Powerful Microscope for Sensitive Samples
"The new multifunctional electron microscope complements existing instruments at KIT and opens up new research horizons", says Professor Dagmar Gerthsen, head of the Laboratory for Electron Microscopy (LEM) at KIT: "The new microscope combines various tools in one instrument and can be used to obtain complementary information about a sample in a few working steps." The resolution of electron microscopes is usually improved by increasing the energy of electrons, but, as a result, these electrons may modify or even destroy structures in the sample to be studied. The new microscope therefore uses comparatively low-energy electrons of about 30 keV.
The microscope can be operated as a scanning electron microscope (SEM) or scanning transmission electron microscope (STEM), making it suitable for studying both the internal structure of a sample, as well as its surface topography. The instrument’s nominal resolution is approximately 0.3 to 0.6 nm (STEM and SEM, respectively), which corresponds to around 3 to 6 atomic radii. Structural properties in materials can thereby be characterised and correlated with important functional properties in order to improve or understand major functions, such as the efficiency of solar cells, the chemical activity of catalysts, as well as the potential toxicological impacts of nanoparticles in biological cells.
Determining chemical and physical properties
The ability to examine samples simultaneously with different detectors makes the microscope particularly powerful. "This yields new degrees of freedom in our investigation, which help us more than resolution alone", explains Dr. Erich Müller of LEM at KIT. Various interactions of the electrons with the sample will be used to offer new findings on the surface or volume properties of the sample. In addition, the chemical composition of the sample will be determined by X-ray analysis. A special camera for imaging diffracted transmitted or backscattered electrons should allow conclusions to be drawn on the crystalline structure of the material studied. "With a single instrument, we can now determine chemical and physical properties of samples much more comprehensively and are given insight in the atomic structure."
An integrated milling tool opens up additional research options for the nanoworld: a focused ion beam, FIB for short, can dig nanometre-sized trenches into the sample and hence uncover "hidden" layers below the surface of the sample. Cross-sections can be produced with high accuracy at interesting points where required.