1. Study of SEY Degradation of Amorphous Carbon Coatings
Nenad Bundaleski
Centro de Física e Investigaçaõ Tecnológica
Universidade Nova de Lisboa, Caparica, Portugal

2. Initial idea Why does the SEY of a-carbon coatings increase in air?
The idea: to expose the samples to different gases
and try to identify which air constituent is responsible
for ageing…
Stainless steel substrate
aC coating (<1µm)
Glass vessel

3. Experimental setup Electron Gun Energy Analyzer Ion Gun X-Ray Source
The experiments were performed in the multipurpose surface analysis apparatus .
Base pressure in low mbar region.
XPS, AES, SIMS, LEIS, SEY, WF.
Sample holder allows heating/cooling of the sample.
Ion Gun
SEY – e-gun and
Faraday cup
X-Ray Source
Sample
Entry lock
And, we have TOF-SIMS…

4. Initial idea CERN, we have a problem: increase of SEY was observed for
any sample, ‘even’ the reference sample which was in mbar!
And then…
pbase ~ mbar
Ageing in high vacuum!?

5. Fast ageing under HV conditions
We bake the HV system 24 h, 106° C, p ~ mbar with the sample inside…
SEY grows in HV much faster than in air
Particularly intensive aging during baking

6. Identifying the cause of SEY increase
RGA analysis:
H2O H2 CO
mass 43…oil from the
rotary pump?
There is no evidence of fast ageing.

7. Identifying the cause of SEY increase
Exposure to vapour of mineral oils (saturated hydrocarbons):
5 min at 5x10-2 mbar
Hydrocarbons are responsible for the fast ageing in HV!

8. Identifying the cause of SEY increase
Even mbar is not a safe environment if…
achieved with oil diffusion pumps

9. XPS analysis Composition analysis Oxygen is the main impurity.
SEY increases with the concentration of impurities

10. XPS analysis
≈0.2 eV
C 1s
Peak shift due to ageing is too small to draw reliable conclusions
Photoelectron intensity at higher binding energies decreases with ageing

11. XPS analysis
O 1s
Shape of the O 1s peak changes with ageing

12. SEE spectra
Energy spectra of secondary electrons – another fingerprint of ageing!

13. Annealing in air – another surprise
The sample annealed in air ages much slower in HV

14. Annealing in air – another surprise
The sample annealed in air ages faster in air?

15. Annealing in air – another surprise
Initially bad sample may be recovered by prolonged
annealing in air

16. TOF-SIMS analysis – first results
SEY increases with the hydrogen content in the coating
Annealing in air triggers surface segregation of hydrogen

17. Conclusions Hydrocarbons are responsible for fast ageing in vacuum
Quality of ‘vacuum’ is more important than the total pressure
O 1s peak in XPS and SEE spectra are fingerprints for ageing
SEY increases with hydrogen contents
SEY properties can be tailored by sample annealing in air.
Could hydrocarbons be also responsible for ageing in air?
If yes, why the ageing is slower?
Their partial pressures are much beyond 10-6 mbar…

18. Surface Science and Vacuum Technology Research Line
prof. Orlando Teodoro
prof. Ana Silva
prof. Augusto Moutinho
Surface science laboratory
Electron Spectroscopies
Dr. Nenad Bundaleski
Joao Trigueiro
Sara Candeias
Bobbie-Jean Shaw*
TOF-SIMS
Dr. Aleksandar Tolstoguzov
Amjad Gouman
Aderito Santos

19. Experimental setup for SEY measurements
SEY (d) : number of secondary electrons emitted from a surface per incident primary electron.