HIGH SPATIAL RESOLUTION ANALYSIS WITH THE FIELD EMISSION ELECTRON PROBE MICROANALYZER (FE-EPMA) JEOL JXA-8530F

摘要

Equipped with a Schottky field emission electron emitter, the Jeol JXA-8530F electron probe microanalyzer is able to reduce the probe diameter to about one-tenth compared to thermic emitters even at high beam current (typically 5 ... 100 nA) and low acceleration voltage (down to 5 kV) . Minimized probe diameters are interesting especially for low electron energies, for which the interaction volume inside the sample is below 100 nanometres enabling a higher spatial resolution for elemental analysis. Which spatial resolution is achieved in practice? What are the applications? An answer is received by the measurement of a line profile across the interface of two electroplated thin layers which contains iron and nickel. Measurements were made with accelerating voltages of 15, 8 and 5 kV, the beam current was held constant at 5 nA. At a magnification of 20,000x, a line of 4.5 μm length is scanned from the iron layer to the nickel layer. 450 points (step size: 10 nm) were analysed with a dwell time per point of 3000 ms. The resolution is measured at the rise of the Ni X-ray intensity (30 - 70 % criterion). We used the Ni Lα-line (0.849 keV) measured with a TAP-crystal to avoid any deterioration due to fluorescence. The following results are obtained: for 15 kV we obtain a spatial resolution of 100 nm, for 8 kV 60 nm and for 5 kV 50 nm. As an example, an application is shown where the high spatial resolution is evident. The magnesium alloy ME21 which contains cerium-rich precipitates was analyzed. Due to the low density, magnesium alloys are applied as construction material in automobile manufacturing e.g., for motor housing and gear boxes. The cerium-rich phases and their sub-structure have an important influence on the mechanical properties of the material like ductility and high temperature strength. Previous examinations with energy-dispersive X-ray spectrometry (EDS) at a conventional SEM with tungsten filament show very small inclusions in this cerium-rich precipitates which could not be identified exactly because of poor spatial resolution. Now with FE-EPMA we can resolve the small manganese-rich inclusions. Not only in the BSE image but also in the X-ray mapping, the estimated size of the manganese particles is about 50 to 200 nm. These analyses show that the Jeol JXA-8530F field emission electron probe microanalyzer enhances the capability of analysis and identification of sub-micrometre structures significantly. The spatial resolution of the FE-EPMA is one order of magnitude better compared to conventional SEM/EDS analysis.