KEKSecondary Electron Emission from Vacuum Materials
and in-situ Surface Characterization
Shigeki KATO
Michiru NISHIWAKI
Masayuki SHIMAMOTO
and Michiru SHIRAI★

Electron Dose Effect on S.E.Y.
= Aging, Conditioning to Reduce S.E.Y.
at Vacuum Surface of Power Fed Devices◆ Comments on Reported Secondary Electron Yields◆ Sample Materials and Experimental Setup◆ Results

 SEYs : Dependences on Materials, Primary Electron
Energy and Surface State
 (Incident Angle Dependence of SEYs, Surface History
Dependence of SEYs, Energy Distributions of EmittedElectrons)◆ Conclusions
Shigeki KATO, KEKB Review, Feb., 2005

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Primary Electron Energy Dependence of SEYs at Unbaked
Copper Surface with Different Electron Doses (CERN data)δmaxUnbakedδmax ofCopper: ˜1.3

Emax

Measured : V. Baglin, J. Bojko, O. Groener, B. Henrist, N. Hilleret , C. Scheuerlein, M. Taborelli (CERN), EPAC2000★ Due to Beam Cleaning Effect ?
However◆ Emax Remains Almost the Same !
◆ Showing Lower δmax than δmax of Copper !
Shigeki KATO, KEKB Review, Feb., 2005

2

KEKElectron or Ion Dose Effects of δmax in UHV
at Different Copper Surfaces (CERN data)

V. BAGLIN, I. COLLINS, O. GROBNER, B. HENRIST, N.HILLERET, G. VORLAUFERCERN - LHC/VAC, NH ﾐ 2STREAMS/01◆ How is the Dose Effect Explained?
◆ What Are Happening on Material Surfaces?
★ However No In-site Surface Data Reported Before---> Now Answers Found with In-situ Surface Characterization !
Shigeki KATO, KEKB Review, Feb., 2005

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KEKSamples & Experimental ProcedureS(1$5')*',&1

★

I'23

★

BNL

AA./0

*5(#*(:!;'*<!("($*5,J$<(B'$#"!!=44'&+!6K7L9

I',3':'F(:!)=5(!*'*#&'=B!#*!G?/H!#4*(5!)'$%"'&+

75@3★

)5()#5(:!!-!',&!)"#*'&+!;'*<!#!4'"B!*<'$%&(11!,4!8PQOB!,5! !-!
B#+&(*5,&! 1)=**(5'&+! ;'*<! #! 4'"B! *<'$%&(11! ,4! /P8R/P?OB!
6L2E9!,&!#!*-)(!./0!1*#'&"(11!1*(("!

$<5,B'=B!1=!,3':(!)"#*'&+!,&!#!*-)(!./0!1*#'&"(11!1*(("!

2'!"#$%!&'$%("!)"#*'&+!,&!#!*-)(!./0!1*#'&"(11!1*(("!

7=,3-+(&!45((!$,))(5!678/8//9!*5(#*(:!;'*<!#!;#*(5!1,"=*',&!
,4!>?@?!#&:!>?A@0D"$<(B'$#""-!),"'1<(:!#"=B'&=BCDE)'%#

M1,*,)'$!
#!<'+<!+5#:(!,4!'1,*5,)'$!+5#)<'*(!)=5'4'(:!;'*<!<#",+(&!+#1N5#)<'*(
DT=#:#+="*5#! 4'&(! )#5*'$"(1! ,4! +5#)<'*(! :(),1'*(:! ,&! $,))(5! ;'*<! #!
4'"B!*<'$%&(11!,4!1,B(!*(&1!OB!

1. Measurement of SEYs in UHV (Ambient Temperature, ⊥ Incident Angle)
 As-received
 After Electron Bombardment
 After Sputter Cleaning★ Electron Beam Dose for a Series of Measurements : < 10 nC mm-2

2. In-situ Surface Analyses with XPS in UHV
Shigeki KATO, KEKB Review, Feb., 2005

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Experimental Setup

Shigeki KATO, KEKB Review, Feb., 2005

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KEK

Secondary Electron Yields of Vacuum Surface Materials
Primary Electron Energy Dependence

2.5TiN_8A

Secondary Electron Yield

2After Sputter

After Electron Bombardment
1e20 e - cm -2
Normal Incidence

As Received
NormalNormalIncidence
Incidence

Normal Incidence

Cu
Ni

1.5Cu

SS
1CuSS

Ni

Ni

TiN_IP

CrOx
Graphite

0.5SS
TiN_8A

TiN_IP(1e21 e- cm-2 )TiN_8ACrOx
TiN_IP

Graphite0

TiN_Cr_Ni_SS_Cu AR EpDepnd.plot

0

1000

2000

3000

Primary Energy [eV]

4000

5000 0TiN_Cr_Ni_SS_Cu EB EpDepnd.plot

1000

2000

3000

Primary Energy [eV]

4000

5000 0TiN_Cr_Ni_SS_Cu Spt EpDepnd.plot

1000

2000

3000

4000

5000

Primary Energy [eV] All as-received Samples except Graphite : High δmax (TiN : Highest δmax)
 After Electron Beam Irradiation of 0.16 Cmm-2 : Drastic Decease After Ion Sputtering : Comparable to δmax After Electron Irradiation◆ Surface Characteristics after Electron & Ion Conditioning : Completely Different.
Shigeki KATO, KEKB Review, Feb., 2005

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KEK Primary Energy Dependence of SEYs at As- received

Copper Surfaces with Different Doses of Electron or Ion

The Surface BecomesContaminated Again After Ion
Beam Irradiation due to Bad Beam
Quality???

Those Explanations are Not Right!!!
Complete Different Story!!!
What Are Happing on the Surfaces
Then???
The Surface Becomes Cleaner
After Electron Beam Irradiation???
Shigeki KATO, KEKB Review, Feb., 2005

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XPS Spectra at As - received Copper

KEK
2.5 10 4

7000

2 104

5%Cu
Intensity [a.u.]

Intensity [a.u.](1x1020e-cm-2)

1.5 10 4

85%

1 104

Electron Beam
Irradiation
6000

5500

(1x1020e-cm-2)

after Sputter Cleaning(30nm)

934< 1%Cu2O

CuO Cu Cu2O

936

3%

932

Binding Energy [eV]930928Cu#20040609-XPS-Cu.plot5000536

CO O 1s
534

532

530

Binding Energy [eV]C

82%
As Received

3500

after Sputter Cleaning(30nm)
5000
938

O

6500

6%

Electron Beam
Irradiation

13%

As Received

Intensity [a.u.]

As Received

4000

91%
3000

Electron Beam
Irradiation(1x1020e-cm-2)

2500

after Sputter Cleaning(30nm)

CuO
528
Cu#20040609-XPS-O.plot

2000
290

C 1s

CO
288

15%

286

284

Binding Energy [eV]282

280!"#$%%&%609'()*'!+,-./

As Received : δmax=2.14 <--- Surface with Carbonatious Contamination Cosisting ofH, C and O + H2O MoleculesCopper Surface Not Oxidized
Electron Beam Conditioning in UHV: δmax=1.00 <--- Graphitized Surface !!!
[ In Poor Vacuum, Polymerization instead of Graphitization : Very High δmax ]Ion Sputtering : δmax=1.32 <--- Almost Clean Surface◆ Carbon Supplyer during Graphitization : Residual Carbonatious

Contamination at Suface◆ Lowest δmax <-- Electron Beam Induced Surface-graphitization
Shigeki KATO, KEKB Review, Feb., 2005

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Summary of Dose Effect on SEYs at Copper Surface& Surface-graphitization Observed with XPS286

XPS Spectrum of Carbon / Cu

285.5
285
284.5
2843

12.5

20.8!max=2.1
0.6

1.5

1.3

0.4
11.0 1.0 1.0

0.5

00.2

Cu#20040122-2_Dose-dmax.data
Cu#20040122-2_Dose-dmax.plot

1017

As Received

★

1.3

1018

1019

Electron Beam
Irradiation1020-[e cm-2]

1021

Ratio of Graphite Form toOther Carbon Forms

Secondary Electron Yield, !max ( )Peak Energy [eV]KEK0Sputter
Cleaning

What is Going on Well-cleaned Copper Surfaces after
Electron Beam Irradiation?

 Graphitization for Sputtered Clean Copper Still Occurs due to Electron Beam
Irradiation or Heating in UHV.
 The Source at Cleaned Copper Surface : Carbon Atoms from Bulk.
Shigeki KATO, KEKB Review, Feb., 2005

9KEKXPS Spectra & SEYs
at As-received Isotropic Graphite Surface

90

100

C80

O
80

5%

95%

Intensity [a.u.]

Intensity [a.u.]

70

60

50

60

As Received

40

40

As Received

2030

C 1s
20290

288

286

284

Binding Energy [eV]282!"#$%&'()*+,)-.$/0'

280

0536

CO534

532

O 1s
530

Binding Energy [eV]528!"#$%&'()*+,)-.$/0'As Received : δmax=0.95, Almost No Adsobate
No Need of Conditioning Even for Need of SEY<1
Other Carbon Materials :DLC (Diamond-like-carbon), s.c. Diamond (110), AmorphousCarbon, HOPG (Highly Oriented Pyrolytic Graphite)
Shigeki KATO, KEKB Review, Feb., 2005

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Primary Energy Dependence of SEYs at Carbon
Material Sufraces after Sputter Cleaning

1.2

After Sputter Cleaning
Normal Incidence

Amorphous Carbon
DLC
Diamond(110)
HOPG

Secondary Electron Yield

10.8

Very Low δmax of 0.7
for Isotropic Graphite !
Why?
---> Surface Roughness
for the Graphite
Microscope Images
50µm

0.6Isotropic
Graphite

0.4

0.20Gra+DLC+A-C+D_EpDep.plot

01000

2000

3000

4000

Primary Energy [eV]

5000

DLC

Graphite

Ra=0.45µm
Ry=0.5µm

Ra=1.383µm
Ry=10.71µm
Ra=1.223µm
Ry=13.71µm
Shigeki KATO, KEKB Review, Feb., 2005

11KEK

Models of Electron Beam Induced Surface-graphitizatione-As-received
Surface
Contaminating
Adsobates

CmHn
H2 H2O
CO CO

eH2O CO2 CmHn

CuCx (CuOx) Cu(CO)x Cu(OH)xO

C H CuCGraphite
Thickness ˜1nm

Electron Beam Assisted Graphitization

HOCuCe- Electron Beam Induced Diffusion

Well-CleanedSurface

2of Carbon to Surface

e-H2 CO CmHn
CO2CC HOGraphiteCuCOCCH

Electron Beam Assisted
Graphitization

CuShigeki KATO, KEKB Review, Feb., 2005

12KEKExplanation for Electron or Ion Dose
Effects in UHV at Different Copper Surfaces
Carbonatious and Oxide Contamination
on As-received Cu Surface

Removal+Reduction+Graphitization

Clean Cu Surface w/ GD

Graphitization via
Diffusion from Bulk

Conditioned Cu Surface( Graphite on Cu Surface )Sputtered-cleaner Cu Surface

Measured : V. BAGLIN, I. COLLINS, O. GROBNER, B. HENRIST, N.HILLERET, G. VORLAUFERCERN - LHC/VAC, NH ﾐ 2STREAMS/01
Comment : S. KATO, KEK, June 04
Shigeki KATO, KEKB Review, Feb., 2005

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SEYs of TiN̲8A with Different Conditions
Primary Electron Energy Dependence
3

TiN_8A
Normal Incidence

2.5!max=2.2
Secondary Electron Yield

KEK

As received
2XPS [at.%] Ti
As Received 11
ElectronBombardment 15
Sputter 44Cleaning

N C O
19 49 2125 44 1651 < 2 4

1.5!max=1.01after Electron Bombardment(1x1020 electrons cm-2)!max=0.87

0.5

after Sputter Cleaning
(4nm)

0

TiN_8A EpDepend.plot.ohp

01000

2000

3000

Primary Energy [eV]

4000

5000
Shigeki KATO, KEKB Review, Feb., 2005

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XPS Spectra & SEYs at TiN Surface
1100

900

Ti

1000

after Electron
Bombardment
700(1x10 20cm -2)

As Received!max=2.2

15%800!max=1.0

600

25%

700

Intensity [a.u.]

Intensity [a.u.]

11%

As Received

900

after Electron
Bombardment

600(1x1020cm-2)

51%

500
500

after44%

(4nm)

Ti2O3
TiN

400 Sputter Cleaning
300
464

TiO 2462

460458456

Binding Energy [eV]

400!max=0.87

Ti 2p 3/2
454

452

after Sputter Cleaning(4nm)

300
401

450

400399!"##$%&'(&)*!&+,-./#$

397

396395394!"##$%&'(&)*!&+,-.#$

1300

C

1000

O

1200

900
800

As Received

700
600 after Electron

44%

Bombardment
500

after Electron

16%(1x1020cm-2)
800

after Sputter Cleaning
(4nm)
C-N
288

As Received
1000

900 Bombardment(1x1020cm-2)

300
290

21%

1100

49%

Intensity [a.u.]

Intensity [a.u.]

TiN

398

Binding Energy [eV]

1100

400

N

19%

800

286

C 1s284Binding Energy [eV]2% TiC282280!"##$%&'(&)*!&+,-.#$

after Sputter Cleaning
(4nm)

700
536

4%CO O 1s TiO2534532

530

Binding Energy [eV]528!"##$%&'(&)*!&+,-.#$ As Received : δmax=2.2 <--- Covered w/ Carbonatious Contamination andHeavy Oxidation of Ti
 Electron Beam Conditioning in UHV: δmax=1.0 <--- More TiN and Graphitizationin spite of Small Decrease of Oxygen Ion Sputtering : δmax=0.87 <--- Almost Clean Surface◆ Dose Effects of Electron and Ion Irradiation on SEYs : Similar But
Surfaces are Remarkbly Different !!!

15Proposal to Reduce SEY at Copper Surface of Power Fed
Devices Using e- Beam Induced Surface Graphitization

KEKSurface Composition★ For Surface
Not be Sputtered !

2!max=1.85
As received
Cu!max=1.37

Normal Incidence

Surface Roughness

after Sputter Cleaning (30nm)
1.2!max=1.02

1After Sputter Cleaning
Normal Incidence

Amorphous Carbon
DLC
Diamond(110)HOPG

1Secondary Electron Yield

Secondary Electron Yield

1.5

0.8

after Electron Beam
Irradiation (1x1020e- cm-2)

0.5

0.6IsotropicGraphite

0.4

0.2

0Cu#20040609_EdDepend.data
Cu#20040609_EpDep_AR+EB+Spt.plt

01000

2000

3000

Primary Energy [eV]

4000

5000

0Gra+DLC+A-C+D_EpDep.plot

01000

2000

3000

4000

Primary Energy [eV]5000

Shigeki KATO, KEKB Review, Feb., 2005

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KEKProposal to Reduce SEY at Copper
Surface of Power Fed Devices (contn’d)★ How to Graphitize Copper Surface
1. Carbon Enrichment into Copper if Necessary.
2. Surface Roughing ( press, tool bit ).
※ Not for Surface Fed with High Electric Field
3. Surface Treatment Could be Simple.
4. Baking Could be Skipped.
5. Electron Irradiation.
with an Energy Range < keV<10C/cm2 is Sufficient (Wired Filament, Low Power e-gun)★ Advantages of Electron Beam Induced Surface - graphitization◆ No Coating Necessary ( vs Other Carbon Materials, TiN, NEG )◆ Stable Surface and Diffusion Barrier of Carbon into Copper◆ No Dust Generation ( vs Aquadag, NEG )◆ Self-recovering Surface during Operation◆ Lateral Homogenity of Graphitizaion Confirmed◆ Small Skin Effect : Equivalent to ˜1nm (1THz -> 2nm )Shigeki KATO, KEKB Review, Feb., 2005

17KEK

CONCLUSIONS

1.

New Findings of SEY Were Done in Conjunction with In - situ Measured Suface State.

2.

First Observation and Proof of Electron Beam Induced Surface-graphitization Causing
Small SEY were Made. The Surface-graphitization Explains the Reported Data Well.

3.

Carbon Supplyer during Graphitization for As-received Materials is Mainly ResidualCarbonatious Contamination on Sufaces.

4.

For Sputtered Clean Copper, Graphitization Still Occurs due to Heating or Electron
Beam Irradiation even in UHV. The Source was Proved Carbon Atoms from Bulk.ʼ

5.

Electron Beam Induced Surface-graphitizaion is Inevitable at Least on Copper inPractical Application Because of the No Passive Layer.

6.

No Need of Conditioning for Graphite was Found Even for Need of SEY<1.

7.

As-received TiN showed Highest δmax because of Heavy Oxidation of Ti.

8.

Dose Effects of Electron or Ion Irradiation on SEYs of TiN and SS are Similar andExplained based on Electron Beam Induced Surface-graphitization.

9.

Carbonatious Contamination and Free Carbon are Evil but Graphite Would be Helper.

10. Beam Conditioning of Vacuum Surface of Power Fed Devices Seems Graphitization
Process.
11. Active Graphitization is Proposed to reduce SEY.

Carbon, cʼest bon !

Shigeki KATO, KEKB Review, Feb., 2005

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KEKFin

Shigeki KATO, KEKB Review, Feb., 2005

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