends on the properties of the material and on the energy of the image-forming electrons. In order to avoid atom displacement for biological and other low-Z materials, the accelerating voltage must be lower than about 80kV. The SALVE project aims for atomic resolution of such objects at electron energies in the range between 20kV and 80kV. A resolution limit of 20 electron wave lengths and a large field of view has been achieved by means of a novel corrector which compensates for spherical aberration, chromatic aberration, and off-axial coma of the objective lens. Methods will be presented for protecting the object and, as a result, enable a large increase of the tolerable dose. The performance of the SALVE electron microscope will be documented by means of first experimental results showing sub-Angstroem resolution down to 50kV acceleration voltage. |