Scanning Electron Microscopy
EM Facility Manager
Mrs Elaine Miller
Phone: 61 8 9266 7511
Fax: 61 8 9266 2377
Scanning Electron Microscopes are powerful tools for gaining instantaneous visual insight into the microstructure of materials. There are a number of variations in the way such images and other data can be obtained, so a number of different instruments with specific capabilities are available.
Zeiss Neon 40EsB FIBSEM
In late 2008, CMR acquired a new Zeiss Neon EsB focussed ion beam scanning electron microscope (FIBSEM). This is a unique facility within Western Australia. The FIBSEM has a field emission electron gun providing high brightness and high resolution (0.8nm achieved). It has the usual array of SE and BSE detectors, as well as in-lens SE and BSE detectors and an integrated EDS/EBSD facility.
The focussed ion beam (FIB) can be used for imaging, milling and deposition using a gallium ion beam. The associated gas injection system is currently set up so that deposition can be carried out with platinum, tungsten, or SiO2 (insulator) or enhanced etching can be carried out with fluorine or water.
The FIB can be used to ablate the polished surface of a sample then perform EBSD upon multiple successive layers to build up a 3D EBSD map of its structure. This facility is also used to cut laminar samples for further investigation by transmission electron microscopy (TEM).
Zeiss Evo 40XVP and the Philips XL30
Both the Zeiss Evo 40XVP and the Philips XL30 scanning electron microscopes can be used to investigate surfaces of samples, most often on a micron and sub-micron scale. High-resolution images with an impressive depth of field are readily obtained.
Small samples and fine powders can be mounted on SEM stubs in the preparation laboratory prior to the session. Coating facilities and technical staff are on-site to assist with all sample preparation requirements.
Imaging can be performed using the secondary electron (SE) detector, the backscattered electron (BSE) detector, and cathodoluminescence (CL) detector. The SE detector is ideal for obtaining surface topography for a wide variety of samples. The BSE detector is ideal for analysing samples that have a wide range of atomic numbers. In addition elemental composition can be determined using an EDS X-ray detector. Examples of analyses include the observation of:
- multi-phase minerals
- different phases and inclusions in metal alloys
- asbestos and other fibres
- heavy metal ions present in doped materials and biological systems
- failure analysis of metal welds.
The Evo SEM also can be operated in variable pressure mode which enables analysis of moist uncoated samples such as biological specimens.
The cathodoluminescence (CL), or light, detector is able to show regions in the sample that produce visible light when struck by electrons. This detector is invaluable for obtaining additional microstructural information from samples such as zircons, diamonds and zirconia and is ideal for mapping regions of interest prior to SHRIMP (sensitive high resolution ion microprobe) analysis.
Electron Backscatter Diffraction (EBSD)
EBSD is fully integrated into both the Evo SEM and the Neon FIBSEM, allowing crystallographic information to be obtained in the same session as imaging or X-ray analysis. The EBSD technique yields valuable clues about morphology, material properties and behaviours on a granular or inter-granular scale and is suitable for a wide variety of materials. Its particular strengths are in:
- phase identification and mapping of materials with similar chemistries (for example oxides, carbides or nitrides) with a spatial resolution of one micron
- identifying changes in crystallographic orientation around sites of deformation, corrosion, migration and recrystallisation to an accuracy of one degree of mis-orientation.
EBSD Map* of a zircon in a lunar breccia that records progressive variations in crystallographic orientation (shown in rainbow colour scheme) and microtwin domains (indicated by the arrows). The grain deformed during an impact-shock event prior to its incorporation into the host rock, collected by NASA scientists.
(* modified from Timms, N.E., Reddy, S.M., Healy, D., Nemchin, A.A., Grange, M.L., Pidgeon, R.T., and Hart R., 2011, Resolution of impact-related microstructures in zircon: A preliminary shock-deformation mechanism map. Meteoritics & Planetary Science submitted June 2011)