1. XPS and SEY Measurements Upon Scrubbing at Different Electron Kinetic Energies: the Case of TiN
R. Flammini
CNR-IMIP
Area della Ricerca di Roma 1
and
INFN-Laboratori Nazionali di Frascati
Ecloud’12, La Biodola, Isola d’Elba

2. Description of the samples Characterization by XPS and SEY
Outline
Introduction
Description of the samples
Characterization by XPS and SEY
Analysis of the C1s core-level spectra
The behaviour of the SEY as a function of the e- dose
The growth of the carbon containing species:
Taborelli
Hitchcock
Conclusion
Ecloud’12, La Biodola, Isola d’Elba

3. The TiN samples and the experimental setup
LEED-Auger
for SEY
Hemispherical analyser
X-Ray source
Kimball e-gun
for scrubbing
Sample 1
* Fresh sample, prepared by magnetron sputtering at LNF by the vacuum group (S. Bini)
Sample 2
* Representative sample of the SLAC accelerator dipole chamber (M. Pivi)
scrubbed at 500 eV
at the same vacuum pressure
scrubbed at 10 eV
Ecloud’12, La Biodola, Isola d’Elba

4. The characterisation by XPS and SEY performed at LNF: sample 1
XPS spectra recorded BEFORE and AFTER
electron conditioning at 500 eV
photon energy eV
SEY before scrubbing: 2.3
SEY after scrubbing: 1.0
Final dose: 0.4 C/mm2
Ecloud’12, La Biodola, Isola d’Elba

5. The characterisation by XPS and SEY performed at LNF: sample 2
XPS spectra recorded BEFORE and AFTER
electron conditioning at 500 eV
SEY before scrubbing: 2.5
SEY after scrubbing: 1.27
Final dose: 0.03 C/mm2
Ecloud’12, La Biodola, Isola d’Elba

6. Description of the technique and of the samples
Outline
Introduction
Description of the technique and of the samples
Characterization by XPS and SEY
Analysis of the C1s core-level spectra
The behaviour of the SEY as a function of the e- dose
The growth of the carbon containing species: the mechanism?
Conclusions
Ecloud’12, La Biodola, Isola d’Elba

7. XPS: decomposition of the C 1s core-level spectra
sp3 -like ibridization
in C-C and C-H
chemical environment
O-C=O
O-C-O
ether groups
-CH2-O-CH2-
graphite-like
Mc Feely et al. PRB 9 (1974) 5268
Larciprete et al J. Phys Chem C, in press (2012)
Díaz et al. PRB 54 (1996) 8064
Ecloud’12, La Biodola, Isola d’Elba

8. 3 2 1 Increasing of the C1s peak, for the sample scrubbed at 500 eV
XPS, before and after scrubbing: 3 effects
Appearance of the graphite –like component 2
Decreasing of the oxygen containing species 1
Increasing of the C1s peak, for the sample scrubbed at 500 eV 3
Ecloud’12, La Biodola, Isola d’Elba

9. Before, during and after the scrubbing : the effect on the SEY
On the sample conditioned at 10 eV, the «fully scrubbed» value of the SEY is reached only upon a new scrubbing done at 500 eV
SEY measured on the «as received samples»
The reduction of the SEY value is delayed during the scrubbing at 10 eV
The fully scrubbed value for the sample is reached only upon a further scrubbing at 500 eV
Ecloud’12, La Biodola, Isola d’Elba

10. Why does the growth of the carbon layer
What does it happen, then? Focus on the C growth
at 10 eV
partial conversion to the sp2 like hybridization
slow decrease of the SEY value, O still present on the surface
at 500 eV
conversion to the sp2 like hybridization
decrease of the SEY value down to the «fully scrubbed value»
growth of a carbon layer
Why does the growth of the carbon layer
occur only upon scrubbing at 500 eV?
Ecloud’12, La Biodola, Isola d’Elba

11. direct exposure to the electron radiation
C growth: the mechanism (1)
direct exposure to the electron radiation
of the residual gas species wandering on the surface
hypothesis :
Ecloud’12, La Biodola, Isola d’Elba

12. Scheuerlein and Taborelli : threshold opening: ~20 eV*
* C. Scheuerlein and M. Taborelli JVSTA 20 (2002) 93
Ecloud’12, La Biodola, Isola d’Elba

13. The mechanism (2): the role of the secondary electrons*
the deposition process is driven by SEs emitted by the surface and hitting the adsorbed molecules
R. Cimino et al. PRL 93 (2004)
Therefore the reason for the absence of 10 eV
may reside in the low amount of secondary electrons generated at low primary energies and on the distribution of secondary electrons with energy enough to overcome the fragmentation thresholds
Why can it be so important?
* A.F.G. Leontowicz and A.P. Hitchcock JVST B 30 (2012)

14. Thank you for your attention!
Conclusion
SEY reduction
graphitic-like layer on top of the technical surface
conversion of the native «C contaminated» surface
to a more graphitic structure (T, e- irr,…)
efficient enough?
e- induced growth of a
carbon layer, by the
secondary electrons
deposition of a graphitic layer by MBE, magneto-sputtering, CVD…
scalability too expensive?
suitable choice of the scrubbing energy
to increase the number of SEs and their kinetic energy distribution (opportunity?)
Thank you for your attention!
Ecloud’12, La Biodola, Isola d’Elba

15. R. Cimino, D. Grosso, M. Commisso, S. Bini
The group
R. Cimino, D. Grosso, M. Commisso, S. Bini
LNF-INFN Laboratori Nazionali di Frscati
R. Larciprete
CNR-ISC Istituto dei Sistemi Complessi
R. Flammini
CNR-IMIP Istituto di Metodologie Inorganiche e Plasmi
M. Pivi
SLAC National Accelerator Laboratory
Ecloud’12, La Biodola, Isola d’Elba