Energy dispersive X-ray spectroscopy (EDX)

Energy dispersive X-ray spectroscopy (EDX)

Subhajit Dutta2nd Year, Mtech C.M.S.N.T.

ContentsWhat is EDX?EDX System SchematicHow it works?What elements can be measured?DetectorsInterpretation of EDX spectraWhy EDX?What is EDX?...is the method to do qualitative and quantitative analysis of elemental composition by excitation of atoms and detection of their characteristic X-rays Qualitative analysis Identification of elements Whats there? Quantitative analysis Determination of concentrations How much? Semi-quantitative analysis Estimation of concentrations About how much?

Energy dispersive X-ray spectroscopy (EDS or EDX)

The detector is used to record both: Energy of X-ray photons Number of X-ray photons at a given energy

EDX System Schematic

How it works?

What elements can be measured?EDX: Sodium Uranium

Detectors

Lithium doped Silicon (SiLi) crystal detector acts as a semiconductor Detectors The detection of X-rays takes place in the intrinsic layer in the middle of the detector.

An X-ray ejects a photoelectron in the Si which loses its energy by promoting electrons from the valence band to the conduction band forming electron-hole pairs.

A reverse bias of 500 to 1000 volts is used to ensure that most of the electron-hole pairs are collected.It is not possible to make silicon pure enough to be intrinsic - it usually contains acceptor impurities and thus acts as a p-type semiconductor.

The acceptor sites are thus filled with Li, and the Si is then called lithium drifted silicon or Si(Li).

These electron-hole pairs are counted by an amplifier, resulting in a pulse whose height is proportional to the X-ray energy.

The signal needs to be amplified by a factor of about 10^10.

The pulses are counted as a function of energy and displayed on a computer.

Interpretation of EDX spectraEnsure that the incident beam energy is high enough. Beam energy > 2 Highest peak energy.Ensure that the spectrum is reliable.Prior knowledge of the sample present.Confirm elements by looking for other peaks from that element.Work from high energy to low energy identifying peaks.Peak shapes and energies.Why EDX?QuickVersatileInexpensiveWidely available