ESTIMATION OF DEPTHS OF NANOLAYERS BY CONVERSION ELECTRON MÖSSBAUER SPECTROSCOPY

1. ESTIMATION OF DEPTHS OF NANOLAYERS BY CONVERSION ELECTRONMÖSSBAUER SPECTROSCOPY Ferenc Nagy Guest researcher of the Chemical Research Center at the Depeartment of Nuclear Chemisty of the Eötvös Loránd University

2. The backscattering technique of Mössbauer-spectroscopy • The detector is around the sample on the side towards the source • Based on the decay of the excited state after the Mb-effect • Information from the surface of the sample • Gamma-rays 10 - 100 mm • X-rays visible depth 1 - 10 mm • Conversion electrons 0.1 - 1 mm e- DEf DEa g g X Source v, [mm/s] Detector Absorbent

3. 57 Fe Formation of the conversion electrons 119Sn

4. Higher sensitivity In case of 57Fe a = N(e)/N(g)=8.21 Surface selectivity The electrons get out from depth of a few hundred nanometers Application areas Preparation of nanolayers Electrolysis Vapor deposited Ion implantation Main questions Corrosion Passivation Magnetic orientation Advantages of conversion electrons

5. Source Detector g-FeOOH Iron-57 Magn-etite Iron-57 goethite Carrier (e.g. Al) Carrier One typical problem • Deposited on a carrier • From vapor • Electrochemically Iron nanolayer having known thickness • To be determined • Not only the quality of the layers formed by oxidation • But their thickness (mass pro surface unit)! O2 • Vértes, A., Vankó Gy., Németh, Z., Klencsár, Z., Kuzmann, E., Homonnay, Z., Kármán, F. H., Szőcs, E., Kálmán, E.:Nanostructure of Vapor-Deposited 57Fe Thin Films. Langmuir. 18:1206-1210, 2002.

6. Dependence from • E initial energy • A atomic mass • Z order number • s path • J average energy of ionisation The path while the energy of the electron decreases from the Eiinital energy to Emin, insufficient to escape Antecedents • Interactions of the electron with he • Nuclei • Electrons • Ancestral description • Bethe-equation, -distance • Averaging rules for Z • Backscattering • Ratio • Saturation depth • Nowadays • Simulation of the interactionsby Monte-Carlo method • Simulator programs • || e-, e+ from outside • For only two homogeneous layers  Mass scaling rule  Transmission function depending on 1 spatial coordinate

7. The modell of the transmission • Final=Initial*Unabsorbed • Initial value T0 =0.5+backscattering (Saturated: T0~0.74) • Unabsorbed as simple function of one variable R, TL • Visible depth as the function of accuracy • Cross-effects in the detector effective tr.

8. The „BEATRICE” program and its applications Backward Estimation of lAyer Thicknesses from tRansmission Integrals of Conversion Electrons.

9. Key isotope  not only Fe-57 Eligible rules  Averaging of order number  Visible depth Debye-Waller factor  Directly given  Counted from the Debye-temperature Basic phys-chem data  Built-in but not fixed  User input Complexity of the sample  Thickness  On carrier  Self supporting  Surface Homogeneous  Inhomogenous Layers Mb-active  Yes  No  Number of components  One  More  Composition  Known  Sought  Fixed  Depth dependent Periodic  Aperiodic Stepwise  Continous News

10. Iron rusting in spots Samples having inhomogeneous surface • 3 columns • 2, 3 and 4 layers, resp. Relative surface areas q1+ q2 + q3 =1

11. Corrosion of iron deposited by pulse electrolysis Kuzmann, E. , Lakatos-Varsányi, M., Varga, L. K., Mikó, A., Kálmán, E., Homonnay, Z., Klencsár, Z., Nagy, F. and Vértes, A.:Mössbauer study of electrodeposited Fe/Fe-oxide multilayers [1] ISIAME’2004 lecture, Madrid, Oct 5, 2004, Abstract book  No. T5 P21 [2] AIP Proceedings, 2005 (being referred) Corrosion of vapor deposited iron [3] Based on Vértes, A., Vankó Gy., Németh, Z., Klencsár, Z., Kuzmann, E., Homonnay, Z., Kármán, F. H., Szőcs, E., Kálmán, E.:Nanostructure of Vapor-Deposited 57Fe Thin Films. Langmuir. 18:1206-1210, 2002. [4] Kálmán, E., Lakatos, M., Kármán, F. H., Klencsár, Z., Nagy, F. , Vértes, A.:Mössbauer spectroscopy for characterization of corrosion products and electrochemically formed layers Corrosion Reviews (Jan 2005) Processed and published cases

12. 7.35 10.90 17.55 12.02 14.53 Evaluation and sensitivity test supposing Fe(OH)3 instead of g-FeOOH

13. Spectra of vapor deposited enriched 57Fesample on Al carrier Figure 3 of [3]: • 57FeCEMS spectra of Sample 1 Figure 5. of [3]: Sample 1 kept at T = 200 °C in atmospheric oxygen for • 30 minutes • 60 minutes [3] Vértes, A., Vankó Gy., Németh, Z., Klencsár, Z., Kuzmann, E., Homonnay, Z., Kármán, F. H., Szőcs, E., Kálmán, E.:Nanostructure of Vapor-Deposited 57Fe Thin Films. Langmuir. 18:1206-1210, 2002.

14. Oxidation of vapor deposited enriched 57Fesamples on Al carrier[4]

15. Source Detector g-FeOOH Magn-etite Iron-57 goethite Carrier (here Al) Oxidation of vapor deposited enriched 57Fesamples on Al carrier[4] Distribution of the deposited iron among the phases [4] Kálmán, E., Lakatos, M., Kármán, F. H., Klencsár, Z., Nagy, F. , Vértes, A.:Mössbauer spectroscopy for characterization of corrosion products and electrochemically formed layers. Corrosion Reviews Jan 2005

16. Check of the model On samples having known composition and layer thicknesses measured by other methods than CEMS  Transmission function Verifyied Calibrated Routine applications Spot corrosion of tubes of atomic energy stations Corrosion inhibitor tensides Langmuir-Bodgett phosphonate layers Electrodeposited hydroxamate layers Test existing services Other key nuclides than iron-57 Extend services Detection X-ray gamma-ray Simultaneous evaluation of samples Fit of Debye-Waller-factors and other sample properties How to advance?

17. I have made the BEATRICE program able to QUANTITATIVE evaluation of CEMS spectra of much more complicated samples I have applied it to the evaluation of nanolayers deposited from Electrolytes Vapor Summary Layer Component Column Mb_isotope Depth_depend Formerly Nowadays

18. Acknowledgement