New materials for DUAL:
the LNL activity
Dual detector : Best material parameters
• Two different materials ‘A’ and ‘B’ with two
different Young modulus Y and density 
•Sensitivity curve optimized in the same frequency
window
• QL readout
•Toroidal shape
•No thermal noise
S    Y 
  B 
S    Y 
Α
hh
B
hh
Α
Α,B
 
Shh
Strain PSD of material A,B
 Α,B
Density of material A,B
2
 B 
  A 
 
Y Α,B Young modulus
of mat. A,B
Dual detector : Candidate Materials
1. Minimize sensitivity curve i.e. maximize
Q / T  108
2. Minimize thermal noise
Mat
Shh
/ ShhAl 5056
-Diamond
Y2 /
Q
163
?
Not well known
expensive
-Silicon carbide
27
available in large size
-Berillium
24
<106
expensive
-Sapphire
13
108
expensive+need bonding
-Molibdenum
6.8
107
available in large size
-Silicon
4.4
>108
need bonding
-others ? (i.e. Alumina (17), MoCu (), CuBe)
Red= Material under investigation
Sintered silicon carbide: results
•Cantilevers of different thickness (0.3-0.5
mm) and lenght (5-10 cm)
•Both optical lever and capacitive readout
1E-3
Loss Angle
Loss angle
8E-4
1E-4
4E-5
0
50
100
150
200
Temperature [K]
250
300
1E-4
5E-5
0
50
100
150
200
250
Temperature [K]
Similar results in E.K. Hu et al. Phys Lett. A 157, 209 (1991) -> Annealing should
improve the Q
300
Sintered silicon carbide: results
•Cantilevers of different thickness (0.3-0.5
mm) and lenght (5-10 cm)
•Both optical lever and capacitive readout
1E-3
Sintered SiC
Sintered SiC
Annealed 1900 C
Annealed 1900 C
Annealed 1200 C
Annealed 1200 C
Loss Angle
Loss angle
8E-4
1E-4
4E-5
0
50
100
150
200
Temperature [K]
250
300
1E-4
5E-5
0
50
100
150
200
250
Temperature [K]
Similar results in E.K. Hu et al. Phys Lett. A 157, 209 (1991) -> Annealing should
improve the Q -->Seem not very much
300
Infiltrated silicon carbide C-SiC: results
•Measured samples: two cantilever
of different thickness and lenght
from Cesic (Germany)
Not Annealed
•Different Carbon matrices
Annealed
•Capacitive readout
1E-3
Infiltrated SiC thickness 3mm
Infiltrated SiC thickness 3 mm 977 Hz
Same annealed at 1900 C
1E-4
Loss Angle
Loss angle
1E-3
Infiltrated SiC thickness 5 mm 1030 Hz
1E-5
1E-4
1E-5
1E-6
0
50
100
150
200
250
300
0
Temperature [K]
•Best achieved loss angle 2x10-6
•Annealing did’nt improve the quality factor
50
100
150
200
Temperature [K]
250
300
Silicon samples: bonding research
A Silicon Wafer bonder is now availabe at the
Mt-Lab in Trento
Machine capabilities
•Ready made for many bond proccesses (Anodic
bonding, Eutetic bonding,Adhesive bonding,Fusion
bonding,Thermocompression bonding)
•Wafer diameter 100 mm
•Stack thickness 6 mm
Silicon samples: bonding loss angle
Silicon wafer
Bonding Layer
Disk loss angle
Ebond
    notbonded( ) 
bond ( )
Etot
Bonded silicon disk h=0.9 mm d=100 nm
Ansys Analysis
Si disk suspension set-up
SS spring
SS piston
Si Disk
Set up #1
Sapphire balls
F1mm
Al
Not in scale cross section
silicon bulk wet etching
Silicon <100>
TMAH
<111> crystal plane side wall
175 mm deep pyramid hole,
with square opening
500 mm side
Si disk suspension set-up
SS piston
Si Disk
SS spring
Sapphire balls
F1mm
Not in scale cross section
Set up #2
Hole about 300 mm in diameter ,
Milled using dentist’s tools
Al
Si disk displacement Readout
Achieved sensitivity
10-8 -10-9 m
Quadrant
photodiode
Laser
Observed warm-up effects
at low temperature !
Thus not ideal for
ultracryogenic operations
Si disk displacement Readout
Vbias
Rotate
View
Vout
Capacitive readout
Si disk: capacitive redout
The comb capacitor capacitance value C(x) is a function of the distance
(gap+x) between them and the opposite dielectric plate
Readout sensitivity
V
x
bias dC
Vout 
C0 dx 1  CPar / C0
High sensitivity require
•Small gap
•Low parasitic capacitance (Cpar)
C(x)
Vbias
•Low noise voltage preamplifiers
(SQUID amplifer can improve
sensitivity very much)
Achieved Sensitivity during run #1
(Vbias=60 Volt, gap= 0.1 mm)
Vout[ mVolt ]  102  x[nm]
Si disk: first cryogenic run set-up
• Si <100> oriented Boron doped
•Disk diameter 4 inch
•Thickness 0.5 mm
F 2mm
SS piston
Si disk
Sapphire
balls
Misalignement problem
Adopted suspension (not optimized)
set-up
1E-4
1E-4
Mode freq 980 Hz
Mode freq 484 Hz
1E-4 Mode freq 997 Hz
Mode freq 383 Hz
1E-5
1E-6
1E-7
Loss Angle
1E-5
Loss Angle
Loss Angle
Si disk: first cryogenic run results
1E-6
0
50
100
150
200
Temperature [K]
250
300
1E-7
1E-5
1E-6
1E-7
0
50
100
150
200
Temperature [K]
250
300
0
50
100
150
200
Temperature [K]
250
300
First Si Disk cryogenic run: Quality factor limitations
• The contribution of thermoelastic damping and surface losses at 4.2 K
should be less then F<10-8
•We are presumably dominated by suspension losses and/or sample
microfracture induced by manufacturing the central hole
•However for this specific run gas damping should play a relelvant role
because we had a cold leak
Christian’s Model
RT 1
 
Q    ρSi  H  ν Mode 
M He P
2
3/2
ρSi  2300 Kg/m3
ν Mode  483 Hz
H  0.5 mm
P  1  10 4 mBar
Q  2.5 108
Bao et al. Model (sqeezed film damping )
RT 1 16  Gap
 
Q    ρSi  H  ν Mode 
M He P
L
2
3/2
Comb
Capacitor
Gap  0.1 mm
L  35 mm
Q  3.6 107
Even worse using true gas dynamic models and outgasing
Conclusions
•SiC is very interesting for its high sound velocity, but the sintered
and the infiltrated silicon carbide, that can be fabricated in large
size as required for the Dual detector, show at low temperature a
quality factor that is at least 2 order of magnitude lower than the
required value. The quality factor of monocristalline SiC should be
better but in this case we have to develop low losses bonding
procedures and take care of the cost.
•Monocristalline Silicon is also a candidate material but it is not
available at the required size. We plan to measure the Si bond
losses to evaluate if a big elastic body can be obtained bonding
togheter smaller pieces without affecting the overall Q fator
•Molybdenum is the best candidate material for the Dual detector
however we are considering other material considering other
materials as MoCu, pure Alumina, CuAl