Technique: SEM with X-ray analysis and variable pressure SEM
The Zeiss EVO 15LS analytical scanning electron microscope (SEM) is a versatile instrument suited to diverse imaging and analytical functions.
The Zeiss EVO 15LS is used for a very wide range of applications, particularly the initial examination of samples. Its user-friendly interface makes it easy to use, even for novices. As little as half a day's training is needed for confidence in most of the common applications.
- Imaging the polished and carbon-coated surface of rocks and minerals
This is the most frequent application, carried out before detailed composition analysis is performed. Backscattered electron images (BEI) are the most common pictures taken. They show variation in the sample's composition as different grey tones. Composition analysis can then be performed using the Cameca SX100 electron microprobe.
- Imaging fine surface detail
Can be used to image conductive or metal-coated specimens, including biological ones.
- Looking at the complex surface of samples that are large, rough and unprepared
Ideal for examining important museum specimens where their preservation is vital as it doesn’t damage their surface.
- Creating stereo pair images
Can be used for colour anaglyphs or even 3D models whose size and shape can be measured.
- Identifying minerals
The energy dispersive X-ray (EDX) detector is routinely calibrated for analysis of major elements in silicates (the most common rock-forming minerals) and can very rapidly give information necessary for mineral identification.
- Analysing composition
The microscope can be controlled automatically by the EDX detector computer and can be programmed to make maps of large areas of the sample. These maps show differences in composition across centimetre-scale areas and allow measurement of areas. Analyses can be taken at preselected locations, and the programme can hunt for particles of interest. If elements are present at very low concentrations or the EDX cannot separate their signals, the wavelength dispersive X-ray (WDX) detector can be used to create spectrum scans. The Cameca SX100 electron microprobe also has WDX detectors.
- Creating cathodoluminescence images
The cathodoluminescence detector can be used to create images from light emitted by a sample. The images can be used to gain information about the history of mineral deposition and crystal growth.
About EDX analysis
Energy dispersive X-ray spectroscopy (EDX) is a kind of scanning electron microscopy that involves X-ray micro-analysis. The key features of this technique are:
- Non-destructive qualitative analysis can be carried out for elements with an atomic number greater than five.
- Detection limits are of the order of 0.2 weight per cent, dependent on the type of specimen, elements of interest, etc.
- Analyses can be undertaken in spot mode or the beam can be scanned to acquire X-ray element maps of areas of the sample surface.
- Automated image and elemental analysis can be carried out over large specimen areas using Oxford Instruments INCA software's feature mode.
- Backscattered electron and X-ray element map montages can be acquired and automatically stitched using Oxford Instruments INCA software's montage mode.
- Energy dispersive X-ray (EDX) detector
Capable of recognising the presence of most elements except hydrogen, helium, lithium and beryllium. Boron is difficult to find unless it is very abundant.
- Wavelength dispersive X-ray (WDX) detector
Used to create spectrum scans when the EDX detector cannot separate signals from different chemical elements, or if the elements are present in very low concentrations.
- Cathodoluminescence detector
Creates images from light emitted by the sample, including red-green-blue colour images.