EPMA technical information

EPMA is a fully quantitative microbeam technique with a spatial resolution of 1µm. Elements between boron and uranium can be analysed with detection limits of ~0.01wt% for solid materials. 

The Electron Probe Microanalyser is capable of fully quantitative analysis of almost every element between boron and uranium, with a spatial resolution as high as 1 micron and excellent analytical precision. 

The technique of EPMA uses a focussed incident electron beam to generate X-rays that identify the elements and their concentrations within samples. Instrument calibration is carried out by analysing reference materials with known compositions.  Routine detection limits are typically 60 – 600 ppm, depending on the element and host material. 

The SX100 is designed for automation and when samples permit, can be set up for automated analyses overnight and during weekends, maximising data collection and cost-effectiveness.

The configuration of our Electron Probe Microanalyser enables high-quality analysis of an extensive range of materials including:

• minerals
• metals and alloys
• glasses
• ceramics 
• bone

The SX100 is therefore exceptionally versatile and has capabilities in fields such as: 

• Earth and environmental sciences
• materials sciences
• engineering
• biological and medical sciences
• archaeology
• forensics
• manufacturing, process and quality control

In addition to quantitative analysis of specific locations on samples, the SX100 can produce qualitative and quantitative element distribution maps with resolutions as high as 1 micron, line profiles and analyses of thin layers.

The facility is actively engaged in technique development to improve current methods and extend the range of applications of EPMA. Developments have led to improved spatial resolutions for analysis of glassy materials with beam diameters of 3 and 5 microns without beam-induced chemical modification (Hayward, 2012). This permits analysis of highly vesicular and/or fine-grained, distal tephras and small melt inclusions. Other developments have improved analysis of elements such as carbon, nitrogen and oxygen.

Electron probe microanalysis

Our CAMECA SX100 is equipped with five vertical crystal spectrometers and a PGT Spirit energy dispersive analyser. 

• Samples can be observed via back-scattered and secondary electron imagery and in reflected and transmitted light
• The optical microscope has magnifications between x100 and x900
• The instrument operates under Windows, using Cameca's PeakSight software

Specialised software functionalities include:

• quantitative X-ray mapping for quantitative elemental spatial distribution
• quantitative line profiles for detailed compositional variation along user-defined lines
• dynamic beam tracking for improved sample positioning (enabling automated analysis of very small areas or grains)
• quantitative analysis of thin layers

Diffracting crystals of six types enable analysis of elements between boron and uranium. The configuration of these within the five WD spectrometers permits analysis of almost any element combination. 

The large analysing crystals (LTAP, LPET and LLIF) enable higher analytical precisions, lower detection limits and faster analysis times. They enable, for example, analysis of glasses at high spatial resolution without Na mobilisation (LTAP), trace element analysis down to tens or hundreds of ppm, and high-quality analysis of beam-sensitive minerals such as carbonates and phyllosilicates.

You can find more details on the suppliers website:

• CAMECA SX100 website

Tephra analysis

The Tephra Analysis Unit uses the world-class Cameca SX100 instrument of the electron probe microanalysis facility. This features:

• five wavelength dispersive spectrometers
• energy dispersive spectrometer
• transmitted and reflected light
• secondary and backscatter imagery

It is operated via Cameca’s Windows-based Peak Sight software. Off-line data processing using Peak Sight is available.

The SX100 is configured in a way that is ideal for tephra analysis. Most importantly, it has large analysing crystals for analysis of volatile elements Na and K, preventing their mobilisation during analysis. Other large crystals enable a rapid and sensitive analysis of trace elements including P and Ti to detection limits of the order of 70 - 80 ppm.

The SX100’s exceptional imaging capabilities include backscattered electron imagery, for identification and avoidance of crystals within glasses, and transmitted and reflected light microscope at magnifications between x100 and x900. The energy dispersive detector allows for rapid discrimination between glass and mineral fragments.

Secondary electron image of an approximately 10 x 15 micron crypto-tephra grain, after analysis. The beam diameter was 5 microns.	Image
Backscattered electron image of plagioclase and magnetite crystals within a melt inclusion within a clinopyroxene of the Fimmvörduhals fissure eruption, Iceland, 2010.	Image

Please discuss any queries related to sample preparation or format with us well in advance of your scheduled booking.

Contact details and access to the facility

Electron probe microanalysis

There are requirements for sample preparation before analysis at the Electron Probe Microanalysis Facility.

• Samples must be vacuum compatible and stable under electron bombardment.
  • The operating vacuum is approximately 10 -5 Pa
• For quantitative analysis, the specimens must be flat, well-polished and as free from surface voids as possible.
  • Final polishing should use 0.25 micron abrasive
  • Samples with porosity should be vacuum-impregnated with resin to fill void space
• Samples must be cohesive, so as not to shed particles whilst in the SX100
• Samples must be in a format compatible with the SX100 sample holders, which accommodate most standard formats. Permitted formats are:
  • Thin sections: 45-48mm long, up to 25mm wide, 1mm thick with up to 0.5mm thick polished sample above the glass slide
  • Disks: 25.5mm or 29.5mm diameter, thickness 5-25mm
  • It may be possible to accommodate other formats - please discuss details with us.
  • Please use epoxy resin for sample preparation. Lakeside, Canada Balsam and styrene-based resins must not be used for preparation.
• Insulating samples need to be coated before analysis with a thin film of carbon. This is performed at the University.
  • Samples should arrive at the Facility two working days before the EPMA session for coating
  • Samples must be cleaned after polishing to remove abrasive particles and lubricants. This can be done at the University if necessary.
  • Other coating materials such as gold can be used if required, but please discuss this as far in advance of making a booking as possible.

There are also facilities at the University of Edinburgh for users to prepare certain types of sample before EPMA analysis. Please contact the EPMA facility staff.

Tephra Analysis

There are requirements for sample preparation before analysis at the Tephra Analysis Unit.

• Tephra samples are commonly prepared either as 25.5 mm diameter resin disks, or as thin sections.
• Please refer to the sample preparation outlined for the Electron Probe Microanalysis Facility above for further details on preparation and formats.

The finest-grained tephras are best prepared according to the method described in:

• Hall M. and Hayward C.L. (2015). Preparation of micro- and crypto-taphras for quantitative microbeam analysis. In: Austin, W. E. N., Abbott, P. M., Davies, S. M., Pearce, N. J. G. & Wastegaard, S. (eds.) Marine Tephras. Geological Society Special Publication, 398. The Geological Society, London.

If you have any questions concerning preparation methods for your tephras, please contact us.