About the Lab
Our Electron Microprobe Laboratory comes with a state-of-the-art CAMECA SX100 to perform non-destructive, space-solved element analyses. The microprobe is equipped with 5 automated wavelength-dispersive spectrometers (WDS) and an energy-dispersive spectrometer (EDS), which can be used to make qualitative and quantitative element analysis of the elements Beryllium-Uranium. Detection limits of 10 ppm to 100 ppm can be achieved depending on the element concentration in the sample and measurement time.
Employees of the Institute and the University staff can book measurement dates by contacting the Microprobe staff via mail or telephone.
Commercial and industrial projects can only be supervised within limited free capacity. Please ask us about the options available.
The electron microprobe is controlled by a PC. The operation is possible exclusively via keyboard/mouse and a roller-board. With the help of a microscope equipped with a variable zoom, autofocus and reflected and transmitted light with polarizer, which is connected to a CCD camera, the sample surface can be continuously monitored on an automated stage. Multiple sensors with several video and digital channels are available for image acquisition and editing. High-resolution BSE (backscattered electron) and SE (secondary electron) images from the sample surface can be generated with two appropriate detectors. A cathodoluminescence camera is integrated in the optical system.
The principle of measurement of the electron microprobe is based on the bombardment of a sample with a high-energy electron beam. Thus, the electron beam interacts with the tightly bound inner shell electrons of a specimen atom, ejecting an electron from a shell. The atom relaxes to its ground state. During this process the specimen emits X-ray. Each element has a characteristic X-ray, which can be detected with the help of the spectrometers.
The diameter of the analyzed area on the specimen surface is under 1 µm at standard conditions (15 kV acceleration potential, 15 nA beam current, sample: iron oxide; volume: 3 x 10-19 m3; mass: 2 x 10-12 g). The analytical error for major and minor elements is comparable to the RFA-method. Detection limits are depends on the chemical system and are between 10 and 100 ppm.
For quantitative analyses, the electron microprobe is equipped with five spectrometers with a precision of 1 x 10-5 sin-theta. All elements with an atomic number > 4 (Be) can be measured wavelength dispersive (WDS). With the help of these spectrometers, five element distribution images can be generated simultaneously. Several changeable analyzer crystals are included in each spectrometer:
- LIF / LLIF (lithium fluoride); d = 2.013 Å; Ka-line from Sc to Rb
- PET / LPET (pentaerithritol); d = 4.375 Å; Ka-line from Si to Mn
- TAP (thallium hydrogen phtalate); d = 12.873 Å; Ka-line from F to P
- PC0 (W-Si-multilayer-crystal); d = 22.5 Å; Ka-line from Na to O
- PC1 (W-Si- multilayer-crystal); d = 30 Å; Ka-line from O to C
- PC2 (Ni-C- multilayer-crystal); d = 47.5 Å; Ka-line from O to B
- PC3 (Mo-B4C- multilayer-crystal); d = 100 Å; Ka-line from B to Be
For elements with atomic numbers > 37 (Rb) the characteristic lines of the L- and M-series, respectively, are used. Additionally, qualitative analyses are possible with an energy dispersive Oxford EDX-detector.
A professional sample preparation is the key requirement for expedient Analysis. Therefore, it is strongly recommended to seek advice from the EPMA staff about the parameters of the sample preparation and to be in doubt, to perform the sample preparation at our institute. By default, samples can be measured with the following dimensions:
- Polished thin section of about 30-100 µm thickness glued on a microscope slide of glass (48 x 28 x 1 mm)
- Polished round mounts, where your sample is embedded in a resin (diameter: 25.5 mm, 1 zoll)
Other sample sizes are available on request. Before the measurement the samples must be cleaned and coated with an approximately 20 nm thick carbon layer for charge dissipation. The exact process is available in the sample pretreatment section.
Before analyze the sample, each user has to follow some important workflow:
1. Apply for the appointed day(s) at the microprobe staff via email, phone or personally. Contact details can be found here.
2. Apply in time for sample preparation at the preparator.
3. This should be done independently for ongoing projects. Undergraduates or PhD-students, who have no experience with the microprobe, have to contact the microprobe staff in advance for information about proper sample preparation. To save time of preparation and analyses, as many samples as possible should be placed on one sample holder, even if this requires appropriate waiting time for enough sample material. The polished section(s) should be prepared a few days previous to the appointed day for further workflow.
4. Analyze the polished sections with a microscope accurately. For natural rock samples, a detailed petrographic description is very helpful.
5. Determine regions of interest: corresponding areas should be marked at the bottom part of the thin section. Note, which phases (minerals) should be measured in these areas.
6. Clean the sample surface before coating.
7. The cleaned and marked samples can be now placed in the box for coating in the microprobe lab. This should be done as early as possible, at least two days in advance of the appointed day, to collect several samples for coating.
8. Inform the advisor about the following points:
- a sample is ready for coating
- which sample should be measured first
- which elements should be measured
- any special features required (e.g. profiles, qualitative analyses, BSE images)
- confirm the date and discuss further details
Goldstein, J., Newbury, D. E., Joy, D. C., Lyman, C. E., Echlin, P., Lifshin, E., Sawyer, L., Michael, J. R. (2003): Scanning Electron Microscopy and X-ray Microanalysis (3rd Edition), Springer
Reed, S. J. B. (2005): Electron Microprobe Analysis and Scanning Electron Microscopy in Geology (2nd Edition), Cambridge University Press
Potts, P. J. (1986): A handbook of Silicate Rock Analysis, Chapman and Hall, New York, NY, 622