QuantitativeQuantitativeElectron Microprobe AnalysisElectron Microprobe AnalysisGoal: Goal: Measurement of concentration Measurement of concentration

of elements in a microscopic volumeof elements in a microscopic volume

Wavelength Dispersive XWavelength Dispersive X--ray ray Spectrometry (WDS)Spectrometry (WDS)

EPMA: Analytical procedureEPMA: Analytical procedure

Sample preparationQualitative analysis with EDSStandard intensity measurement (calibration)Measurement of X-ray intensities in the specimenData reduction through matrix corrections

Sample preparationSample preparationSample cut and mounted in epoxyPolished first with coarse SiC paper, then with alumina grit slurry (final size: ≤0.25 μm) 1

Washed with water in ultrasonic cleaner 2

Dried with blow duster and airCarbon coated 3

1: diamond paste or colloidal silica for some samples; dry polishing paper for water-soluble samples

2: ethanol may be used sparingly; cleaned with blow duster and cloth for samples that dissolve in water

3: for insulators; if standards are coated, however, all samples must be coated

Carbon coaterCarbon coater

Samplechamber(bell jar)

Carbon coatingCarbon coatingTo monitor coat-thickness, a

polished brass block is coated with the samples

Carbon coatingCarbon coating

Color of the brass surface changes with carbon-coat thickness

Recommended: 225-250 Å

WDS: XWDS: X--ray intensity measurementray intensity measurement

peak minus background intensitypeak minus background intensity

A polynomial fit to the background A polynomial fit to the background may be more accuratemay be more accurate

Background modeling in XBackground modeling in X--ray spectraray spectra

Peak overlap in XPeak overlap in X--ray spectraray spectra

WDS detector optimization withWDS detector optimization withpulse height analysis (PHA)pulse height analysis (PHA)

SCA scan: baseline and window optimized throughPHA

WDS spectraWDS spectra

Peak overlap: KPeak overlap: Kαα and Kand Kββ energies (energies (keVkeV))of Ti, V and Crof Ti, V and Cr

Kα Kβ

IIIII std-Ti

std-Ti

measmeascorr

VK

TiK

TiKVKVK α

α

ααα−=

CrK CrKVK

VK

CrKcorr meas

corr

V - stdV - std

α αα

α

αI I II

I= −

Peak overlap correctionsPeak overlap corrections

MIT OpenCourseWarehttp://ocw.mit.edu

12.141 Electron Microprobe Analysis by Wavelength Dispersive X-ray SpectrometryJanuary (IAP) 2010

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