1. M. Laitinen, M. Rossi, P. Rahkila, H. J. Whitlow and T. Sajavaara
New high resolution spectrometer for nanometer level elemental depth profiling
M. Laitinen, M. Rossi, P. Rahkila, H. J. Whitlow and T. Sajavaara
Department of Physics, P.O.B 35, FIN University of Jyväskylä, Finland

2. The New Spectrometer: What does it look like and how does it works ?

3. The new spectrometer: How does it look like and how it works ?
1) Energetic ions from the accelerator are directed to the sample 2) while travelling in the material ions undergo collisions with sample atoms and as a result they lose energy and also they kick out sample atoms. Sometimes they also scatter out of the sample. 3) velocity and energy are measured from scattered particles and different masses can be distinguished
In principle all sample elements can be quantified
M. Putkonen, T. Aaltonen, M. Alnes, T. Sajavaara, O. Nilsen, and H. Fjellväg, Atomic layer deposition of lithium containing thin films, J. Mater. Chem. 19 (2009) 8767.

4. Time-of-Flight – Elastic Recoil Detection (ToF-ERD)
Quantitative method:
Energy from well known kinematics
Time-resolution better than E-detector resolution
Element (mass) from ToF and E signals
Scattering propability to detectors
Coulombic interaction potential
Depth information
Semi-empiric parametrization for energy loss
“Quantitative TOF-ERD analyses are based on well know measurement geometry and kinematics, separation of different masses, well known scattering probability and trusted energy losses. Energiaspektrit ja siis syvyysprofiilit lasketaan kahden syyn takia TOF-signaalista: (energia)resoluutio on parempi raskaille massoille ja kalibraatio on lineaarinen

5. TOF detection efficiency
All sample elements, also H, can be detected
Can get better only by getting more electrons out of the carbon foils
-> coating the carbon foils with Atomic Layer Deposition, ALD
Better than 98% for C
and heavier masses
~ 90 % for 4He
~ 10-60% for H
Sample holder backwall
Energiailmaisimen tehokkuus on 100% mutta lentoaikaporttien tehokkuus on matalampi kevyille alkuaineille, koska hiilikalvosta irtoaa elektroneja silloin vähemmän.
Measured with 1600 V MCP voltage,
3000 V mirror voltage and 200x preamplifier

6. Time-of-flight resolution
Timing with external 200x preamplifier, CFD and TDC
Current resolution timing resolution 300 ps for 4.5 MeV incident He ions scattered from 1 nm Au film on Si substrate
Timing: 300 ps equals ~ 4mm for 4.4 MeV He
Upgrade: fast preamplifiers inside the chamber
300 ps
Tärkeää tässä on sanoa tuo että tämä on määritetty sironneelle suihkulle.

7. Diamond-like carbon films
2.3 µm thick diamond-like-carbon film on Si
Measured with 9 MeV 35Cl
All isotopes can be determined for light masses
Light elements can be well quantified (N content 0.05±0.02 at.%)
Menetelmä soveltuu bulk-näytteiden mittaamiseen.

8. First results: 8.6 nm Al2O3
Atomic layer deposited Al2O3 film on silicon (Prof. Ritala, U. of Helsinki)
Density of 2.9 g/cm3 and thickness of 8.6 nm determined with XRR (Ritala)
Elemental concentrations in the film bulk as determined with TOF ERDA are O 60±3 at.%, Al 35±2 at.%, H 4±1 at.%. and C 0.5±0.2 at.%.
Parhaimmillaan menetelmä on ohutkalvotutkimuksessa. hiili eroaa pinnassa ja rajapinnassa (surface and interface).

9. Example with high mass element
Atomic layer deposited Ru film on HF cleaned Si (Dr. Kukli, U. of Helsinki)
Bulk density of 12 g/cm3 used in the depth profiles
Monte Carlo simulations needed for getting reliable values for light impurities
Metallic films have traditionally been difficult to deposit with ALD. This is one example of ongoing analysis of these Ru thin films. Scattered 35Cl is used for Ru depth profile, recoiled Ru suffers too much from multiple scattering.

10. Future improvements: New TOF-gate
ALD-coated thin C-foils for high electron yields (coming)
Timing from backwards emitted electrons
Position (scattering angle) from forward emitted electrons and delay line anode
Anodes made on PCB
Myös etusironneita elektroneja: paikkaherkkään anodiin
Commercial MCP stacks by TECTRA

11. Future improvements: Gas ionization detector
Massaerotuskyky raskaammille massoille paranee huomattavasti, huomaa mm Si:n isotoopit
TOF-E results from Paul Scherrer Institute
Incident ion 12 MeV 127I and borosilicate glass target
Nucl. Instr. and Meth. B 248 (2006)

12. Conclusions New high resolution spectrometer has been built in JYFL
ToF-ERDA provides unique capabilities for quantitative depth profiling of all the sample elements, including hydrogen
Depth resolution of <2 nm at the surface has been reached in Jyväskylä, further improvements coming within months
1st timing detector,
3 μg/cm2 C-foil
2nd timing detector,
10 μg/cm2 C-foil

13. Accelerator based materials physics goup in JYFL
Acknowledgements
Mikko Ritala, U. of Helsinki Matti Putkonen, Beneq Oy and Aalto University Kaupo Kukli, U. of Helsinki TEKES-EU Regional Funds Academy of Finland TEKES
Accelerator based materials physics goup in JYFL

15. 1st timing detector, 3 μg/cm2 C-foil
2nd timing detector, 10 μg/cm2 C-foil