Rutherford Backscattering Spectrometry

Transcription

1 Rutherford Backscattering Spectrometry Timothy P. Spila, Ph.D. Frederick Seitz Materials Research Laboratory University of Illinois at Urbana-Champaign 214University of Illinois Board of Trustees. All rights reserved.

2 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.

3 Rutherford Backscattering Spectrometry 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.

4 Van de Graaff accelerator

5 Rutherford Backscattering Spectrometry 2 MeV Van de Graaff accelerator beam size Φ1-3 mm flat sample can be rotated

6 energy loss per cm log(de/dx) Primary Beam Energy 1 kev 1 MeV (log E) 1 kev 1 MeV thin film projected on to a plane: atoms/cm 2 (Nt)[at/cm 2 ] = N[at/cm 3 ] * t[cm] Figure after W.-K. Chu, J. W. Mayer, and M.-A. Nicolet, Backscattering Spectrometry (Academic Press, New York, 1978).

7 Elastic Two-Body Collision Elastic Scattering M 1 v o 2 = M 1 v M 2 v 2 2 M 1 v o = M 1 v 1 + M 2 v 2 K M E 1 = KE o 2 2 sin 2 cos t M i M i M i M t 2 Kinematic factor: K He 4 = 15 o Target mass (amu) M 1 <M 2, θ 18 o Φ 9 o RBS: He backscatters from M 2 >4

8 Rutherford Scattering Cross Section 2 2 Z1Z2 4 M Z 1 2 4E 2 M 2 E ( E, ) sin ( ) 2( ) R Coulomb interaction between the nuclei: exact expression -> quantitative method

9 energy loss per cm log(de/dx) Electron Stopping 1 kev 1 MeV (log E) Figure after W.-K. Chu, J. W. Mayer, and M.-A. Nicolet, Backscattering Spectrometry (Academic Press, New York, 1978).

10 Kinematic factor: K 16 RBS Simulated Spectra hypothetical alloy Au.2 In.2 Ti.2 Al.2 O.2 /C Element (Z,M): O(8,16), Al(13,27), Ti(22,48), In(49,115), Au(79,197) (, ) Z R E E He 4 1 ML 2 = 15 o Target mass (amu) 2 In Au 12 8 C 1 ML 1 ML Au O Al Ti In Au ML 1 ML C O Al Ti In C O Al Ti

11 SIMNRA Simulation Program for RBS and ERD 27.5% Hf N O 13% Al 1.8% Zr

12 Thickness Effects Counts 11,5 11, 1,5 1, 9,5 9, 8,5 8, 7,5 7, 6,5 6, 5,5 5, 4,5 4, 3,5 3, 2,5 2, 1,5 1, nm N, O, Mg Energy [kev] N surface Channel 45 5 Ti TiN/MgO Series Series 1 Ti surface Scattered D N Incident He Energy [kev] Energy [kev] , 13, 12, 11, 1, nm Series Simulated 14, 13, 12, 11, 1, 6 nm Series Simulated Counts 9, 8, 7, 6, 5, 4, 3, 2, 1, N, O, Mg N surface Channel 45 Ti Ti surface Counts 9, 8, 7, 6, 5, 4, N, 3,O, Mg 2, 1, N surface Channel Ti Ti surface

13 Incident Angle Effects Scattered TiN/MgO N Incident He N 14, 13, 12, 11, Energy [kev] nm Ti surface Series Simulated 8,5 8, 7,5 7, 6,5 Energy [kev] nm Ti surface Series Simulated 1, 6, Counts 9, 8, 7, 6, N surface Counts 5,5 5, 4,5 4, 3,5 N surface 5, 4, 3, 2, 1, N, O, Mg Channel 45 Ti , N, O, Mg 2,5 2, 1,5 1, Channel Ti Surface peaks do not change position with incident angle

14 Example: Average Composition I. Petrov, P. Losbichler, J. E. Greene, W.-D. Münz, T. Hurkmans, and T. Trinh, Thin Solid Films, (1997)

15 RBS: Oxidation Behavior TiN/SiO 2 As-deposited Experimental spectra and simulated spectra by RUMP Annealed in atmosphere for 12 min at T a = 6 C

16 RBS Summary Scattered D N Incident He Quantitative technique for elemental composition Requires flat samples; beam size Φ1-3 mm Non-destructive Detection limit varies from.1 to 1-6, 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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