Slides - Agenda

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
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
Hemispherical
analyser
LEED-Auger
for SEY
X-Ray source
Sample 1
* Fresh sample, prepared by magnetron
sputtering at LNF by the vacuum group (S.
Bini)
Kimball e-gun
for scrubbing
scrubbed at 500 eV
Sample 2
* Representative sample of the SLAC
accelerator dipole chamber (M. Pivi)
scrubbed at 10 eV
at the same
vacuum
pressure
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
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
O-C-O
ether groups
-CH2-O-CH2-
sp3 -like ibridization
in C-C and C-H
chemical environment
graphite-like
O-C=O
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
XPS, before and after scrubbing: 3 effects
1
Decreasing of the oxygen
containing species
3
2
Appearance of the graphite –
like component
Increasing of the C1s peak, for the sample scrubbed at 500 eV
Ecloud’12, La Biodola, Isola d’Elba
Before, during and after the scrubbing : the effect on the SEY
SEY measured on
the «as received
samples»
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
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
What does it happen, then? Focus on the C growth
at 10 eV
at 500 eV
• partial conversion to the sp2 like hybridization
• slow decrease of the SEY value, O still present on the surface
• 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
C growth: the mechanism (1)
hypothesis :
direct exposure to the electron radiation
of the residual gas species wandering on
the surface
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
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
suitable choice of the scrubbing energy
to increase the number of SEs and their
kinetic energy distribution (opportunity?)
deposition of a
graphitic layer by
MBE, magnetosputtering, CVD…
scalability too expensive?
Thank you for your attention!
Ecloud’12, La Biodola, Isola d’Elba
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