Presentation on theme: "EDX-Spectra Simulation"— Presentation transcript:
1 EDX-Spectra Simulation Optimization of Excitation Conditions and Detection Limit Calculations in EPMAF. Eggert, Röntgenanalytik Apparatebau GmbH, BerlinIntroductionTheory of simulation complete spectraApplications of spectra simulationDetermination of detection limits with spectra simulationSummary
2 EDX – Spectra Simulation Inroduction IntroductionToday the standardless evaluation of measured spectra is an established methodology in Electron Probe Microanalysis (EPMA) with Energy Dispersive Spectrometer (EDX) in Scanning Electron Microscope (SEM)New developments offer the possibility to calculate complete spectra in dependence to analytical conditions (spectra simulation).The basics are:- Exact knowledge about all X-ray lines of elements and about other atomic data- Knowledge about absolute cross-sections of both, the Characteristic X-rays and the Bremsstrahlung- Calculation of excitation and absorption of X-rays in specimen and detector (characteristic radiation and Bremsstrahlung)- Calculation of the entire Bremsstrahlung-deviation as the main background and simulation of other background components- Simulation of detector-resolution influence and count-statistics to simulate realistic spectraThe content of presentation is to show the benefits of spectra simulation to daily analytical work with Electron Microscope and EDX.
3 EDX – Spectra Simulation Basics Theory of SimulationThe ratio of emitted counts of characteristic X-ray quanta to the counts of emitted Bremsstrahlung-quanta with same energy (in an specified energy region) is known as P/B-ratio (or P/U in this equation).Calculation of the Bremsstrahlung deviation for all spectra channels taking into account the self-absorption Albr and detector-absorption l in specimen. mass absorption coefficients (µ/) = f (Z , E) absorption jumps of (µ/) with energies ECXLifshin empiric 2.parametersKramersl is the index of current channel during spectra calculation
4 EDX – Spectra Simulation Basics Theory of Simulation+All line- and shell- energiesRelative emission rates of a single shellExcitation of sub-shellsCoster-Kronig transitionsFluoresence yieldsBremsstrahlung + LinesEscape + Artefacts (ICC)Count statistics (Noise)____________________= Simulated Spectrum(2000 cps, 3 minutes)
5 The accuracy of data base is crucially for quality of simulation! EDX – Spectra Simulation BasicsAtomic Data Library (Data Base)To make the simulation possible, an atomic data library with fast access to all element specific data is necessary:The accuracy of data base is cruciallyfor quality of simulation!
6 EDX – Spectra Simulation Application Optimization Before the Measurement: Eo15 keV20 keV25 keV30 keV
7 EDX – Spectra Simulation Application Verification: Excitation of Lines (Eo)Excitation of Au-L lines (Sub-Shells !) with different Eo
14 EDX – Spectra Simulation Detection Limits Calculation of Detection LimitsThe question is, whether an element in specimen with expected concentration is detectable or not?If an element is detectable... How are the optimal measurement and excitation conditions (SEM and spectrometer parameters) and how long does it take (acquisition time)?The signal/background-ratio is the base for calculations of detection limits ( P/B-ratio)... determination is possible with spectra-simulation !CountsCountsProbabilityProbabilitySignificance Level NSDetection Limit NDL
15 EDX – Spectra Simulation Detection Limits Detection-Limit of an Element with Different SpecimensMDL for Pd in TeM L KMDL for Pd in Au
16 EDX – Spectra Simulation Detection Limits Detection-Limits with Varying ConditionsAl in CuM L K
17 EDX – Spectra Simulation Detection Limits Simulation of Spectra-Acquisition Near Detection-Limits MDL = 0.2 %Significant element presence !Concentration below the detection-limit !Is it really possible ... ?Yes You had luck !Al: 0.15 %Al: 0.3 %#1#3#2Al: 1 %
19 EDX – Spectra Simulation Summary It is possible to calculate the entire EDX-spectrum with a standardless EPMA-correction model taking into account all effects of specimen- and detector-interaction.Spectra simlation is useful for a better understanding and interpretation of measured spectra.With spectra simulation all complex effects of excitation, absorption and detection are shown very descriptive and didactically (teaching, coaching, …)The simulation of several excitation situations gives the possibility to optimize all conditions even before the actual specimen maesurement and data acquisition.With spectra simulation the analyst is able to make estimations for detection limits.Effects of counting-statistics are possible to verify.Future View: Application of spectra simulation for interactive qualitative analysis(displacement of simple line-mark identification)Calculation of entire spectrum for a visual comparison after quantitativeevaluation (reconstruction) for an improvement of final result-reliabilities