Rutherford Backscattering Spectrometry Timothy P. Spila, Ph.D

Rutherford Backscattering Spectrometry

Timothy P. Spila, Ph.D.Materials Research Laboratory

University of Illinois

amc.mrl.Illinois.edu

© 2019 University of Illinois Board of Trustees. All rights reserved.


Geiger-Marsden Experiment

Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed.

Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated positive charge.

2



He+

He

RBS is an analytical technique where high energy ions (~2 MeV)

are scattered from atomic nuclei in a sample. The energy of the

back-scattered ions can be measured to give information on

sample composition as a function of depth.

3


Van de Graaff accelerator

http://archive.thedailystar.net/newDesign/print_news.php?nid=73473

http://cnx.org

4



3 MeV Van de Graaff accelerator

beam size Φ1-3 mm

flat sample

can be rotated

5



3 MeV Pelletron accelerator

beam size Φ1-3 mm

flat sample

can be rotated

6


NEC Pelletron

Pelletron system consists of• Ionization chamber• Acceleration tube• Focusing quadrupole• Steering magnet• RBS end station

7


NEC Pelletron


8


NEC Pelletron


9


NEC Pelletron


10


NEC Pelletron


11


Primary Beam Energy

thin film projected on to a plane: atoms/cm2

Figure after W.-K. Chu, J. W. Mayer, and M.-A. Nicolet, Backscattering Spectrometry (Academic Press, New York, 1978).

(Nt)[at/cm2] = N[at/cm3] * t[cm]

en

erg

y loss p

er

cm

lo

g(d

E/d

x)

1 keV 1 MeV(log E)

1 keV 1 MeV

12


Elastic Two-Body Collision

22 22 sin cos

t i i

i t

MMMKM M

E1 = KEo

M1<M2, 0 ≤θ≤180o

RBS: He backscatters

from M2>4

0 ≤Φ≤90o

0 50 100 150 2000.0

0.2

0.4

0.6

0.8

1.0

= 150o

He4

K

ine

ma

tic f

acto

r: K

Target mass (amu)

M1vo2 = M1v1

2 + M2v22

M1vo = M1v1 + M2v2

Elastic Scattering

13


Rutherford Scattering Cross Section

2 2

41 2 21

2( , ) sin ( ) 2( )

4 2R

Z Z ZMEME E

Coulomb interaction between the nuclei:

exact expression -> quantitative method

14


Electron Stopping

Figure after W.-K. Chu, J. W. Mayer, and M.-A. Nicolet, Backscattering Spectrometry (Academic Press, New York, 1978).

1 keV

en

erg

y loss p

er

cm

lo

g(d

E/d

x)

1 MeV(log E)

15


RBS – Simulated Spectra

Element (Z,M): O(8,16), Al(13,27), Ti(22,48), In(49,115), Au(79,197)

hypothetical alloy Au0.2In0.2Ti0.2Al0.2O0.2/C

Au

In

TiAlO

C

10 ML 100 ML Au

In

TiAlOC

1200 8000

Au

In

TiAlOC

1000 ML

16000

2

2( , )R

ZE

E

0 50 100 150 2000.0

0.2

0.4

0.6

0.8

1.0

= 150o

He4

Kin

em

atic f

acto

r: K

Target mass (amu)

4000 ML 10000 ML20000 50000

16


SIMNRA Simulation Program for RBS and ERD

27.5%

Hf

1.8% Zr13% Al

NO

17


Calibration Sample

Au

Cu

Si

α = 22.5°β = 52.5°θ = 150.0°

18


Cu-Nb-W Alloy on SiO2/Si

Cu91.2%

Nb8.0%

W0.8%

Si

O

Courtesy N. Vo and R.S. Averback19


Thickness Effects

Series 0

Series 1

Channel700650600550500450400350300250200150100500

Co

un

ts

11,500

11,000

10,500

10,000

9,500

9,000

8,500

8,000

7,500

7,000

6,500

6,000

5,500

5,000

4,500

4,000

3,500

3,000

2,500

2,000

1,500

1,000

500

0

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Energy [keV]

N surface

300 nm

Ti surface

Ti

interface

N, O, Mg

interface

Series 0

Simulated

Channel700650600550500450400350300250200150100500

Co

un

ts

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Energy [keV]

Ti surface

400 nm

Ti

interface

N, O, Mg

interface

N surface

Series 0

Simulated

Channel700650600550500450400350300250200150100500

Co

un

ts

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Energy [keV]

600 nm

Ti surface

Ti

interface

N, O, Mg

interface

N surface

TiN/MgO

N

He

DScattered

15

15

Incident

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Incident Angle Effects

TiN/MgO

Series 0

Simulated

Channel700650600550500450400350300250200150100500

Co

un

ts

14,000

13,000

12,000

11,000

10,000

9,000

8,000

7,000

6,000

5,000

4,000

3,000

2,000

1,000

0

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Energy [keV]

Ti surface400 nm

Ti

interface

N, O, Mg

interface

N surface

Series 0

Simulated

Channel700650600550500450400350300250200150100500

Co

un

ts

8,500

8,000

7,500

7,000

6,500

6,000

5,500

5,000

4,500

4,000

3,500

3,000

2,500

2,000

1,500

1,000

500

0

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500

Energy [keV]

400 nm

N surface

Ti surface

Ti

interface

N, O, Mg

interface

22.5

52

N

N

He

Scattered

15

15

Incident

Surface peaks do not change position with incident angle21


Example: Average Composition

I. Petrov, P. Losbichler, J. E. Greene, W.-D. Münz, T. Hurkmans, and T. Trinh, Thin Solid Films, 302 179 (1997)

22


RBS: Oxidation Behavior

TiN/SiO2

Annealed in

atmosphere for 12

min at Ta = 600 °C

As-deposited

Experimental

spectra and

simulated spectra

by RUMP

23


Areal mass density by RBS

200 400 600 800

Co

un

ts

Channel

Si wafer

40 nm Pt

Si wafer

20 nm Pt

20 nm Pt10 nm PA

200 400 600 800

Co

un

ts

Channel

Si wafer

20 nm Pt

20 nm Pt

20 nm PA

200 400 600 800

Co

un

ts

Channel

• Free-standing polyamide films are too thin to give sufficient signal in the RBS.

• Use the added stopping power of the polymer to split the Pt peak in the RBS spectrum.

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Areal mass density by RBS

0.1 0.2 0.5 1.0 2.0

0.005 0.0125 0.025 0.05 0.1

0.5

1.0

1.5

2.0

QCM

[TMC] (wt%)

Are

al M

ass D

ensity (

g c

m-2

)[MPD] (wt%)

RBS

1700 1750 1800 1850 1900 1950 2000

0

2000

4000

6000

8000

10000

12000

14000

Co

un

ts

Energy (keV)

0.005 wt% TMC, 0.1 wt % MPD

25


RBS Summary

N

He

DScattered

15

15

Incident

• Quantitative technique for elemental composition• Requires flat samples; beam size Φ1-3 mm• Non-destructive• Detection limit varies from 0.1 to 10-6, depending on Z

•optimum for heavy elements in/on light matrix, e.g. Ta/Si, Au/C…• Depth information from monolayers to 1 m

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Sponsor Presentation

Optimizing Simultaneous PIXE and RBS Capabilities

Thomas J. Pollock1, Robert White2

1National Electrostatics Corp., Middleton, Wisconsin, U. S. A. 53562-0310 [email protected]

2National Renewable Energy Laboratory, Golden, Colorado, U. S. A. 80401 [email protected]

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Rutherford Backscattering Spectrometry Timothy P. Spila, Ph.D