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

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

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

The characterisation by XPS and SEY performed at LNF: sample 1 XPS spectra recorded BEFORE and AFTER electron conditioning at 500 eV photon energy 1253.6 eV SEY before scrubbing: 2.3 SEY after scrubbing: 1.0 Final dose: 0.4 C/mm2 Ecloud’12, La Biodola, Isola d’Elba

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

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

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

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

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

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

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

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

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) 014801 Therefore the reason for the absence of growth @ 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) 030601

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

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