EPMA

Electron Probe Microanalysis (EPMA) Services

Electron Probe Microanalysis (EPMA) is a bulk chemical analysis technique which utilizes a focused beam of electrons to generate x-rays with wavelengths characteristic to those elements present.  These x-rays are then diffracted through Bragg crystals to prevent x-rays of other wavelengths from reaching the detector (wavelength dispersive spectroscopy, WDS).  All compositions are calculated based upon x-ray intensities detected in the sample and standard materials, yielding extremely accurate and precise measurements for most the periodic table.  It is a non-destructive, in situ technique with a high signal to noise ratio and outstanding spectral resolution that provides reliable low detection chemical compositions on a variety of materials.

APPLICATION AREAS FOR EPMA:

Optimized for thin films, metallurgical studies, particles, failure analysis, and ceramic and mineral analyses. For film samples, EPMA can obtain the composition and thickness of nanometer-scale layers by measuring x-ray intensities at multiple voltages. Due to the high sensitivity and accuracy of the technique it is ideal for understanding trace element variations in materials resulting from diffusion, corrosion, processing methods, etc.

MEASUREMENTS FROM EPMA:

  • Quantitative elemental analysis down to ~10-100ppm sensitivity (lower for some systems) for Be to U
  • Single point and chemical mapping capabilities
  • Five WDS detectors allows data to be collected on up to five elements concurrently
  • Simultaneous WDS and energy dispersive spectroscopy (EDS) acquisition for single point analyses (will soon be available for mapping also)

LIMITATIONS:

  • Elements must be tuned and calibrated to standards, so measurements can be time consuming
  • Light elements (Be-N) can be difficult to achieve quantitative results on in some matrices
  • Spatial resolution limited to 1μm due to beam size and electron scattering effects (can be larger depending on the material and beam energy utilized)
  • Samples must be able to go under high vacuum and be conductive or capable of being coated with a conductive material
  • Ideally samples are innately or polished flat, however, with modeling some spherical and fibrous materials can also be examined

EXAMPLE OUTPUTS FROM EPMA

Traverse of single points across a nickel-based, high temperature alloy standard reference material (NIST SRM C2402 – Hastelloy7C)

Mg elemental map of the diffusion zone in an Al-Mg95Gd5 diffusion couple

INSTRUMENTS

Cameca SX100 Electron Probe Microanalyzer

Our instrument is equipped with five WDS detectors and a Thermo System Six Silicon Drift EDS detector for chemical analysis.  Two of the WDS spectrometers are also outfitted with large area diffraction crystals, providing even greater sensitivity.  Additionally, our SX100 has several crystals optimized for light element analyses.   The combination of detectors allows for low concentration elements to be analyzed with WDS detectors while utilizing the EDS detector for high concentration elements, resulting in a quicker, but still fully quantitative, analysis.  The instrument also has secondary electron, backscatter electron, and cathodoluminescence detectors for imaging.