Carbon film for electron cloud mitigation deposited by PLD

Valeria Russo 2 POLITECNICO shall contribute to the feasibility study for carbon coating of beampipes by PLD technique and to the characterization by Raman spectroscopy of carbon films produced both by CERN and by POLITECNICO itself. CERN – PoliMi (addendum n° 1 to collaboration agreement KN2274) POLITECNICO team Carlo Casari David Dellasega Andrea Li Bassi Alessandro Maffini Matteo Passoni Valeria Russo

3 Low SEY (1.1) Thickness 100 nm Adhesion on Cu and StSt, also under cooling at 15 K The film must be resistant to radiation In general a rougher film presents lower SEY, but it is important to avoid that small chips of the film detach and interact with the beam (no dusty film). It must be deposited in situ in LHC. It is possible to use vacuum conditions or any gas that is not corrosive or reactive for Cu or StSt and can be pumped out (air, inert gas) Requirements

Valeria Russo QCM 4 Nd:Yag Laser (λ = 1064, 532 nm) Energy density on target Target to substrate distance background pressure (vacuum, He, O 2, Ar) Target: pyrolitic graphite Low pressure high kinetic energy Atom-by-atom deposition High pressure Low energy clusters background pressure 200 nm 1 μm Pulsed Laser Deposition (PLD)

Valeria Russo 5 Carbon films deposited by PLD substrates (nm) Energy (mJ) Spot Area (mm 2 ) Fluence (J/cm 2 )Pressure dT-S (cm) Time (min) C0142 Si, Cu, SS ,259vacuum10 -5 mbar55 C0152 Si, Cu, SS ,259O25 Pa55 C0162 Si, Cu, SS ,259He20 Pa55 C0172 Si, Cu, SS ,51,579vacuum10 -5 mbar55 C0182 Si, Cu, SS ,51,579He20 Pa55 Realistic for optical fibers

Valeria Russo 6 C014 – vacuum nm Thickness  100nm nm, 50x, 1 mW  max (Cu)  1,3  max (StSt)  1,25

Valeria Russo 7 C016 – He 20Pa nm Thickness  100 nm nm, 50x, 1 mW  max (Cu)  1,2  max (StSt)  1,25

Valeria Russo 8 C015 – O 2 5Pa nm Thickness  100 nm nm, 50x, 1 mW  max (Cu)  1,3  max (StSt)  1,3

Valeria Russo 9 C017 – vacuum- 532 nm Thickness  60 nm nm, 50x, 1 mW  max (Cu)  1,4  max (StSt)  1,3

Valeria Russo 10 C017 – He 20Pa- 532 nm Thickness  80 nm nm, 50x, 1 mW  max (Cu)  1,25  max (StSt)  1,1

Valeria Russo 11 SEY of carbon PLD coatings on Cu He 20Pa (0.2 mbar); O 2 5Pa (0.05mbar); Vacuum = 1e-5 mbar 2 points on each sample have identical SEY, seems homogeneous Assuming the differences are significant (reproducibility of coatings) we have the following ranking: 532 vac > 1064 O2> 532 He> 1064 vac >1064 He Next: XPS, SEM (surface and thickness in EDX if possible)  max  1,2 1064nm He 20Pa Best value

Valeria Russo 12 SEY of carbon PLD coatings on StSt He 20Pa (0.2 mbar); O 2 5Pa (0.05mbar); Vacuum = 1e-5 mbar 2 points on each sample have identical SEY, seems homogeneous The ranking is different from copper….: 1064 O 2 > 532 vac >1064 He> 1064 vac >1064 vac > 532 He (on Cu: 532 vac > 1064 O 2 > 532 He> 1064 vac >1064 He) Next: XPS, SEM (surface and thickness in EDX if possible)  max  1,1 532nm He 20Pa Best value

Valeria Russo 13 atmosphere (nm)  max (Cu)  max (StSt) C014Vacuum10641,31,25 C015O2 5Pa10641,3 C016He 20Pa10641,21,25 C017vacuum5321,41,3 C018He 20Pa5321,251,1

Valeria Russo 14 XPS XPS of Cu PLD C16 is thinner or scratched (Cu is much more visible) C15 has much more O/C (made in O 2 ), followed by C18/C16 He and finally those in vac C17/C14 XPS of StSt PLD C15 has much more O/C (made in O 2 ) and C17/C14 (vac) is the lowest

Valeria Russo 15 samples in O 2 Ref?? correlation SEY - XPS is it related to surface oxygen? Measure of surface area? More compact film, lower intensity at 289 eV? Vacuum PaHe 532

Valeria Russo 16 CNe CAr

Valeria Russo 17 Film with the lowest SEY has been deposited in He at 20 Pa Morphology is rougher than other films We can work in this direction by increasing pressure in a controlled way Post-deposition processing by laser (roughening, local fast- annealing) ….. Conclusions and perspectives 40 Pa He

Valeria Russo 18 Rough films 40 Pa He 200nm

Valeria Russo 19 Film deposited by PLD at 40 Pa He

Valeria Russo 20 As-dep C-foam After laser irradiation (graphitization) Post-deposition processing by laser Roughening (film/substrate) local fast-annealing

Valeria Russo 21

Valeria Russo 22 clustering of the sp 2 phase bond disorder presence of sp 2 rings or chains sp 2 /sp 3 ratio Raman spectrum of amorphous C [Robertson J, Mat. Sci.&Eng R 37 (2002) 129] [A. C. Ferrari, PRB 61, (2000)]

Valeria Russo 23 Raman spectroscopy ( nm, 50x, 1 mW ) fixing deposition wavelength, varying atmosphere

Valeria Russo 24 Fixing atmosphere, varying deposition wavelength Raman spectroscopy ( nm, 50x, 1 mW )