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Report on WP1/M1: Status report on silicate bonding of silicon
S.Reid1, I Martin1, W. Cunningham1, J. Hough1, S. Rowan1, K. Tokmakov1, M. Lorenzini2,
G. Cagnoli1, 2, E. Campagna2, E. Cesarini2, G. Losurdo2, F. Martelli2
1
2
The University of Glasgow, Glasgow, UK
INFN Sezione Firenze, Sesto Fiorentino, Italy
Coordinator: V. Loriette (ESPCI), M. Punturo (INFN Perugia)
Sample preparation
Pairs of silicon disks have been successfully bonded in Glasgow using different volumes of
sodium silicate bonding solution (1 part commercial sodium silicate solution to 6 parts
water, using volumes in the range 0.4l/cm2 to 0.1l/cm2). A complete set of these samples
has been sent to Florence for thermal conductivity measurements, having been given 2-3
months for curing. In addition to thermal conductivity tests, mechanical strength
measurements are planned both at room and low temperature (see the M5 report).
Initial mechanical testing at room temperature shows that a 5cm2 silicon-silicon bond is
capable of supporting a 40kg load over a period of two weeks with no observed distortion
or damage (a shear force of ~100 N/cm2, 1×106 Pascals).
cleaned silicon samples
placed in furnace at 1000°C
after ~1hr, 50 to 100nm oxide growth
Fig1: Preparation of silicon samples to be bonded: the required surface flatness ≤ /10, the surfaces
were thoroughly cleaned from contaminants prior to bonding, and oxidised prior to silicate bonding
Considerable studies have been carried out of the dependence of bond settling time on the
temperature and pH of the bonding solutions used for fused silica samples [1]. Samples of
silicon have been purchased for comparison.
Cryogenic system in Firenze for thermal conductivity studies
A liquid Helium cryogenic facility has been set up in
Firenze for carrying out both thermal conductivity
and thermal expansion measurements.
Initial
thermal conductivity measurements were carried out
on a pure silicon rod sample with purity 10-6 and
resistivity 42 cm and are shown in Figure 2. The
temperature dependence and magnitude of the
measured conductivity are also shown to agree
closely with literature values of comparable silicon
samples [2].
(c)
(a)
(d)
(b)
Fig2: thermal conductivity as a function for (a)
measured Si rod and (b), (c) and (d) literature
data for Si samples of comparable dimensions
and with resistivities of 15-25 cm, 260 cm
and 5000 cm respectively [2]
Cold plate
Heat
sink
Heater
Temperature sensors
Fig2: Bonded Si samples,
1/2" radius and 6mm thick
Fig3: Cryogenic facility in Florence for thermal conductivity
studies of silicon substrates and silicate bonds
Repeated measurements have been taken at room temperature and show a clear, albeit
relatively small, change in the thermal conductivity of the bonded sample compared to that
of the pure silicon. At room temperature, the thermal conductivity of the pure silicon is
160 W/mK and across the silicate bonded silicon disks 150 W/mK.
heater on
heater off
steady state
Fig3: rise and fall of temperature difference across the bonded and
unbonded samples at heat is applied and removed.
The relatively small addition of thermal resistance as a result of silicate bonding again
suggests that this bonding technique fulfils the requirements for the construction of 3rd
generation interferometers built and cooled through their monolithic silicon suspensions.
Delays and possible alteration of the planning
No delays are expected.
[1] Influence of Temperature and Hydroxide Concentration on the Setting Time of
Hydroxy-Catalysis Bonds, S. Reid, G. Cagnoli, E. Elliffe, J. Faller, J. Hough, I.Martin, S.
Rowan, Phys. Lett. A, 363, 341-345, 2006.
[2] Thermophysical Properties of Materials, Y.S. Touloukian, E.H. Buyco, Plenum, New
York (1970).