Quantitative trace element analysis with sub-micron lateral resolution

摘要

In recent years many nuclear microprobes have developed to sophisticated tools for elemental analysis with high resolutions down to about 1 μm. The application to trace element analysis is mainly in the field of biological and medical research. Numerous successful studies on microscopic scale structures, e.g. cells, lead to the demand for higher spatial resolution or lower detection limits. Therefore, several labs started new efforts for sub-micron resolutions, sometimes intending 100 nm. The Leipzig microprobe laboratory LIPSION has recently improved its analytical capabilities. We are now able to perform quantitative trace element analysis with sub-micron spatial resolution (beam diameter 0.5 μm at 120 pA). As an example we give the trace element distribution in neuromelanin (intracellular pigment of neurons). Furthermore, when the scan size is reduced from cellular level, i.e. about 50 μm, to sub-cellular level of about 10 μm, the beam diameter can further be reduced by choosing smaller object diaphragms. The unavoidable reduction in beam current will not affect the mapping sensitivity unless the accumulated charge per spatial resolution is not decreased. The smallest beam diameter with analytical capabilities for elemental analysis we achieved thus far was about 300 nm in diameter. It enables an outstanding microPIXE resolution. However, some difficulties appeared in high-resolution work, which limited the acquisition time to less than 30 min.