1. Ronny Nawrodt 1st ELiTES General Meeting Tokyo 04/10/2012 Silicon Surfaces – Silicon Loss and Silicon Treatments –

2. Collaboration Friedrich-Schiller-Universität G. Hofmann, D. Heinert, C. Schwarz, J. Komma, S. Kroker, E. Butz, B. Walter, R. Nawrodt Glasgow University I. Martin, L.-E. Wittrock, E. Wisniewski-Barker, G. Hammond, M. Abernathy, K. Craig, J. Hough, S. Rowan University of the West of Scotland S. Reid

3. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 3 / 17 Friedrich-Schiller-Universität Jena Overview silicon as test mass material surface loss of silicon surface loss vs. treatment technologies for surface treatments applications

4. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 4 / 17 Friedrich-Schiller-Universität Jena Silicon as a Test Mass Material candidate materials for ET-LF: silicon, sapphire very low mechanical loss at cryogenics vanishing thermo-elastic loss at 18 and 125 K good thermal and mechanical properties open questions: – available size (float zone vs. Czochralski) – breaking strength – optical properties (dn/dt, absorption, etc.) DS based on silicon

5. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 5 / 17 Friedrich-Schiller-Universität Jena Surface Loss of Silicon (1) overview of loss processes (example: Si-flexure, similar for bulk) „invisible barrier“ always present

6. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 6 / 17 Friedrich-Schiller-Universität Jena Surface Loss of Silicon (2) surface loss extraction / model „invisible barrier“ = surface loss 1/3 Volume / Surface bulk samples surface loss always noticeable

7. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 7 / 17 Friedrich-Schiller-Universität Jena Surface Loss of Silicon (3) surface loss vs. surface quality „smooth“ „rough“ example: Si flexures

8. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 8 / 17 Friedrich-Schiller-Universität Jena Surface Loss of Silicon (4) surface loss vs. treatment blank etched grating Temperature (K) measured mechanical loss  blank etched grating origin of occuring peak so far unclear: - lower underground loss might reveal a hidden loss peak - loss peak is accociated with the etching-process -> surface effect? radiation damage?

9. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 9 / 17 Friedrich-Schiller-Universität Jena Surface structure of Silicon (1) crystal structure of silicon surface desity planesurface density (atoms / cm 2 ) {100} 6.8  10 14 {110} 9.6  10 14 {111} 11.8  10 14 different chemical and physical properties

10. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 10 / 17 Friedrich-Schiller-Universität Jena Surface structure of Silicon (2) silicon surfaces manifold surface configurations / terminations all dependent on surface density -> orientation -> detailed study of surface treatments needed to be able to minimize surface loss of Si based components

11. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 11 / 17 Friedrich-Schiller-Universität Jena Surface treatments (1) wet chemical etching isotropic etch  HNA (HF, nitric acid, acetic acid)  fluorine termination of surface bonds anisotropic etch  alkaline hydroxides (typ. KOH)  organic hydroxides (TMAH) Si(100) wafer 5 mm

12. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 12 / 17 Friedrich-Schiller-Universität Jena Surface treatments (2) dry etching (chemical vs. physical processes) chemical reaction occurs in gas phasepurely physical process (transfer of momentum) SF 6 -> SF 5 + + F - inside plasma Ar Si SiF 4 F-F-

13. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 13 / 17 Friedrich-Schiller-Universität Jena Surface treatments (3) plasma treatment low pressure / voltage plasma can be used to alter to surface chemistry or etch off top layers -> use of physical and chemical components new machine being comissioned at FSU Jena (4 different gas/vapour ports, up to 300 W power)

14. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 14 / 17 Friedrich-Schiller-Universität Jena Applications understanding of surface losses is important in all fields as it affects bulk as well as small structures important in Si-suspension design as all other losses will be minimized structured surfaces (e.g. AR-structures, HR-structures –> „resonant waveguide structures“)

15. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 15 / 17 Friedrich-Schiller-Universität Jena Microstructures experiment: R=99.79 % demonstrated detailed study of a general thermal noise treatment in grating structures involving ET and Kagra members (D. Heinert, D. Friedrich, S. Hild, S. Kroker, S. Leavey, I. Martin, R. Nawrodt, S. Vyatchanin, K. Yamamoto)

16. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 16 / 17 Friedrich-Schiller-Universität Jena Tasks detailed study of mechanical loss vs. treatment analysis technique of surface termination controlled termination -> stable configuration study of surface quality vs. thermal conductivity (link between WPs)

17. 1st ELiTES General Meeting / Tokyo Ronny Nawrodt, 04/10/2012 17 / 17 Friedrich-Schiller-Universität Jena Summary surface loss is an important contribution to the overall loss of silicon-based structures different treatment techniques available detailed study of the effect of surface treatment on mechanical loss as well as its durability is needed