Rutherford Backscattering Spectrometry (RBS)

Rutherford Backscattering Spectrometry

Quiz

[3] “natural” unit in RBS (a) atoms/cm3

(b) atoms/cm2

(c) molecules/cm3

[2] typical depth resolution in RBS (a) 0.2 nm

(b) 2 nm

(c) 20 nm

[1] RBS is more sensitive for (a) heavy elements

(b) light elements

[4] with RBS it is easy to measure (a) an impurity with low atomic number in a matrix of high atomic number

(b) an impurity with high atomic number in a matrix of low atomic number

[5] RBS is more sensitive for (a) backscattering (180°)

(b) scattering at (90°)

Literature

http://www.iac.ethz.ch/staff/krieger/pdf/RBS_Lecture.pdf

4 Basic concepts (i) Energy transfer from a projectile to a target nucleus in an

elastic two-body collision (kinematic factor)

(ii) Likelihood of occurrence of such a two-body collision (scattering cross section)

(iii) Average energy loss of an high energy atom through a dense medium (stopping cross section)

(iv) Statistical fluctuations in energy loss of an atom moving through a dense medium (energy straggling)

Surface impurity

50 100 150 200 250 300 350 400

0

200

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600

800

1000

1200

1400

1600

1800

ba

cksca

tte

r yie

ld, co

un

ts

channel

Schematic of experimental setup

mu Multichannel analyzer

Surface impurity

50 100 150 200 250 300 350 400

0

200

400

600

800

1000

1200

1400

1600

1800

ba

ckscatte

r yie

ld, cou

nts

channel

Surface impurity

50 100 150 200 250 300 350 400

0

200

400

600

800

1000

1200

1400

1600

1800

0.0

0.2

0.4

0.6

0.8

1.0

b

acksca

tte

r yie

ld, co

un

ts

channel

0.92

0.56

0.36

K

5 keV/channel

0.25

Surface impurity

0.25 0.36 0.56 0.92

Θ=170°

Surface impurity

100 150 200 250 300 350 400

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

E =0.01327+0.00496·channelk·E

0 [M

eV

]

channel

Surface impurity

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

0

200

400

600

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1800

b

ackscatte

r yie

ld, cou

nts

Energy [MeV]

C

OSi

Au

Surface impurity

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

0

200

400

600

800

1000

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1400

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ba

cksca

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Energy [MeV]

C

OSi

Au

Element Channel K E1 σ C [MeV] [10-24 cm] [counts]

----------------------------------------------------------------------------------------- C 98 0.2526 0.5052 0.037 1100 O 145 0.3625 0.725 0.074 390 Si 225 0.5657 1.1314 0.248 460 Au 369 0.9225 1.845 8.2 1400

Θ=170°, Ω=4.11 msr, Q=10 μC = 6.25·1013 ions

Surface impurity

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

0

200

400

600

800

1000

1200

1400

1600

1800

ba

cksca

tte

r yie

ld, co

un

ts

Energy [MeV]

C

OSi

Au

Element Channel K E1 σ C (N·t) [MeV] [10-24 cm] [counts] [1015 atoms/cm2]

----------------------------------------------------------------------------------------------------------------- C 98 0.2526 0.5052 0.037 1100 O 145 0.3625 0.725 0.074 390 20.5 Si 225 0.5657 1.1314 0.248 460 7.2 Au 369 0.9225 1.845 8.200 1400 0.67

Θ=170°, Ω=4.11 msr, Q=10 μC = 6.25·1013 ions

Surface impurity

Elemental film

Elemental film

1.4 1.5 1.6 1.7 1.8 1.9 2.0

0

2000

4000

6000

8000

10000

12000

E* = k

Pt·E

0- E

ba

ckscatte

r yie

ld [cou

nts

]

E1 [MeV]

E1 = k

Pt·E

0

Stopping cross section

𝜖 ≡1

𝑁

𝑑𝐸

𝑑𝑥

Elemental film

1.4 1.5 1.6 1.7 1.8 1.9 2.0

0

2000

4000

6000

8000

10000

12000

E* = k

Pt·E

0- E

ba

cksca

tte

r yie

ld [co

un

ts]

E1 [MeV]

E1 = k

Pt·E

0

𝐸 = 𝜖Nt ≅ 𝜀0𝑁𝑡 E1 = 1.844 MeV E*= 1.524 MeV ΔE = 320 keV

Stopping cross section

Elemental film

Spectrum Height

Surface impurity

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

0

200

400

600

800

1000

1200

1400

1600

1800

ba

cksca

tte

r yie

ld, co

un

ts

Energy [MeV]

C

OSi

Au

Element Channel K E1 σ C (N·t) [MeV] [10-24 cm] [counts] [1015 atoms/cm2]

----------------------------------------------------------------------------------------------------------------- C 98 0.2526 0.5052 0.037 1100 O 145 0.3625 0.725 0.074 390 20.5 Si 225 0.5657 1.1314 0.248 460 7.2 Au 369 0.9225 1.845 8.200 1400 0.67

Θ=170°, Ω=4.11 msr, Q=10 μC = 6.25·1013 ions

Surface impurity

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0

0

200

400

600

800

1000

1200

1400

1600

1800

ba

cksca

tte

r yie

ld, co

un

ts

Energy [MeV]

C

OSi

Au

Element Channel K E1 σ C (N·t) (N·t) [MeV] [10-24 cm] [counts] [1015 atoms/cm2] [1015 atoms/cm2]

----------------------------------------------------------------------------------------------------------------------------- C 98 0.2526 0.5052 0.037 1100 O 145 0.3625 0.725 0.074 390 20.5 20.9 Si 225 0.5657 1.1314 0.248 460 7.2 7.4 Au 369 0.9225 1.845 8.200 1400 0.67 0.68

Θ=170°, Ω=4.11 msr, Q=10 μC = 6.25·1013 ions

Diffusion Profile

Diffusion Profile

Example 1:

Krieger et al., Science 295, 1048 (2002)

Example 2: Liquid Target PEG400 with trace of TEABr

Polyethylene glycol (PEG)

Tetraethylammonium bromide (TEABr)

Example 2: Liquid Target PEG400 with trace of TEABr

Lanford et al., Nucl. Instr. and Meth. in Phys. Res. B 161-163 ,202 (2000)

Example 2: Liquid Target PEG400 with trace of TEABr

Example 2: Liquid Target PEG400 with trace of TEABr

Williams, NUCLEAR INSTRUMENTS AND METHODS 26, 205 (I975)

Example 2: Liquid Target PEG400 with trace of TEABr

Summary: 4 Basic concepts (i) Energy transfer from a projectile to a target nucleus in an

elastic two-body collision (kinematic factor)

(ii) Likelihood of occurrence of such a two-body collision (scattering cross section)

(iii) Average energy loss of an high energy atom through a dense medium (stopping cross section)

(iv) Statistical fluctuations in energy loss of an atom moving through a dense medium (energy straggling)

Example 2: