epma presentation

Applied lab techniquesApplied lab techniquesPresentation on: EPMAPresentation on: EPMA

Presented By:Presented By:Muhammad Zubair Idrees Muhammad Zubair Idrees BS (HONS) GeologyBS (HONS) GeologyInstitute Of Geology Institute Of Geology

Punjab University Punjab University LahoreLahore

Electron Probe Micro Electron Probe Micro Analyzer (EPMA)Analyzer (EPMA)

DEFINITIONDEFINITION

Electron micro probe analyser (EMPA), Electron micro probe analyser (EMPA), is an analytical tool used to non-destructively is an analytical tool used to non-destructively determine the chemical composition of small determine the chemical composition of small volumes of solid materials.volumes of solid materials.

It is also known as:It is also known as:

Electron microprobe (EMP)Electron microprobe (EMP)Electron probe microanalyser (EPMA)Electron probe microanalyser (EPMA)

It works similarly to a scanning electron It works similarly to a scanning electron microscope, the sample is bombarded with an microscope, the sample is bombarded with an electron beam, and signals that come from the electron beam, and signals that come from the sample are collected.sample are collected.

PRINCIPLEPRINCIPLE

It work on the same principle as SEM.It work on the same principle as SEM.Electrons are bombarded with the target Electrons are bombarded with the target and the X-rays are produced, which is and the X-rays are produced, which is characteristics X-rays and use to determine characteristics X-rays and use to determine the composition of that very substance. the composition of that very substance.

INSTRUMENTATIONINSTRUMENTATION

EPMA consists of four major EPMA consists of four major components, from top to bottom: components, from top to bottom:

An electron source, commonly a W-An electron source, commonly a W-filament cathode referred to as a "gun." filament cathode referred to as a "gun."


A series of electromagnetic lenses located A series of electromagnetic lenses located in the column of the instrument, used to in the column of the instrument, used to condense and focus the electron beam condense and focus the electron beam emanating from the source; this emanating from the source; this comprises the electron optics and operates comprises the electron optics and operates in an analogous way to light optics. in an analogous way to light optics.


A sample chamber, with movable sample A sample chamber, with movable sample stage, that is under a vacuum to prevent stage, that is under a vacuum to prevent gas and vapor molecules from interfering gas and vapor molecules from interfering with the electron beam on its way to the with the electron beam on its way to the sample; a light microscope allows for sample; a light microscope allows for direct optical observation of the sample. direct optical observation of the sample.


A variety of detectors arranged around the A variety of detectors arranged around the sample chamber that are used to collect x-sample chamber that are used to collect x-rays and electrons emitted from the rays and electrons emitted from the sample.sample.

STRENGTH AND STRENGTH AND LIMITATIONSLIMITATIONS

STRENGTHSTRENGTH

An electron probe is essentially the same An electron probe is essentially the same instrument as an SEM, but differs in that it is instrument as an SEM, but differs in that it is equipped with a range of crystal equipped with a range of crystal spectrometers that enable quantitative spectrometers that enable quantitative chemical analysis at high sensitivity.chemical analysis at high sensitivity.

An electron probe is the primary tool for An electron probe is the primary tool for chemical analysis of solid materials at small chemical analysis of solid materials at small spatial scales (as small as 1-2 micron spatial scales (as small as 1-2 micron diameter); hence, the user can analyze even diameter); hence, the user can analyze even minute single phases (e.g., minerals) in a minute single phases (e.g., minerals) in a material (e.g., rock) with "spot" analyses. material (e.g., rock) with "spot" analyses.

Spot chemical analyses can be obtained Spot chemical analyses can be obtained in in situsitu, which allows the user to detect even , which allows the user to detect even small compositional variations within textural small compositional variations within textural context or within chemically zoned materials.context or within chemically zoned materials.

LIMITATIONSLIMITATIONS

Although electron probes have the ability to Although electron probes have the ability to analyze for almost all elements, they are analyze for almost all elements, they are unable to detect the lightest elements (H, He unable to detect the lightest elements (H, He and Li); as a result, for example, the "water" and Li); as a result, for example, the "water" in hydrous minerals cannot be analyzed. in hydrous minerals cannot be analyzed.


Some elements generate x-rays with Some elements generate x-rays with overlapping peak positions (by both energy overlapping peak positions (by both energy and wavelength) that must be separated.and wavelength) that must be separated.


Microprobe analyses are reported as oxides Microprobe analyses are reported as oxides of elements, not as cations; therefore, cation of elements, not as cations; therefore, cation proportions and mineral formulae must be proportions and mineral formulae must be recalculated following stoichiometric rules.recalculated following stoichiometric rules.


Probe analysis also cannot distinguish Probe analysis also cannot distinguish between the different valence states of Fe, so between the different valence states of Fe, so the ferric/ferrous ratio cannot be determined the ferric/ferrous ratio cannot be determined and must be evaluated by other techniques.and must be evaluated by other techniques.

SAMPLE PREPARATIONSAMPLE PREPARATION

Unlike an SEM, which can give images of 3D Unlike an SEM, which can give images of 3D objects, analysis of solid materials by EPMA objects, analysis of solid materials by EPMA requires preparation of flat, polished sections. requires preparation of flat, polished sections.


In most cases, samples are prepared as In most cases, samples are prepared as standard-size 27 x 46 mm rectangular standard-size 27 x 46 mm rectangular sections, or in 1-inch round disks. sections, or in 1-inch round disks.


The most critical step prior to analysis is The most critical step prior to analysis is giving the sample a fine polish so that surface giving the sample a fine polish so that surface imperfections do not interfere with electron-imperfections do not interfere with electron-sample interactions. sample interactions.


Prior to analysis, samples are typically coated Prior to analysis, samples are typically coated with a thin film of a conducting material with a thin film of a conducting material (carbon, gold and aluminum are most (carbon, gold and aluminum are most common) by means of evaporative common) by means of evaporative deposition. deposition.


Samples are loaded into the sample Samples are loaded into the sample chamber via a vacuum interlock and chamber via a vacuum interlock and mounted on the sample stage. The sample mounted on the sample stage. The sample chamber is then pumped to obtain a high chamber is then pumped to obtain a high vacuum. vacuum.


To begin a microprobe session, suitable To begin a microprobe session, suitable analytical conditions must be selected, such analytical conditions must be selected, such as accelerating voltage and electron beam as accelerating voltage and electron beam current, and the electron beam must be current, and the electron beam must be properly focused.properly focused.

USESUSES

Material sciences and engineeringMaterial sciences and engineeringMineralogy and PetrologyMineralogy and PetrologyPaleontologyPaleontology

REFERENCESREFERENCES

www.wikipedia.comwww.serc.carleton.edu.uswww.serc.carleton.edu.uswww.epmalab.uoregon.edu.uswww.epmalab.uoregon.edu.uswww.ncemp.orgwww.ncemp.org

http://www.wikipedia.com/

THANK YOUTHANK YOU