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-40014 University of Jyväskylä, Finland email: mikko.i.laitinen@jyu.fi

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

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.

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

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

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.

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.

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).

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.

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

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) 155-162

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

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

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