Anti e-cloud coatings, AEC’09 CERN

Lowering SEY by Rough Surfaces

I. Montero

L. Aguilera, L. Galán, V. Nistor, J.L. Sacedón, M.Vázquez F. Caspers, D. Raboso

Anti e-cloud coatings, AEC’09 CERN

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 SpaceLow secondary electron emission coatings

Stability with exposure to air (months)

Secondary Electron Emission Suppression Surface Roughness of High Aspect Ratio:

Chemical Etching methodsMicro-Particulated surfaces

Nano-structured surfacesMagnetic Materials

Summary and Conclusions


Outline







• Low secondary electron emission • High first cross-over energy• Low surface RF resistance• Stability with exposure to air (months)

Conditioning in situ, not possible heat treatments electron beams ion beams

Anti-Multipactor Coatings for

Space

EXPOSURE TO AIRMETAL

LOW SEY LOW Rsurf

OXIDE

HIGH SEY HIGH Rsurf

Time / Reactivity

REQUIREMENTS

Conditioning


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

0.5

1.0

1.5

2.0

SE

Y

clean

air-exposed

Au

Alo

din

e

Nb

N

TiC

TiN

VN

CrN

a-C

:H

a-C

N:H

CN

TiS

i

CrS

i

COATINGS

Initial Selection of Potential Materials

AEC’09 I. Montero CERN 12.10.09 Stability with exposure to air

(months)Previo

us

results

Effect of exposure to air on SEY

(months)

SEY OF VN SEY OF CrNSEY OF TiN

0

5

10

15

20

25

1E-12 1E-10 1E-08 1E-06 0.0001 0.01 1 100

Time of Exposure to Air [day]

SEE

FoM

[eV

1/2

]

TiN/Ti ion implantation

TiN/Ag evaporation

TiN/Al evaporation

TiN/Au evaporation

TiN/Al evaporation

TiN/Si sputtering

TiN/Ag cathodic arc

TiN/Rh/Ag evaporation

Alodine 1200 (ESTEC)

c)


SEY FoM (E1/m)1/2 E1 = Firt cross-over energym= SEY maximum


Outline



Secondary Electron Emission SuppressionSurface Roughness of High Aspect Ratio:




Silver 40 μm

Electroplating Ni + Ag

SilverSilver Silver

Nickel 10 μm

Micro-structured Gold

Coating

Chemical Etching and Sputtering

Methods

Nickel 10 μm Nickel 10 μm

Chemical etching

Aluminum alloy device



silver Gold


Sputtering method

Micro-structured Gold

Coating

Chemical Etching and Sputtering Methods

Anti-Multipactor Coatings for Space

it is possible by secondary emission suppression by surface roughness of high aspect ratio


0.0

0.5

1.0

1.5

2.0

2.5

0 200 400 600 800 1000 1200 1400Primary Electron Energy [eV]

SE

E c

oefic

ient

Ag plated

chem. etched

Au coated

Au / c-Si

WR75 12 GHz transformer 0.14 mm gap

E1


Outline




Chemical Etching methodsMicro-Particulated surface

Nano-structured surfacesMagnetic Materials.


Angular dependence of secondary emission yield

EmpiricalVaughanIEEE (1989)IEEE (1993)

Empirical ( MEST)


= 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)

Aluminum alloy substrate

Sprinkled Al particles

Al particles / SEY ((Incidence Angle)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 200 400 600 800 1000Primery Electron Energy (eV)

SE

Y

Al particl -5º

Al particl 0º

Al particl 10º

Al particl. 25º

Al particl. 35º

Al particl. -20º

Al particl. -35º

Al particl. -45º

Aluminium foil /SEY (Incidence Angle)

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 200 400 600 800 1000Primary Electron Energy (eV)

SE

Y

Al foil-5º

Al foil 0º

Al foil 10º

Al foil 25º

Al foil 35

Al foil -20º

Al foil -35º

Al foil -45º

Flat surface

Angular dependence of secondary emission yield


AEC’09 I. Montero CERN 12.10.09 Conductive particulated

surfaces

Gold-Coated Aluminum Particles

Sputtering 5 nm AuSprinkled Al particles


Au / Al particles

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

0 200 400 600 800 1000

Primary Electron Energy (eV)

SE

Y

Al part +Au-312ºAl part +Au-317ºAl part +Au-327ºAl part +Au-342ºAl part +Au-352ºAl part +Au-297ºAl part +Au-282ºAl part +Au-272º


0.00000

0.00005

0.00010

0.00015

0.00020

0.00025

200 500 SEYMax


Roughnes

s fa

ctor

Al partículas

Al part+Au

Al foil

AEC’09 I. Montero CERN 12.10.09 Angular dependence of secondary emission yield

SEY a2-b+cSimple aproximation

a

The effect of angle is more sensitive a lower

energies

Aluminum

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

270 290 310 330 350

Incidence Angle

SE

Y

Al part- SEYMax

Al part+Au- SEYMax

Ep = Emax

Aluminum foil

y = 0.00018183x2 - 0.11367224x + 20.17658972R2 = 0.96478276

2

2.1

2.2

2.3

2.4

2.5

2.6

2.7

2.8

260 280 300 320 340 360

incidence angle (sample manipulator)

SEY

(normal incidence 313º)

Ep = Emax

5030 5010-10-30-50

AlFlat surface

3010-10-30-50

Micrometrical Dielectric Particles

CoatingFrom suspension of nano-metrical Al2O3 particles


Al2O3

Indentation of micro-metrical ceramic particles


0.0

0.5

1.0

1.5

2.0

2.5

0 400 800 1200 1600 2000Primary Electron Energy [eV]

SEE

coef

ficie

nt

25 nm Au coating (continuous)

as prepared (pulse)

25 nm Au coating (pulse)


0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 200 400 600 800 1000Primary Electron Energy [eV]

SE

E c

oeff

icie

nt

continuous technique

pulse technique

SEY

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0


SE

Y c

oe

ffic

ien

t

Al2O3 75%+Al 25%+Au

Al2O3 50%+ Al 50% +Au

Al2O3 25%+ Al 25% +Au

Metallic/Dielectric Microparticles

Coatings

Al particle

Al2O3 particle

Surface top view


Extreme reduction of SEY

Gold coated

SEY

0,0

0,5

1,0

1,5

2,0

0 500 1000 1500 2000 2500 3000 3500 4000


SE

Y c

oef

fici

ent

Al2O3 75%+Al 25%+Au

Al2O3 50%+ Al 50% +Au

Al2O3 25%+ Al 25% +Au

Metallic/Dielectric MicroParticle

Mixture Al particle

Al2O3 particle

Surface top view


Gold coated


Outline







Outer oxide

Nanostrured anodic aluminium oxide

templates


100 nm

SEM Image of the Aluminium

Anodic Oxide

Porous-type Alumina Barrier-type Alumina

Aluminium

Inner-oxide

Gold coated

2,8

2,8

2,8

2,9

2,9

2,9

2,9

2,9

3,0

270 290 310 330 350

Incidence Angle

SEY

Anod24h

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5


SE

Y

Anodización 24h-312º







AEC’09 I. Montero CERN 12.10.09 Nanostrured anodic aluminium

oxides

Image of the AluminiumçAnodic Oxide Sample

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

1,6

1,8

2,0


SE

Y c

oeffi

cien

t

Anodización 24h+Au-312º







1,6

1,7

1,7

1,8

1,8

1,9

1,9

2,0

2,0

270 290 310 330 350Incidence Angle

SE

Y SEYMax

AEC’09 I. Montero CERN 12.10.09 Gold coated Nanostrured anodic aluminium

oxides

() = cte.

Outline




Chemical Etching methodsMicro-Particles




Magnetic suppression of

SEY


target

Magnetic field

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.

D. J. Rej, et al. J. Vac. Sci.Technol. B 12, 861 1994

a magnetic field II to the sample surface would confine a layer of secondary electrons near the surface, forming a virtual cathode.

Virtual CathodeEmitted electrons

Ing Hwie Tan, J. Appl. Phys. 100, 033303 2006

e-e-

Ferrite FeTi

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

0 100 200 300 400 500 600 700 800 900Primary Electron Energy (eV)

SE

Y C

oeffic

ient


NiZnC and MnZn powders

SEY

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

0 500 1000 1500 2000 2500 3000 3500 4000


SE

Y c

oef

fici

ent

MnZn/Cu

NiZn/Cu +Au

SEM

Magnetic Materials

SEY max>1with and without gold


0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0 1000 2000 3000 4000Primary Electron Energy (eV)

SE

Y c

oeffic

ient

magnetic viewer cards

Magnetic sample

magnetic domains

Magnetic Materials


Gold coated Micrometrical Magnetic

Particles MagneticMicro- particles


0.0E+00

1.0E-05

2.0E-05

3.0E-05

4.0E-05

5.0E-05

6.0E-05

7.0E-05

8.0E-05

9.0E-05

200 500 Sey max

Primary electron energy (eV

Roughnes

s fa

ctor

Ferrita part+Au

Ferrita part+Au+Hilos H

Ferrita part+Au+Hilos V

0.0

0.2

0.4

0.6

0.8

1.0

1.2


SE

Y c

oeff

icie

nt

Ferrita+Au-312º

Ferrita+Au-342º

Ferrita +Au-300º

Ferrita +Au-352º

Ferrita +Au-352º

ferrite

gold

Magnetic Materials


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.


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)


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 .


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 InsulatorsCharging on insulators alters

electron yields.

SE’s

Vbias = 0 Vbias < 0 Vbias > 0

Experimental Technique:• Pulsed beam current <100nA, <700ns

Q < 106 electrons/pulse

10-100 mV/pulse• Neutralization methods

Flood gun, and VUV neutralization for repeated electron pulsed yields at 200 eV

• low noise level

ECM'08 (Electron Cloud Mitigation 2008)

Documents

Anti e-cloud coatings, AEC’09 CERN