EPMA (Electron Probe Micro Analyzer)

Central Facilities 

  EPMA Details
1 Name of Instrument : Electron Probe Micro Analyzer (EPMA)
2 Model/make : CAMECA -SX-100 model

  3 Principle

The basic principal involved is, an electron beam is applied on a polished solid surface of the sample causing the emission of characteristic X-rays, are diffracting by crystal involving the principle of Bragg's Law (nl = 2d Sin q). Each atomic element emits specific and identical wavelength of characteristic X-rays that are focused onto a detector where they are counted. From the intensity of the characteristic X-rays the concentration atomic element in the sample are calculated, and proper matrix corrections are applied.

  4 Description

EPMA is generally considered to be a micro-analytical technique which is able to image or analyze materials. The instrument is provided with a gun chamber with tungsten filament for the generation of electrons, a column with condenser and probe lens to de-magnify the electron beam. It is provided with 4 spectrometers (three vertical and one inclined with diffracting crystals like PET, TAP, LIF and some pseudo-crystals for the generation of good resolution X-rays, and a gas proportional counter to measure the intensities. The instrument is operated using "Peak-Sight Software", which also helps to carry out its various applications. The instrument is also provided with two rotary pumps, one diffusion pump and an ion pump to maintain good vacuum all along the path of electron beam.

 5 Applications

EPMA applications have special advantage, as they involve non-destructive in-situ analysis of minerals in polished thin sections, retaining textural relationships among coexisting minerals. It allows qualitative and quantitative analysis of individual mineral grains a few micrometers in diameter. The elements can be qualitatively or quantitatively mapped. Incorporation of a coaxial light optical microscope in the electron optics provides the familiar optical image capability used by mineralogists and geologists for identification of mineral grains and textural features of interest for chemical analysis. Fine-scale mineralogical features, such as zoning in minerals, minute inclusions, and exsolution lamellae can be measured because of the small analytical excitation volume. The instrument can be used to generate back scattered and secondary electron images. The geological application is even extended to date the minerals like monazites with this instrument. Material science applications are even more varied, from thin film semi-conductors to photonics materials to super conductors. The other applications include measurement of cathodoluminescence to characterization of minerals; chemical diffusion studies at materials interfaces. It has also lot of applications in other branches of sciences too.

 6 Material needed for analyses

(i) Very good fine polished Thin Sections of 48 x 30 x 2 mm size.

(ii) High quality epoxy mounted polished sample sections of 25 mm diameter.




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