1

ECLOUD 07

Measurement of Secondary ElectronYields from Bulky and Coated Materials

for Beam Ducts

Michiru Nishiwaki*1 and Shigeki Kato*1*2

*1 KEK*2 The Graduate University for Advanced Studies

9-12 Apr. 2007

2

Contents

• Introduction

• Experimental Setup

• Results —SEY & XPS—– Air Exposure

– Sputter Cleaning

– Electron Irradiation

– Heating Treatment

• Summary

3

Secondary Electron Yields (SEY)

Materials, Surface States

AirEnergetic Particles

(Electron, Ion, Photon)Heat

Introduction

For proper understanding of the relation,the measurements of SEY and the surface analyses

should be carried outin one vacuum experimental setup.

In-situ Experiment

4

Surface Analysis with XPS(X-ray Photoelectron Spectroscopy)

Measurements of Secondary Electron Yields(Primary Electron Energy and Incident Angular Dependence)

ElectronIrradiation

SputterCleaning

Heating

In-situ Experiment of Our Study

in UHV

As-received (Air Exposed) Sample

5

In-situ Experiment ;SEY Measurement, Surface Analyses (XPS, AES, SIMS), Surface Conditioning (Electron Irradiation, Sputtering, Heating)

Base Pressure: 5××××10-9 Pa

Experimental Setup

6

ultra fine particles of graphite deposited on copper with a film thickness of some tensµm

highly oriented pyrolytic graphite

single crystal of diamond (110) doped with boron

amorphous carbon film on Si with a thickness of 100nm formed by ECR plasmadeposition

diamond like carbon film with a thickness of 3µm formed by plasma CVD method ona type 304 stainless steel (Shinko Seiki)

high grade of isotropic graphite purified with halogen gas

non-evaporable getter (TiZrV) film coating on a type 304 stainless steel (SAESGetters S.p.A.)

black nickel plating on a type 304 stainless steel (KEK)

chromium suboxide plating on a type 304 stainless steel (KEK)

oxidized pure titanium at 720K (KOBELCO)

titanium nitride prepared by ion plating with a film thickness of 1.5µm (TiGold) and bymagnetron sputtering with a film thickness of 0.1∼ 0.2µm (P. He et al, BNL) on a type304 stainless steel

lathed in Ar environment and treated with corona discharge (EXP) for high-purityaluminum (99.99%)

type 304 stainless steel (substrate of TiN) (BNL)

oxygen free copper (C10100) treated with a water solution of H2O2 and H2SO4

Aquadag

HOPG

Diamond (110)

AmorphousCarbon

DLC

IsotropicGraphite

NEG

Ni

CrOx

Ti

TiN

Al

SS

CuM

etal

Nitr

ide

& O

xide

Allo

yC

arbo

n M

ater

ials

Tested Materials

7

Air Exposed SurfaceThe surfaces were covered with carbon,oxygen, metal oxide, carbon oxide, etc,according to XPS results.

Cu, SS, NEG, TiN

19800

20000

20200

20400

20600

20800

21000

928930932934936938����������������������Binding Energy [eV]

CuO Cu2OCu

5at%

Air Exposed CuCu

CuOx

2800

3000

3200

3400

3600

3800

4000

280282284286288290Cu#20040122-2-XPS-C-AR2���

C 1s

81at%

Binding Energy [eV]

Air Exposed

C-Ox, C-(OH)x, etc

CCu

Inte

nsity

[a.

u.]

650

700

750

800

850

900

950

1000

1050

280282284286288290���� ����������Binding Energy [eV]

49at%

C 1s TiC

Air Exposed

C-Ox, C-(OH)x, etc

CTiN

800

850

900

950

1000

1050

1100

450452454456458460462464

TiO2 Ti 2p3/2

���� ����� ������Binding Energy [eV]

11at%

Ti2O3TiN

Air Exposed TiTiN

Ti2O3

TiNx

Inte

nsity

[a.

u.]

0

0.5

1

1.5

2

2.5

0 1000 2000 3000 4000 5000Primary Energy [eV]

����������������������������������������

Cu

SS

TiN

NEG

�� �� ��� ��� ��!���"����

Normal Incidence

Air Exposed

δδδδmax=1.8~2.2

8

Sputter Cleaned Surface

* The carbon and oxygen,oxide, etc, were removed byAr+ sputtering.

* SEY values decreaseddepending on the materialelements.

* TiN coating showed low SEYsand δδδδmax was less than 0.9.

All Samples

However, it is difficult toobtain completely cleansurface in a practicalconditions of accelerator.

0

0.5

1

1.5

2

2.5

0 1000 2000 3000 4000 5000Primary Energy [eV]

����������������������#$��������%

�� �� ���������"��&�

Cu

SS

TiN

Normal Incidence

Ar+, 5 keV

After Sputter Cleaning

9

Electron Irradiation to Air Exposed Surface

* δδδδmax ≈1* Reduction of metal oxide occurred.* The amount of oxygen decreased. * Large amount of carbon remained.

All Samples

ElectronIrradiated

SputterCleaned

δδδδmax of Cu

10

0

0.5

1

1.5

2

2.5

1018 1019 1020

Electron Dose [e-/cm2]Air

Exposed

1.34

Cu#20040122-2_Dose-dmax3-2.qpc

1.011.05

1.00

2.14

Electron Dose Dependence of SEY and Surface State of Cu

* δδδδmax decreased to 1.* Peak energy shifted to lowerbinding energy.

Electron Beam Induced Graphitization

2000

2500

3000

3500

4000

4500

280282284286288290�������������������! �'����

C 1sCO

81at%

Binding Energy [eV]

1x1020e-/cm2

1x1018e-/cm2

1x1019e-/cm2

82at%

82at%84at%

ElectronIrradiated

Air Exposed

CCu

δδδδmax=1

Carbon Oxide and HydroxideChanged into GraphiticCarbon.

0

20

40

60

80

100

Graphite component increased with electron dose.

11

Electron Beam Induced Graphitization in Other Materials

Electron Beam Induced Graphitization resulted the decrease of SEY for any materials !!

300

400

500

600

700

800

280282284286288290��������! �'���Binding Energy [eV]

79at% 81at%

C 1sCO

SS

ElectronIrradiated

Air Exposed

CSS

1x1020e-/cm2

1600

2000

2400

2800

3200

280282284286288290����(� ��������Binding Energy [eV]

35at% 44at%

CarbideC 1s

ElectronIrradiated

Air Exposed

CNEG1x1020e-/cm2

300

350

400

450

500

550

600

650

700

280282284286288290������������! �'����Binding Energy [eV]

49at%

C 1s

44at%

Graphite

Air Exposed

C-Ox,

CTiN

C-(OH)x, etcElectronIrradiated1x1020e-/cm2

1500

2000

2500

3000

280282284286288290���������������������

C 1s81at%

Binding Energy [eV]

Cu

84at%

1x1020e-/cm2

ElectronIrradiated

Air Exposed

CCu

GraphiteC-Ox,C-(OH)x, etc

12

0

0.5

1

1.5

2

2.5

0 1000 2000 3000 4000 5000Primary Energy [eV]

Cu

Sputtered Cu

5 keV, 1x1020 e-/cm2���������������������������#$��������%������������

�� �� ��� �# �����'���"����

Electron Irradiation

Electron Iraddiatedto Sputtered Cu

Normal Incidence

1600

2000

2400

2800

280282284286288290��������������������������������' �� �'���

C 1s

C

Binding Energy [eV]

1x1020e-/cm2

84at%

Cu

23at%

6at%After SputterCleaning (150nm)

Electron Irradiated to Sputtered Surface

Electron Irradiated to Air Exposed Surface

Electron Beam Induced Graphitization at Sputter Cleaned Cu Surface

* δmax decreased to 1.2.* The amount of carbon increased.* Carbon showed graphite state.

What is the origin of the carbon?

13

100

101

102

103

104

105

106

0 5 10 15 20 25

Depth [µµµµm]

Sample 2

Sample 1

Sample 3

GD-MS Cu DepthProfile-C3.plot

C

GD-MS

XPS

OCu

C

The amounts of carbon were10 times larger than that of

oxygen in bulk of Cu.

Origin of Carbon in Cu

The carbon atomsdiffused from the bulkof Cu and graphitized

with electronirradiation.

zoom

< 20N.D.ASTM

Standardof OFC

1.5913.1Sample 3

2.2210.4Sample 2

0.9112.3Sample 1

OC[at.ppm] at 25µm

100101102103104105106

0 0.1 0.2 0.3 0.4 0.5

Depth [µµµµm]

CuGD-MS Cu DepthProfile-C4.plot

XPSCO

GD-MSC

* Oxygen Free Copper (OFC)* Surface Treated with CP

(1.1µm removed)

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� The origin of the carbon was found to be thecarbon impurities at the surface and diffusedfrom the bulk.

� The graphitization influenced SEY values.

� δmax decreased to ≈1 by the graphitization atthe air exposed surfaces due to the existenceof large amount of carbon for any materialsour measured.

� Even cleaned Cu surface, the graphitizationoccurred and δδδδmax decreased.

Electron Beam Induced Graphitization

15

Heat Treated Cu and NEG (no gas saturation)

InsufficientGraphitization

Cu

High SEY

NEG coating on beam duct is effective.

1000

1200

1400

1600

1800

2000

2200

280282284286288290���������%�������! )����

88at%

Binding Energy [eV]

70at%

Peak Energy after ElectronIrradiationAir Exposed

CCu

C-Ox, C-(OH)

x, etc

After Heating

1600

2000

2400

2800

3200

280282284286288290����(�������! )����Binding Energy [eV]

35at% 31at%

Carbide

Graphite

Air Exposed

CNEG

C-Ox, C-(OH)

x, etc

After Heating

0

0.5

1

1.5

2

2.5

0 1000 2000 3000 4000 5000Primary Energy [eV]

�� ����)����"����

Cu

NEG

���������%�������������

200 degrees C x 24 hrs

Normal Incidence

After Heating

Metal CarbideFormation

NEG(no gas saturation)

Low SEY

16

1600

2000

2400

2800

3200

3600

4000

280282284286288290NEGLT+CO-XPS-C-HT2.��Binding Energy [eV]

MetalCarbideGraphite

CNEG

C-Ox, C-(OH)

x, etc

After Heating

CO GasSaturated

No GasSaturation

0

0.5

1

1.5

2

2.5

0 1000 2000 3000 4000 5000Primary Energy [eV]

NEGLT+LTCO-HT-SEY4.qpc

����(� (��*

200 degrees C x 24 hrs

Normal Incidence

After Heating

NEG (No Gas Saturation)

NEG (CO Gas Saturated)

NEG without and with Gas Saturation

We need to pay attention to the increase of SEYwith the decrease of pumping speed in use ofNEG film coated beam duct.

* Exposed to CO Gas until

17

Measured Materials and Results. 1

after e-

BeamIrradiation

afterSputtering(90 nm)

after e-

BeamIrradiation

afterSputtering(60 nm)

after e-

BeamIrradiation

afterHeating(200°C)

E max 200 eV 500 eV 250 eV 300 eV 375 eV 350 eV?max 1.1 1.2 1.0 0.97 1.0 1.0E max 400eV 700eV 400 eV 425eV 475 eV?max 1.6 1.5 1.3 1.1 1.2

C 79 81 9 C 81 84 C 26 < 1 C 35 44 31O 19 16 2 O 14 6 O 42 3 O 47 21 17Fe

18

Measured Materials and Results. 2

after e-Beam

Irradiation

afterSputtering

(4 nm)

as-received

SlightSputtering

as-received

after e-Beam

Irradiation

afterSputtering

(4 nm)

Emax 325 eV 225 eV 225 eV 200 eV 250 eV 250 eV 200 eVδδδδ

max 0.78 0.72 1.31 0.98 1.53 1.1 1.0Emax 400 eV 275 eV 350 eVδδδδ

max 0.86 0.80 1.83C 99 > 99 > 99 99 99 90 97 > 98O 1 < 1 < 0.5 1 1 10 3 < 2

afterSputtering(20 nm)

Non-Sputtered

Area

SputteredArea

afterAdditionalSputtering(+20 nm)

Non-Sputtered

Area

SputteredArea

(40 nm)

SlightSputtering

SlightSputtering

Emax 250 eV 250 eV 250 eV 250 eV 250 eV 250 eV 175 eV 175 eVδδδδ

max 1.3 1.2 1.2 0.84 0.88 0.84 1.07 0.99Emax 300 eV 300 eV 300 eV 300 eV 300 eV 300 eV 275 eVδδδδ

max 1.5 1.5 1.3 0.94 1.1 0.94 1.48C 77 95 91 93 100 100 100 95 96O 23 5 9 7 0 0 0 5 4

XPS [at%]

0°200 eV

1.8

60°250 eV

2.3

Diamond(110)before Baking after Heating (250°C, 48h)

after Re-Heating(500°C)

XPS [at%]

θθθθ

AquaDag / Cu (pre-heated in vacuum)Amorphous

Carbon

beforeSputtering

0°275 eV

1.0

60°350 eV

1.2

θθθθ

Isotropic Graphite HOPG DLC

as-received

19

Summary� We measured SEYs from Cu, SS, NEG film, TiN

coating, etc with in-situ XPS surface analyses.

� Even TiN and NEG film, SEYs were high for the airexposed surfaces due to the existence of thecarbon impurities and the metal oxide.

� Electron Beam Induced Graphitization occurred atany materials surface even cleaned surface.

� δmax decreased to ≈1.0 by electron beam inducedgraphitization of air exposed surfaces due to theexistence of large amount of carbon.

� In NEG film without gas saturation, δmax ≈1.0 wasobtained with heating in the practical bakingtemperature due to the metal carbide formation.