Anti e-cloud coatings, AEC’09 CERN

Lowering SEY by Rough Surfaces I.MonteroL. Aguilera, L. Galán, V. Nistor, J.L. Sacedón, M.Vázquez F. Caspers, D. Raboso Anti e-cloud coatings, AEC’09 CERN

AEC’09 I. Montero CERN 12.10.09 • Main goal: • Avoid multipactor discharge by low secondary electron emission coatings • Support:

AEC’09 I. Montero CERN 12.10.09 • Outline • Anti-Multipactor Coatings for Space • Low secondary electron emission coatings • Stability with exposure to air (months) • Secondary Electron Emission Suppression • Surface Roughness of High Aspect Ratio: • Chemical Etching methods • Micro-Particulated surfaces • Nano-structured surfaces • Magnetic Materials • Summary and Conclusions

AEC’09 I. Montero CERN 12.10.09 Anti-Multipactor Coatings for Space • Low secondary electron emission • High first cross-over energy • Low surface RF resistance • Stability with exposure to air (months) REQUIREMENTS Time /Reactivity EXPOSURE TO AIR METAL OXIDE LOW SEY LOW Rsurf HIGH SEY HIGH Rsurf Conditioning Conditioning in situ, not possible heat treatments electron beams ion beams

AEC’09 I. Montero CERN 12.10.09 • Stability with exposure to air (months) Previous results Initial Selection of Potential Materials 2.0 Deposition techniques: Cr and Ti silicides: coevaporation with ion assistance hydrogenated and nitrogenated amorphous carbon: reactive evaporation with ion assistance, plasma Ti, V, and Cr nitrides and carbides, reactive evaporation or sputtering with ion assistance COATINGS air-exposed clean 1.5 SEY 1.0 0.5 Au CrN VN CN TiN TiC NbN CrSi TiSi a-C:H a-CN:H Alodine

AEC’09 I. Montero CERN 12.10.09 Effect of exposure to air on SEY (months) SEY FoM (E1/m)1/2 E1 = Firt cross-over energy m= SEY maximum SEY OF VN SEY OF TiN SEY OF CrN

AEC’09 I. Montero CERN 12.10.09 Silver Silver Chemical Etching and Sputtering Methods Micro-structured Gold Coating Electroplating Ni+ Ag Silver 40 μm Silver Nickel 10 μm Nickel 10 μm Nickel 10 μm Aluminum alloy device Aluminum alloy device Aluminum alloy device Gold silver Chemical etching Sputtering method

AEC’09 I. Montero CERN 12.10.09 Chemical Etching and Sputtering Methods Ag plated chem. etched Au coated Au / c-Si Micro-structured Gold Coating WR75 12 GHz transformer 0.14 mm gap 2.5 2.0 1.5 SEE coeficient 1.0 E1 0.5 0.0 0 200 400 600 800 1000 1200 1400 Primary Electron Energy [eV] Anti-Multipactor Coatings for Space it is possible by secondary emission suppression by surface roughness of high aspect ratio

AEC’09 I. Montero CERN 12.10.09 • Outline • Anti-Multipactor Coatings for Space • Low secondary electron emission coatings • Stability with exposure to air (months) • Secondary Electron Emission Suppression • Surface Roughness of High Aspect Ratio: • Chemical Etching methods • Micro-Particulated surface • Nano-structured surfaces • Magnetic Materials. • Summary and Conclusions

AEC’09 I. Montero CERN 12.10.09 Angular dependence of secondary emission yield Empirical (MEST) Empirical Vaughan IEEE (1989) IEEE (1993)  = electron incident energy • = angle of incidence measured with respect to the surface normal, max SEY max.at normal incidence. • ksd and ksw = rough surface parameters (both can vary between 0 for rough surfaces and 2 for polished)

AEC’09 I. Montero CERN 12.10.09 Conductive particulated surfaces Angular dependence of secondary emission yield SprinkledAl particles Flat surface Aluminum alloy substrate Aluminum alloy substrate

AEC’09 I. Montero CERN 12.10.09 Sputtering 5 nm Au Sprinkled Al particles Aluminum alloy substrate Gold-Coated Aluminum Particles

AEC’09 I. Montero CERN 12.10.09 Ep = Emax Ep = Emax Al Flat surface -50 -30 -10 10 30 50 -50 -30 -10 10 30 50 Angular dependence of secondary emission yield Simple aproximation SEY  a2-b+c a The effect of angle is more sensitive a lower energies

AEC’09 I. Montero CERN 12.10.09 Micrometrical Dielectric Particles Coating From suspension of nano-metrical Al2O3 particles Indentation of micro-metrical ceramic particles Al2O3 Aluminum alloy substrate Aluminum alloy substrate

AEC’09 I. Montero CERN 12.10.09 Metallic/Dielectric Microparticles Coatings Extreme reduction of SEY Al particle Al2O3 particle Gold coated Surface top view

AEC’09 I. Montero CERN 12.10.09 Metallic/Dielectric MicroParticle Mixture Al particle Al2O3 particle Gold coated Surface top view

AEC’09 I. Montero CERN 12.10.09 Nanostrured anodic aluminium oxide templates Outer oxide Porous-type Alumina Barrier-type Alumina Inner-oxide Aluminium Gold coated SEM Image of the Aluminium Anodic Oxide 100 nm

AEC’09 I. Montero CERN 12.10.09 Nanostrured anodic aluminium oxides Image of the Aluminiumç Anodic Oxide Sample

AEC’09 I. Montero CERN 12.10.09 Gold coated Nanostrured anodic aluminium oxides () = cte.

AEC’09 I. Montero CERN 12.10.09 • Outline • Anti-Multipactor Coatings for Space • Low secondary electron emission coatings • Stability with exposure to air (months) • Secondary Electron Emission Suppression • Surface Roughness of High Aspect Ratio: • Chemical Etching methods • Micro-Particles • Nano-structured surfaces • Magnetic Materials • Summary and Conclusions

AEC’09 I. Montero CERN 12.10.09 Magnetic suppression of SEY Magnetic field Virtual Cathode Emitted electrons e- e- target D. J. Rej, et al. J. Vac. Sci.Technol. B 12, 861 1994 Ing Hwie Tan, J. Appl. Phys. 100, 033303 2006 a magnetic field II to the sample surface would confine a layer of secondary electrons near the surface, forming a virtual cathode. SEY suppression will be achieved through the reduction of the local electric field near the surface of the sample by this virtual cathode, and further secondary electrons emitted in this low electric field environment could be reabsorbed.

AEC’09 I. Montero CERN 12.10.09 Magnetic Materials Ferrite FeTi NiZnC and MnZn powders SEM SEY max>1 with and without gold

AEC’09 I. Montero CERN 12.10.09 Magnetic Materials Magnetic sample magnetic domains magnetic viewer cards

AEC’09 I. Montero CERN 12.10.09 Magnetic Materials Gold coated Micrometrical Magnetic Particles gold Magnetic Micro- particles ferrite Aluminum alloy substrate

AEC’09 I. Montero CERN 12.10.09 Summary and Conclusions Rough low-SEY surfaces can “suppress” significantly secondary emission yield Rough coatings shows high 1st-crossover-energy Multipactor effect can be suppressed using rough surfaces of adequate morphology The “suppression” of SEY of rough coatings is more effective at low primary energies, where it affects more to multipactor Surface roughness should be in the micro scale.

AEC’09 I. Montero CERN 12.10.09 Cont. Low electrical resistivity is now more important since roughness increases surface resistance Strong roughness for SEY suppression could implies highly porous coating with poor mechanical properties. Silver and gold required for their electrical conductivity are too soft. Gold is more stable in air but has bad adherence. ECM'08 (Electron Cloud Mitigation 2008)

AEC’09 I. Montero CERN 12.10.09 Cont. Rough surfaces has the ability to absorb partially emitted electrons for any incident direction of primary electrons. We have made several efforts to achieve near-total supression of SEY using particulated surfaces. Here we have showed that near total absorption of electrons can be achieved in metal/dielectric particulated coatings. The effect is realized over a wide range of incident primary energy .

AEC’09 I. Montero CERN 12.10.09 Cont. The SEY curves do not seem to be explained by known simulations for rough surfaces Magnetized surfaces, apart from surface roughness, will be investigated to explain these results. They deserve further research on their potential application

Thank you for your attention

SEE Yield Measurements on Insulators Charging on insulators alters electron yields. • ExperimentalTechnique: • Pulsed beam current • <100nA, <700ns • Q < 106electrons/pulse • 10-100 mV/pulse • Neutralization methods • Flood gun, and VUV • neutralization • for repeated electron • pulsed yields • at 200 eV • low noise level SE’s ECM'08 (Electron Cloud Mitigation 2008)

Anti e-cloud coatings, AEC’09 CERN