Molecular Imaging: Design of the PMP Imaging Spectrometer, Resolution Limits, and Radiation Sensitivity
| Autor: | Y. Heng, F.P. Ottensmeyer, M.M.G. Barfels |
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| Rok vydání: | 1996 |
| Předmět: | |
| Zdroj: | Proceedings, annual meeting, Electron Microscopy Society of America. 54:424-425 |
| ISSN: | 2690-1315 0424-8201 |
| DOI: | 10.1017/s0424820100164581 |
| Popis: | One of the main applications of an energy filter is to obtain elemental distribution images by electron spectroscopic imaging. This technique has been pushed to the imaging of fine structure such as the sp2 and sp3 states of carbon at a sub-nanometer spatial resolution. However, low energy loss imaging in the region of the molecular excitations has largely remained unexplored due to the limitation in the energy resolution obtainable in the energy filters. Molecular absorptions in the visible and UV regions of the spectrum occur at 1.5 eV to 10 eV. Thus it would be necessary to have an energy resolution of about 1 eV or better.An optimized Prism-Mirror-Prism energy filter has been built by altering the straight faced pole pieces to circular curvatures. See Figure 1. The optimum curvatures for each of the faces were determined iteratively. In order to simulate the electron path accurately through the Prism-Mirror-Prism filter, it was necessary to calculate the magnetic fringing fields using the Boundary Element Method as outlined by Kasper. The ray-tracing procedure indicated a theoretical energy resolution of 1.3 eV for the optimized magnetic prism. This has been tested on our prototype spectrometer currently installed in the Siemens EM 102. An energy resolution of 1.1 eV was obtained. |
| Databáze: | OpenAIRE |
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