EDX (Energy Dispersive X-ray analysis)

Introduction:

EDX Analysis stands for Energy Dispersive X-ray analysis. It is sometimes referred to also as EDS or EDAX analysis. It is a technique used for identifying the elemental composition of the specimen, or an area of interest thereof.  The EDX analysis system works as an integrated feature of a scanning electron microscope (SEM).Interaction of an electron beam with a sample target produces a variety of emissions, including x-rays. An energy-dispersive (EDS) detector is used to separate the characteristic x-rays of different elements into an energy spectrum, and EDS system software is used to analyze the energy spectrum in order to determine the abundance of specific elements. EDS can be used to find the chemical composition of materials down to a spot size of a few microns, and to create element composition maps over a much broader raster area. Together, these capabilities provide fundamental compositional information for a wide variety of materials.

Principle:

During EDX Analysis, the specimen is bombarded with an electron beam inside the scanning electron microscope. The bombarding electrons collide with the specimen atoms' own electrons, knocking some of them off in the process. A position vacated by an ejected inner shell electron is eventually occupied by a higher-energy electron from an outer shell. To be able to do so, however, the transferring outer electron must give up some of its energy by emitting an X-ray.      The amount of energy released by the transferring electron depends on which shell it is transferring from, as well as which shell it is transferring to. Furthermore, the atom of every element releases X-rays with unique amounts of energy during the transferring process. Thus, by measuring the amounts of energy present in the X-rays being released by a specimen during electron beam bombardment, the identity of the atom from which the X-ray was emitted can be established.

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EDX (Energy Dispersive X-ray analysis)

EDX spectrum :

The output of an EDX analysis is an EDX spectrum (see Figure 2 on Page 2). The EDX spectrum is just a plot of how frequently an X-ray is received for each energy level. An EDX spectrum normally displays peaks corresponding to theenergy levels for which the most X-rays had been received. Each of these peaks are unique to an atom, and therefore corresponds to a single element. The higher a peak in a spectrum, the more concentrated the element is in the specimen.     An EDX spectrum plot not only identifies the element corresponding to each of its peaks, but the type of X-ray to which it corresponds as well. For example, a peak corresponding to the amount of energy possessed by X-rays emitted by an electron in the L-shell going down to the K-shell is identified as a K-Alpha peak. The peak corresponding to X-rays emitted by M-shell electrons going to the K-shell is identified as a K-Beta peak shown in the figure below.

Figure .   Elements in an EDX spectrum are identified based on the energy content of the X-rays emitted by their electrons as these electrons transfer from a higher-energy shell to a lower-energy one.

When performing EDX analysis, the following must be observed:    1) The probe current must be adjusted such that data collection is just between 10%-30% dead.2) Spot Mode operation must be used for contaminants suspected to be concentrated in very small regions.3) The EHT level used during the analysis must be higher than the energy peaks corresponding to the elements of interest.  Failure Mechanisms/Attributes Tested for by EDX Analysis: Inorganic Contamination Elemental Composition

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EDX (Energy Dispersive X-ray analysis)

A typical EDS spectrum is portrayed as a plot of x-ray counts vs. energy (in keV). Energy peaks correspond to the various elements in the sample. Generally they are narrow and readily resolved, but many elements yield multiple peaks. For example, iron commonly shows strong Kα and Kβ peaks. Elements in low abundance will generate x-ray peaks that may not be resolvable from the background radiation.

Figure .   Example of an EDX Spectrum

Strengths Of EDX:

When used in "spot" mode, a user can acquire a full elemental spectrum in only a few seconds. Supporting software makes it possible to readily identify peaks, which makes EDS a great survey tool to quickly identify unknown phases prior to quantitative analysis.

EDS can be used in semi-quantitative mode to determine chemical composition by peak-height ratio relative to a standard.

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EDX (Energy Dispersive X-ray analysis)

SEM/EDX analysis:

A Scanning electron microscope (SEM) can be utilized for high magnification imaging of almost all materials. With SEM in combination of EDX it is also possible to find out that different parts of the sample contains which elements.This means the  SEM/EDX instrument is a powerful and flexible tool for solving a wide range of product and processing problems for a diverse range of metals and materials.SEM/EDX analysis carried out in many industrial sectors including electronics and semiconductors, pharmaceutical, petrochemicals, plastics and polymers, aerospace, automotive, medical devices, engineering, chemicals, materials and metallurgy .

APPLICATIONS OF EDX:Typical Applications include:-

Identification of metals and materials Particle contamination identification and elimination Classification of materials Product and process failure and defect analysis Examination of surface morphology (including stereo imaging) Analysis and identification of surface and airborne contamination Powder morphology, particle size and analysis Cleaning problems and chemical etching Welding and joining technology quality evaluation and failure investigation Paint and coating failure and delamination investigation Identification and elimination of corrosion and oxidisation problems Contamination or stain investigation Structural analysis Reverse engineering of products and processes

The SEM/EDS is the ultimate tool for:

Deposits and Wear Debris Analysis Particle Sizing and Characterization Failure Analysis Contaminant Analysis Metallurgical Studies

Range of Materials for Invesigation by SEM/EDX:-

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EDX (Energy Dispersive X-ray analysis) Metals, Glass and Ceramics Semiconductors Plastics and polymers Powders and Dust Composite Materials Fibres (Textile, fabric , man-made, natural, carbon fibres, glass fibres, kevlar)

Some Applications of EDX are explained below:

EDX ANALYTICAL CAPABILITIES:

Viewing three dimensional images of microscopic areas only solves half the problem in an analysis. It is often necessary to identify the different elements associated with the a specimen. This is accomplished by using the “built-in” spectrometer called an Energy Dispersive X-ray Spectrometer. EDS is an analytical technique which utilizes x-rays that are emitted from the specimen when bombarded by the electron beam to identify the elemental composition of the specimen. To explain further, when the sample is bombarded by the electron beam of the SEM, electrons are ejected from the atoms on the specimens surface.A resulting electron vacancy is filled by an electron from a higher shell, and an x-ray is emitted to balance the energy difference between the two electrons. The EDS x-ray detector measures the number of emitted x-rays versus their energy. The energy of the x-ray is characteristic of the element from which the x-ray was emitted. A spectrum of the energy versus relative counts of the detected x-rays is obtained and evaluated for qualitative and quantitative determinations of the elements present as shown in Image below

Figure 1 EDS spectrum of elements detected in sample . The order of abundance is Fe, Cr, and Ni suggest stainless steel.

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EDX (Energy Dispersive X-ray analysis)Analysis of Thin Films:

EDX analysis was carried out on a thin evaporated layer on top of a nickel / iron alloy.

The layer contained a mixture of barium, strontium and oxygen, with a small amount of magnesium. The thickness of the layer was calculated to be ~ 38 nm.

Identification of the Type and Source of ParticulateContamination in a Ceramic Component Using SEM / EDX:

Figure 2 Optical image of dark specks of contamination in sintered glass ceramic

A ceramic preform is used not only to hold together several metal components in a holder forthermionic cathodes but also to provide an electrically insulating barrier. The ceramic is white, and in-line optical inspection is used to look for the presence of contamination on the preform.This inspection rejected holders for the presence of dark specks on the surface of the glass that could lead to later insulation or poisoning problems for the cathode at the customer. The preform is produced from a glass powder, which is pressed into shape and sintered.The metal components are then assembled together with the preform and thermally processed to first melt the glass around the metal and then re-crystallise it to form a rigid ceramic.The contamination appeared to be within the surface, therefore some samples were fracture sectioned to look for the presence of contamination inside the ceramic.Backscatter electron imaging was used to look for particles of a different chemical composition tothat of the surrounding ceramic.

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EDX (Energy Dispersive X-ray analysis)

SEM and EDX Investigations:

The scanning electron microscope (SEM) was used to examine the contamination at a highermagnification to determine whether the contamination was lying on the surface of the ceramic (surface contamination), embedded in the surface (contamination from the pressing operation) or within the surface (contamination in the glass powder).

Figure 3 Contamination on the holder ceramic

By taking samples of sintered preforms from earlier in the process, it was possible to confirmthat the contamination was present before the final assembly and thermal processing, implying that it was most likely to be present in the original glass powder, either as a result of contamination in the preform pressing process or from contamination in the incoming glass powder.

Figure 4. Contamination inside the holder ceramic

The particle of contamination was analysed by EDX and compared to the composition of theholder ceramic.

The particle contained a mixture of silicon, lead,potassium, aluminium, oxygen, sodium and zinc,whereas the normal holder ceramic contained mainly zinc, silicon and oxygen.

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EDX (Energy Dispersive X-ray analysis)

Figure 5 EDX spectra of particle (red) and the

Characterisation of Smaller Drug Particles:

This application note details the laboratory’s capabilities to mimic optical microscopy methods using SEM, and extend beyond the capability of optical techniques using manual or automated image collection and analysis. The SEM can automatically perform analysis down to a particle size of 2 .m, below this manual operation is required (ultimate resolution of SEM is 2 nm) with the advantage of chemical characterisation using EDX. The field of view is determined by the particle size range to be analysed.

Identification of glass flakes:

Another way to use SEM/EDX is to make quantitative chemical analysis of an unknown material.We use that for example when we want to determine the origin of glass fragments,found in different types of foodstuffs.

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EDX (Energy Dispersive X-ray analysis)Application of Energy-Dispersive X-ray Fluorescence toTrace Metal Analysis of Natural Waters:

Energy-dispersive X-ray fluorescence has much to offer in the field of trace metal monitoring of ecological systems.Coupled with dithiocarbamate precipitation for conversion of water samples to XRF targets, it is capable of rapid, multielement analysis at relatively low cost. It is also a convenient technique for performing separate analyses on dissolved and particulate fractions. For studies requiring analyses of only one or two metals, atomic absorption spectrophotometry or colorimetric methods may be more appropriate.

References:

http://www.lpdlabservices.co.uk/analytical_techniques/sem/sem_instrument.phphttp://www.lpdlabservices.co.uk/analytical_techniques/sem/index.phphttp://www.siliconfareast.com/edxwdx2.htmhttp://www.herguth.com/technical/sem.pdfhttp://serc.carleton.edu/research_education/geochemsheets/eds.htmlhttp://www.amazingrust.com/Experiments/background_knowledge/EDAX.htmlhttp://www.edax.com/applications/xrf-index.cfm

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