Conversion Electron Mössbauer Spectroscopy (CEMS) : Basis and applications.

Sameh HamzamyIngrid GnemegnaMESC9

Outline

Introduction Basis Applications Conclusion

1957 → Rudolf Mössbauer achieved 1rst experimental observation of resonant adsorption of γ-radiation and discovered recoil free in solid emission.

Introduction

The Mössbauer effect → basis of Mössbauer spectroscopy and CEMS.

Need radioactive source which decays via excited state called Mössbauer isotope (Fe,Sn).

Mössbauer effect

Nuclear decay scheme

Mössbauer effect

Solid matrix = no recoil

Ephoton = Enucleartransition

Means to probe hyperfine interactions of atoms nucleus and their surrounding!

Ephoton = Enucleartransition-Erecoil

Mössbauer spectroscopy

Transmission effect

As radiation leave the sample, only a layer at the surface contributes to the backscattered spectrum. The thickness of this layer depends on the range of the radiation. Resulting method: CEMS

Mössbaueur spectroscopy

CEMS and Mössbauer Sprectroscopy

Basis of CEMS

K

L

K

M

A nucleus promoted to an excited state by gamma ray adsorption can

de-excite by two categories of mechanism :

Radiative: emission of a gamma ray with a probability of N(γ)

Non-Radiative: internal conversion and the ejection of an atomic electron

with a probability of N(e)Internal conversion coefficient α:

α=8.21 for 57Fe , internal conversion is 8.21 times more probable than γ-ray

(photon) emission.

Conversion coefficient

Emitted electron energy

Ec = Eγ – Eb

Eγ :energy of the transition

Eb:binding energy of the electron

In 57Fe the internal conversion can occur from K, L and M shells, in order of probability.

Emitted electron energy

Equipement for CEMS

→ Source irradiate sample

→Electrons emitted from the sample accelerated towards the anode

→ionising atoms in the counting gas

→ produce avalanche effect amplifying signal

→ electronic pulse detected and recorded

Applications

Steel Corrosion Analysis

Metal Alloy Characterization

Ultra Thin Films Analysis

Steel Corrosion Analysis

CEM spectra of the corrosion layers form on iron by immersing it in 3% sodium chloride solution of initial pH 6.5 at 318 K for:

(a)12h (pH changed to 7.0)(b)24h (pH changed to 7.3), (c) 48 h (pH changed to 7.7)(d) 96 h (pH changed to 8.0)

Journal of Radioanalytical and Nuclear Chemistry, Articles, Vol. 202,Nos 1-2 (1996) 103-199.

Characterization of tin coated Al alloy

Depth selective CEMS spectra of Sn coated Al alloy plate untreated in a molybdate solution

Journal of Radioanalytical and Nuclear Chemistry, Vol. 257, No. 1 (2003) 97–103

Depth selective CEMS spectra of Sn coated Al alloy plate treated in a molybdate solution

Schematic cross section of Sn coated Al alloy treated with molybdate ions

Ultra thin films of Fe on Mo substrate

CEMS spectrum of the 3 A film evaporated at 600 K on polycrystalline Mo substrate. Spectrum was measured at 300 K.

T. Tyliszczak, J.A. Sawicki and W. Wilk

Surface analysis

Spray Deposition(SD)Technique.

Artificial oxide films

Surface and interface reaction

Ion implanted layers

Other applications

CEMS is a highly-selective and non-destructive method.

Conversion electrons are very easy to detect efficiently.

Information on the configuration of magnetic spin in the

surface layer can be obtained.

CEMS has become an important tool of materials surface

analysis.

Advantages

Loss of electron energy in their passage through matter

cannot be calculated.

Compton scattering and the photoelectric effect produce

"non-resonant electrons".

Electrons do not move through matter in straight lines.

Only windowless detectors may be used.

Disadvantages

Conclusion

CEMS seems a valuable technique for either thin films or the surface of bulk samples.

Applicable to a wide range of low-area materials containing iron (or tin) while Mössbauer spectroscopy requires high-area solids.

The high sensitivity and attractive probing depth from the first atomic layer on the surface to 1μm below the surface.

Thanks for your

attention.

Questions ?

References

https://wiki.umn.edu/MXP/MossbauerLabIntroduction

Mössbauer Spectroscopy in Materials Science,Marcel Miglierini,Dimitris

http://korek.uci.agh.edu.pl/cemsnew.html

Mössbaueur1, Structural Investigation and Characterization of Materials, Carlos familyname

http://phobos.chemie.uni-mainz.de/moessbauer.php