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Bonding Experiments for Cryogenic Detectors R. Douglas1, K. Haughian1, A. A. van Veggel1, L. Cunningham1, G. Hammond1, G. Hofmann2, J. Hough1, A. Khalaidovski3, J. Komma2, I. Martin1, P. Murray1, R. Nawrodt2, S. Rowan1, Y. Sakakibara3, T. Suzuki3, K. Yamamoto3 Thursday 5th December 2013 1University of Glasgow; ELiTES Meeting, Tokyo 2Friedrich-Schiller-Universität Jena; 3University of Tokyo Talk outline • • • • • Hydroxide catalysis bonding Sapphire bonding at the IGR Sapphire bonding at the ICRR Indium bonding Summary Hydroxide catalysis bonding • Thermal noise of the test masses and suspensions in GW detectors is an important limit to detector sensitivity. Steel wires Penultimate mass Attachment or ‘ear’ Steel wire break-off prism Silica fibres Fibres Weld horns Ear End/input test mass Ear • Hydroxide catalysis bonding can be used (GEO, aLIGO, aVirgo) to form quasimonolithic suspensions of fused silica • One possible way to reduce thermal noise is to cool test masses and suspensions (of appropriate materials): Sapphire (KAGRA) and Silicon (ET) are candidate materials for cooled use. • Studies of the properties of hydroxide catalysis bonds formed between sapphire and silicon (breaking strength, thickness, thermal conductivity etc) are required to assess feasibility for use in cooled crystalline suspensions The hydroxide catalysis bonding procedure Chemistry of bonding of OH ions from the bonding solution fused silica: fill any open bonds OH ions form weak Aqueous alkaline hydroxide bonds with surface Si on the surface atoms Bonding solution placed between solution with OH OH OH OH lots of free surfaces to be jointed OH ions • Hydration and etching Si O Si Si • Polymerisation Si O O O Bonds between the Si Bulk Silica • Dehydration - Silicate molecule breaking away from the bulk and into the bonding solution - Bonding solution with lots of free OH ions Si(OH) -5 OH OH OH Si Si O OH Si O O O - Bulk Silica atoms and the bulkweaken due to the extra OH- ions bonding to the Si atom Similar chemistry for jointing other oxide surfaces Small volumes of solution used (~0.4ml/cm2) Several stringent requirements which must be fulfilled if bonds are to be successful • Surface must be very clean • Surfaces must have good match of global figure (typically flat to l/10) OH SiO2 Si H H2O OH OH H O Si i OH OH H H H2O OH OH H O Si OH H2O OH OH H O Si OH SiO2 OH H Bond Once made bonds are allowed to cure for four weeks to reach their maximum strength Both tensile and shear strength of interest Tensile strength A 4-point-bending test is applied to break the bonds. This allows a value of tensile strength to be calculated. Shear strength Experiments to test shear strength designed both at the ICRR and Glasgow Sapphire bonding • Sapphire has a hexagonal crystal structure: • We are interested in the a-axis, the c-axis and the m-axis Sapphire axes in KAGRA • The mirrors will have an orientation such that the sapphire cplane in the mirror will be perpendicular to the c-plane of the fibre • Thus investigating the properties of bonds between c-plane and aplane sapphire and cplane to m-plane sapphire is of interest Hydroxide catalysis bonding of sapphire Areas for investigation: • • • • • How does bond strength depend on type of solution used? Strength of bonds at cryogenic temperatures Effect of thermal cycling on bond strength Can we re-bond if something breaks? How strong will bonds be if different crystalline axes are bonded together? • Can we bond if surfaces jointed have flatness poorer than l/10? • Will increasing the volume of bonding solution used help in bonding surfaces with flatness poorer than l/10? Red = Results obtained Blue = Ongoing Studies of bond tensile strength vs. chemical composition of solution • Aqueous solutions studied: – sodium silicate (as used in aLIGO) C-plane • contains pre-dissolved SiO2 ; aids formation of polymer-like chains in bond – sodium hydroxide and potassium hydroxide • absence of SiO2 may allow thinner bonds – sodium aluminate • of interest for optical purposes – better index match to sapphire? • All solutions were prepared with de-ionised water to have a pH of 12 – (to match the pH obtained when using a ratio of commercial sodium silicate solution to water of 1:6 as used in aLIGO) • The samples were bonded, cured and broken at room temperature to assess their tensile strength Bonding surface Tensile strength (MPa) Bond tensile strength at room T as a function of solution used For comparison: • GEO and aLIGO: K. Haughian Thesis (2012): Silica jointed using sodium silicate solution (Tensile strengths ~16 MPa) • Suzuki et al (2006): Sapphire-sapphire jointed using potassium hydroxide solution (Shear strengths of ~7 MPa) • Dari et al (2010): Sapphire-sapphire bonds jointed using potassium hydroxide solution (Shear strengths of ~1.5 MPa) • For KAGRA strengths of ~10 MPa will be sufficient. Bonds tensile strength at cryogenic temperature, and after thermal cycling Tensile strength (MPa) Two further sets of sodium silicate bonds created: • One set were broken in a liquid nitrogen bath • One set were thermally cycled – cooled to 10 K and then increased back to room T three times Re-bonding sapphire • Almost all sapphire pieces survive strength testing intact – of order 15% are damaged when the bonds are broken • Re-bonding the pieces could provide information about ability to repair breakages in bonded sections of a suspension Example of undamaged surfaces after strength testing Example of damaged surfaces after strength testing • Samples already used once in bonding experiments were cleaned and re-bonded using sodium silicate solution Tensile strength (MPa) Tensile strength of bonded sapphire after re-bonding Slightly lower than those made with pristine samples; however the strengths are still good (and are strong enough for use in typical detector suspensions) Strength of bonds between different crystalline axes • Bonds for KAGRA will be C-to-A or C-to-M due to the crystal orientation of the mirror and the fibres • A new set of bonds were created to measure the effects of bonding different crystal axes together Are we able to bond at all if parts aren’t as flat as hoped? • Generally samples are used which have surfaces to be jointed with flatness of <λ/10 (λ=633 nm) • Unfortunately, sapphire is difficult to polish and most of the samples procured by ICRR for the study of the effect of crystal axis/plane on bond strength had poorer flatness than λ/10 • For the initial set of experiments the best samples were chosen, Allowing 9 bonds each of C-to-A, C-to-M and C-toC type samples to be produced. These each had a flatness of <λ/4 Bonding surface and plane of interest Shear strength of bonds between different crystalline axes tested at KEK at 10 K (Preliminary) • C-to-M appears to be the most promising of the available options • Both the C-to-A and C-to-M bonds are strong enough for KAGRA • The red point in the C-to-C set could not be broken, and may have a strength even greater than 119 MPa Are we able to bond at all if parts aren’t as flat as hoped? • A new set of experiments was devised, using the remaining samples which had flatnesses ranging from ~ λ/4 to ~λ To determine the effect on bond strength if one surface is significantly flatter than the other 1. C-to-A with samples with flatnesses of ~λ/4 bonded to samples with flatnesses of >λ/4. To determine the effect on bond strength if one surface is significantly flatter than the other 2. A-to-A with samples with flatnesses of >λ/4; half using the 0.4 μl/cm2 of solution and half using 0.8 μl/cm2 of solution. To determine whether increasing the volume 3. M-to-M the same way as experiment 2 • These bonds have been created and their strengths will be measured at by somebody at the ICRR in the New Year, when they will be fully cured of solution will improve strength when bonding with surfaces of poor flatness Thermal conductivity of bonds • Sapphire was jointed using sodium silicate solution to allow studies of bond thermal conductivity (Glasgow) • Typical bond brought to the ICRR where an experiment was set up to test its thermal conductivity – Work ongoing Thermal conductivity set-up at IGR Thermal conductivity set-up at ICRR Summary - Sapphire • Sodium silicate solution produces the strongest bonds • Breaking bonds at liquid nitrogen temperatures appears to have no detrimental effect on the measured strength compared to breaking them at room temperature • Thermally cycling bonds appears to reduce the average bond strength; after 3 cycles average strength still ~40MPa • Re-bonding samples reduces average bond strength; however re-bonded samples still have average strength >40MPa • C-to-M bonds initially appear to be stronger than C-to-A at 10 K. Alternative bonding techniques: • Work in Glasgow in mid-90s considered range of techniques for jointing fused silica to use in GEO600 suspensions at room T: – Optical contacting (rejected due to poor reliability and possibility for substrate damage) – Direct welding of fibres to silica test masses (rejected due to likelihood of damaging test masses due to relaxation of thermal stresses) – Indium bonding (well known as a technique to joint glasses) In addition to: – Hydroxide catalysis bonding • Reported in PhD thesis of S. Twyford. Fused quartz test mass suspended by silica fibres jointed using different techniques • • • • Comparison of loss measurements were made of internal modes of test mass when: – slung by wires – suspended via an indium bond: – suspended via a hydroxide catalysis bond To form indium joint: the samples were heated to 140 °C (just below the melting temperature of indium) An ultrasonic soldering iron was used to deposit indium on surfaces to be jointed - breaks the thin oxide later that forms on the surface of the indium Bond ~50 µm thick formed (estimated from measuring the mass of the indium used) Fused silica fibres welded to T-piece fused quartz T-piece, stub and cylinder post jointed to mass using Indium bond 15 mm wide flat polished along the mass 64 mm diameter by 70 mm long fused quartz test mass Measured Mechanical Losses of Test mass modes: Bond Type 39.7 kHz 49.5 kHz 50.6 kHz 60.1 kHz Weld (5.5 ± 0.2) × 10-7 (6.2 ± 0.1) × 10-7 (1.9 ± 0.1) × 10-6 (7.1 ± 1.1) × 10-7 Indium (1.4 ± 0.2) × 10-5 (2.1 ± 0.2) × 10-6 (4.3 ± 0.3) × 10-5 (3.0 ± 0.2) × 10-5 Hydroxide catalysis (1.8 ± 0.1) × 10-5 (7.7 ± 1.8) × 10-7 (2.9 ± 1.2) × 10-7 (4.8 ± 0.6) × 10-6 Wire-slung 7.3 × 10-7 - - - Initial Results • Concluded – mechanical losses associated with using indium jointing were tolerable when scaled to use in fullsize suspensions – low melting point meant it was not practical for use in Room T suspensions (e.g: suspensions are heat treated for cleaning purposes) – of interest for cryogenic suspensions? Recent studies • • • • • Kelvin Nanotechnology Ltd in (Glasgow) fabricated silicon cantilevers: 35 mm long, 5 mm wide and 54.5 µm thick Thin layer of indium (tIndium = 530 ± 30 nm) evaporated onto one face of the cantilever at Univ. of Jena Mechanical losses measured between 10 K and 80 K with and without indium applied Mechanical loss of indium calculated Nb : – exposed surface layer of indium oxidised – Indium coating rather than a joint or bond Clamped cantilever with indium layer applied Loss of indium film at cryogenic temperature -4 14 2222.3 Hz x 10 • Loss of approximately 5 x 10-4 at a few 10’s of K • Broadly consistent with values from Liu et al (1999) 13 Coating Loss 12 11 10 9 8 7 6 5 4 0 10 20 30 40 50 Temperature (K) Mode 4 at f = 2222 Hz 60 70 • FEA models of thermal noise from indium bonds used in an Advanced detector-like suspension geometry at 40K suggest noise would be ~x10 lower 80 than sensitivity of ET. Summary – indium bonding • Not ideal for use at room temperature when suspensions may be heated for e.g. cleaning purposes • Loss at low (10’s of K) temperatures makes it of potential interest for use in construction of cryogenic suspensions • Further work: construction of small prototype sapphire suspensions using indium bonding. Thank you for your attention References: [1] A. Dari et al. Breaking strength tests on silicon and sapphire bonding for gravitational wave detectors. Classical and Quantum Gravity, 27(4): 045010, 2010 [2] T. Suzuki et al. Application of sapphire bonding for suspension of cryogenic mirrors. Journal of Physics: Conference series, 32, pp 309, 2006 [3] K. Haughian. PhD Thesis. University of Glasgow, 2013 [4] A. A. van Veggel et al. Strength testing and SEM imaging of hydroxide-catalysis bonds between silicon. Classical and Quantum Gravity, 26(17): 175007, 2009 [5] X. Liu et al. Low-temperature internal friction in metal films and in plastically deformed bulk aluminium. Physical Review B, 59(18), 1999