Making a UHV seal

Rotary Vane Pump a) Without gas ballast a) Pump is connected to the vessel, which is already almost empty of air (70 mbar) – it must thus transport mostly vapor particles b) Pump chamber is separated from the vessel – compression begins c) Content of pump chamber is already so far compressed that the vapor condenses to form droplets – overpressure is not yet reached d) Residual air only now produces the required overpressure and opens the discharge valve, but the vapor has already condensed and the droplets are precipitated in the pump.

Fundamental of Vacuum Technology, Leybold catalogue

a b

c d

Turbo Pump

Fundamental of Vacuum Technology, Leybold catalogue

Ion Pump

Finite Line Width of X-ray source …

Mg Kα1,2 x-ray energy 1253.6 eV ± 0.75 eV

Al Kα1,2 x-ray energy 1486.7 eV ± 0.85 eV

Mg Al Kα’ 4.5 eV (1%) 5.6 eV (1%) Kα3 8.4 eV (9.2%) 9.6 eV (7.8%) Kα4 10.0 eV (5.1%) 11.5 eV (3.3%)

D. Briggs and M. P. Seah “Practical Surface Analysis”

X-ray Satellites in XPS

X-ray satellites observed in carbon 1s spectrum

D. Briggs and M. P. Seah “Practical Surface Analysis”

Aperture Determines Region of Analysis

Aperture settings !   Large Area 4mm diameter !   Small Area:

! 100µm ! 200µm ! 350µm ! 600µm

!   Angular resolved

aperture

deceleration sector

electron path

entrance slit

detector

sample

exit slit

Pass Energy and Slit Width Determine Resolution

V

V0

entrance/exit slits:

0.5 mm 1 mm 2 mm 5 mm

detector

Pass Energy Ep =eV0 Resolution ΔE:

⎟⎟⎠

⎞⎜⎜⎝

⎛≅Δ

02RwEE p

380 375 370 365

870 875 880

Cou

nts

/ sec

Binding Energy (eV)

Kinetic Energy (eV)

Ag 3d3/2

Ag 3d5/2

R0=150mm

For 5mm slit, the analyzer resolution is ~1.5% of pass energy

Resolution vs Count Rate

1 100.7

0.8

0.9

1

Al Kα (15kV, 26mA)

Mg Kα (15kV, 20mA)

Res

olut

ion

(ΔEm

, eV

)

Pass Energy (Ep, eV)

Slit Width = 0.5mm Slit Width = 2.0mm Slit Width = 5.0mm

0.8 1 2 4 6 8 10 20 40 60102

103

104

105

106

107

nPEI ∝

1.841.741.55

1.571.77

1.90

Slit Width = 0.5mm Slit Width = 2.0mm Slit Width = 5.0mm

Mg Kα (15kV, 20mA)

Al Kα (15kV, 26mA)C

ount

s / S

ec

Pass Energy, Ep (eV)

BE

Metallic Samples & Analyzer Work Function

E

vac φs analyzer

work function

KE = hν – BE – φΑ

0

KE

BE

φA= 4.6V

BE Z

Sample Analyzer

Fermi Energy

BE

Metallic Samples & Analyzer Work Function

E

vac φs

KE = hν – BE – φΑ - V

0

KE

BE

BE

V

Z

Sample Analyzer V

analyzer work function

φA= 4.6V

BE

Insulating Samples

E

vac φs

KE = hν – BE – ?

0

KE

BE

φA

BE

V ?

Z

Sample Analyzer Charging V ?

Ways of Reducing Charging !   Reduce insulator thickness !   Decrease resistivity (doping) !   Lower x-ray power !   Use metal grid over sample !   Evaporate Au overlayer !   Electron flood gun

Ways of Accounting for the charging !   Estimate Vs by measuring shift in the C 1s peak from

hydrocarbon contamination BE(C 1s) = 285.0 eV ± 0.2 eV ! Not valid for inhomogeneous sample

!   Compare Auger and XPS peaks

Line Width Measured by XPS !   Factors contributing to measured photoelectron line width:

! Natural line width: Lorentzian ! X-ray line width 0.75 - 0.85 eV ! Analyzer (example: Ep = 50eV, 5mm slit → 0.8eV resolution) ! Measured line-width ∆Emeasured

2 ≈ ∆Enat

2 + ∆Ex-ray2 + ∆Espec

2

!   Voigt function is a more accurate account of the correlation of the natural line width with the x-ray & analyzer

!   Phenomenological Gaussian-Lorentzian product more commonly used

( ) ⎟⎟⎠

⎞⎜⎜⎝

⎛

Δ

−−−

Δ+−

Δ= )2ln()(1exp

)()( 2

20

220

2

EEEM

EEEMEEf

XPS Measurement of Overlayer Thickness

⎟⎟⎠

⎞⎜⎜⎝

⎛⎟⎟⎠

⎞⎜⎜⎝

⎛−−=

⎟⎟⎠

⎞⎜⎜⎝

⎛−=

∞

∞

θλ

θλ

cos)(exp1

cos)(exp

AA

AAA

BA

ABB

EdII

EdII

!   Overlayer thickness can be determined by: ! Measuring IB as a function of angle θ ! Measuring the ratio of IB / IA

B

A

z

θ dA

Practical Surface Analysis - Auger and X-ray Photoelectron Spectroscopy D. Briggs and M. P. Seah (Editors), Wiley Interscience, 1990 (2nd ed.)

Angular Dependent XPS

708090100110

Inte

nsity

(Arb

. Uni

ts)

Binding Energy (eV)

θ=40

708090100110

Inte

nsity

(Arb

. Uni

ts)

Binding Energy (eV)

θ=55

708090100110

Inte

nsity

(Arb

. Uni

ts)

Binding Energy (eV)

θ=70

Si

Au

z

θ dAu

708090100110

Inte

nsity

(Arb

. Uni

ts)

Binding Energy (eV)

θ=0

Shake-up Satellites

Siegbahn, Rev. Mod. Phys. 54, 709–728 (1982)

Electron Scattering Effects Plasmon Loss Peak

a

A=15.3 eV

a a aAl 2s

Metal