Non-Evaporable Getter Coating for UHV/XHV Applications

Dr. Oleg B. Malyshev

Senior Vacuum ScientistASTeC Vacuum Science Group, STFC Daresbury Laboratory, UK

11th February 2010

Two concepts of the ideal vacuum chamber:

Traditional:� surface which outgasses as little

as possible (‘nil’ ideally)� surface which does not pump

otherwise that surface is contaminated over time

Results in� Surface cleaning, conditioning,

coatings � Vacuum firing, ex-situ baling

� Baking in-situ to up to 300°C� Separate pumps

2

New (NEG coated surface)� surface which outgasses as little

as possible (‘nil’ ideally)� a surface which does pump,

however, will not be contaminated due to a very low outgassing rate

Results in� NEG coated surface� There should be no un-coated

parts� Activating (baking) in-situ at 150-

180°C� Small pumps for CxHy and noble

gases

Source of Gas in a Vacuum System

Thermal, photon, electron or ion stimulated desorption:

� Molecules diffused through the bulk material (mainly subsurface layers) of the vacuum chamber, entering the surface and desorbing from it

� Molecules adsorbed on the surface (initially or after the air venting) and desorbing when vacuum chamber is pumped

Outgassing rate depends on many factors: choice of material, cleaning procedure, pumping time, bombardment (irradiation) dose, etc...

Surface Conditioning for Ultra High Vacuum

Vacuum Subsurface Bulklayers

What NEG coating does

� A pure metal film ~1-µµµµm thick without contaminants.

� A barrier for molecules from the bulk of vacuum chamber.

� A sorbing surface on whole vacuum chamber surface

Surface Conditioning for Ultra High Vacuum 4

Vacuum NEG Subsurface BulkCoating Layers

Deposition method

Planar magnetron deposition

Cylindrical magnetron deposition

Region scan of XPS core levels of Ti, Zr, C and V of a Ti-Zr-V film(surface composition and chemical bounding)

RBS (film compositions in bulk)

XRD of Ti-Zr-V film (microstructure and morphology)

Set-up for NEG pumping evaluation in ASTeC VS lab.

Test chamber 1 (option)

ASTeC activation procedure

NEG pumping properties

Twisted wires vs. alloy target

1.E-02

1.E-01

1.E+00

140 160 180 200 220 240 260 280 300 320

Activation temperature, oC

CO

sti

ckin

g p

rob

abili

ty

TiZrV(twisted wires)

TiZrV (alloy wire)

TiZrV (alloy wire)

NEG composition: Ti, Zr, V, Hf

140 160 180 200 220 240 260 280 300 3201 10

3−×

0.01

0.1

1

TiZrVHf

Single metal NEG coatings

CO

sti

ckin

g pr

obab

ilit

y

140 160 180 200 220 240 260 280 300 3201 10

3−×

0.01

0.1

1

Ti-ZrTi-VZr-V

Binary metal NEG coatings

CO

sti

ckin

g pr

obab

ilit

y

140 160 180 200 220 240 260 280 300 3201 10

3−×

0.01

0.1

1

10

TiZrVHf

CO

pum

ping

cap

acit

y [M

L]

140 160 180 200 220 240 260 280 300 3201 10

3−×

0.01

0.1

1

10

Ti-ZrTi-VZr-V

CO

pum

ping

cap

acit

y [M

L]

140 160 180 200 220 240 260 280 300 3201 10

4−×

1 103−×

0.01

0.1

TiZrVHf

Activation temperature [ C]

H2

stic

king

pro

babi

lity

140 160 180 200 220 240 260 280 300 3201 10

4−×

1 103−×

0.01

0.1

Ti-ZrTi-VZr-V

Activation temperature [ C]

H2

stic

king

pro

babi

lity

140 160 180 200 220 240 260 280 300 3201 10

3−×

0.01

0.1

1

Ti-Zr-VHf-Zr-VTi-Zr-HfTi-Hf-VTi-Zr-Hf-V

Ternary and quatornaly NEG coating

CO

sti

ckin

g pr

obab

ilit

y

140 160 180 200 220 240 260 280 300 3201 10

3−×

0.01

0.1

1

10

Ti-Zr-VHf-Zr-VTi-Zr-HfTi-Hf-VTi-Zr-Hf-V

CO

pum

ping

cap

acit

y140 160 180 200 220 240 260 280 300 320

1 104−×

1 103−×

0.01

0.1

Ti-Zr-VHf-Zr-VTi-Zr-HfTi-Hf-VTi-Zr-Hf-V

Activation temperature [ C]H

2 st

icki

ng p

roba

bili

ty

Stainless steel vs TiZrV NEG coated vacuum chamber under SR

Reducing the gas desorption from the NEG coatings

� Main gases in the NEG coated vacuum chamber are H2 and CH4

� H2 can diffuse through NEG film under bombardment or heat

� CH4 is most likely created on the NEG surface from diffused H2 and C (originally from sorbed CO and CO2)

� Therefore the H2 diffusion must be suppressed

Vacuum NEG Subsurface BulkVacuum NEG Subsurface BulkCoating Layers Coating Layers

Reducing the gas desorption from the NEG coatings

Solution:

� The coating consists of two layers:

� 1st layer is a barrier with low diffusion for the H2

� 2nd layers is usual NEG coating with columnar structure to provide good pumping

� The resulting coating will be tested with electrons on the lab, later on SR beamline or beam vacuum chamber in accelerator

Vacuum NEG Barrier Subsurface BulkVacuum NEG Barrier Subsurface BulkCoating Layers Coating Layers

22-26 September 2008Lake Balaton, Hungary

10th European Vacuum Conference Oleg Malyshev 17

SEM images of films (film morphology )

columnar dense

Best for pumping A first candidate for a barrier

Reducing the gas desorption w/o NEG coatings

Solution

� The coating consists of two layers:

� A barrier layer is a with low diffusion for the H2

� A controlled smooth oxide layer to create smooth surface with low outgassing

� The resulting coating will be tested with electron on the lab, later on SR beamline or beam vacuum chamber in accelerator

Vacuum Barrier Subsurface BulkVacuum Barrier Subsurface BulkLayers Layers

New programme: electron stimulated desorption

Modified NEG pumping properties evaluation rig:

� To measure sticking probability α� To measure electron stimulated gas

desorption as a function of� Electron energy� Dose

� Wall temperature (20-100°C)� Activation/bakeout temperature

� Can be used for samples with:� NEG coating� Low desorption coating� No coatings

Electron Bombardment

e-

e-

CH4

CO

H2

CO2

Filament:

Th/W,

Th/Ir or

Y/Ir

Electron Stimulated Electron Stimulated DesorptionDesorption (ESD) studies programme(ESD) studies programme

� ESD from different materials� Stainless steel� Al� Cu� NEG coated samples � Coating for low outgassing

� ESD as a function of • Activation/bakeout temperature • Electron energy• Electron dose• Coating density, morphology and structure

ESD: stainless steel vs non-activated NEG coated vacuum chamber

ESD: stainless steel vs activated NEG coated vacuum chamber

ESD: electron energy dependence

10 100 1 103× 1 10

4×1 10

6−×

1 105−×

1 104−×

1 103−×

0.01

Stainless Steel

TiZrV - 160

Energy Dependance

energy [eV]

yiel

d [m

olec

ules

per

ele

ctro

n]

ESD: self activation

Example of NEG application: ILC DR arc

An aluminium tube after bakeout at 220°C for 24 hrs and 100 Ahr beam conditioning: • a pump with Seff = 200 l/s every 5 m• H2, CO and CO2

Inside a NEG coated tube after activation at 160°C for 24 hrs and 100 Ahr beam conditioning:

• a pump with Seff = 20 l/s every 30 m• A H2 and CH4

Conclusions:

� NEG coating is a technology for UHV/XHV vacuum

� It is a delicate material but allows to reach XHV at lower costs.

� ASTeC VS group in a collaboration with MMU has improved and continue improving the NEG coatings.

� The knowledge and experience available for the UK vacuum industry and applications in ASTeC VS group.

Acknowledgments

Co-authors: ASTeC .

� Dr. K.J. Middleman� Mr. A.N. Hannah� Mr. A. Smith

� Dr. S. Patel

Managerial support:� Dr. R. Reid� Mr. J. Herbert� Prof. M. Poole

MMU .� Dr. R. Valizadeh

� Prof. J.S. Colligon� Dr. V. Vishnyakov