SEM / EDX
Scanning Electron Microscopy (SEM)
Scanning electron microscopy is a state of the art technique for the analysis and imaging of micro- and nanostructures. The Walther-Meißner-Institute operates two Scanning Electron Microscopes (SEMs). The one (Philips XL30 SFEG, minimum spot size ~1nm) is equipped with a hot field emitter and an in-lens detector is mainly used for electron beam lithorgaphy. The XL30-SFEG is a high-resolution scanning electron microscope capable of resolutions better than 2 nm, magnifications over 600.000, and operating voltages from 200 V up to 30 kV with 1 kV and 2 kV being routine.
The other is equipped with a Tungsten hairpin gun and an Energy Dispersive X-ray (EDX) analysis system. It is mainly used for spatially resolved chemical analyis of bulk and thin film samples.
Energy Dispersive X-Ray (EDX) Analysis
Energy Dispersive X-ray (EDX) analysis is a valuable tool for qualitative and quantitative element analysis. This method allows a fast and non-destructive chemical analysis with a spatial resolution in the micrometer regime. It is based on the spectral analysis of the characteristic X-ray radiation emitted from the sample atoms upon irradiation by the focussed electron beam of a SEM. In our system the spectroscopy of the emitted X-ray photons is performed by a Si-Li detector with an energy resolution of about 150 eV at 5 mm working distance.
Principle of Operation
The incident beam electrons excite electrons in a lower energy states, prompting their ejection and resulting in the formation of electron holes within the atom’s electronic structure. Electrons from an outer, higher-energy shell then fill the holes, and the excess energy of those electrons is released in the form of X-ray photons. The release of these X-rays creates spectral lines that are highly specific to individual elements. In this way the X-ray emission data can be analyzed to characterize the sample in question. For example, the presence of copper is indicated by two so called K peaks (Kα and Kβ) at about 8.0 and 8.9 keV and a Lα peak at 0.85 eV. In heavy elements like tungsten, a ot of different transitions are possible and many peaks are therefore present.