Silicon Surfaces Silicon Loss and Silicon Treatments Ronny

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

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

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

Friedrich-Schiller-Universität Jena Silicon as a Test Mass Material • candidate materials for ET-LF: silicon, sapphire DS based on silicon • 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. ) Ronny Nawrodt, 04/10/2012 1 st ELi. TES General Meeting / Tokyo 4 / 17

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

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

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

Friedrich-Schiller-Universität Jena Surface Loss of Silicon (4) blank grating etched measured mechanical loss f(w) • surface loss vs. treatment Temperature (K) blank grating etched Temperature (K) 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? Ronny Nawrodt, 04/10/2012 1 st ELi. TES General Meeting / Tokyo 8 / 17

Friedrich-Schiller-Universität Jena Surface structure of Silicon (1) • crystal structure of silicon surface desity plane surface density (atoms / cm 2) {100} 6. 8 1014 {110} 9. 6 1014 {111} 11. 8 1014 different chemical and physical properties Ronny Nawrodt, 04/10/2012 1 st ELi. TES General Meeting / Tokyo 9 / 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 Ronny Nawrodt, 04/10/2012 1 st ELi. TES General Meeting / Tokyo 10 / 17

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

Friedrich-Schiller-Universität Jena Surface treatments (2) • dry etching (chemical vs. physical processes) chemical reaction occurs in gas phase SF 6 -> SF 5+ + F- inside plasma F- Ronny Nawrodt, 04/10/2012 purely physical process (transfer of momentum) Ar Si. F 4 1 st ELi. TES General Meeting / Tokyo Ar Si 12 / 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) Ronny Nawrodt, 04/10/2012 1 st ELi. TES General Meeting / Tokyo 13 / 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“) Ronny Nawrodt, 04/10/2012 1 st ELi. TES General Meeting / Tokyo 14 / 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) Ronny Nawrodt, 04/10/2012 1 st ELi. TES General Meeting / Tokyo 15 / 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) Ronny Nawrodt, 04/10/2012 1 st ELi. TES General Meeting / Tokyo 16 / 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 Ronny Nawrodt, 04/10/2012 1 st ELi. TES General Meeting / Tokyo 17 / 17