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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.
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New high resolution spectrometerfor nanometer levelelemental 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 ? • In principleallsampleelementscanbequantified 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
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 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:fastpreamplifiers inside the chamber 300 ps
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.%)
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.%.
Example with high mass element • AtomiclayerdepositedRufilm on HF cleanedSi(Dr. Kukli, U. of Helsinki) • Bulkdensity of 12 g/cm3used in the depthprofiles • Monte Carlo simulationsneeded for gettingreliablevalues for lightimpurities
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 Commercial MCP stacksby TECTRA
Future improvements: Gas ionization detector TOF-E results from Paul Scherrer Institute Incident ion 12 MeV 127I and borosilicate glass target Nucl. Instr. and Meth. B248 (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 2nd timing detector, 10 μg/cm2 C-foil 1st timing detector, 3 μg/cm2 C-foil
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