Energy-dispersive X-ray spectroscopy, commonly EDX, EDS, or EDXA, refers to the analytical technique used in conjunction with a scanning electron microscope (SEM) in order to identify composition and provide chemical characterization of a specimen. An electron beam is focused onto the sample that collides with and possibly ejects some of the sample’s electrons, forcing them to give up some of their energy, causing the x-ray.
The amount of energy released is based upon the starting and ending shell of the electron. The resulting x-ray can be converted into an EDX spectrum plot. This plot shows the different peaks that correspond to the energy levels of the x-rays received. Each part of the sample can be identified by comparing the x-ray against other known atomic structures, since each element has a unique structure. These plots can be shown as a elemental map to evaluate several elements at once or as a line profile to identify a single element.
There are two major types of detectors used for EDX, Lithium drifted Silicon Detector (SiLi) or the Silicon Drift Detector (SDD). While the SiLi must be operated at liquid nitrogen temperatures, the SDD is capable of being used at relatively high temperatures. The SDD has several other advantages over the SiLi, including faster analytical capabilities and better resolution, as well as higher count rate. The larger count rates also have the added benefit of reducing the damage to the sample because smaller specimen currents can be used.
While there are some free-standing EDX machines, SEMs are the typical equipment of choice. Since SEMs have the added bonus of imaging, they can become an integrated SEM-EDX instrument. Aspex’s Personal Scanning Electron Microscope (PSEM(R)) comes standard with an EDX spectrometer and utilizes a SDD X-Ray. Capable of EDX resolution of 135 eV and a particle detection range of 100nm to 5mm, the PSEM is a reliable, easy to use instrument.
Typical uses for EDX include foreign particle analysis, corrosive evaluation, coating composition analysis, and small component material analysis. Industries such as defense, automotive, pharmaceutical and aerospace (Should we link to these industry pages) are common places EDX analysis is used. The PSEM Express is a benchtop SEM that, when combined with Aspex software such as Automated Feature Analysis (AFA) and Complex Feature Analysis (CFA), becomes a fast, fully automated, affordable desktop SEM analysis system.
Reference:
Aspex, http://www.aspexcorp.com/products/psem-express.html
EDX Analysis and WDX Analysis, http://www.siliconfareast.com/edxwdx.htm
Materials Evaluation and Engineering, Inc., http://mee-inc.com/eds.html
Wikipedia, http://en.wikipedia.org/wiki/Energy-dispersive_X-ray_spectroscopy
