EDAX (Data analysis)
Dear students welcome to EPG part shala I am dr. Rajesh Sharma an associate professor from chemistry department at a university today we are going to discuss about the module analysis of energy dispersive x-ray spectroscopy under the paper of surface and little techniques - you know as the name suggests analysis means detailed examination of elements or structures of a material similarly now in this module we will study about how to interpret the data obtained from a PDS spectrometer in this module we are going through the following topics number one the analysis then some sample preparation data interpretation qualitative analysis quantitative analysis elemental mapping line profile analysis window type and lastly the graph interpretation so let's start with analysis part EDX is a qualitative and quantitative x-ray analytical technique that provides information on the chemical composition of a sample it involves the generation of excess spectrum from the integrated scan area of the SEM scanning electron microscope or the micrograph there are certain energy constraints which are used in this analysis now what is energy constraint it means something that controls you by keeping within particular limits this means we will study about the energy limitation that we have to keep in mind while dealing with edx system these limits are the energy resolution that is a pro hundred-thirty electron volt which is seen at full width at half maximum the limit of detection is thousand to three thousand ppm the element identified are elements having atomic number greater than three the spatial resolution is for low atomic weight it is 1 to 5 micro meter cube and high is 2 to 1 micro meter cube the precision is approaching plus minus 0.1 percent the basic principle of edx analysis energy dispersive x-ray spectroscopy is based on the detection of characteristic x-rays emitted from an element as a result of the D excitation of core electron holes created by a high-energy electron beam an electron from a higher binding energy electron level falls into the core hole and an x-ray with the energy of the difference of the electron double binding energies is emitted due to the quantization of electron energy levels the emitted characteristic x-ray energies for element will generally be different from the element 2 element with only a few spectral Peaks overlapping if the identification of one peak is ambiguous other peeps or limited knowledge of the sample history will often allow a reasonable element identification of the peak the normal electron beam of a scanning electron microscope is used as the excitation source the sample is effectively the anode of an x-ray source the addition of an energy measuring exit detector with a thin low mass element window on a SEM enables EDS for all elements from carbon on up in atomic masses a spectrum consists of all the characteristic x-rays emitted by the elements present in the sample on a continuous background due to pressure emblem x-ray emission caused by the deceleration of the high-energy electrons of the electron beam in the sample the important DDX parameters the important EDX parameters are number one the count rate for a good quality spectrum that is good resolution and fewest artifacts there should be used of 50 200 microsecond time constant that is processing time with a dead time of 20 to 40 percent and 500 to 35 CPS counts per second these are good numbers if sample consists largely of high-energy Peaks that is greater than one kilo electron volt but if the spectrum is dominated by low energy Peaks that is less than one collector on volt then account rate of 500 mm CPS is better and the 100 microsecond time constant should be used the other parameter is accelerating voltage the over voltage is a ratio of accelerating voltage used to the critical excitation energy of a given line of an element typically the over voltage should be at least two for the highest energy line and no more than ten to twenty times the lowest energy line of interest the parameter third is takeoff angle typically take-off angles will range from 25 to 40 degrees this angle is a combination of the detector angle its position sample working distance and the sample tilt the sensitivity for low energy x-ray and our signals characterized by high absorption can be enhanced by increasing the take-off angle some incline detectors for example a detector angle of approximately 35 degree above the horizontal some incline detectors do not require sample tilt horizontal entry detectors require that the sample be tilted to achieve an optimum takeoff angle now we will talk about edx spectrum interpretation continuum x-rays as a result of inelastic scattering primary beam electrons in which the electrons are decelerated and lose energy without producing an ion digestion of the atoms in the sample continuum x-rays are formed the continuum x-rays are the background of our EDF spectrum and are sometimes referred to as the base Imbler in theory the continuum can be expected to extend from the maximum energy of the primary beam electrons and increase exponentially 2-0 kilo electron volt energy in reality the background goes to zero at the low end of the energy spectrum due to absorption by the detector window the detector that layer and the gold layer the intensity of the container is related to both the atomic number of the sample as well as the beam energy the continuum intensity also increases with beam current the characteristic x-rays in elastic scattering events between primary beam electrons and inertial electrons which result in the ejection of the electron from the atom within the sample and may lead to the formation of a characteristic x-ray the ejection of the electron leaves the atom in an ionized excited state and permits an outer shell electron to move to the inner shell because the energy levels of the various shells are related to the number of charges in the nucleus the energy of the emitted axis is characteristic of the element the beam electron must have an energy greater that is just slightly greater than the energy of the shell electron this is called the critical ionization energy the depth of excitation although electrons may penetrate in specific gaps within a sample which can be stated with a variety of equations or with Montecarlo programs the electrons actually lose energy in steps as they go to greater depth in the sample as a result an electron may soon do the sufficient amount of its energy such that it can no longer excite characteristic x-rays typically this occurs when its energy drops below the critical ionization energy of the elements in the sample each element within the sample will have its own critical ionization energy and its own excitation depth the ratio of the primary beam energy to the excitation energy of the element is referred to as the depth of excite the sample preparation it is the most important part to prepare a sample for proper analysis using PDX this means what all parameters one must keep in mind while preparing the samples so while preparing these samples following points must be kept in mind the sample taken must be stable under vacuum as the sample chamber is evacuated to prevent the atmosphere from interfering with the electron beam or x-rays since EDS is a surface phenomenon so it is advisable to keep the surface as clean as possible as any impurity on the surface will alter the compositional calculations qualitative calculations can be obtained by taking solid of any thickness but reliable calculations are obtained from qualitative measurement by keeping the sample as thin as possible so if the above-mentioned points are not kept in mind there might be chances of contamination and we will not be able to get accurate results about the data interpretation once the sample is prepared the process begins and there comes the point where we need to interpret the data the interpretation of data is broadly done by using different techniques like qualitative analysis and quantitative analysis elemental mapping and line profile analysis we will be discussing each one of the above techniques in details in the subsequent slides the diagram in the slide shows how data is being interpreted we have sample from which characteristic X's are being generated out of which are further analyzed by a detector and final data is shown with the help of Peaks to begin with what we have the first is qualitative analysis from the name we can guess what all we are going to deal with under this analytical part qualitative means we are talking about the quality of the myth or the sample in this analysis the elements that are present in the sample are characterized from their characteristic x-ray Peaks elements with atomic number from beryllium to uranium can be detected the variation of detection limit depends on the elect element and the sample matrix if there are large number of elements the peaks that are obtained are overlapping peaks and they are identified depending on their peaks in the different x-ray families general guidelines for PDS qualitative analysis only Peaks which are statistically significant should be considered for identification the mini size of the peak should be three times of the standard deviation of the background at the peak position beam should be greater than three B power half their brain waves of peak members in a family provide an important source of information in identifying elements for example a family k alpha is 1 K beta 0.
1 L family L alpha 1 alveta 1 is 0.7 L beta 2 0.2 albita 3 0.008 albita 4 0.05 L gamma 1 0.08 L gamma 3 0.03 and L 0.04 and M family am alpha 1 M beta is 0.6 m gamma 0.05 and AM Zeta 0.06 begin with the most intense line towards the high-energy region of the spectrum where lines within a very within a family are well separated if it is about 3.5 kilo electron volt it must be either a K or L line using the klm markers.
Compare the location of the peak so that of the marker check the relative intensities if you identify a K alpha line then K beta line should be about 10% and the KL fall intensity K alpha and K beta lines are typically resolved at sulfur and above below the K beta is so small that K alpha and K beta collectively show themselves as one symmetry poppy if a clear line is identified then look for L lines if they occur for that particular element if the line chosen does not correspond to a k line try and L series if the line is identified as the L alpha several other lines both above and below the L alpha should be present and correspond to the element the EDX system should be able to display them at their correct relative intensities M lines do not exist above three point two kilo electron volt so one would not look for them at this point then continue to identify lines while working towards lower energies and consider the possibility of M lines the lines of an M series are generally not all resolved but contribute to an asymmetrical peak in fact M lines can often be recognized by this distortion but aware but beware of overlap that may look similar when all high-energy lines and low-energy L and M lines are identified light elements can be a template these will be K lines and may be overlap with L lines from heavier elements if it is not possible to distribute them pigby convolution software or peak stripping may be necessary peak stripping is a mathematical process that allows the analyst to remove identified fee structures to reveal possible hidden Peaks if they exist after all major and minor peaks are located trace elements can be attempted in this case problem is to confidently find peak above background only the major peaks of the series will be visible and that may be lost in a background in quantitative analysis from the name we can guess what all we are going to deal with quantity quantitative means we are talking about the qua quantity of the material.
Or the sample it can be obtained from X account in different energy levels on the basis of analysis parameters and the sample composition semi qualitative results are easily available without standard without standards with the help of the mathematical Corrections we move on to the elemental mapping what elemental mapping is the intensity of x-ray is measured with respect to the later position of the sample the concentration of the element across the surface is indicated by the variation in X intensity so it is kind of it line profile how the compositional variations are occurring along that line in a given sample the line profile analysis acts as the identified for particular position along the line by analyzing the x-ray energy spectrum at each position it gives a plot of relative elemental concentration for each element versus the position about the window type in sdd we have discussed about the window which is there so basically student these windows are of two types number one the pendulum window type number two polymer thin film window let us study about them shows a comparison between Balian window and polymer base window the perilymph window types they are highly robust they strongly absorb low energy x-rays as a result element from sodium can be analyzed the thickness is about 8 to 10 micrometer the polymer based window these are less robust they are transparent to much lower energy access mainly allowing detection of x-rays down to 100 lectronimo the thickness is less than 8 micrometer the interpretation of the graph obtained in TDX analysis and graphs of electron diffraction spectrum of the type showing the K peaks of sodium a1 and aluminum and silicon let us in tribute this graph by taking in example this graph is a PD spectrum of the edge showing peaks of potassium silicon aluminum in case of excess spectrum graph the energy which is in kilo electron volt is plotted on x axis and the number of counts on y axis by examining the pattern of pigs.
On the spectrum different elements present in the sample ask observed you can see the relative intensities and the area under the teeth are different the interpretation of the graph when any sample is being evaluated by EDX the information is usually represented as histogram or spectrum the spectrum is characteristic of a particular element and every element has fixed clear alpha and alpha energy values for these energy values the elements present in the sample are identified in media's k alpha emission lines develop when an electron transition to the K shell that is principal quantum number 1 from a 2p orbital of L shell that is principal quantum number 2 the line is actually a doublet having slightly different energies depending on the spin orbit energy between the electron spin and the orbital momentum of the 2p orbital k alpha is typically by for the strongest excess spectral line for an element more barded with energy sufficient to cause maximally intense x-ray emission similarly L alpha lines are developed when an electron takes place to be alchun from the emption in this glass you can easily see that excitation of electrons takes place as a result of which the electron moves to a higher excited state and then after losing energy it will turns back to its original state the energies are represented by the values of K alpha and alpha every element has fixed values of K alpha and alpha now next example is of bio tile by tile is a silo silicate material which is a mica group having formula potassium magnesium iron host wise aluminum si o si 3o 10 H hole twice it is a shell ticket in which iron magnesium aluminum silicon oxygen and hydrogen form sheets that are weakly bonded together with potassium ions in biotite strong peaks of magnesium aluminum silicon potassium and iron are seen the peaks of hydrogen oxygen and fluorine are not visible which shows that the instrument has a barrel in window the small peak of titanium shows that it may be present in small.
Amount from the table having values of K alpha 1 K beta 1 alpha 1 albita 1m alpha 1 and beta 1 we can match the energy values and identify the elements present in the sample the EDX spectrum of bio tile is shown above students you can easily see the different peaks of different elements is a typical picture of EDX spectrum this is the case study of biotin students in this you can clearly see the different elements are highlighted or D represent the graph is plotted in counts versus energy in electron volt the various elements seen are magnesium aluminum silicon potassium titanium iron the periodic table of elements with their corresponding x-ray energies from this table you can easily match the different values of K alpha and L alpha and identify the presence of a particular element and as we responsive micro analysis from the value of K alpha and alpha we can find out the element that are present as main edx technique it tells us about the various element that represent their weight percentage along with the atomic percentage now we will talk about the accuracy of EDX PBS or EDX can be used to determine chemical composition that are present in a sample and also the relative abundance the accuracy of quantitative analysis of the sample composition is affected by various factors many elements will have overlapping x-ray emission Peaks for example the titanium K beta vanadium k alpha manganese k beta and iron k alpha the accuracy of the measured composition is also affected by the nature of the sample x-rays are generated by an atom in the sample that is sufficiently excited by the incoming beam these x-rays are emitted in all directions this emission is isotropic in nature and so they may not all escape the sample the likelihood of an x-ray escaping the specimen and thus being available to detect and measure it depends on the energy of the x-rays and the compulsion comma amount and the density of the material it has to pass through to reach the detector because.
Of the x-ray absorption effect and similar other effects accurate estimation of the sample composition from the measured x-ray emission spectrum requires the application of quantitative correction Precision's which are sometimes referred to as matrix correction the strengths and limitations in these strengths we use 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 PDS a great survey tool to quickly identify unknown phases prior to quantitative analysis ideas can be used in semi-quantitative mode to determine chemical composition by peak height ratio relative to a standard now about the limitations there are energy peak overlaps among different elements particularly those corresponding to X is generated by emission from different energy level shells that is K L and M in different elements for example there are close overlaps of manganese K alpha and chromium K beta or titanium K alpha and various Airlines in beryllium particularly at high energies individual Peaks may correspond to several different elements in this case the user can apply deconvolution methods to try P separation or simply consider which element make more sense given the known context of the sample the wavelength dispersive method that is WDS is more precise and capable of detecting lower elemental abundances EBS is less commonly used for actual chemical analysis EDS cannot detect the lightest elements typically below the atomic number of sodium for detectors equipped with a beryllium window polymer based in Windows allow the detection of light elements depending on the instrument and operating conditions so students let us summarize what we have studied in this module use analysis of EDX or x-ray dispersive x-ray analysis data you know EDX is an analytical technique that is used for the analysis of an element or chemically characterizing example this is a non-destructive technique and.
Is useful for studying a range of materials elements whose atomic number are less than 11 are difficult to be detected by energy dispersive x-ray analysis as the silicon lithium detector is produced by beryllium window in order to get the best results there has to be balance between the count rate and the resolution limits resolution limit by extending the period of measuring each x-ray spectral resolution can be improved we went to photons arrive at the detector at the same time then they are not measured as a separate event rather they are added to the energy histogram as one single count making the resultant peak distorted therefore in order to avoid this in order to avoid piling up of the peaks it is advised to keep the dead time below 30% EDX has been widely used in material science and nanotechnology and in several biological applications although it is not good for low atomic number samples like carbon hydrogen and nitrogen but it is still widely used for biological applications as well although new analytical techniques have come into existence EDX is firmly established as a standard micro analytical technique and will remain at the forefront of the micro analysis thank you so very much.
1 L family L alpha 1 alveta 1 is 0.7 L beta 2 0.2 albita 3 0.008 albita 4 0.05 L gamma 1 0.08 L gamma 3 0.03 and L 0.04 and M family am alpha 1 M beta is 0.6 m gamma 0.05 and AM Zeta 0.06 begin with the most intense line towards the high-energy region of the spectrum where lines within a very within a family are well separated if it is about 3.5 kilo electron volt it must be either a K or L line using the klm markers.
Compare the location of the peak so that of the marker check the relative intensities if you identify a K alpha line then K beta line should be about 10% and the KL fall intensity K alpha and K beta lines are typically resolved at sulfur and above below the K beta is so small that K alpha and K beta collectively show themselves as one symmetry poppy if a clear line is identified then look for L lines if they occur for that particular element if the line chosen does not correspond to a k line try and L series if the line is identified as the L alpha several other lines both above and below the L alpha should be present and correspond to the element the EDX system should be able to display them at their correct relative intensities M lines do not exist above three point two kilo electron volt so one would not look for them at this point then continue to identify lines while working towards lower energies and consider the possibility of M lines the lines of an M series are generally not all resolved but contribute to an asymmetrical peak in fact M lines can often be recognized by this distortion but aware but beware of overlap that may look similar when all high-energy lines and low-energy L and M lines are identified light elements can be a template these will be K lines and may be overlap with L lines from heavier elements if it is not possible to distribute them pigby convolution software or peak stripping may be necessary peak stripping is a mathematical process that allows the analyst to remove identified fee structures to reveal possible hidden Peaks if they exist after all major and minor peaks are located trace elements can be attempted in this case problem is to confidently find peak above background only the major peaks of the series will be visible and that may be lost in a background in quantitative analysis from the name we can guess what all we are going to deal with quantity quantitative means we are talking about the qua quantity of the material.
Or the sample it can be obtained from X account in different energy levels on the basis of analysis parameters and the sample composition semi qualitative results are easily available without standard without standards with the help of the mathematical Corrections we move on to the elemental mapping what elemental mapping is the intensity of x-ray is measured with respect to the later position of the sample the concentration of the element across the surface is indicated by the variation in X intensity so it is kind of it line profile how the compositional variations are occurring along that line in a given sample the line profile analysis acts as the identified for particular position along the line by analyzing the x-ray energy spectrum at each position it gives a plot of relative elemental concentration for each element versus the position about the window type in sdd we have discussed about the window which is there so basically student these windows are of two types number one the pendulum window type number two polymer thin film window let us study about them shows a comparison between Balian window and polymer base window the perilymph window types they are highly robust they strongly absorb low energy x-rays as a result element from sodium can be analyzed the thickness is about 8 to 10 micrometer the polymer based window these are less robust they are transparent to much lower energy access mainly allowing detection of x-rays down to 100 lectronimo the thickness is less than 8 micrometer the interpretation of the graph obtained in TDX analysis and graphs of electron diffraction spectrum of the type showing the K peaks of sodium a1 and aluminum and silicon let us in tribute this graph by taking in example this graph is a PD spectrum of the edge showing peaks of potassium silicon aluminum in case of excess spectrum graph the energy which is in kilo electron volt is plotted on x axis and the number of counts on y axis by examining the pattern of pigs.
On the spectrum different elements present in the sample ask observed you can see the relative intensities and the area under the teeth are different the interpretation of the graph when any sample is being evaluated by EDX the information is usually represented as histogram or spectrum the spectrum is characteristic of a particular element and every element has fixed clear alpha and alpha energy values for these energy values the elements present in the sample are identified in media's k alpha emission lines develop when an electron transition to the K shell that is principal quantum number 1 from a 2p orbital of L shell that is principal quantum number 2 the line is actually a doublet having slightly different energies depending on the spin orbit energy between the electron spin and the orbital momentum of the 2p orbital k alpha is typically by for the strongest excess spectral line for an element more barded with energy sufficient to cause maximally intense x-ray emission similarly L alpha lines are developed when an electron takes place to be alchun from the emption in this glass you can easily see that excitation of electrons takes place as a result of which the electron moves to a higher excited state and then after losing energy it will turns back to its original state the energies are represented by the values of K alpha and alpha every element has fixed values of K alpha and alpha now next example is of bio tile by tile is a silo silicate material which is a mica group having formula potassium magnesium iron host wise aluminum si o si 3o 10 H hole twice it is a shell ticket in which iron magnesium aluminum silicon oxygen and hydrogen form sheets that are weakly bonded together with potassium ions in biotite strong peaks of magnesium aluminum silicon potassium and iron are seen the peaks of hydrogen oxygen and fluorine are not visible which shows that the instrument has a barrel in window the small peak of titanium shows that it may be present in small.
Amount from the table having values of K alpha 1 K beta 1 alpha 1 albita 1m alpha 1 and beta 1 we can match the energy values and identify the elements present in the sample the EDX spectrum of bio tile is shown above students you can easily see the different peaks of different elements is a typical picture of EDX spectrum this is the case study of biotin students in this you can clearly see the different elements are highlighted or D represent the graph is plotted in counts versus energy in electron volt the various elements seen are magnesium aluminum silicon potassium titanium iron the periodic table of elements with their corresponding x-ray energies from this table you can easily match the different values of K alpha and L alpha and identify the presence of a particular element and as we responsive micro analysis from the value of K alpha and alpha we can find out the element that are present as main edx technique it tells us about the various element that represent their weight percentage along with the atomic percentage now we will talk about the accuracy of EDX PBS or EDX can be used to determine chemical composition that are present in a sample and also the relative abundance the accuracy of quantitative analysis of the sample composition is affected by various factors many elements will have overlapping x-ray emission Peaks for example the titanium K beta vanadium k alpha manganese k beta and iron k alpha the accuracy of the measured composition is also affected by the nature of the sample x-rays are generated by an atom in the sample that is sufficiently excited by the incoming beam these x-rays are emitted in all directions this emission is isotropic in nature and so they may not all escape the sample the likelihood of an x-ray escaping the specimen and thus being available to detect and measure it depends on the energy of the x-rays and the compulsion comma amount and the density of the material it has to pass through to reach the detector because.
Of the x-ray absorption effect and similar other effects accurate estimation of the sample composition from the measured x-ray emission spectrum requires the application of quantitative correction Precision's which are sometimes referred to as matrix correction the strengths and limitations in these strengths we use 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 PDS a great survey tool to quickly identify unknown phases prior to quantitative analysis ideas can be used in semi-quantitative mode to determine chemical composition by peak height ratio relative to a standard now about the limitations there are energy peak overlaps among different elements particularly those corresponding to X is generated by emission from different energy level shells that is K L and M in different elements for example there are close overlaps of manganese K alpha and chromium K beta or titanium K alpha and various Airlines in beryllium particularly at high energies individual Peaks may correspond to several different elements in this case the user can apply deconvolution methods to try P separation or simply consider which element make more sense given the known context of the sample the wavelength dispersive method that is WDS is more precise and capable of detecting lower elemental abundances EBS is less commonly used for actual chemical analysis EDS cannot detect the lightest elements typically below the atomic number of sodium for detectors equipped with a beryllium window polymer based in Windows allow the detection of light elements depending on the instrument and operating conditions so students let us summarize what we have studied in this module use analysis of EDX or x-ray dispersive x-ray analysis data you know EDX is an analytical technique that is used for the analysis of an element or chemically characterizing example this is a non-destructive technique and.
Is useful for studying a range of materials elements whose atomic number are less than 11 are difficult to be detected by energy dispersive x-ray analysis as the silicon lithium detector is produced by beryllium window in order to get the best results there has to be balance between the count rate and the resolution limits resolution limit by extending the period of measuring each x-ray spectral resolution can be improved we went to photons arrive at the detector at the same time then they are not measured as a separate event rather they are added to the energy histogram as one single count making the resultant peak distorted therefore in order to avoid this in order to avoid piling up of the peaks it is advised to keep the dead time below 30% EDX has been widely used in material science and nanotechnology and in several biological applications although it is not good for low atomic number samples like carbon hydrogen and nitrogen but it is still widely used for biological applications as well although new analytical techniques have come into existence EDX is firmly established as a standard micro analytical technique and will remain at the forefront of the micro analysis thank you so very much.