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Moseley’s Law
The law states that “the wavelength of any particular line decreased as the
atomic number of the emitter is increased”
A linear relationship exists between the square root of the line frequency ν
and the atomic number Z
𝜈 = 𝐶(𝑍 − 𝜎)
Where C and σ are constants,
Z is atomic number of emitter
• Lα lines are not always of long
wavelength
• Lα1 of Tungsten has about
same wavelength as Kα lines of
copper (K lines have smaller
wavelengths) Fig. Moseley’s relation between, 𝜈 and
Dr. Mohsin Ali Raza
Z for two characteristic lines
Energy Dispersive X-ray Spectroscopy (EDX or EDS)
• EDS makes use of x-ray spectrum emitted by solid sample
when bombarded with a focused beam of electrons to obtain
localised chemical analysis.
• By principle all elements from atomic number 4 to 92 can be
detected (difficult for light elements such as O, H) (Na
onwards)
• Qualitative analysis involves identification of lines in the
spectrum (simple and straight forward)
• Quantitative analysis measure line intensities of each
element in the sample and for the same elements in
Calibration standards of known composition
• Elements maps or element distribution images can also be
produced
• X-ray spectrometer is attached with electron microscopes.
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Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Dr. Mohsin Ali Raza
Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Microanalysis technique
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Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Schematic of inner atomic electron shells
Dr. Mohsin Ali Raza
Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Energy difference of x-ray
photon is equal to energy
difference between the levels
concerned
E1-E2= hν
In the case of Kα1
hνα1= Wk- WLIII
ℎ𝜈𝐾𝛼1 = ℎ𝜈𝐾 − ℎ𝜈𝐿𝐼𝐼𝐼
1 1 1
𝜆𝐾𝛼1 = 𝜆𝜅 − 𝜆𝐿𝐼𝐼𝐼
Energy level diagram for Ag showing transitions responsible
Dr. Mohsin Ali Raza for K and L emission lines
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Energy Dispersive X-ray Spectroscopy (EDX or EDS)
The incident electrons must have energy greater than Eo called critical
excitation energy to produce K or L shell vacancy.
Mosely’s law is basis of element identification in EDS
Fig. Energies of principal characteristic lines and their excitation energies
Dr. Mohsin Ali Raza
Energy Dispersive X-ray Spectroscopy (EDX or EDS)
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Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Dr. Mohsin Ali Raza
Energy Dispersive X-ray Spectroscopy (EDX or EDS)
x-rays are treated as photons possessing specific energy (E)
Eλ= 12396
Where E is eV, λ= Å
ℎ𝑐
𝑒𝑉𝑘 = 𝑊𝑘 = ℎ𝜈𝑘 =
𝜆𝑘
12.40 × 103
𝑉𝑘 = 𝐸𝑘 =
𝜆𝑘
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Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Typical K spectra
Electron bombardment not only produces characteristic x-ray lines but
also continuous x-ray spectrum ( “continuum” Covering energy from 0
to E0)
Dr. Mohsin Ali Raza
Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Peak to Background Ratio
Highest P/B would occur at the highest accelerating voltages
Dr. Mohsin Ali Raza
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Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Typical K spectra
Dr. Mohsin Ali Raza
Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Typical L spectra
Dr. Mohsin Ali Raza
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Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Element mapping
Dr. Mohsin Ali Raza
Energy Dispersive X-ray Spectroscopy (EDX or EDS)
Components of EDS system
• X-ray detector
• Pulse processor
• Multi channel analyser
Sample preparation: Flat and polished sample should be used for high accuracy.
Powders can also be used.
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XRF (X-ray Fluorescence Spectroscopy)
• The emission of characteristic "secondary" (or
fluorescent) X-rays from a material that has been
excited by bombarding with high-energy X-rays or gamma
rays.
• XRF is used for elemental analysis in almost every field
(mineralogy, geology, metallurgy, biotechnology, forensic
etc)
• XRF is used for general chemical analysis
• XRF is fast, accurate, non destructive, and usually
requires minimal sample preparation.
• XRF is a reference method, standards are required for
quantitative results.
Dr. Mohsin Ali Raza
XRF (X-ray Fluorescence Spectroscopy)
X-ray Fluorescence Spectrometry
– Wavelength Dispersive XRF
– Energy Dispersive XRF - Portable, Transportable
(Benchtop)
– Total Reflection XRF
Conventional XRF (The angle of
incidence is greater than the
critical angle and the primary
radiation penetrates into the
sample)
TXRF (the incidence angle is
smaller than critical angle and
the primary radiation is reflected
Dr. Mohsin Ali Razaoff of the surface of sample)
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XRF (X-ray Fluorescence Spectroscopy)
Dr. Mohsin Ali Raza
XRF (X-ray Fluorescence Spectroscopy)
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XRF (X-ray Fluorescence Spectroscopy)
Measurement ranges
Dr. Mohsin Ali Raza
XRF (X-ray Fluorescence Spectroscopy)
XRF Instrumentation
• Source
• Sample
• Detection system
The source irradiates sample, and the detector measures
fluorescence radiation emitted from sample
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XRF (X-ray Fluorescence Spectroscopy)
Dr. Mohsin Ali Raza
XRF (X-ray Fluorescence Spectroscopy)
XRF radiation sources
• Conventional X-ray tube (End window or side window)
• Radioisotopes (Gamma rays sealed sources such
Americium-241, Co-57)
End
Window
X-ray tube
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XRF (X-ray Fluorescence Spectroscopy)
XRF Detector Principles
• Detector is a semi conducting or non-conducting material
between two charged electrodes
• X-ray radiation ionises the detector material causing to become
conductive, momentarily
• The newly freed electrons are accelerated toward the detector
anode to produce output pulse
• An ionised semi-conductor produces electron-hole pairs, the
number of pairs produces is proportional to the X-ray photon
energy
𝑬
• 𝒏 = 𝒆 , where n = number of electron-hole pairs produced, E = X-
ray photon energy, and e= 3.8 eV for Silicon at liquid nitrogen
temperature. Dr. Mohsin Ali Raza
XRF (X-ray Fluorescence Spectroscopy)
Types of Detectors
• Si(Li) detector
• Proportional counter
• Scintillation detector
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XRF (X-ray Fluorescence Spectroscopy)
Types of Detectors
• Proportional Counter
Ideal for measurement of longer wavelength, but it is insensitive to wavelengths shorter
than 0.15 nm
Dr. Mohsin Ali Raza
XRF (X-ray Fluorescence Spectroscopy)
Types of Detectors
• Si(Li) detector
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XRF (X-ray Fluorescence Spectroscopy)
Types of Detectors
Tl doped
• Scintillator detector
Ce-sb
• Blue photons with wavelengths 410 nm are produced
• No of blue photon is related to energy of incident x-ray photon
• Photons produce electrons and current produced by PMT is converted to voltage
Dr. Mohsin Ali Raza
pulse
XRF (X-ray Fluorescence Spectroscopy)
WDXRF
• Relatively inefficient, operated at much higher power than EDXRF
• Diffraction devices are also temperature
Dr. Mohsin Ali Raza sensitive
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XRF (X-ray Fluorescence Spectroscopy)
WDXRF
Czerny-Turner monochromator
• The diffraction grating disperses light by diffracting different wavelengths at
different angles.
• The particular wavelength that passes through the monochromator is
selected by rotating the angle of Dr.
the grating.
Mohsin Ali Raza
XRF (X-ray Fluorescence Spectroscopy)
Multilayers
While the crystal spacing is based on the natural atomic spacing,
at a given orientation the multilayer uses a series of thin film
layers of dissimilar elements to do the same thing.
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XRF (X-ray Fluorescence Spectroscopy)
EDXRF
Dr. Mohsin Ali Raza
XRF (X-ray Fluorescence Spectroscopy)
EDXRF
The height of pulse produced is proportional to the energy of the
respective incoming X-ray
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XRF (X-ray Fluorescence Spectroscopy)
Multichannel Analyser
The height of pulse produced is proportional to the energy of the
respective incoming X-ray
Dr. Mohsin Ali Raza
XRF (X-ray Fluorescence Spectroscopy)
Rayleigh Scattering
If the energy of the photon is the same before and after scattering, the
process is called elastic or Rayleigh scattering. Elastic scattering takes
place between photons and bound electrons and forms the basis of X-ray
diffraction.
Rayleigh scattering appears as
source peak in the spectrum
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XRF (X-ray Fluorescence Spectroscopy)
Compton Scattering
If the photon loses some of its energy, the process is called inelastic or
Compton scattering.
Compton scatter appears
slightly less in energy than
Rayleigh Scatter.
Dr. Mohsin Ali Raza
XRF (X-ray Fluorescence Spectroscopy)
Example
file:///E:/CEET/Materials%20Characterisation/XRF%20fun
damentals%20complete%20transitions.pdf
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XRF (X-ray Fluorescence Spectroscopy)
Sample Preparation
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